A method for recycling waste polyester textiles

Abstract

The application belongs to the technical field of regenerated polyester, and particularly relates to a recycling method of waste polyester textiles, which comprises the following steps: decolorizing colored waste polyester textiles by using a decolorizing agent, wherein the decolorizing agent is one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; depolymerizing the decolorized polyester textiles by using a depolymerizing agent to obtain terephthalate, wherein the depolymerization rate of the decolorized polyester textiles is 98.0-100%; converting the terephthalate into DMT first, and then performing a re-polymerization reaction on the DMT, ethylene glycol, a catalyst and a functional additive to obtain regenerated PET. The application adopts a process of decolorizing first and then depolymerizing, and the decolorizing and depolymerizing are coordinated, so that the process is simplified, the energy consumption and pollution are reduced, and the economy and sustainability of the recycling of waste polyester textiles are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of regenerated polyester, and particularly relates to a recycling method of waste polyester textiles. BACKGROUND

[0002] With the rapid development of the global textile industry, polyester (PET, polyethylene terephthalate) as the largest synthetic fiber, its consumption continues to rise. Due to the highly stable molecular structure of polyester, the covalent bond formed by the traditional dyeing process has high binding firmness, which makes the decolorization and regeneration of waste polyester textiles a technical difficulty in the field of circular economy.

[0003] The traditional decolorization method commonly used in the industry at present mainly relies on high-boiling organic solvent systems, such as N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and other polar solvents. This kind of solvent realizes decolorization by destroying the intermolecular force between the dye and the fiber, has the advantages of high decolorization efficiency and wide application range, and occupies a dominant position in large-scale decolorization.

[0004] For example, the patent application with the application publication number CN119465612A discloses a decolorization method of waste colored polyester fabric, which adopts a mixed decolorization solvent prepared by mixing organic solvent tetramethyl urea and reducing agent sulfourea aqueous solution for multi-stage soaking decolorization, and then obtains regenerated white textiles through solid-liquid separation, and recovers regenerated decolorization solvent after distillation and rectification of the dark decolorization solvent after repeated use.

[0005] However, the above high-boiling organic solvents have significant limitations: first, the boiling points of these high-boiling organic solvents are generally higher than 150℃, for example, the boiling point of tetramethyl urea is 176.5℃, and its recovery process needs to maintain a high-temperature environment, which significantly increases the energy consumption and production cost; second, the above high-boiling organic solvents have high biological toxicity and environmental risk, long-term contact may cause occupational health hazards, and are difficult to degrade through conventional sewage treatment systems; finally, the low volatility of these high-boiling organic solvents makes it difficult to control the residual amount of solvent in the decolored fiber, and the residual solvent not only affects the spinnability and dyeing performance of the regenerated fiber, but also may release harmful gases in the subsequent processing process, which restricts the quality improvement of regenerated textiles, and these problems seriously hinder the development of efficient recycling technology of waste polyester textiles.

[0006] Therefore, it is necessary to develop a recycling method of waste polyester textiles by using a solvent with low boiling point, low toxicity and high volatility. SUMMARY

[0007] The application aims to solve the problems in the prior art and provide a recycling method of waste polyester textiles.

[0008] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0009] A recycling method of waste polyester textiles, comprising the step of decolorizing colored waste polyester textiles with a decolorizing agent, the decolorizing agent being one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0010] In colored polyester textiles, the short-range interaction between dyes and polyester mainly relies on van der Waals force and hydrogen bond; under high-temperature conditions of 130-140 DEG C (the dyeing temperature of polyester), dyes will enter the amorphous region of polyester, which means that, if the decolorization of such dyeing system is to be realized by physical method, the interaction between the decolorizing agent and dyes and polyester should be considered; in the process of physical decolorization, when polyester swells in the decolorizing agent, its internal pores will be expanded, however, to realize decolorization, dyes must effectively interact with the decolorizing agent, if the decolorizing agent cannot dissolve dyes and simultaneously destroy the binding force between dyes and polyester, even if polyester has swelled, dyes will still remain on polyester; therefore, in the process of physical decolorization, swelling is a necessary prerequisite for decolorization, but not a sufficient condition; taking toluene as an example, toluene can make polyester slightly swell, but it is difficult to decolorize colored waste polyester textiles because of its low solubility for dyes and its ability to destroy the binding force between dyes and polyester.

