A recycling method for depolymerization of waste polyester and mild selective depolymerization of blended textiles thereof

Abstract

The disclosed recycling method of waste polyester depolymerization and mild selective depolymerization of blended textiles is to use waste polyester and blended textiles as raw materials, under the action of alkaline catalyst, or use mixed solvents composed of alcohol compounds and aprotic solvents as reaction solvents, or use alcohol compounds or mixed solvents composed of alcohol compounds and aprotic solvents as reaction solvents, so that the polyester in waste polyester and blended textiles undergoes hydrolysis, selective hydrolysis, alcoholysis or selective alcoholysis, and then depolymerizes to generate small molecule degradation products, while other non-polyester components do not undergo chemical changes. The alkaline catalyst and reaction solvent selected by the application not only can reduce the reaction temperature, but also can efficiently catalyze the depolymerization of polyester without causing chemical changes in non-polyester components, so that the energy consumption and reaction time can be greatly reduced, the recycling efficiency can be improved, the purity and yield of polyester depolymerization products can be greatly improved, and the recycling and utilization of all components in textiles can be realized.

Description

Technical Field

[0001] This invention belongs to the field of solid waste recycling technology, specifically relating to a mild and selective depolymerization and recycling method for waste polyester and its blended textiles. Background Technology

[0002] Synthetic fibers are one of the three major organic synthetic polymer materials. In 2020, global fiber production exceeded 100 million tons, with synthetic fibers accounting for more than 74%. Polyester (polyethylene terephthalate fiber, also known as PET fiber) is the most produced and widely used synthetic fiber, accounting for more than 80% of the total synthetic fiber production, leading to a rapid increase in its waste proportion. Although some companies at home and abroad have achieved chemical recycling of polyester textiles in industry, the recycling rate is still less than 20%. Most waste polyester textiles are disposed of by incineration and landfill, which not only wastes a large amount of natural resources but also causes environmental pollution.

[0003] Currently, the main chemical recycling methods for polyester fibers include ammonolysis, hydrolysis, and alcoholysis. Ammonolysis uses ammonia (amines) to depolymerize polyester into smaller molecules such as terephthalamide. Although ammonia (amine) compounds have high reactivity and the reaction conditions are mild, they do not yield the monomers needed to synthesize polyester. Hydrolysis and alcoholysis, on the other hand, depolymerize polyester into monomers, which can then be further polymerized to produce recycled polyester, achieving a closed-loop PET cycle. Therefore, these are the most researched depolymerization methods. Hydrolysis depolymerizes polyester into terephthalic acid (PTA) monomers. Although water is used as the solvent, the reaction conditions for this depolymerization process are harsh, generally requiring high temperature and high pressure [Temperature > 130℃, Pressure 1–4 MPa — Green Chem., 2022, 24, 1362; J. Clean. Prod., 2019, 2081469]. It also requires strong acids and bases as catalysts, which can easily corrode equipment. Alcohololysis is mainly divided into two categories: methanololysis and ethylene glycol alcohololysis. Methanololysis depolymerizes polyester into the monomer dimethyl terephthalate (DMT). Although DMT is easily sublimated and can be prepared into high-purity DMT, methanol has a low boiling point, and the reaction requires relatively harsh high-temperature [temperature > 160℃, Polym. Degrad. Stab., 2002, 75, 185; US Pat, 5414022A, 1995; US Pat, 3403115A, 1968.] and high-pressure conditions. Ethylene glycol alcoholysis is the process of depolymerizing polyester to obtain the monomer diethylene terephthalate (BHET). Although ethylene glycol has a high boiling point, the reaction can usually be carried out at atmospheric pressure between 180 and 220 °C [GreenChem., 2022, 24, 1294; Polymer Degradation and Stability 183(2021) 109463; ACSSustain.Chem.Eng. 2019, 7, 3292]. However, the recovered monomer often contains BHET oligomers, making the purification process relatively complex. First, excess water needs to be added to the ethylene glycol alcoholysis solution to dissolve the BHET. The undissolved portion consists of incompletely depolymerized polyester and BHET oligomers. Then, the BHET solution is separated by filtration. Subsequently, the BHET solution is concentrated under reduced pressure to remove the water. Finally, BHET is precipitated by cold crystallization.

[0004] Furthermore, for waste polyester blended textiles, the existing hydrolysis and alcoholysis technologies have harsh depolymerization conditions. Besides polyester, they lack selectivity for other non-polyester fiber components, making selective depolymerization of polyester in the blend virtually impossible. This results in a complex composition of recycled materials containing various non-polyester fiber components. These non-polyester fiber components, such as nylon and spandex, contain highly polar functional groups like urethane, amide, ester, and ether bonds in their main chains. Under the chemical recycling conditions of polyester textiles, these components undergo numerous side reactions, causing the depolymerization products of various fibers to mix together. This not only makes it difficult to separate the polyester depolymerization products but also significantly reduces the recovery rate and purity of the polyester depolymerization products. Additionally, the structural damage to non-polyester fiber components during degradation renders them unrecyclable, leading to resource waste. Currently, in order to avoid the influence of these non-polyester components, pure polyester or raw materials with extremely high polyester content are often selected for depolymerization and recycling in industry. This results in a small amount of recycled raw materials. Therefore, achieving selective depolymerization of polyester in blended textiles is an urgent problem to be solved in industry.

[0005] Therefore, if selective depolymerization of polyester fibers in the blended fabric can be achieved during the chemical recycling process, while preventing chemical changes in the non-polyester fibers, it will not only improve the recovery rate and purity of polyester depolymerization products, but also allow for the reuse of non-polyester fiber components in the blended fabric. This is undoubtedly of great significance for resource recycling and environmental protection. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a method for the recycling of waste polyester and its blended textiles through mild and selective depolymerization. This method can depolymerize and recycle pure polyester, or selectively depolymerize polyester fibers in blended textiles into raw material monomers, while other non-polyester fiber components do not undergo chemical changes, so that these undepolymerized non-polyester fiber components can be collected and reused.

[0007] This invention provides a method for the mild and selective depolymerization and recycling of waste polyester and its blended textiles. The method uses waste polyester and its blended textiles as raw materials. Under the action of an alkaline catalyst, or with a mixed solvent composed of alcohols and aprotic solvents as the reaction solvent, the polyester in the waste polyester textiles or waste polyester blended textiles undergoes hydrolysis or selective hydrolysis. Alternatively, with alcohols or a mixed solvent composed of alcohols and aprotic solvents as the reaction solvent, the polyester in the waste polyester textiles or waste polyester blended textiles undergoes alcoholysis or selective alcoholysis, resulting in depolymerization into easily separable and repeatedly polymerizable small-molecule degradation products. Other non-polyester components do not undergo chemical changes. The specific process steps and conditions are as follows:

[0008] Waste polyester and its blended textiles are placed in a reaction solvent at a mass ratio of 1:1 to 100. Then, 0.01% to 500% alkaline catalyst based on the mass of the waste polyester and its blended textiles is added. The reaction is carried out at room temperature to 250°C for 5 to 600 minutes. After the reaction is completed, the reaction solution is filtered while hot to separate the incompletely reacted polyester textile solids and a solution containing easily separable and reproducible small molecule depolymerization products. Alternatively, the reaction solution is filtered while hot to separate the non-polyester components that have not been depolymerized, the incompletely reacted polyester textile solids and a solution containing easily separable and reproducible small molecule depolymerization products. The solution is then separated to obtain the reaction solvent and the reproducible small molecule depolymerization products.

[0009] In the above methods, after the reproducible small molecule degradation products precipitate out of the reaction solution or cool and crystallize into depolymerized polyester monomers, the reaction solution obtained after separating the depolymerized polyester monomers can be directly reused for the mild and selective depolymerization and recycling of waste polyester and its blended textiles. Alternatively, the reaction solvent and catalyst in the reaction solution can be collected separately and reused for the mild and selective depolymerization and recycling of waste polyester and its blended textiles.

