Method for recovering bhets from polyester blended textile waste

Abstract

The application discloses a polyester blended textile waste recycling BHET method, and utilizes ethylene glycol to degrade polyester blended textile waste under the action of a catalyst, wherein the catalyst is zinc pyrithione; the antibacterial agent SH-ANTI408 disclosed by the application can be applied to ethylene glycololysis of polyester blended textile waste as a catalyst, can make polyester / cotton / spandex blended fabric depolymerize in stages while keeping the structure of cotton fibers, and can make the BHET product yield reach 80-90%, the product selectivity is high, the fabric separation efficiency reaches more than 98%, the catalyst is not needed to be recycled, and a practical and sustainable method for chemical recycling of polyester blended textile waste is provided.

Description

Technical Field

[0001] This invention relates to the fields of green / clean catalytic technology and degradation of polyester blended textile waste, specifically to a method for recycling BHET from polyester blended textile waste. Background Technology

[0002] In 2024, global fiber production reached 132 million tons (of which polyester accounted for 57%), resulting in 92 million tons of textile waste annually. This causes significant resource waste and environmental harm, thus the recycling of post-consumer polyester textile waste has attracted increasing attention. Although recycled polyethylene terephthalate (PET) accounts for approximately 12% of the plastic recycling market, this mainly originates from the recycling of pure plastic bottle flakes, rather than textile recycling. BHET, or dihydroxyethyl terephthalate, is an important intermediate product in PET production, used to further convert PET into PET. PET is depolymerized into BHET, and through further reactions, new PET can be synthesized. This method effectively realizes the recycling of PET and is of great significance for environmental protection.

[0003] Polyester fabrics are difficult to degrade and recycle due to their high crystallinity and issues related to dyeing and blending. Currently used chemical depolymerization methods, such as methanololysis and hydrolysis, require stringent conditions, while enzymatic hydrolysis is limited by the stability and cost of depolymerizing enzymes. Pre-sorting and product separation of blended textiles further exacerbate the recycling difficulties. Pyrolysis and hydrogenolysis routes suffer from low selectivity and stringent conditions. Although ethylene glycololysis has advantages, existing catalytic systems still have shortcomings. Homogeneous and heterogeneous catalysts exhibit certain reaction efficiencies in pure PET matrix, but homogeneous catalysts suffer from low selectivity, high energy consumption for product separation, and difficulty in catalyst recovery; heterogeneous catalysts require high-temperature activation solvents, have limited mass transfer efficiency, and are prone to deactivation due to product aggregation. Therefore, the development of a low-cost, high-activity, separation-free polyester blended fabric regeneration system is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies by providing a method for recycling BHET from polyester blended textile waste. This method can be applied to polyester-cotton blended textiles to obtain high-purity BHET monomers and whole cotton fibers.

[0005] The inventors unexpectedly discovered that when the polyester blended textile waste contains SH-ANTI408 antibacterial agent, the main active ingredient of SH-ANTI408 antibacterial agent is zinc pyridinethione, and zinc pyridinethione itself can be used as a catalyst in the BHET process for recycling polyester blended textile waste.

[0006] To address the aforementioned technical problems, this invention discloses a method for recycling BHET from polyester blended textile waste. The method utilizes ethylene glycol to degrade the polyester blended textile waste under the action of a catalyst, wherein the catalyst is zinc pyridinethione.

[0007] Preferably, the zinc pyrithione accounts for less than 10% of the mass of the polyester blended textile waste.

[0008] Preferably, the zinc pyrithione is an inherent compound of the polyester blended textile waste and / or an additionally added compound. When the textile waste contains SH-ANTI408 antibacterial agent (generally, the mass of SH-ANTI408 antibacterial agent in the textile waste accounts for 2 wt% of the mass of the textile waste), zinc pyrithione may not be added or may be added in small amounts; when the textile waste does not contain SH-ANTI408 antibacterial agent, zinc pyrithione is added as a catalyst to catalyze the ethylene glycol hydrolysis of the blended fabric.

[0009] Preferably, the degradation is thermal degradation, with a heating temperature of 155~195℃ and a degradation time of 20~200min.

[0010] Preferably, the mass ratio of ethylene glycol to polyester blended textile waste is (1-8):1.

[0011] Preferably, the method includes a post-processing step after degradation, comprising: (1) Add all the degraded materials to water and mix well to obtain a mixture; (2) After separating the solid and liquid components of the mixture, collect the filtrate and the undegraded PET solids respectively; (3) Concentrate the filtrate, refrigerate and let it stand, separate the solid and liquid to obtain BHET crystals, and dry them to obtain the final product.

[0012] Furthermore, in step (3), the refrigerated stand is kept at a temperature of 0 to 4°C.

[0013] Furthermore, in step (3), the refrigerated standing time is 6 to 12 hours.