[0011] The present inventors have carried out a large number of experiments and theoretical calculations, and after numerous attempts and analysis, the decolorizing agent used in the present application is determined, the solubility parameter of which is very close to that of polyester, this property enables the decolorizing agent to smoothly penetrate into the interior of polyester fibers without dissolving polyester, and to cause the swelling of polyester fibers; the decolorizing agent can also dissolve dyes and simultaneously destroy the binding force between dyes and polyester, thus realizing the separation of dyes from the surface of polyester fibers.

[0012] As a preferred technical scheme:

[0013] The specific process of decolorizing colored waste polyester textiles with a decolorizing agent according to the recycling method of waste polyester textiles as described above is as follows: firstly, under the protection of nitrogen or inert gas, the colored waste polyester textiles are put into the decolorizing agent for preliminary decolorization, and then solid-liquid separation is carried out to obtain decolorized polyester textile semi-product and decolorizing liquid; then, under the protection of nitrogen or inert gas, the decolorized polyester textile semi-product is put into the decolorizing agent for deep decolorization, and then solid-liquid separation is carried out to obtain decolorized polyester textiles and decolorizing liquid; finally, all the decolorizing liquid is subjected to recovery treatment to obtain recovered decolorizing agent and recovered dyes.

[0014] The waste polyester textile product recovery method as described above, in the preliminary decolorization, the bath ratio (the mass ratio of the colored waste polyester textile product and the decolorizing agent) is 1:10-70, the decolorization temperature is 120-140 DEG C, and the decolorization time is 10-40 min;

[0015] After preliminary decolorization, the decolorization rate of the colored waste polyester textile product is 97.6-98.7% according to the K / S value, the strength retention rate is 95.8-97.9% according to GB / T3923.1-2013, and the whiteness is 73.2-76.3% according to GB / T17644-2008;

[0016] In the deep decolorization, the bath ratio (the mass ratio of the decolorized polyester textile product semi-finished product and the decolorizing agent) is 1:10-70, the decolorization temperature is 120-140 DEG C, and the decolorization time is 10-40 min;

[0017] After deep decolorization, the decolorization rate of the colored waste polyester textile product is 98.8-99.7% according to the K / S value, the strength retention rate is 94.1-96.8% according to GB / T3923.1-2013, and the whiteness is 75.6-77.4% according to GB / T17644-2008;

[0018] The solid-liquid separation method includes one or more of normal pressure filtration, reduced pressure filtration (suction filtration) and centrifugal filtration;

[0019] The recovery treatment method includes one or more of distillation, reduced pressure distillation, rotary evaporation and rectification, and the purity of the recovered decolorizing agent is 99.7-99.9%.

[0020] The waste polyester textile product recovery method as described above further includes the step of using a depolymerization agent to depolymerize the decolorized polyester textile product to obtain terephthalate, which refers to an ester formed by terephthalic acid, such as DMT (dimethyl terephthalate);

[0021] In the depolymerization reaction, the depolymerization agent attacks the ester group in the polyester molecular chain through nucleophilic attack, causing the polyester molecular chain to break, and at the same time, the depolymerization agent and the ethylene glycol generated by the breaking of the polyester molecular chain spontaneously form a ring to generate ethylene carbonate, thereby promoting the depolymerization reaction balance to move forward, and finally obtaining terephthalate through efficient depolymerization, realizing the rapid depolymerization of the colored waste polyester textile product and the high conversion rate of the monomer;

[0022] The present application adopts the process of decolorization first and then depolymerization, which greatly reduces the dye residue of the depolymerization product and improves the purity of the depolymerization product. When these depolymerization products are used for re-polymerization to produce recycled PET, the performance of the recycled PET can be met.

[0023] The specific process of obtaining terephthalate by depolymerizing the decolorized polyester textile with a depolymerization agent is as follows: under the protection of nitrogen or inert gas, the decolorized polyester textile, the depolymerization agent and the first catalyst are mixed, and then a depolymerization reaction is performed, and then the depolymerization solution is separated and purified to obtain terephthalate.

[0024] The depolymerization agent is one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0025] In the prior art, different decolorizing agents and depolymerization agents are used when recycling colored waste polyester textiles, and even multiple decolorizing agents and multiple depolymerization agents are used at the same time, which is prone to cause the problem of incompatibility of multiple solvents, and the dyes in the polyester are usually removed by decolorization after chemical depolymerization, and the dyes are separated from the depolymerization product or solution by means of physical adsorption, electrochemistry or recrystallization, etc.