[0010] The alkaline catalyst mentioned in the above methods is an inorganic or organic base. The inorganic base is sodium hydroxide and / or potassium hydroxide; the organic base is urea, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), metformin, tetramethylguanidine, 2-tert-butyl-1,1,3,3-tetramethylguanidine, 1,1,2,3,3-pentamethylguanidine, 1,3-dimethylthiourea, betaine, 4-dimethylaminopyridine, tetrabutylammonium bromide, and tetrabutylphosphine bromide. At least one of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, and phosphazene base, preferably at least one of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), metformin, tetramethylguanidine, 2-tert-butyl-1,1,3,3-tetramethylguanidine, 1,1,2,3,3-pentamethylguanidine, 4-dimethylaminopyridine, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, and phosphazene base, wherein the phosphazene base has at least one of the following structures:

[0011]

[0012] When waste polyester and its blended textiles undergo alcoholysis or selective alcoholysis, the alcohols used are at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, primary butanol, tert-butanol, n-pentanol, n-hexanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, glycerol, 1,6-hexanediol, and diethylene glycol; the catalyst used is at least one of organic bases.

[0013] In the above methods, when waste polyester and its blended textiles undergo hydrolysis or selective hydrolysis, the alcohol compound used in the mixed solvent is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, primary butanol, tert-butanol, n-pentanol, and n-hexanol, preferably at least one of isopropanol, isobutanol, primary butanol, tert-butanol, n-pentanol, and n-hexanol. The aprotic solvent used is at least one of dichloromethane, dimethyl sulfoxide, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolinone, hexamethylphosphoric triamine, N-methylpyrrolidone, acetonitrile, methyl ethyl ketone, diethyl ether, methyl ethyl ether, and methyl propyl ether, preferably at least one of dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and methyl propyl ether; the catalyst used is at least one of inorganic bases.

[0014] When waste polyester and its blended textiles undergo alcoholysis or selective alcoholysis, the alcohols used in the mixed solvent are at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, primary butanol, tert-butanol, n-pentanol, n-hexanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, glycerol, 1,6-hexanediol, and diethylene glycol. The aprotic solvents are dichloromethane, dimethyl sulfoxide, tetrahydrofuran, acetone, and N,N-dimethylformyl. The catalyst is at least one of the following: amine, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolinone, hexamethylphosphoric triamine, N-methylpyrrolidone, acetonitrile, methyl ethyl ketone, diethyl ether, methyl ethyl ether, and methyl propyl ether; preferably at least one of dichloromethane, dimethyl sulfoxide, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetonitrile, methyl ethyl ketone, and methyl propyl ether; the catalyst used is at least one of the following organic bases.

[0015] In the above methods, when waste polyester and its blended textiles undergo hydrolysis or selective hydrolysis, and the reaction solvent used is an alcohol compound and an aprotic solvent, the reaction temperature is room temperature to 120°C, preferably 25 to 120°C, more preferably 25 to 100°C, and the reaction time is 5 to 300 min, preferably 5 to 120 min.

[0016] In the above methods, when waste polyester and its blended textiles undergo alcoholysis or selective alcoholysis, when the reaction solvent is an alcohol compound, the reaction temperature is 50–250°C, preferably 50–180°C, more preferably 50–160°C, and the reaction time is 5–600 min, preferably 5–300 min. When the reaction solvent is an alcohol compound and an aprotic solvent, the reaction temperature is 50–160°C, preferably 50–140°C, more preferably 50–120°C, and the reaction time is 5–600 min, preferably 5–300 min. The reaction temperature for the methanolysis of waste polyester and its blended textiles is 50–150°C, preferably 50–100°C. The selective methanololysis reaction time for waste polyester and its blended textiles is 5–180 min, preferably 5–120 min; the selective ethylene glycololysis reaction temperature for waste polyester and its blended textiles is 50–250 °C, preferably 50–150 °C, more preferably 50–120 °C. The selective ethylene glycololysis reaction time for waste polyester and its blended textiles is 5–600 min, preferably 5–300 min, more preferably 5–120 min.

[0017] In the above methods, when waste polyester and its blended textiles undergo hydrolysis or selective hydrolysis, the mass ratio of the waste polyester and its blended textiles to the reaction solvent is preferably 1:1 to 50, more preferably 1:1 to 10; the amount of inorganic alkali added is preferably 0.01 to 500% of the mass of the waste polyester and its blended textiles.

[0018] In the above methods, when waste polyester and its blended textiles undergo alcoholysis or selective alcoholysis, the mass ratio of the waste polyester and its blended textiles to the reaction solvent is preferably 1:1 to 10, more preferably 1:1 to 5; the amount of organic alkali added is preferably 0.01 to 500% of the mass of the waste polyester and its blended textiles, more preferably 0.1 to 50%.

[0019] In the above methods, polyester textiles are pure polyester textiles; blended textiles are blended textiles prepared by blending polyester with at least one of cotton, polypropylene, spandex, nylon, acrylic, vinylon, viscose fiber, lyocell, regenerated cellulose fiber and acetate fiber.

[0020] The above methods are also applicable to the depolymerization and recycling of polyester flakes, polyester films, polyester engineering plastics, and polyester nonwoven fabrics.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) When the reaction solvent in the recycling method provided by the present invention is a simple alcohol compound, the alkaline catalyst used can not only form hydrogen bonds with the hydroxyl group of the alcohol compound to activate the alcohol compound, but also form hydrogen bonds with the carbonyl group of polyester to increase the electronegativity of the carbonyl carbon atom. Therefore, on the one hand, it can catalyze the depolymerization process of polyester more efficiently. On the other hand, and more importantly, because the catalyst will not form hydrogen bonds with non-polyester components and interact with them, it will not activate the non-polyester components and thus will not depolymerize them. Therefore, selective depolymerization of polyester in blended textiles can be achieved, while other non-polyester components do not undergo chemical changes.

[0023] (2) In the recovery method provided by the present invention, when the reaction solvent is a mixture of alcohol and aprotic solvent, the addition of aprotic solvent can make the dielectric constant of the mixture solvent greater than that of a simple alcohol solvent. This allows the alkaline catalyst and the alcohol in the mixture solvent to generate more alcohol anions through dissociation, which then rapidly attack the carbonyl carbon of polyester. Therefore, on the one hand, polyester can be depolymerized at a lower temperature. On the other hand, for the non-polyester components in the blended textiles, the selected catalyst will not activate them. At the same time, the lower reaction temperature also reduces the activity of alcohol compounds attacking the non-polyester components. Thus, polyester can also be depolymerized without chemical changes to the non-polyester components.

[0024] (3) Since the reaction solvent of the recovery method provided by the present invention can be used under the action of an alkaline catalyst, the depolymerization temperature of polyester is greatly reduced. For example, compared with the existing polyester hydrolysis technology, the present invention can not only reduce the hydrolysis temperature to room temperature, but also the reaction is an atmospheric pressure reaction; compared with the existing polyester ethylene glycol hydrolysis technology, the present invention can also reduce the ethylene glycol hydrolysis temperature to 80°C; compared with the existing polyester methanol hydrolysis technology, the present invention can reduce the methanol hydrolysis temperature to 80°C. Therefore, it can not only greatly reduce energy consumption, but also achieve a high depolymerization rate of polyester (up to 100%).

[0025] (4) Since the reaction solvent in the recovery method provided by the present invention can be a mixed solvent composed of alcohol compounds and aprotic solvents, the addition of aprotic solvents can not only promote the interaction with alcohol compounds and promote the rapid depolymerization of polyester textiles, but also enhance the mass transfer between the solvent and polyester textiles. Therefore, under the action of alkaline catalysts, the reaction time can be greatly shortened and the recovery efficiency can be improved.

[0026] (5) Since the depolymerization temperature of the recycling method provided by the present invention can be greatly reduced, the generation of oligomers during the depolymerization process is suppressed. Therefore, the purity of the recovered monomers in the depolymerization products that can be repeatedly polymerized is high. For example, after the depolymerization of polyester ethylene glycol, there is no need to add excessive water to the alcoholysis liquid to separate BHET oligomers during the monomer separation process. The non-protic solvent can be removed by vacuum distillation and then cold crystallization can be carried out to obtain high-purity BHET. This not only avoids the generation of wastewater, but also reduces the separation steps and separation costs.