[0014] Furthermore, in step (3), the drying temperature is 40℃~60℃.

[0015] Preferably, the method has a PET conversion rate of 100%, a BHET yield of 80-90%, and a separation rate of 100%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention is based on the zinc pyridine thione active ingredient of SH-ANTI408 antibacterial agent in polyester textiles, and constructs a staged catalytic recovery system to solve the defects of existing technologies and achieve efficient recovery of blended textiles. Experiments have verified that its catalytic performance is excellent, and the BHET yield and catalytic performance are better than those of commonly used catalysts. It can be applied to polyester-cotton blended textiles and has both environmental benefits and economic feasibility.

[0017] 2. The catalyst raw material used in this invention is contained in the polyester textile waste itself after consumption, so there is no need to add a catalyst or add a small amount of catalyst, no need to recycle, low cost, high polyester conversion rate, high selectivity of target product, green and pollution-free reaction process, mild reaction conditions, high purity of degradation product, low requirements for raw materials, easy separation and purification of degradation product, and high separation rate of blended components. Attached Figure Description

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0019] Figure 1 Comparison of infrared spectroscopy and nuclear magnetic resonance analysis of antibacterial agent SH-ANTI408 and zinc pyrithione (ZPT).

[0020] Figure 2 The nuclear magnetic resonance spectrum of BHET monomer obtained by ethylene glycol hydrolysis using ZPT as a catalyst.

[0021] Figure 3 The flowchart shows the process from the separation of products to the ethylene glycololysis reaction of 10 g of polyester-cotton fabric using ZPT as a catalyst. Detailed Implementation

[0022] The present invention will be further described below with reference to the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0023] In the following examples, the conversion rate of polyester, the yield of depolymerization products, and the separation rate of different components of the blended fabric were calculated according to formulas (1), (2), and (3), respectively: (1) (2) (3) Example 1: Effect of commonly used antibacterial agents as catalysts on the ethylene glycol hydrolysis of PET powder Five common commercial catalysts, namely tannic acid, chitosan, methacryloyloxyethyltrimethylammonium chloride (TMAEMC), 4,4-bis(4-hydroxyphenyl)valeric acid (BHPVA), and polyhexamethylene biguanide hydrochloride (PHMB), were compared with SH-ANTI408 as catalysts for the ethylene glycol hydrolysis of PET powder. The six catalysts were added to 20 mL screw-top vials (catalyst mass accounting for 2% of the PET powder mass), followed by the addition of PET powder and ethylene glycol (ethylene glycol to PET powder mass ratio of 5:1). The mixture was heated to 185 °C and magnetically stirred (400 rpm) for 1 h under air. After the reaction, 250 mL of 60 °C distilled water was added to the reaction system, stirred for several minutes, and then filtered. The solids (undegraded PET and oligomers) and filtrate were collected. The filtrate was then diluted to volume, and 1 mL was taken for HPLC analysis to determine the BHET monomer content, and the yield and conversion rate were calculated. The effects of different antibacterial agents on the catalytic ethylene glycol hydrolysis of PET are shown in Experiments 1a to 1f in Table 1. The results show that only the antibacterial agent SH-ANTI408 has a good catalytic effect on the ethylene glycol hydrolysis of PET powder, with a conversion rate of up to 100% and a yield of 89.1%.

[0024] Table 1. Effects of different antibacterial agents on the ethylene glycol hydrolysis of PET

[0025] Example 2: Identification of components and crystal analysis of antibacterial agent SH-ANTI4308 40 mL of the antibacterial agent SH-ANTI408 was dried in a vacuum oven at 60℃ for 24 h, ground, and then tested on an ATR (Automatic Fourier Transform Infrared) attachment to obtain an infrared spectrum. The scanning range was 400 ~ 4000 cm⁻¹. -1 The resolution is 4 cm. -1 A total of 32 scans were performed, and the resulting spectrum showed consistent chemical shifts with the characteristic peaks of the known chemically structured drug zinc pyridinethione (ZPT) (e.g., ...). Figure 1 (as shown in a); then dissolve 20 mg of the test sample in 0.55 mL of deuterated dimethyl sulfoxide (DMSO) for further processing. 1 1H NMR analysis showed that the chemical shifts and number of hydrogen atoms in the obtained spectrum were consistent with those of the known chemically structured drug zinc pyrithione (ZPT) (e.g., ...). Figure 1 (As shown in b), the resonance frequency of the nuclear magnetic resonance is 400 MHz. Another appropriate amount of sample was placed on a benchtop X-ray diffractometer with a low background sample holder for flattening testing. The 2θ scanning range was 5-60°. The crystal form and crystal plane were consistent with the known chemical structure of the reagent zinc pyridinethione (ZPT) (e.g., ...). Figure 2 (As shown).