[0026] For polyester, ethylene glycol is the most commonly used depolymerization agent, and under the condition of a certain catalyst at 200-250℃, the molecular chain of polyester will be broken to generate the main depolymerization product bis-hydroxyethyl terephthalate (BHET) and other oligomers for subsequent repolymerization; however, there are many problems in the ethylene glycol depolymerization of colored waste polyester textiles: first, it is difficult to completely remove the dyes and auxiliaries during the depolymerization process, resulting in low product purity and affecting the quality of the subsequent regenerated polyester; second, the presence of dyes will inhibit the depolymerization reaction, reduce the reaction efficiency, and increase the process difficulty and cost of subsequent separation, purification and decolorization; finally, ethylene glycol depolymerization requires high temperature and high pressure conditions, which increases energy consumption and equipment requirements, limiting its economic efficiency and industrial application.

[0027] For example, patent application No. CN118344565A discloses a method for preparing heavy metal-free regenerated polyester from waste polyester textiles, which comprises the following steps: placing the waste polyester textiles in benzyl ether or a mixed solvent of benzyl ether and at least one of methanol, ethanol, ethylene glycol and isopropyl alcohol for decolorization treatment, adding a non-heavy metal catalyst and an alcoholysis agent, performing alcoholysis reaction on the obtained decolorized polyester fabric, separating and purifying the obtained alcoholysis liquid to obtain depolymerized regenerated monomers, adding a non-heavy metal catalyst and a functional auxiliary, and catalyzing the repolymerization of the regenerated monomers to obtain heavy metal-free regenerated polyester; in this method, multiple solvents including ethylene glycol are used in the decolorization and depolymerization stages, which increases the process complexity and increases the difficulty of solvent separation and recovery.

[0028] For example, patent application publication No. CN109574835A discloses a method for decolorizing polyester alcoholysis product BHET by ion-modified activated carbon, which is decolorized by ion-modified activated carbon and polyester alcoholysis product after polyethylene terephthalate is alcoholized by ethylene glycol. The method has the problems of low efficiency, long process, increased production cost and process complexity, and the dye is difficult to separate from the activated carbon, which finally affects the adsorption performance or causes pollution problems.

[0029] In the entire recycling process of the waste polyester textile, the decolorizing agent and the depolymerizing agent used in the present application are one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. The types of the decolorizing agent and the depolymerizing agent are the same or similar. In the decolorizing stage, the decolorizing agent can efficiently remove the dye in the colored waste polyester textile. After being recycled, the decolorizing agent can also be used as the depolymerizing agent in the depolymerizing stage. The decolorizing and depolymerizing processes are organically combined, realizing efficient cooperation of decolorizing and depolymerizing, and simplifying the overall process flow.

[0030] The molar ratio of the depolymerizing agent to the repeating structural unit of the decolorized polyester textile (the decolorized polyester textile is polyethylene terephthalate, which has a repeating structural unit: -O-CH2-CH2-O-CO-C6H4-CO-, and the molar mass of the repeating structural unit is 192 g / mol) is 3-30:1. The mass addition amount of the first catalyst is 0.1-5 wt.% of the mass of the decolorized polyester textile.

[0031] The first catalyst is a mixture of zinc acetate and an alkaline catalyst. The content of zinc acetate in the first catalyst is 50-100 wt.%. The alkaline catalyst is one or more of potassium carbonate, sodium carbonate, sodium hydroxide and potassium hydroxide. In this way, the first catalyst can avoid decomposition of the depolymerizing agent.

[0032] The temperature of the depolymerization reaction is 160-200°C, and the time of the depolymerization reaction is 30-200 min.

[0033] The terephthalate is obtained by separating and purifying the depolymerization solution. First, the depolymerization solution is subjected to vacuum devolatilization at 140-190°C to collect the removed volatile components. Then, the solid product is obtained by centrifugal separation at 70-100°C. Finally, the refined terephthalate is obtained by treating the solid product.

[0034] The depolymerization rate of the decolorized polyester textile (= the mass reduction value of the decolorized polyester textile after depolymerization / the mass of the decolorized polyester textile before depolymerization x 100%) is 98-100%.

[0035] The waste polyester textile recycling method as described above further comprises the step of performing a repolymerization reaction to obtain regenerated PET.

[0036] The process of the repolymerization reaction is as follows: first, converting terephthalate into DMT (if terephthalate itself is DMT, no conversion is needed), then mixing DMT, ethylene glycol, a second catalyst and a functional additive to perform an ester exchange reaction to obtain bis-hydroxyethyl terephthalate, and then mixing bis-hydroxyethyl terephthalate and a third catalyst to perform a polycondensation reaction.