[0027] (6) Since the recycling method provided by the present invention can achieve mild and selective depolymerization of polyester in blended textiles, while non-polyester components do not undergo chemical changes, the polyester depolymerization products do not contain by-reaction products of non-polyester components, which greatly improves the purity and yield of polyester depolymerization products. For example, the yield of hydrolyzed product terephthalic acid (PTA) can be >98% and the purity can be >99%; the yield of DMT can be >98% and the purity can be >99%; and the yield of BHET can be >99% and the purity can be >97%.

[0028] (7) Since the recycling method provided by the present invention can realize the complete recycling of all components in textiles, the utilization rate of resources is improved. Attached Figure Description

[0029] Figure 1 These are digital microscope images of the waste polyester-spandex blended textile before and after depolymerization in Example 24 of this invention. The digital microscope images show that before depolymerization, the polyester and spandex fibers had a tight weave structure. However, after selective glycololysis, the polyester fibers were completely depolymerized, leaving no remaining polyester fibers on the spandex, and the weave structure remained intact.

[0030] Figure 2 This is a comparison of the hydrogen NMR spectra of the monomer BHET obtained after depolymerization of waste polyester-spandex blended textiles in Example 16 of this invention and commercial BHET. Comparison with commercially purchased BHET reveals that the chemical shifts and peak area integral ratios of the hydrogen atom peaks in both BHETs are almost identical, and there are no other impurity peaks. This indicates that the BHET obtained after selective depolymerization of polyester in the polyester-spandex blended textiles has high purity and selectivity.

[0031] Figure 3 The images show the NMR spectra of the solids obtained before and after depolymerization of the waste polyester-cotton blended textiles in Example 82 of this invention. Compared with the original polyester-cotton blended textile spectrum, no polyester peaks were observed in the recovered cotton fiber spectrum, indicating that the polyester in the polyester-cotton blended textiles had undergone selective hydrolysis, while the cotton fibers did not undergo chemical changes, demonstrating high selectivity.

[0032] Figure 4This is a comparison of the hydrogen NMR spectra of the monomer DMT obtained after depolymerization of polyester and nylon blended textiles in Example 6 of this invention and commercial DMT. Comparison with the spectrum of commercially purchased DMT reveals that the chemical shifts of the hydrogen atom peaks in both DMTs are completely identical, and there are no other impurity peaks, indicating that the DMT obtained after selective depolymerization of polyester in the polyester and nylon blend has high purity and selectivity. Detailed Implementation

[0033] The following embodiments are provided to further illustrate the present invention in detail. However, the following embodiments should not be construed as limiting the scope of protection of the present invention. If those skilled in the art make some non-essential improvements and adjustments to the present invention based on the content of the present invention, they shall still fall within the scope of protection of the present invention.

[0034] It is worth noting that, 1) the degradation rate and monomer recovery rate of the polyester obtained in the following examples were calculated according to formulas (1) and (2):

[0035] (1) The depolymerization rate (D) of polyester is calculated using the following formula (1):

[0036]

[0037] In the formula W PET0 W represents the original polyester mass in polyester and its blended textiles. PET1 This represents the mass of polyester fibers that did not depolymerize after the reaction.

[0038] (2) The recovery rate (Y) of the monomer is calculated using the following formula (2):

[0039]

[0040] In the formula m mon M represents the actual mass of the recovered monomers. mon m is the molar mass of the monomer. PET0 M represents the mass of the raw polyester in the textile. PET It is the molar mass of the repeating unit of PET (192 g / mol).

[0041] 2) The purity of the monomers obtained in the following examples was directly measured by liquid chromatography standard curve method.

[0042] 3) The proportions of the mixed solvents used in the following examples are by mass.

[0043] Example 1

[0044] Waste polyester-cotton blended textiles (90% polyester content) were placed in a 1:1 mixture of methanol and dichloromethane (1:1 by mass). Then, 1% betaine (based on the mass of the waste polyester and the blended textiles) was added, and the mixture was reacted at 50°C for 10 hours. After the reaction, the reaction solution was filtered to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomer. In this example, the polyester degradation rate was 80%, the DMT monomer recovery rate was 75%, and the purity of the DMT solid was 90%.

[0045] Example 2

[0046] Waste polyester-cotton blended textiles (90% polyester content) were placed in a 1:5 mass ratio of methanol and dimethyl sulfoxide (DMSO) in a 1:1 mixture. Then, 10% urea (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 60°C for 8 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this embodiment, the polyester degradation rate was 90%, the DMT recovery rate was 78%, and the purity of the DMT solid was 95%.

[0047] Example 3

[0048] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of methanol and tetrahydrofuran (1:2) at a mass ratio of 1:5. Then, 14% TBD (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 80°C for 8 hours. After the reaction was completed, the reaction solution was filtered while hot to separate unreacted spandex and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of DMT was 95%, and the purity of the DMT solid was 96%.

[0049] Example 4

[0050] Waste polyester-spandex blended textiles (95% polyester content) were placed in a 1:15 mixture of methanol and diethyl ether (1:5) at a mass ratio of 1:15. Then, 15% DBU (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 80°C for 7 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted spandex and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the DMT recovery rate was 96%, and the purity of the DMT solid was 96%.

[0051] Example 5

[0052] Waste polyester and nylon blended textiles (85% polyester content) were placed in a 1:20 mass ratio of methanol and methyl ethyl ether (1:1) as a mixed solvent. Then, 20% metformin (based on the mass of the waste polyester and nylon blended textiles) was added, and the mixture was reacted at 100°C for 2 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted polyester and nylon blended textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 95%, the DMT recovery rate was 89%, and the purity of the DMT solid was 92%.

[0053] Example 6

[0054] Waste polyester and nylon blended textiles (85% polyester content) were placed in a 1:20 mass ratio of methanol and methyl propyl ether (1:1) as a mixed solvent. Then, 10% pentamethylguanidine (based on the mass of the waste polyester and nylon blended textiles) was added, and the mixture was reacted at 100°C for 9 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted polyester and nylon blended textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the DMT recovery rate was 91%, and the purity of the DMT solid was 95%.

[0055] Example 7

[0056] Waste polyester textiles were placed in a 1:5 mass ratio of methanol and dichloromethane (1:1) as a mixed solvent, and then 50% (by weight of the waste polyester textiles) of 2-tert-butyltetramethylguanidine was added. The mixture was reacted at 60°C for 10 hours. After the reaction, a solution containing small-molecule depolymerization products was obtained. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of DMT was 93%, and the purity of the DMT solid was 97%.

[0057] Example 8

[0058] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of methanol and dichloromethane (1:0.5) at a mass ratio of 1:10. Then, 17% of 1,3-dimethylthiourea (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 80°C for 8 hours. After the reaction was completed, the reaction solution was filtered while hot to separate the incompletely reacted polyester-spandex blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 91%, the recovery rate of DMT was 83%, and the purity of the DMT solid was 95%.

[0059] Example 9

[0060] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of methanol and dichloromethane (1:0.25) at a mass ratio of 1:15. Then, 20% tetramethylguanidine (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 90°C for 6 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted spandex and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the DMT recovery rate was 95%, and the purity of the DMT solid was 94%.

[0061] Example 10

[0062] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of methanol and dimethyl sulfoxide (1:0.1) at a mass ratio of 1:20. Then, 23% of 4-dimethylaminopyridine (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 75°C for 5 hours. After the reaction was completed, the reaction solution was filtered while hot to separate the incompletely reacted polyester-spandex blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 90%, the recovery rate of DMT was 84%, and the purity of the DMT solid was 90%.