[0026] Example 3: Degradation of PET catalyzed by zinc pyridinethione (ZPT) catalyst under different reaction time conditions PET powder, ZPT (catalyst mass of 2% of PET powder mass), and ethylene glycol (ethylene glycol to PET powder mass ratio of 5:1) were added to a 20 mL screw-top vial. The mixture was heated to 185℃ and magnetically stirred (400 rpm) for 20–100 min. After the reaction, 250 mL of 60℃ distilled water was added to the reaction system, stirred for several minutes, and then filtered. The solid (undegraded PET and oligomers) and filtrate were collected. The volume was then adjusted, and 1 mL was taken for HPLC analysis to determine the content of the monomer BHET, and the yield and conversion were calculated. The effect of the antibacterial agent on the catalytic degradation of PET under different reaction time conditions is shown in Table 2, Experiments 2a–2e. The results show that under the same conditions, the conversion rate reached 100% and the yield reached 89.28% at 60 min.

[0027] Table 2. Effects of ZPT as a catalyst on PET degradation at different times.

[0028] Example 4: Degradation of PET catalyzed by zinc pyridinethione (ZPT) catalyst under different mass ratios PET powder, ZPT (catalyst mass of 0.1-10% of PET powder mass), and ethylene glycol (ethylene glycol to PET powder mass ratio of 5:1) were added to a 20 mL screw-top vial. The mixture was heated to 185℃ and magnetically stirred (400 rpm) for 60 min. After the reaction, 250 mL of 60℃ distilled water was added to the reaction system, stirred for several minutes, and then filtered. The solid (undegraded PET and oligomers) and filtrate were collected. The filtrate was then diluted to a final volume, and 1 mL was taken for HPLC analysis to determine the content of the monomer BHET. The yield and conversion rate were calculated. The effects of different antibacterial agents on the catalytic degradation of PET by ethylene glycol are shown in Table 3, Experiments 3a-3f. The results show that, under the same conditions, when the catalyst mass percentage is 2% of the PET powder mass, the conversion rate reaches 100%, and the yield can reach 89.1%.

[0029] Table 3. Effects of ZPT as a catalyst on the degradation of PET at different mass ratios.

[0030] Example 5: Degradation of PET catalyzed by zinc pyridinethione (ZPT) catalyst under different reaction temperatures PET powder, ZPT (catalyst mass of 2% of PET powder mass), and ethylene glycol (ethylene glycol to PET powder mass ratio of 5:1) were added to a 20 mL screw-top vial. The mixture was heated to 155–195 °C and magnetically stirred (400 rpm) for 60 min. After the reaction, 250 mL of 60 °C distilled water was added to the reaction system, stirred for several minutes, and then filtered. The solid (undegraded PET and oligomers) and filtrate were collected. The filtrate was then diluted to a final volume, and 1 mL was taken for HPLC analysis to determine the content of the monomer BHET. The yield and conversion rate were calculated. The effects of different antibacterial agents on the catalytic degradation of PET by ethylene glycol are shown in Table 4, Experiments 4a–4e. The results show that, under the same conditions, the conversion rate reached 100% and the yield reached 84.88% at a reaction temperature of 185 °C.

[0031] Table 4. Effects of ZPT as a catalyst on PET degradation at different temperatures.

[0032] Example 6: Effect of Zinc Pyridine Thione (ZPT) Catalyst on the Glycol Hydrolysis of Pure Polyester Fabrics Pure polyester fabrics (pure polyester fabric, pink quick-drying clothing, light green fabric, blue graduation gown, black graduation gown, and purple silk-like fabric) collected in the laboratory were washed, cut into 5×5 mm fragments, dried, and then added to a 20 mL screw-top vial with ZPT (catalyst mass accounting for 0.1%-10% of the pure polyester fabric mass, preferably 2%) and ethylene glycol (ethylene glycol to pure polyester fabric mass ratio of 5:1). The mixture was heated to 185℃ and magnetically stirred (400 rpm) for 60 min. After the reaction was completed, 250 mL of 60℃ distilled water was added to the reaction system, stirred for several minutes, and then filtered. The solid (undegraded PET and oligomers) and filtrate were collected. The filtrate was then diluted to a final volume, and 1 mL was taken for HPLC analysis to determine the content of the monomer BHET, and the yield and conversion rate were calculated. The purification and recovery of the BHET monomer component from pure polyester fabric degradation involved rotary evaporation to concentrate the above filtrate to 50 mL, allowing it to stand in a 4°C refrigerator for 12 h, followed by filtration to obtain needle-like crystals, and then drying in a vacuum drying oven at 40-60°C. Results showed that under the reaction conditions explored in this invention, ZPT catalytic degradation of pure polyester fabric exhibited excellent results, with a conversion rate as high as 100% and a product yield exceeding 85%, and the product was easily purified and separated. Other finishing agents in the fabric did not significantly affect the performance of this catalyst.