[0037] Advantages:

[0038] (1) The decolorizing agent used in the present application is a low-boiling-point solvent with a boiling point lower than 130 DEG C, especially dimethyl carbonate with a boiling point of only 90 DEG C. Compared with traditional high-boiling-point decolorizing agents such as dimethyl sulfoxide with a boiling point of 189 DEG C, the present application reduces the recovery temperature and energy consumption of the decolorizing agent. At the same time, the decolorizing agent of the present application also has low toxicity and high volatility, which greatly reduces its residue in the regenerated PET material, reduces the environmental risk, improves the quality and application performance of the regenerated PET material, and meets the development direction of green chemistry, providing a more economical and efficient solution for the industrialized closed-loop recycling of colored waste polyester textiles.

[0039] (2) The decolorizing agent used in the present application has excellent solubility, and its solubility is similar to that of PET, which can efficiently remove dyes and additives in colored waste polyester textiles under mild conditions, while avoiding damage to the structure of polyester fibers. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A flowchart of the waste polyester textile recycling method of embodiments 1-4 of the present application;

[0041] Figure 2 A real object picture of the colored waste polyester textile of embodiment 1 of the present application before and after decolorization treatment;

[0042] Figure 3 A real object picture of the recycled dimethyl carbonate and the recycled dye of embodiment 1 of the present application;

[0043] Figure 4 A real object picture of the refined DMT of embodiment 1 of the present application;

[0044] Figure 5 A nuclear magnetic resonance hydrogen spectrum of the refined DMT of embodiment 1 of the present application;

[0045] Figure 6 A nuclear magnetic resonance hydrogen spectrum of the regenerated PET of embodiment 1 of the present application;

[0046] Figure 7DSC melting curve of the regenerated PET of Example 1 of the present application. DETAILED DESCRIPTION

[0047] The application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the present application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims of the present application.

[0048] The following are the test methods of the relevant performance indicators in each example and comparative example:

[0049] (1) The decolorization rate of the decolorized polyester textile semi-finished product and the decolorized polyester textile: calculated according to the K / S value, specifically as follows:

[0050] Decolorization rate (%) = (K / S value of the untreated textile - K / S value of the decolorized textile) / K / S value of the untreated textile × 100%

[0051] Among them, K / S value of the untreated textile (colored waste polyester textile), K / S value of the decolorized textile; it should be noted that the color depth of the samples before and after decolorization treatment is evaluated according to AATCC test method 110-2011 (issued by American Association of Textile Chemists and Colorists), and the result is expressed by K / S value (the ratio of color material absorption coefficient K to color material scattering coefficient S). The K / S value of the samples before and after decolorization treatment is measured using a calibrated benchtop spectrophotometer (the manufacturer of the benchtop spectrophotometer is Tianjin Trus Technology Co., Ltd., and the model is S81), and the test conditions use D65 light source and CIE 10° viewing angle. The textile to be tested is folded twice to ensure that the sample is not transparent when measuring the color, and 5 groups of each sample are measured and the average value is taken.

[0052] (2) The strength retention rate of the decolorized polyester textile semi-finished product and the decolorized polyester textile: the breaking strength of the sample is measured by an electronic fabric strength machine according to GB / T 3923.1-2013 "Textiles - Determination of tensile properties of fabrics - Part 1: determination of breaking force and elongation at break (strip method)", the strength retention rate is calculated, repeated 5 times, and the average value is taken;

[0053] The effective width of each sample should be 50mm±0.5mm (excluding selvedge), and the length should be able to meet the gauge length of 200mm;

[0054] Strength retention rate (%) =

[0055] Among them, Breaking strength of the decolorized textile; ​​The breaking strength of the textile without decolorization treatment (colored waste polyester textile).

[0056] (3) The whiteness of the decolorized polyester textile semi-finished product and the decolorized polyester textile: the fabric whiteness was calculated according to GB / T 17644-2008 Textile Fiber Whiteness Colorimetric Test Method, repeated 5 times, and the average value was taken;

[0057] Whiteness W = 100 - [(100 - L*) 2 +(a*) 2 +(b*) 2 ] 1 / 2 ; wherein L* is the lightness index; a* and b* are the chroma indexes, in the L*a*b* index system, L* shows the whiteness color direction; a* positive value indicates red, a* negative value indicates green, b* positive value indicates yellow, and b* negative value indicates blue; L*, a*, and b* are measured by a desktop spectrophotometer, each piece of textile is repeated 5 times, and the average value is taken.