[0063] Example 11

[0064] Waste polyester and nylon blended textiles (90% polyester content) were placed in a mixed solvent of methanol and dimethyl sulfoxide (1:0.1) at a mass ratio of 1:20. Then, 30% tetrabutylammonium bromide (based on the mass of the waste polyester and nylon blended textiles) was added, and the mixture was reacted at 100°C for 2 hours. After the reaction was completed, the reaction solution was filtered while hot to separate the incompletely reacted polyester and nylon blended textiles from a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 95%, the recovery rate of DMT was 88%, and the purity of the DMT solid was 91%.

[0065] Example 12

[0066] Waste polyester-spandex blended textiles (96% polyester content) were placed in a mixed solvent of ethanol and acetone (1:10) at a mass ratio of 1:20. Then, 10% tetrabutylphosphine bromide (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 50°C for 8 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted polyester-spandex blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 82%, the recovery rate of diethyl terephthalate was 73%, and the purity of the diethyl terephthalate solid was 89%.

[0067] Example 13

[0068] Waste polyester-cotton blended textiles (80% polyester content) were placed in a mixture of ethanol and DMF (1:1) at a mass ratio of 1:20. Then, 5% betaine (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 50°C for 10 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 96%, the recovery rate of diethyl terephthalate was 85%, and the purity of the diethyl terephthalate solid was 95%.

[0069] Example 14

[0070] Waste polyester-spandex blended textiles (96% polyester content) were placed in a mixed solvent of ethanol and DMAc (1:4) at a mass ratio of 1:1. Then, 12% urea (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 75°C for 6 hours. After the reaction was completed, the reaction solution was filtered while hot to separate the incompletely reacted polyester-spandex blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 99%, the recovery rate of diethyl terephthalate was 87%, and the purity of the diethyl terephthalate solid was 95%.

[0071] Example 15

[0072] Waste polyester-cotton blended textiles (70% polyester content) were placed in a mixed solvent of ethanol and NMP (1:5) at a mass ratio of 1:3. Then, 17% TBD (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 75°C for 6 hours. After the reaction was completed, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of diethyl terephthalate was 95%, and the purity of the diethyl terephthalate solid was 96%.

[0073] Example 16

[0074] Waste polyester textiles were placed in a mixture of ethanol and acetone (1:4) at a mass ratio of 1:5, and then 20% TBD (by weight of the waste polyester textiles) was added. The mixture was reacted at 85°C for 5 hours. After the reaction, the reaction solution was filtered while hot to separate incompletely reacted polyester and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 83%, the recovery rate of diethyl terephthalate was 65%, and the purity of the diethyl terephthalate solid was 90%.

[0075] Example 17

[0076] Waste polyester and nylon textiles (85% polyester content) were placed in a mixed solvent of ethanol and dichloromethane (1:0.5) at a mass ratio of 1:10. Then, 25% TBD (by weight of the waste polyester and nylon textiles) was added, and the mixture was reacted at 100°C for 4 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted nylon and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomer. In this example, the degradation rate of polyester was 100%, the recovery rate of diethyl terephthalate was 90%, and the purity of the diethyl terephthalate solid was 96%.

[0077] Example 18

[0078] Waste polyester and nylon blended textiles (85% polyester content) were placed in a mixed solvent of ethanol and dichloromethane (1:0.1) at a mass ratio of 1:15. Then, 5% TBD (by weight of the waste polyester and nylon textiles) was added, and the mixture was reacted at 55°C for 10 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted nylon and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 95%, the recovery rate of BHET was 84%, and the purity of the BHET solid was 89%.

[0079] Example 19

[0080] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of ethylene glycol and tetrahydrofuran (1:0.1) at a mass ratio of 1:20. Then, 5% tetramethylguanidine (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 65°C for 10 hours. After the reaction, the reaction solution was filtered to separate the incompletely reacted polyester-spandex blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 85%, the recovery rate of BHET was 80%, and the purity of the BHET solid was 98%.

[0081] Example 20

[0082] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of ethylene glycol and hexamethylphosphoric acid triamine (1:0.2) at a mass ratio of 1:20. Then, 10% tetramethylguanidine (based on the mass of the waste polyester-spandex blended textiles (95% polyester content)) was added, and the mixture was reacted at 75°C for 10 hours. After the reaction was completed, the reaction solution was filtered while hot to separate the incompletely reacted polyester-spandex blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 90%, the BHET recovery rate was 83%, and the purity of the BHET solid was 95%.

[0083] Example 21

[0084] Waste polyester-spandex blended textiles (95% polyester content) were placed in a 1:20 mass ratio of ethylene glycol and acetonitrile (1:1) mixed solvent. Then, 15% tetramethylguanidine (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 80°C for 10 hours. After the reaction was completed, the reaction solution was filtered while hot to separate unreacted spandex and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomer. In this example, the degradation rate of polyester was 100%, the recovery rate of BHET was 95%, and the purity of the BHET solid was 94%.

[0085] Example 22

[0086] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of ethylene glycol and acetonitrile (1:0.7) at a mass ratio of 1:20. Then, 15% tetramethylguanidine (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 90°C for 6 hours. After the reaction was completed, the reaction solution was filtered while hot to separate unreacted spandex and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomer. In this example, the degradation rate of polyester was 100%, the recovery rate of BHET was 96%, and the purity of the BHET solid was 93%.

[0087] Example 23

[0088] Waste polyester-spandex blended textiles (95% polyester content) were placed in a mixed solvent of ethylene glycol and acetonitrile (1:0.5) at a mass ratio of 1:18. Then, 20% tetramethylguanidine (based on the mass of the waste polyester-spandex blended textiles) was added, and the mixture was reacted at 90°C for 5 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted spandex and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomer. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 95%, and the purity of the BHET solid was 95%.

[0089] Example 24

[0090] Waste polyester textiles were placed in a mixed solvent of ethylene glycol and methyl ethyl ketone (1:0.5) at a mass ratio of 1:15, and then 20% pentamethylguanidine (based on the mass of the waste polyester textiles) was added. The mixture was reacted at 100°C for 5 hours. After the reaction, a solution containing small-molecule depolymerization products was obtained. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of BHET was 96%, and the purity of the BHET solid was 93%.

[0091] Example 25

[0092] Waste polyester-cotton blended textiles (70% polyester content) were placed in a mixed solvent of ethylene glycol and methyl ethyl ketone (1:1) at a mass ratio of 1:15. Then, 30% of phosphazene alkali a (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 120°C for 8 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of BHET was 93%, and the purity of the BHET solid was 92%.

[0093] Example 26

[0094] Waste polyester and polypropylene blended textiles (40% polyester content) were placed in a 1:10 mass ratio mixed solvent of ethylene glycol and methyl ethyl ketone (1:1). Then, 50% of phosphazene base b (based on the mass of the waste polyester and polypropylene blended textiles) was added, and the mixture was reacted at 120°C for 5 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted polypropylene and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomer. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 94%, and the purity of the BHET solid was 93%.

[0095] Example 27

[0096] Waste polyester-cotton blended textiles (20% polyester content) were placed in a 1:10 mixture of ethylene glycol and DMSO (1:1) at a mass ratio of 1:10. Then, 25% phosphazene alkali (C) based on the mass of the waste polyester-cotton blended textiles was added, and the mixture was reacted at 140°C for 6 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 92%, and the purity of the BHET solid was 93%.

[0097] Example 28

[0098] Waste polyester and acrylic blended textiles (50% polyester content) were placed in a 1:10 mixture of ethylene glycol and DMSO (1:1) at a mass ratio of 1:10. Then, 20% phosphazene alkali (d) based on the mass of the waste polyester and acrylic blended textiles (95% polyester content) was added, and the mixture was reacted at 150°C for 6 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted acrylic fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of BHET was 95%, and the purity of the BHET solid was 95%.

[0099] Example 29

[0100] Waste polyester and acrylic blended textiles (95% polyester content) were placed in a mixed solvent of ethylene glycol and DMSO (1:2) at a mass ratio of 1:15. Then, 0.1% phosphazene base e (based on the mass of the waste polyester and acrylic blended textiles) was added, and the mixture was reacted at 160°C for 8 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted acrylic fibers and a solution containing small-molecule depolymerization products. The solution containing small-molecule depolymerization products was then separated by cooling and crystallization to obtain depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of BHET was 93%, and the purity of BHET solid was 95%.

