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JP-2026075245-A - Method for depolymerizing polyester and method for obtaining purified ester monomer.

JP2026075245AJP 2026075245 AJP2026075245 AJP 2026075245AJP-2026075245-A

Abstract

[Problem] The objective is to provide a depolymerization method that uses recycled polyester molded products with low bulk density as raw materials while simultaneously achieving high efficiency in chemical recycling and reduced energy consumption. [Solution] The solution is to provide a method for depolymerizing polyester, which involves adding a polyester molded product having a bulk density of 0.03 or more and less than 0.80 to an alkylene glycol solution of an ester monomer, heating and stirring to depolymerize it back into the ester monomer. [Selection Diagram] None

Inventors

  • 渡 一平
  • 牧野 正孝

Assignees

  • 東レ株式会社

Dates

Publication Date
20260508
Application Date
20241022

Claims (10)

  1. A method for depolymerizing polyester, comprising adding a polyester molded product having a bulk density of 0.03 or more and less than 0.80 to an alkylene glycol solution of an ester monomer, and heating and stirring to depolymerize it back into the ester monomer.
  2. A method for depolymerizing polyester, comprising the continuous depolymerization process of adding a polyester molded article with a bulk density of 0.03 or more and less than 0.80 to an alkylene glycol solution of an ester monomer, heating and stirring to depolymerize it to the ester monomer, transferring a portion of the resulting alkylene glycol solution of ester monomer, and then adding the polyester molded article with a bulk density of 0.03 or more and less than 0.80 to the remaining alkylene glycol solution of ester monomer, followed by heating and stirring.
  3. The depolymerization method according to claim 1 or 2, wherein the alkylene glycol solution of the ester monomer is composed of 120 to 570 parts by weight of alkylene glycol per 100 parts by weight of the ester monomer.
  4. The depolymerization method according to claim 1 or 2, wherein the amount of alkylene glycol solution of ester monomer is 230 parts by weight or more and 810 parts by weight or less per 100 parts by weight of the polyester molded product to be introduced.
  5. The depolymerization method according to claim 1 or 2, wherein the heating temperature is 180°C or higher and 210°C or lower, and the heating time is 0.5 hours or higher and 3.0 hours or lower.
  6. The depolymerization method according to claim 1 or 2, wherein 50% to 100% by weight of the polyester molded article is polyethylene terephthalate, 80% to 100% by weight of the ester monomer is bis(2-hydroxyethyl) terephthalate, and 80% to 100% by weight of the alkylene glycol is ethylene glycol.
  7. The depolymerization method according to claim 1 or 2, wherein the polyester molded product is a fiber and/or film, and is introduced in any form of sewn product, fabric, yarn, film, or shredded thereof, without pelletizing by thermoforming or compression molding before introduction.
  8. A method for obtaining a purified ester monomer by sequentially carrying out the following steps (A) to (D) with an alkylene glycol solution or a portion thereof of an ester monomer obtained by depolymerizing a polyester molded article by the method of claim 1 or 2. (A) A step of removing alkylene glycol from an alkylene glycol solution containing ester monomers after depolymerization until the alkylene glycol is in the range of 0% to 20% by weight to recover the ester monomers. (B) A step of dissolving the recovered ester monomers in hot water at 85°C to 100°C and filtering them while hot. (C) A step of treating the filtered solution at 85°C to 100°C with activated carbon and/or ion exchange. (D) A step of cooling the filtered solution at 85°C to 100°C to 2°C to 40°C to crystallize and recover the ester monomers.
  9. A method for obtaining a regenerated polyester resin from a purified ester monomer obtained by the method described in claim 8.
  10. A method for obtaining recycled polyester fibers or recycled polyester film from a recycled polyester resin obtained by the method described in claim 9, through a process of melt spinning or melt film formation.

Description

This invention relates to a method for depolymerizing polyester and a method for obtaining a purified ester monomer. As a result of maintaining a social system based on mass production, mass consumption, and mass disposal, various negative environmental impacts have been observed, such as the depletion of natural resources and the destruction of nature due to resource extraction. Therefore, in order to efficiently utilize limited resources and continue sustainable growth, it is essential to build a circular social system that reduces waste generation and reuses or recycles waste in a way that does not burden the environment. To realize such a circular economy system, the establishment of recycling systems for waste plastics, including thermal recycling, material recycling, and chemical recycling, is required. In particular, the establishment of chemical recycling technology that decomposes waste plastics into monomers, purifies them, and then uses the resulting purified monomers as raw materials to regenerate high-quality plastic materials is urgently needed. Polyester, which is widely used in various fields due to its low cost and excellent mechanical properties, is also being considered for regeneration through chemical recycling. Generally, chemical recycling of waste polyester involves a depolymerization process in which polyester is reacted with diols to decompose it into ester monomers. For example, Patent Document 1 proposes a method to obtain ester monomers by directly reacting polyester fibers with a large amount of diol in a single step, while Patent Document 2 proposes a method in which polyester fibers are pre-depolymerized with a small amount of diol using a kneader, and then reacted with a larger amount of diol to obtain ester monomers. International Publication No. 2023/176649Japanese Patent Publication No. 2005-330444 This invention relates to a method for depolymerizing polyester, specifically a method for depolymerizing a polyester molded article having a bulk density of 0.03 or more and less than 0.80 by adding it to an alkylene glycol solution of an ester monomer, heating and stirring. The present invention will be described in detail below. In carrying out the polyester depolymerization method of the present invention, the polyester raw material used is a polyester molded article having a bulk density of 0.03 or more and less than 0.80. Examples of polyester molded articles include fiber molded articles, film molded articles, resin molded articles, and their crushed and shredded products. In particular, because of its low bulk density and its susceptibility to the yield improvement and energy reduction effects of applying the present invention, it is preferably applicable to fibers, film molded articles, and their crushed and shredded products, and most preferably to crushed and shredded fiber molded articles. The polyester-containing fiber molded articles to which this invention applies refer to fibers and structures made therefrom in general, and may be monofilament yarns, multifilament yarns, spun yarns of short fibers, or twisted yarns combining these. Furthermore, these may be fabrics (woven cloths) knitted or woven from these fibers or yarns, or cut pieces of these fabrics, or clothing items processed and sewn from them. In particular, because the materials can be easily introduced into the depolymerization tank in this invention, it is preferably applied to clothing items or fabric pieces cut into several-centimeter squares. It is most preferably applied to knitted fabric pieces cut into several-centimeter squares, as these have a low bulk density and are more susceptible to the yield improvement and energy reduction effects when applying this invention. The polyester fibers to which this invention is applied are not limited in origin and may be fabrics, cloths, or scraps before product processing; they may be derived from clothing; they may be derived from interior fabrics such as curtains, sofa fabrics, and carpets; or they may be derived from industrial textile materials such as airbags, seat belts, and car seat fabrics. From the standpoint of product recycling, it is preferably applied to scraps generated during the clothing manufacturing process and clothing that has been discarded without being worn. Most preferably, it is applicable to worn clothing, used interior fabrics, industrial textile materials, and their cut fabric scraps collected from consumers. The polyester fibers to which this invention is applied may contain polymers or additives other than the polyester component. For example, they may be, but are not limited to, blended yarns of polyester and polyurethane, polyester and cotton, polyester and acrylic, polyester and polyamide, and/or blended yarns. They may also contain pigments and dyes; examples of pigments include titanium dioxide, calcium carbonate, and carbon black, while examples of dyes include disperse dyes and cationic dyes, but are not limited to th