[0058] (4) Purity of recovered decolorizing agent: a GC-2010 Pro gas chromatograph produced by Shimadzu Corporation was configured with a hydrogen flame ionization detector (FID) and a chromatographic data processing workstation to quantitatively analyze the purity of the recovered decolorizing agent, and the purity fitting was performed by external standard method;

[0059] Test conditions: carrier gas is high-purity nitrogen (purity ≥ 99.95%, by volume fraction), split ratio is 13:1, column pressure is 94 kPa, vaporization chamber temperature is 240℃, detector temperature is 240℃, column temperature: initial temperature is 60℃, holding for 3 min, increasing to 120℃ at a rate of 20℃ / min, holding for 4 min;

[0060] The recovery rate of decolorizing agent (%) = .

[0061] Wherein, is the mass (g) of the recovered decolorizing agent, is the mass (g) of the decolorizing liquid, is the mass (g) of the recovered dye.

[0062] (5) Depolymerization rate of decolorized polyester textile:

[0063] Depolymerization rate (%) = .

[0064] Wherein, is the mass (g) of the colored waste polyester textile, is the mass (g) of the waste polyester textile that has not been depolymerized after the depolymerization reaction (i.e. residual solid).

[0065] (6) Conversion rate of refined DMT:

[0066] Conversion rate (%) of refined DMT = ;

[0067] in, The mass (g) of the purified DMT collected. The molar mass (g / mol) of the collected DMT is given. The mass (g) of colored waste polyester textiles. The molar mass of the repeating structural unit of colored waste polyester textiles (192 g / mol).

[0068] (7) Purity of refined DMT: The purity of the collected DMT was quantitatively analyzed using a GC-2010 Pro gas chromatograph manufactured by Shimadzu Corporation of Japan, equipped with a flame ionization detector (FID) and a chromatographic data processing workstation, and the purity was fitted by the internal standard method.

[0069] The DMT content was determined using the internal standard curve method, with dipropyl phthalate as the internal standard and chloroform as the solvent. Quantification was based on peak area. The test conditions were as follows: carrier gas was high-purity nitrogen (purity ≥99.95%, by volume fraction), split ratio was 15:1, injection port temperature was 280°C, column temperature was 60°C, total flow rate was 3.7 mL / min, and column flow rate was 0.7 mL / min.

[0070] (8) Oligomer content of purified DMT: The oligomer content of purified DMT was qualitatively and quantitatively analyzed using a LC-16 high performance liquid chromatograph (HPLC) equipped with a WondaSil C18-WR column (200 mm in length, 4.6 mm in inner diameter, and 5 μm in particle size) and an ultraviolet detector, manufactured by Shimadzu Corporation of Japan. The detection wavelength was 254 nm, the detection temperature was 40 °C, the mobile phase was methanol and water with a volume ratio of 3:1, and the flow rate was 0.8 mL / min.

[0071] (9) Nuclear magnetic resonance hydrogen spectrum ( 1 H NMR test: Weigh 5-10 mg of the dried sample and place it in a 5 mm outer diameter NMR tube. Add 0.5 mL of deuterated trifluoroacetic acid (CF3COOD) reagent. After the sample is fully dissolved, test it using an NMR spectrometer (manufacturer: Bruker, Germany, model Avance-400). Use tetramethylsilane (TMS) as the standard and run at 600 MHz.

[0072] (10) Melting point: 5-10 mg of dried regenerated PET was weighed in an aluminum crucible, and then a DSC melting curve and melting point were obtained by using a differential scanning calorimeter (manufacturer: TA Instruments, model: Q-20), the specific process being: heating from 30℃ to 280℃ at a rate of 10℃ / min, holding for 5 min, and then analyzing by using Universal Analysis software to obtain the melting point of the regenerated PET.

[0073] In order to facilitate the obtaining of the depolymerization product DMT, the following embodiments of the present application are described only by using dimethyl carbonate as the depolymerization agent. However, the depolymerization agent can also be diethyl carbonate or methyl ethyl carbonate, and the depolymerization agent can also be two or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. Such a selection of the depolymerization agent can also make the bleached polyester textile depolymerize, and the depolymerization product can be subjected to a polymerization reaction after being refined, or can be subjected to a polymerization reaction after being converted into DMT through an ester exchange reaction involving methanol, thereby meeting the requirements of producing regenerated PET; the ester exchange reaction involving methanol can be carried out according to the following scheme: the depolymerization product (phthalate ester), methanol and a catalyst (sodium hydroxide) are mixed according to a mass ratio of 1:5:0.01, and are reacted at 65℃ for 3h under the protection of nitrogen, to obtain an ester exchange liquid, which is cooled to precipitate solids at 25℃, and the obtained solids are washed with methanol to obtain crude DMT, and then the crude DMT is mixed with methanol according to a mass ratio of 1:10, and is stirred at 60℃ for 30min, to remove impurities through a dissolution-recrystallization process, and finally refined DMT is obtained through solid-liquid separation.