[0101] Example 30

[0102] Waste polyester and vinylon blended textiles (90% polyester content) were placed in a mixture of ethylene glycol and DMSO (1:3) at a mass ratio of 1:15. Then, 0.1% phosphazene alkali f (based on the mass of the waste polyester and vinylon blended textiles) was added, and the mixture was reacted at 160°C for 4 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted vinylon and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 88%, and the purity of the BHET solid was 91%.

[0103] Example 31

[0104] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixed solvent of ethylene glycol and DMF (1:0.5) at a mass ratio of 1:50. Then, 5% (by weight of the waste polyester-cotton blended textiles) of phosphazene alkali was added, and the mixture was reacted at 160°C for 2.5 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this embodiment, the polyester degradation rate was 100%, the BHET recovery rate was 85%, and the purity of the BHET solid was 90%.

[0105] Example 32

[0106] Waste polyester, lyocell, and viscose blended textiles (75% polyester content) were placed in a 1:80 mass ratio of ethylene glycol and DMF (1:1). Then, 7% phosphazene alkali (h) based on the mass of the waste polyester, lyocell, and viscose blended textiles was added, and the mixture was reacted at 155°C for 2.5 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted lyocell and viscose fibers from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 91%, and the purity of the BHET solid was 92%.

[0107] Example 33

[0108] Waste polyester, regenerated cellulose fiber, and acetate fiber blended textiles (80% polyester content) were placed in a 1:100 mixture of ethylene glycol and DMF (1:1). Then, 10% phosphazene base (based on the mass of the waste polyester, regenerated cellulose fiber, and acetate fiber blended textiles) was added, and the mixture was reacted at 150°C for 2 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted regenerated cellulose fiber and acetate fiber from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 95%, and the purity of the BHET solid was 94%.

[0109] Example 34

[0110] Waste polyester, cotton, and viscose blended textiles (80% polyester content) were placed in a 1:20 mass ratio of ethylene glycol and NMP (1:1) mixture. Then, 20% phosphazene alkali (based on the mass of the waste polyester, cotton, and viscose blended textiles) was added, and the mixture was reacted at 140°C for 1 hour. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton and viscose fibers from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 89%, and the purity of the BHET solid was 90%.

[0111] Example 35

[0112] Waste polyester, polypropylene, regenerated cellulose fiber, and acetate fiber blended textiles (70% polyester content) were placed in a 1:20 mass ratio of ethylene glycol and NMP (1:1) mixture. Then, 30% phosphazene base K (based on the mass of the waste polyester, polypropylene, regenerated cellulose fiber, and acetate fiber blended textiles) was added, and the mixture was reacted at 140°C for 1 hour. After the reaction, the reaction solution was filtered while hot to separate unreacted polypropylene, regenerated cellulose fiber, and acetate fiber from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the BHET recovery rate was 91%, and the purity of the BHET solid was 90%.

[0113] Example 36

[0114] Waste polyester textiles were placed in a mixture of ethylene glycol and NMP (1:1) at a mass ratio of 1:20. Then, 50% of phosphazene alkali (based on the mass of the waste polyester textiles) was added, and the mixture was reacted at 120°C for 5 minutes. After the reaction was completed, the reaction solution was filtered while hot to separate the incompletely reacted polyester textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 90%, the recovery rate of BHET was 81%, and the purity of the BHET solid was 91%.

[0115] Example 37

[0116] Waste polyester and polypropylene blended textiles (50% polyester content) were placed in a mixed solvent of ethylene glycol and NMP (1:0.5) at a mass ratio of 1:20. Then, 50% of phosphazene alkali (m) based on the mass of the waste polyester and polypropylene blended textiles was added, and the mixture was reacted at 150°C for 25 minutes. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted waste polyester and polypropylene blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 95%, the BHET recovery rate was 88%, and the purity of the BHET solid was 94%.

[0117] Example 38

[0118] Waste polyester engineering plastics were placed in a 1:10 mass ratio of ethylene glycol and acetonitrile (1:1) mixed solvent, followed by the addition of 25% TBD (based on the mass of the waste polyester engineering plastics). The reaction was carried out at 100°C for 5 hours. After the reaction was completed, the reaction solution was filtered while hot to obtain a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of the polyester engineering plastics was 100%, the recovery rate of BHET was 93%, and the purity of the BHET solid was 97%.

[0119] Example 39

[0120] Waste polyester nonwoven fabric was placed in a 1:10 mass ratio of methanol and acetonitrile (1:1) mixture, followed by the addition of 50% DBU (based on the mass of the waste polyester nonwoven fabric). The mixture was reacted at 100°C for 5 hours. After the reaction, the reaction solution was filtered while hot to obtain a solution containing small-molecule depolymerization products. This solution was then cooled and crystallized to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of the waste polyester nonwoven fabric was 100%, the DMT recovery rate was 92%, and the purity of the DMT solid was 95%.

[0121] Example 40

[0122] Waste polyester-cotton blended textiles (50% polyester content) were placed in a 1:10 mass ratio of n-propanol and dichloromethane (1:1) mixture. Then, 0.1% phosphazene alkali a (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 95°C for 3 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the di-n-propyl terephthalate recovery rate was 90%, and the purity of the di-n-propyl terephthalate solid was 96%.

[0123] Example 41

[0124] Waste polyester-cotton blended textiles (50% polyester content) were placed in a 1:15 mass ratio of isopropanol and dichloromethane (1:1) mixture. Then, 0.5% phosphazene alkali a (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 80°C for 5 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the diisopropyl terephthalate recovery rate was 93%, and the purity of the diisopropyl terephthalate solid was 95%.

[0125] Example 42

[0126] Waste polyester-cotton blended textiles (50% polyester content) were placed in a mixed solvent of n-butanol and tetrahydrofuran (1:1) at a mass ratio of 1:10. Then, 50% of phosphazene base b (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 115°C for 5 hours. After the reaction was completed, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing small-molecule depolymerization products was then separated by cooling and crystallization to obtain depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of di-n-butyl terephthalate was 91%, and the purity of the di-n-butyl terephthalate solid was 94%.

[0127] Example 43

[0128] Waste polyester and nylon blended textiles (50% polyester content) were placed in a mixed solvent of isobutanol and tetrahydrofuran (1:3) at a mass ratio of 1:20. Then, 50% of phosphazene base b (based on the mass of the waste polyester and nylon blended textiles) was added, and the mixture was reacted at 100°C for 3 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted nylon and a solution containing small-molecule depolymerization products. The solution containing small-molecule depolymerization products was then separated by cooling and crystallization to obtain depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of diisobutyl terephthalate was 91%, and the purity of diisobutyl terephthalate solid was 94%.

[0129] Example 44

[0130] Waste polyester textiles (50% polyester content) were placed in a mixed solvent of sec-butanol and tetrahydrofuran (1:3) at a mass ratio of 1:5. Then, 50% of phosphazene base c (based on the mass of the waste polyester textiles) was added, and the mixture was reacted at 100°C for 10 hours. After the reaction, a solution containing small-molecule depolymerization products was obtained. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of di-sec-butyl terephthalate was 90%, and the purity of the di-sec-butyl terephthalate solid was 91%.

[0131] Example 45

[0132] Waste polyester-cotton blended textiles (80% polyester content) were placed in a 1:1 mass ratio of tert-butanol and tetrahydrofuran (1:1) as a mixed solvent. Then, 50% of phosphazene alkali c (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 85°C for 10 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the di-tert-butyl terephthalate recovery rate was 88%, and the purity of the di-tert-butyl terephthalate solid was 90%.

[0133] Example 46

[0134] Waste polyester-cotton blended textiles (80% polyester content) were placed in a 1:1 mixture of n-pentanol and dichloromethane (1:1) at a mass ratio of 1:1. Then, 40% of phosphazene alkali C (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 130°C for 7 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the di-n-pentyl terephthalate recovery rate was 95%, and the purity of the di-n-pentyl terephthalate solid was 93%.

