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CN-122010724-A - Method for depolymerizing copolyesters, depolymerized products and application of depolymerized products in preparing copolyesters

CN122010724ACN 122010724 ACN122010724 ACN 122010724ACN-122010724-A

Abstract

The invention relates to the technical field of recycling of waste polyesters and discloses a method for depolymerizing copolyester, a depolymerized product and application of the depolymerized product in preparing the copolyester, wherein the method for depolymerizing the copolyester comprises the step of carrying out depolymerization reaction on the copolyester with the average particle size of 0.1-5cm in the presence of a catalyst and a depolymerizing agent to obtain depolymerization liquid containing bis (2-hydroxyethyl) terephthalate, bis (2-hydroxyethyl) terephthalate dimer and cyclohexanedimethanol terephthalate, the copolyester is polyethylene glycol terephthalate-1, 4-cyclohexanedimethanol terephthalate, the water content of the copolyester is less than or equal to 2 wt%, and the catalyst is a titanium-containing catalyst. The method can realize the chemical depolymerization of the PETG (or PCTG) copolyester, improve the depolymerization rate of the copolyester and obtain the recyclable polymerized monomer.

Inventors

  • HAN LING
  • WANG LU
  • YIN JIE
  • ZHANG LONGGUI
  • ZHANG XINRU
  • ZHANG WEI
  • SONG JIANHUI
  • ZHU GUIXIANG
  • REN MINQIAO
  • JIA XUEFEI

Assignees

  • 中国石油化工股份有限公司
  • 中石化(北京)化工研究院有限公司

Dates

Publication Date
20260512
Application Date
20241112

Claims (11)

  1. 1. A method for depolymerizing copolyester is characterized by comprising the step of carrying out depolymerization reaction on copolyester with an average particle size of 0.1-5cm in the presence of a catalyst and a depolymerizing agent to obtain depolymerization liquid containing bis (2-hydroxyethyl) terephthalate, bis (2-hydroxyethyl) terephthalate dimer and cyclohexanedimethanol terephthalate, wherein the copolyester is polyethylene terephthalate-1, 4-cyclohexanedimethanol ester, the water content of the copolyester is less than or equal to 2 wt%, and the catalyst is a titanium-containing catalyst.
  2. 2. The method of claim 1, wherein the catalyst is at least one of an organo-titanium catalyst, a titanium-silicon complex catalyst, and a titanium-rare earth complex catalyst; And/or the catalyst is used in an amount of 0.1 to 0.5g, preferably 0.1 to 0.3g, per 100g of copolyester.
  3. 3. The method of claim 1 or 2, wherein the depolymerizing agent is ethylene glycol; and/or the weight ratio of depolymerizing agent to copolyester is 2-6:1, preferably 2.5-5:1.
  4. 4. A process according to any one of claims 1 to 3, wherein the conditions of the depolymerization reaction comprise a temperature of 190-240 ℃, preferably 200-230 ℃, a pressure of 0.2-0.6MPa, preferably 0.35-0.5MPa, and a time of 1-10h, preferably 2.5-5h.
  5. 5. The process according to any one of claims 1 to 4, wherein the oxygen content in the reaction system during the depolymerization reaction is less than 3.5% by weight, preferably the depolymerization reaction is carried out under an inert atmosphere, more preferably the inert atmosphere comprises nitrogen and/or an inert gas.
  6. 6. The process according to any one of claims 1 to 5, wherein the copolyester has an average particle size of 0.1 to 3cm; And/or the water content of the copolyester is less than or equal to 1 weight percent.
  7. 7. The method of any one of claims 1-6, wherein the method further comprises purifying the product from the depolymerization reaction, the purification comprising the steps of: (a) Carrying out first solid-liquid separation on the depolymerization liquid to obtain first filtrate; (b) Mixing the first filtrate with a diluent, and then performing second solid-liquid separation to obtain a second filtrate; (c) Mixing the second filtrate with activated carbon, and then performing third solid-liquid separation to obtain a third filtrate; (d) The third filtrate is crystallized and dried to obtain a mixture containing bis (2-hydroxyethyl) terephthalate, bis (2-hydroxyethyl) terephthalate dimer and cyclohexanedimethanol terephthalate.
  8. 8. The method of claim 7, wherein the first solid-liquid separation is performed at 80-105 ℃; and/or the diluent is water, preferably deionized water, the weight ratio of the depolymerization liquid to the diluent is 1:1-10, more preferably 1:2-5, and the condition of mixing the first filtrate with the diluent comprises the temperature of 70-90 ℃ and the time of 1-3h.
  9. 9. The process according to claim 7 or 8, wherein the amount of activated carbon is 1-10g per 100g of copolyester, and the condition of mixing the second filtrate with activated carbon comprises a temperature of 70-90 ℃ for 0.1-2h; and/or the crystallization conditions comprise a temperature of 2-10 ℃ and a time of 4-12h; And/or the drying conditions comprise a temperature of 50-90 ℃ and a time of 1-3h.
  10. 10. A depolymerized product prepared by the process of any one of claims 1-9.
  11. 11. Use of the depolymerized product of claim 10 for the preparation of polyethylene terephthalate-1, 4-cyclohexanedimethanol ester.