[0033] Table 5. Effects of ZPT as a catalyst on the degradation of pure polyester fabrics

[0034] Example 7: Effect of Zinc Pyridine Thione (ZPT) Catalyst on the Glycol Hydrolysis of Polyester Blended Fabrics Polyester blended fabrics (grey sweatpants (PET:cotton:spandex = 30:65:5), polyester-cotton fabric (PET:cotton = 75:25), towels (PET:cotton = 50:50), polyester-spandex blended fabric (PET:spandex = 70:30), and polyester-nylon blended fabric (PET:nylon = 70:30)) collected in the laboratory were washed, cut into 5×5mm fragments, dried, and then added to a 20mL screw-top vial with ZPT (catalyst mass accounting for 0.1%-10% of the polyester blended fabric mass, preferably 2%) and ethylene glycol (ethylene glycol to polyester blended fabric mass ratio of 5:1). The mixture was heated to 185℃ and magnetically stirred (400 rpm) for 60 min. After the reaction was complete, 250 mL of 60℃ distilled water was added to the reaction system, stirred for several minutes, and then filtered to collect the solid (undegraded PET and oligomers) and filtrate. The filtrate was then brought to a final volume, and 1 mL was taken for HPLC analysis to determine the content of the monomer BHET, and the yield and conversion rate were calculated. The purification and recovery of the degraded monomer BHET component in the polyester blended fabric involved rotary evaporation to concentrate the above filtrate to 50 mL, allowing it to stand in a 4℃ refrigerator for 12 h, filtering again to obtain needle-like crystals, and drying in a vacuum drying oven at 40-60℃. The separation of the remaining blended components of the polyester blended fabric was achieved by washing the filtered solid with dimethyl sulfoxide (DMSO), followed by washing with ethanol and deionized water, drying, and weighing to calculate the separation rate.

[0035] The results show that under the reaction conditions explored in this invention, ZPT catalyzes the degradation of polyester blended fabrics with excellent performance, achieving a conversion rate of up to 100% and a product yield of over 80%. The product is also easy to purify and separate, with a separation rate of over 98%. Furthermore, it has no significant impact on the blended components, and other finishing agents and blended components in the fabric do not have a significant impact on the performance of the catalyst.

[0036] Table 6. Effects of ZPT as a catalyst on the degradation of polyester blended fabrics

[0037] The method of this invention utilizes the SH-ANTI408 antibacterial agent contained in polyester blended textile waste as a catalyst in the ethylene glycol depolymerization reaction to complete the autocatalytic depolymerization of polyester blended textile waste. When the textile waste contains SH-ANTI408 antibacterial agent (generally, the mass of SH-ANTI408 antibacterial agent in the textile waste accounts for 2wt% of the mass of the textile waste), zinc pyridine thione can be added without or with a small amount to achieve autocatalytic recovery; when the textile waste does not contain SH-ANTI408 antibacterial agent, zinc pyridine thione is added as a catalyst to catalyze the ethylene glycol depolymerization of the blended fabric.

[0038] This invention provides a method for recycling BHET (Breakfast and End-of-Life) polyester blended textile waste. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for recycling BHET (biologically modified) polyester blended textile waste, characterized in that, ethylene glycol is used to degrade the polyester blended textile waste under the action of a catalyst, and the method is as follows: The catalyst is zinc pyridinethione.

2. The method according to claim 1, characterized in that, The zinc pyridinethione accounts for less than 10% of the mass of the polyester blended textile waste.

3. The method according to claim 1, characterized in that, The zinc pyrithione is a compound inherent to the polyester blended textile waste and / or an additional compound.

4. The method according to claim 1, characterized in that, The degradation is thermal degradation, with a heating temperature of 155~195℃ and a degradation time of 20~200min.

5. The method according to claim 1, characterized in that, The mass ratio of ethylene glycol to the polyester blended textile waste is (1-8):

1.

6. The method according to claim 1, characterized in that, The method includes a post-processing step after degradation, comprising: (1) Add all the degraded materials to water and mix well to obtain a mixture; (2) After separating the solid and liquid components of the mixture, collect the filtrate and the undegraded PET solids respectively; (3) Concentrate the filtrate, refrigerate and let it stand, separate the solid and liquid to obtain BHET crystals, and dry them to obtain the final product.

7. The method according to claim 6, characterized in that, In step (3), the refrigerated stand is kept at a temperature of 0 to 4°C.

8. The method according to claim 6, characterized in that, In step (3), the refrigerated standing time is 6 to 12 hours.

9. The method according to claim 6, characterized in that, In step (3), the drying temperature is 40℃~60℃.

10. The method according to claim 6, characterized in that, The method achieves a PET conversion rate of 100%, a BHET yield of 80-90%, and a separation rate of 100%.

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