[0135] Example 47

[0136] Waste polyester-cotton blended textiles (80% polyester content) were placed in a mixed solvent of hexanol and acetonitrile (4:1) at a mass ratio of 1:10. Then, 40% of phosphazene alkali (d) based on the mass of the waste polyester-cotton blended textiles was added, and the mixture was reacted at 150°C for 9 hours. After the reaction, the reaction solution was filtered while hot to separate unreacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of di-n-hexyl terephthalate was 90%, and the purity of the di-n-hexyl terephthalate solid was 93%.

[0137] Example 48

[0138] Waste polyester-cotton blended textiles (80% polyester content) were placed in a 1:1 mixture of 1,2-propanediol and acetonitrile (1:1) at a mass ratio of 1:1. Then, 30% phosphazene alkali (d) based on the mass of the waste polyester-cotton blended textiles was added, and the mixture was reacted at 75°C for 5 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 71%, and the recovery rate of the alcoholysis products was 90%.

[0139] Example 49

[0140] Waste polyester textiles were placed in a mixed solvent of 1,3-propanediol and DMSO (4:1) at a mass ratio of 1:10. Then, 13% phosphazene base e (based on the mass of the waste polyester textiles) was added, and the mixture was reacted at 150°C for 30 minutes. After the reaction, a solution containing small-molecule depolymerization products was obtained. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of di-n-propanol terephthalate was 91%, and the purity of di-n-hexyl terephthalate solid was 95%.

[0141] Example 50

[0142] Waste polyester-cotton blended textiles (80% polyester content) were placed in a mixed solvent of 1,4-butanediol and DMSO (5:1) at a mass ratio of 1:10. Then, 25% sodium methoxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 160°C for 9 hours. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 100%, the recovery rate of di-n-butyl terephthalate was 89%, and the purity of the di-n-butyl terephthalate solid was 90%.

[0143] Example 51

[0144] Waste polyester-cotton blended textiles (80% polyester content) were placed in a 1:5 mass ratio of glycerol and dichloromethane (1:1) as a mixed solvent. Then, 50% potassium methoxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 60°C for 30 minutes. After the reaction, the reaction solution was filtered to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 67%, and the recovery rate of the alcoholysis products was 60%.

[0145] Example 52

[0146] Waste polyester-cotton blended textiles (80% polyester content) were placed in a mixed solvent of 1,6-hexanediol and DMF (4:1) at a mass ratio of 1:5. Then, 25% sodium ethoxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 80°C for 1 hour. After the reaction, the reaction solution was filtered while hot to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 81%, the recovery rate of dihexanediol terephthalate was 77%, and the purity of the dihexanediol terephthalate solid was 89%.

[0147] Example 53

[0148] Waste polyester-cotton blended textiles (80% polyester content) were placed in a 1:10 mass ratio of diethylene glycol and acetonitrile (1:1) as a mixed solvent. Then, 50% potassium ethoxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 90°C for 5 minutes. After the reaction, the reaction solution was filtered to separate the incompletely reacted waste polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 7%, the alcoholysis product recovery rate was 3%, and the purity was 90%.

[0149] Example 54

[0150] Waste polyester textiles were placed in methanol at a mass ratio of 1:100, followed by the addition of 10% phosphazene alkali a (based on the mass of the waste polyester textiles). The mixture was reacted at 80°C for 10 hours. After the reaction, the reaction solution was filtered while still hot to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then cooled and crystallized to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of polyester was 85%, the recovery rate of DMT was 78%, and the purity of the DMT solid was 95%.

[0151] Example 55

[0152] Waste polyester textiles were placed in methanol at a mass ratio of 1:1, followed by the addition of 0.1% phosphazene alkali a (based on the mass of the waste polyester textiles). The mixture was reacted at 50°C for 400 minutes. After the reaction, the reaction solution was filtered to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of polyester was 90%, the recovery rate of DMT was 88%, and the purity of the DMT solid was 94%.

[0153] Example 56

[0154] Waste polyester textiles were placed in methanol at a mass ratio of 1:1, followed by the addition of 1% phosphazene alkali a (based on the mass of the waste polyester textiles). The mixture was reacted at 50°C for 300 minutes. After the reaction, the reaction solution was filtered to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of polyester was 95%, the recovery rate of DMT was 92%, and the purity of the DMT solid was 95%.

[0155] Example 57

[0156] Waste polyester textiles were placed in methanol at a mass ratio of 1:5, followed by the addition of 10% phosphazene alkali a (based on the mass of the waste polyester textiles). The mixture was reacted at 80°C for 200 minutes. After the reaction, the reaction solution was filtered to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of polyester was 99%, the recovery rate of DMT was 96%, and the purity of the DMT solid was 95%.

[0157] Example 58

[0158] Waste polyester textiles were placed in methanol at a mass ratio of 1:10, followed by the addition of 15% phosphazene alkali a (based on the mass of the waste polyester textiles). The mixture was reacted at 120°C for 100 minutes. After the reaction, the reaction solution was filtered to obtain a solution containing small-molecule depolymerization products. This solution was then cooled and crystallized to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of polyester was 100%, the recovery rate of DMT was 98%, and the purity of the DMT solid was 95%.

[0159] Example 59

[0160] Waste polyester textiles were placed in methanol at a mass ratio of 1:10, followed by the addition of 0.01% phosphazene alkali a (based on the mass of the waste polyester textiles). The mixture was reacted at 150°C for 100 minutes. After the reaction, the reaction solution was filtered to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this embodiment, the degradation rate of polyester was 84%, the recovery rate of DMT was 80%, and the purity of the DMT solid was 91%.

[0161] Example 60

[0162] Waste polyester textiles were placed in ethanol at a mass ratio of 1:100, followed by the addition of 5% phosphazene base b (based on the mass of the waste polyester textiles). The mixture was reacted at 90°C for 120 minutes. After the reaction, the reaction solution was filtered to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 71%, the recovery rate of diethyl terephthalate was 67%, and the purity of the diethyl terephthalate solid was 89%.

[0163] Example 61

[0164] Waste polyester textiles were placed in ethanol at a mass ratio of 1:20, followed by the addition of 10% phosphazene base b (based on the mass of the waste polyester textiles). The mixture was reacted at 100°C for 120 minutes. After the reaction, the reaction solution was filtered to separate incompletely reacted waste polyester textiles from a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 87%, the recovery rate of diethyl terephthalate was 84%, and the purity of the diethyl terephthalate solid was 90%.

[0165] Example 62

[0166] Waste polyester-cotton blended textiles (90% polyester content) were placed in ethylene glycol at a mass ratio of 1:80, followed by the addition of 1% phosphazene alkali c (based on the mass of the waste polyester-cotton blended textiles). The reaction was carried out at 100°C for 180 minutes. After the reaction, the reaction solution was filtered to separate the incompletely reacted polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 75%, the BHET recovery rate was 65%, and the purity of the BHET solid was 90%.

[0167] Example 63

[0168] Waste polyester-cotton blended textiles (90% polyester content) were placed in n-propanol and isopropanol (1:1) at a mass ratio of 1:70. Then, 10% phosphazene alkali (d) based on the mass of the waste polyester-cotton blended textiles was added, and the mixture was reacted at 60°C for 4 hours. After the reaction, the reaction solution was filtered to separate the incompletely reacted polyester-cotton blended textiles and a solution containing small molecule depolymerization products. The solution containing the small molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 70%, and the recovery rate of the alcoholysis products was 65%.

[0169] Example 64

[0170] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixture of n-butanol, isobutanol, primary butanol, and tert-butanol (1:1:1:1 by mass) at a ratio of 1:50. Then, 10% phosphazene base e (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 150°C for 5 hours. After the reaction, the reaction solution was filtered to separate the incompletely reacted polyester-cotton blended textiles and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the polyester degradation rate was 90%, and the recovery rate of the alcoholysis products was 79%.