Description

Method for depolymerizing copolyesters, depolymerized products and application of depolymerized products in preparing copolyesters Technical Field The invention relates to the technical field of waste polyester recycling, in particular to a method for depolymerizing copolyester, a depolymerized product and application of the depolymerized product in preparation of the copolyester. Background PETG or PCTG polyester is a copolyester formed by copolymerizing terephthalic acid (PTA), ethylene Glycol (EG) and 1, 4-Cyclohexanedimethanol (CHDM) as monomers, and is totally called ethylene terephthalate-1, 4-cyclohexanedimethanol ester, wherein the copolyester with CHDM content more than 50% is called PCTG, and the copolyester with CHDM content less than 50% is called PETG. Compared with ethylene terephthalate (PET), 1, 4-Cyclohexanedimethanol (CHDM) is randomly inserted into a polymer chain, so that the regular arrangement of the molecular chain is hindered, and the crystallinity is obviously reduced, so that the PETG copolyester has excellent light transmittance, high impact resistance, toughness, glossiness and weather resistance, and has been commercially applied to the fields of high-transparency beverage bottles, plates, films for labels, photochemistry, medical equipment and the like. PETG or PCTG's processability is excellent, because its crystallization rate is slow, and CHDM is the rigid chain, and impact resistance is excellent, can adopt multiple shaping methods such as injection molding, extrusion, mould pressing, blowing, plastic uptake etc. to process according to designer's design, makes thick wall transparent goods or panel, sheet, tubular product, section bar, profile etc. and the usage is extensive. The main manufacturers of PETG or PCTG copolyester are the Ikman and Korean SK company in the United states, the total production amount is about 40 ten thousand tons in 2022, the domestic sales amount is about 12 ten thousand tons, the domestic demand for PETG is increasing, and the used PETG or PCTG copolyester can only be treated by adopting a physical recovery mode because of being unable to degrade. But the PETG or PCTG process can also be blended with other materials, making recovery more difficult. Aiming at the increasing demands of PETG or PCTG copolyester products in China, the localization yield of the monomer CHDM is low, most of the monomer CHDM depends on import, the price of the PETG or PCTG copolyester is very high, and if the PETG or PCTG copolyester is not recycled, the PETG or PCTG copolyester is extremely wasted. The physical recycling means can only degrade and recycle, is simple to operate, but cannot obtain regenerated polyester products with stable performance, and can cause the performance degradation of the polymer after multiple times of circulation, so that the performance requirement cannot be met. At the moment, the waste PETG or PCTG polyester products are depolymerized to the monomer level by a chemical method, and the high-purity monomers obtained from the depolymerized waste PETG or PCTG polyester products are reused and polymerized into high-quality regenerated products, so that the true closed-loop regeneration is realized. Disclosure of Invention The invention aims to solve the problems of recycling waste PETG or PCTG polyester products in the prior art, and provides a method for depolymerizing copolyester, a depolymerized product and application of the depolymerized product in preparing the copolyester. In order to achieve the aim, the first aspect of the invention provides a method for depolymerizing copolyester, which comprises the step of carrying out depolymerization reaction on copolyester with an average particle size of 0.1-5cm in the presence of a catalyst and a depolymerizing agent to obtain depolymerization liquid containing bis (2-hydroxyethyl) terephthalate, bis (2-hydroxyethyl) terephthalate dimer and cyclohexanedimethanol terephthalate, wherein the copolyester is polyethylene terephthalate-1, 4-cyclohexanedimethanol, the water content of the copolyester is less than or equal to 2 wt%, and the catalyst is a titanium-containing catalyst. In a second aspect, the invention provides a depolymerized product produced by the method described above. In a third aspect the invention provides the use of the depolymerization product as described above in the preparation of polyethylene terephthalate-1, 4-cyclohexanedimethanol. Through the technical scheme, the invention has the following beneficial effects: (1) According to the invention, the PETG (or PCTG) copolyester is subjected to chemical depolymerization recovery by adopting the titanium-containing catalyst, and the average particle size and the water content of the copolyester are controlled, so that the depolymerization rate of the copolyester can be improved, and a recyclable polymerized monomer can be obtained. The CHDM has higher boiling point (283 ℃), is difficult to remove in the synthesis process of