[0171] Example 65

[0172] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixture of n-pentanol and n-hexanol (1:1:) at a mass ratio of 1:20. Then, 15% phosphazene alkali f (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 180°C for 500 min. After the reaction, the reaction solution was filtered to separate the reacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, and the recovery rate of the alcoholysis products was 86%.

[0173] Example 66

[0174] Waste polyester-cotton blended textiles (90% polyester content) were placed in 1,2-propanediol and 1,3-propanediol (1:1:) at a mass ratio of 1:10. Then, 20% (by weight of the waste polyester-cotton blended textiles) of phosphazene alkali was added, and the mixture was reacted at 200°C for 600 min. After the reaction, the reaction solution was filtered to separate the reacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, and the recovery rate of the alcoholysis products was 93%.

[0175] Example 67

[0176] Waste polyester-cotton blended textiles (90% polyester content) were placed in 1,4-butanediol at a mass ratio of 1:5, followed by the addition of 30% phosphazene alkali (h) based on the mass of the waste polyester-cotton blended textiles. The reaction was carried out at 160°C for 600 min. After the reaction, the reaction solution was filtered to separate the reacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of di-n-butyl terephthalate was 95%, and the purity of di-n-butyl terephthalate was 94%.

[0177] Example 68

[0178] Waste polyester-cotton blended textiles (90% polyester content) were placed in glycerol at a mass ratio of 1:2, followed by the addition of 40% phosphazene base I (based on the mass of the waste polyester-cotton blended textiles). The reaction was carried out at 180°C for 400 minutes. After the reaction, the reaction solution was filtered to separate the reacted cotton fibers and a solution containing small-molecule depolymerization products. The solution containing the small-molecule depolymerization products was then separated by cooling and crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, and the recovery rate of the alcoholysis products was 95%.

[0179] Example 69

[0180] Waste polyester textiles were placed in 1,6-hexanediol at a mass ratio of 1:1, followed by the addition of 50% phosphazene base K (based on the mass of the waste polyester textiles). The reaction was carried out at 240°C for 300 minutes. After the reaction, a solution containing small-molecule depolymerization products was obtained. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of di-n-hexanediol terephthalate was 94%, and the purity was 95%.

[0181] Example 70

[0182] Waste polyester textiles were placed in diethylene glycol at a mass ratio of 1:1, followed by the addition of 50% phosphazene alkali (based on the mass of the waste polyester textiles). The mixture was reacted at 250°C for 200 minutes. After the reaction, a solution containing small-molecule depolymerization products was obtained. The solution containing the small-molecule depolymerization products was then separated by cooling crystallization to obtain the depolymerized polyester monomers. In this example, the degradation rate of polyester was 100%, the recovery rate of the alcoholysis products was 91%, and the purity was 96%.

[0183] Example 71

[0184] Waste polyester textiles were placed in a mixture of n-propanol, isopropanol, and dichloromethane (1:1:1) at a mass ratio of 1:10. Then, 0.01% sodium hydroxide (based on the mass of the waste polyester textiles) was added, and the mixture was reacted at 50°C for 300 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 5%, the PTA yield was 2%, and the purity was 95%.

[0185] Example 72

[0186] Waste polyester-spandex blended textiles (94% polyester content) were placed in a mixture of n-propanol, isopropanol, and dichloromethane (1:1:1) at a mass ratio of 1:50. Then, 1% sodium hydroxide (based on the mass of the waste polyester textiles) was added, and the mixture was reacted at 75°C for 4 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 10%, the PTA yield was 6%, and the purity was 97%.

[0187] Example 73

[0188] Waste polyester and polypropylene blended textiles (90% polyester content) were placed in a mixture of n-propanol, isopropanol, and dichloromethane (1:1:1) at a mass ratio of 1:20. Then, 10% sodium hydroxide (based on the mass of the waste polyester textiles) was added, and the mixture was reacted at 80°C for 3 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 78%, the PTA yield was 71%, and the purity was 98%.

[0189] Example 74

[0190] Waste polyester-cotton blended textiles (90% polyester content) were placed in methanol and acetonitrile (1:1) at a mass ratio of 1:10, followed by the addition of 100% sodium hydroxide (based on the mass of the waste polyester-cotton blended textiles). The mixture was reacted at 25°C for 6 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 98%, and the purity was 99%.

[0191] Example 75

[0192] Waste polyester-cotton blended textiles (90% polyester content) were placed in ethanol and acetonitrile (1:1) at a mass ratio of 1:15, followed by the addition of 80% sodium hydroxide (based on the mass of the waste polyester-cotton blended textiles). The mixture was reacted at 50°C for 1 hour. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 70%, the PTA yield was 61%, and the purity was 95%.

[0193] Example 76

[0194] Waste polyester and acrylic blended textiles (80% polyester content) were placed in n-propanol and tetrahydrofuran (1:1) at a mass ratio of 1:20. Then, 130% sodium hydroxide (based on the mass of the waste polyester and acrylic blended textiles) was added, and the mixture was reacted at 70°C for 2 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 91%, the PTA yield was 88%, and the purity was 95%.

[0195] Example 77

[0196] Waste polyester, viscose fiber, and lyocell blended textiles (90% polyester content) were placed in a mixture of n-pentanol, n-hexanol, and tetrahydrofuran (1:1:1) at a mass ratio of 1:10. Then, 50% sodium hydroxide (based on the mass of the waste polyester and acrylic blended textiles) was added, and the mixture was reacted at 70°C for 3 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 95%, the PTA yield was 90%, and the purity was 95%.

[0197] Example 78

[0198] Waste polyester, regenerated cellulose fiber, and acetate fiber blended textiles (85% polyester content) were placed in a mixture of tert-butanol, dimethyl sulfoxide (1:1:1) at a mass ratio of 1:15. Then, 60% sodium hydroxide (based on the mass of the waste polyester and acrylic blended textiles) was added, and the mixture was reacted at 75°C for 0.5 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 90%, the PTA yield was 84%, and the purity was 95%.

[0199] Example 79

[0200] Waste polyester and acrylic blended textiles (95% polyester content) were placed in a mixture of n-butanol, isobutanol, and DMF (1:1:1) at a mass ratio of 1:15. Then, 40% sodium hydroxide and potassium hydroxide (1:1) based on the mass of the waste polyester and acrylic blended textiles were added, and the mixture was reacted at 80°C for 1 hour. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 90%, the PTA yield was 88%, and the purity was 96%.

[0201] Example 80

[0202] Waste polyester-cotton blended textiles (75% polyester content) were placed in methanol and dichloromethane (1:1) at a mass ratio of 1:10. Then, 35% potassium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 25°C for 4 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 88%, the PTA yield was 85%, and the purity was 98%.

[0203] Example 81

[0204] Waste polyester-cotton blended textiles (75% polyester content) were placed in methanol, acetonitrile, and methyl propyl ether (1:1:0.5) at a mass ratio of 1:20. Then, 50% potassium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 80°C for 1 hour. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 95%, the PTA yield was 93%, and the purity was 97%.

[0205] Example 82

[0206] Waste polyester-cotton blended textiles (90% polyester content) were placed in ethanol and dichloromethane (1:1) at a mass ratio of 1:20, followed by the addition of potassium hydroxide at 150% of the mass of the waste polyester-ammonia blended textiles. The mixture was reacted at 25°C for 30 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 96%, and the purity was 97%.

[0207] Example 83

[0208] Waste polyester-cotton blended textiles (75% polyester content) were placed in ethanol and tetrahydrofuran (1:0.5) at a mass ratio of 1:15, followed by the addition of potassium hydroxide at 150% of the mass of the waste polyester-ammonia blended textiles. The mixture was reacted at 40°C for 2 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 95%, and the purity was 98%.

[0209] Example 84

[0210] Waste polyester-cotton blended textiles (75% polyester content) were placed in methanol and tetrahydrofuran (1:1) at a mass ratio of 1:2, followed by the addition of 0.01% potassium hydroxide (based on the mass of the waste polyester-cotton blended textiles). The mixture was reacted at 70°C for 5 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 10%, the PTA yield was 5%, and the purity was 90%.

[0211] Example 85

[0212] Waste polyester-cotton blended textiles (75% polyester content) were placed in methanol and methyl ethyl ketone (1:1) at a mass ratio of 1:20. Then, potassium hydroxide at 250% of the mass of the waste polyester-cotton blended textiles was added, and the mixture was reacted at 70°C for 5 hours. The reaction solution was filtered while hot to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 98%, and the purity was 99%.

[0213] Example 86

[0214] Waste polyester-cotton blended textiles (75% polyester content) were placed in n-propanol and tetrahydrofuran (1:1) at a mass ratio of 1:20. Then, 250% potassium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 100°C for 5 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 99%, and the purity was 99%.

[0215] Example 87

[0216] Waste polyester and polypropylene blended textiles (75% polyester content) were placed in a mixture of n-butanol, acetonitrile, and methyl ethyl ether (1:1:1) at a mass ratio of 1:20. Then, 300% sodium hydroxide (based on the mass of the waste polyester and polypropylene blended textiles) was added, and the mixture was reacted at 120°C for 5 hours. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 100%, the PTA yield was 98%, and the purity was 98%.

[0217] Example 88

[0218] Waste polyester and polypropylene blended textiles (75% polyester content) were placed in ethanol and dichloromethane (1:1) at a mass ratio of 1:20. Then, 300% sodium hydroxide (based on the mass of the waste polyester and polypropylene blended textiles) was added, and the mixture was reacted at room temperature for 5 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 98%, the PTA yield was 92%, and the purity was 98%.

[0219] Example 89

[0220] Waste polyester and polypropylene blended textiles (75% polyester content) were placed in ethanol and dichloromethane (1:1) at a mass ratio of 1:20. Then, 500% potassium hydroxide (based on the mass of the waste polyester and polypropylene blended textiles) was added, and the mixture was reacted at 25°C for 5 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 100%, the PTA yield was 99%, and the purity was 99%.

[0221] Example 90

[0222] Waste polyester bottle flakes were placed in ethanol and dichloromethane (1:1) at a mass ratio of 1:20, followed by the addition of 200% sodium hydroxide (based on the mass of waste polyester and polypropylene blended textiles). The mixture was reacted at 25°C for 30 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 100%, the PTA yield was 98%, and the purity was 99%.

[0223] Example 91

[0224] Waste polyester film was placed in ethanol and diethyl ether (1:1) at a mass ratio of 1:20, and then 200% potassium hydroxide (based on the mass of waste polyester and polypropylene blended textiles) was added. The mixture was reacted at 25°C for 25 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 99%, and the purity was 99%.

[0225] Example 92

[0226] Waste polyester-cotton blended textiles (90% polyester content) were placed in methanol, ethanol, and hexamethylphosphoric acid triamine (1:1:1) at a mass ratio of 1:10. Then, 0.01% sodium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at room temperature for 5 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 3%.

[0227] Example 93

[0228] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixture of n-propanol, isopropanol, and 1,3-dimethyl-2-imidazolinone (1:1:1) at a mass ratio of 1:10. Then, 0.1% sodium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 25°C for 100 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 11%, the PTA yield was 9%, and the purity was 95%.

[0229] Example 94

[0230] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixture of n-butanol, isobutanol, primary butanol, and N,N-dimethylacetamide (1:1:1:1 by mass) at a ratio of 1:1. Then, 20% sodium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 60°C for 200 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 15%, the PTA yield was 11%, and the purity was 96%.

[0231] Example 95

[0232] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixture of n-pentanol, n-hexanol, tert-butanol, and N,N-dimethylformamide (1:1:1:2) at a mass ratio of 1:50. Then, 50% sodium hydroxide (based on the mass of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 100°C for 300 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 54%, the PTA yield was 50%, and the purity was 98%.

[0233] Example 96

[0234] Waste polyester textiles were placed in a mixture of n-pentanol, n-hexanol, tert-butanol, and acetone (1:2:1:1) at a mass ratio of 1:20. Then, potassium hydroxide (200% of the mass of the waste polyester textiles) was added, and the mixture was reacted at 120°C for 500 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the degradation rate of polyester was 100%, the PTA yield was 98%, and the purity was 98%.

[0235] Example 97

[0236] Waste polyester-cotton blended textiles (90% polyester content) were placed in a mixture of hexanol and N-methylpyrrolidone (1:1) at a mass ratio of 1:100. Then, potassium hydroxide (500% by weight of the waste polyester-cotton blended textiles) was added, and the mixture was reacted at 120°C for 600 minutes. While still hot, the reaction solution was filtered to separate the solid and liquid components. The solid product was filtered again after adding a small amount of water, and the filtrate was acidified and dried to obtain the product PTA. In this example, the polyester degradation rate was 100%, the PTA yield was 91%, and the purity was 95%.

[0237] In the above methods, after the small molecule degradation products precipitate out of the reaction solution or cool and crystallize into depolymerized polyester monomers, the reaction solution obtained after separating the depolymerized polyester monomers can be directly reused for the mild and selective depolymerization and recycling of waste polyester and its blended textiles. Alternatively, the reaction solvent and catalyst in the reaction solution can be collected separately and reused for the mild and selective depolymerization and recycling of waste polyester and its blended textiles.

Claims

1. A mild and selective depolymerization recycling method for waste polyester blended textiles. This method uses waste polyester blended textiles as raw materials. Under the action of an alkaline catalyst, and with alcohols or a mixture of alcohols and aprotic solvents as the reaction solvent, the polyester in the waste polyester blended textiles undergoes selective alcoholysis, depolymerizing to generate easily separable and repeatedly polymerizable small-molecule degradation products. Other non-polyester components do not undergo chemical changes. The specific process steps and conditions are as follows: Waste polyester blended textiles are placed in a reaction solvent at a mass ratio of 1:1~100, followed by the addition of 0.01~500% alkaline catalyst (based on the mass of the waste polyester blended textiles). The reaction is carried out at room temperature to 250℃ for 5~600 min. After the reaction is complete, the reaction solution is filtered while hot to separate the undepolymerized non-polyester components, the incompletely reacted polyester textile solids, and a solution containing easily separable and repolymerizable small molecule depolymerization products. The solution is then separated to obtain the reaction solvent and the repolymerizable small molecule depolymerization products. The alkaline catalyst used is an organic base, specifically at least one of the following: urea, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, bimethylguanidine, tetramethylguanidine, 2-tert-butyl-1,1,3,3-tetramethylguanidine, 1,1,2,3,3-pentamethylguanidine, 1,3-dimethylthiourea, betaine, 4-dimethylaminopyridine, tetrabutylammonium bromide, tetrabutylphosphine bromide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, and phosphazene base; The alcohols used are at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, primary butanol, tert-butanol, n-pentanol, n-hexanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, glycerol, 1,6-hexanediol, and diethylene glycol. The aprotic solvent used is at least one of dichloromethane, dimethyl sulfoxide, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolinone, hexamethylphosphoric triamine, N-methylpyrrolidone, acetonitrile, methyl ethyl ketone, diethyl ether, methyl ethyl ether, and methyl propyl ether.

2. The recycling method according to claim 1, characterized in that... The phosphazene base mentioned in this method is at least one of the following structures: 。 3. The recycling method according to claim 1 or 2, characterized in that... In this method, when waste polyester blended textiles undergo selective alcoholysis, the reaction temperature is 50~250℃ and the reaction time is 5~600 min when the reaction solvent is an alcohol compound; and the reaction temperature is 50~160℃ and the reaction time is 5~300 min when the reaction solvent is an alcohol compound and an aprotic solvent.

4. The recycling method according to claim 1 or 2, characterized in that... In this method, when waste polyester blended textiles undergo selective alcoholysis, the reaction temperature is 50~180℃ and the reaction time is 5~600 min when the reaction solvent is an alcohol compound; and the reaction temperature is 50~140℃ and the reaction time is 5~300 min when the reaction solvent is an alcohol compound and an aprotic solvent.

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