[0074] The colored waste polyester textile used in the present application has a washing color fastness of at least 4-5 grades, and is obtained by using a disperse dye (azo disperse dye, anthraquinone disperse dye, heterocyclic disperse dye, etc.) through a high-temperature high-pressure dyeing method, a carrier dyeing method, a hot melt dyeing method or an atmospheric pressure high-temperature dyeing method, or is obtained by using a cationic dye through a dyeing and fixing process, or is obtained by using an acid dye through an acid bath dyeing and fixing process, or is obtained by using a vat dye through a reduction, oxidation and soaping process. Since the disperse dye is a common dye for dyeing polyester textiles, the following embodiments of the present application are described only by taking the colored waste polyester textile dyed by the disperse dye as an example.

[0075] Example 1

[0076] A recycling method of waste polyester textiles, as shown in Figure 1 , the specific steps are as follows:

[0077] (1) Raw material preparation;

[0078] Protective gas: nitrogen;

[0079] Colored waste polyester textiles: dark green waste polyester textiles, the dye is disperse green 9, which belongs to azo disperse dye;

[0080] Decolorizing agent: dimethyl carbonate, boiling point 90℃;

[0081] Depolymerization agent: dimethyl carbonate;

[0082] First catalyst: mixture of zinc acetate and basic catalyst, the content of zinc acetate in the first catalyst is 70wt.%, and the basic catalyst is potassium carbonate;

[0083] Methanol;

[0084] Ethylene glycol;

[0085] Second catalyst: zinc acetate;

[0086] First functional aid: trimethyl phosphate as a heat stabilizer;

[0087] Second functional aid: antioxidant 1010 as an antioxidant;

[0088] Third catalyst: titanium tetrabutoxide;

[0089] (2) using a decolorizing agent to decolorize the colored waste polyester textiles;

[0090] (2.1) under the protection of protective gas, the colored waste polyester textiles are put into the decolorizing agent for preliminary decolorization, and then solid-liquid separation is performed to obtain decolorized polyester textile semi-product and decolorizing liquid;

[0091] During the preliminary decolorization, the bath ratio is 1:40, the decolorization temperature is 140℃, and the decolorization time is 30min;

[0092] During the preliminary decolorization, the solid-liquid separation method is normal pressure filtration;

[0093] After the preliminary decolorization, the decolorization rate of the colored waste polyester textiles calculated according to the K / S value is 98.7%, the strength retention rate measured according to GB / T3923.1-2013 is 97.6%, and the whiteness measured according to GB / T17644-2008 is 75.4;

[0094] (2.2) under the protection of protective gas, the decolorized polyester textile semi-product is put into the decolorizing agent for deep decolorization, and then solid-liquid separation is performed to obtain decolorized polyester textiles and decolorizing liquid;

[0095] During the deep decolorization, the bath ratio is 1:40, the decolorization temperature is 130℃, and the decolorization time is 20min;

[0096] During the deep decolorization, the solid-liquid separation method is normal pressure filtration;

[0097] After deep decolorization, the decolorization rate of the colored waste polyester textile was 99.7% according to the K / S value, the strength retention rate was 96.8% according to GB / T3923.1-2013, and the whiteness was 76.1% according to GB / T17644-2008;

[0098] The color depth of the colored waste polyester textile before decolorization, after preliminary decolorization, and after deep decolorization is shown in Figure 2

[0099] (2.3) All the decolorizing solutions were recovered to obtain the recovered decolorizing agent (i.e. recovered dimethyl carbonate) and the recovered dye as shown in Figure 3

[0100] The recovery method was distillation, and the purity of the recovered decolorizing agent was 99.9%;

[0101] (3) The depolymerization agent was used to depolymerize the decolorized polyester textile to obtain DMT;

[0102] The decolorized polyester textile, the depolymerization agent, and the first catalyst were mixed under the protection of the protective gas, and then the depolymerization reaction was carried out, and then the depolymerization solution was separated and purified to obtain DMT;

[0103] The molar ratio of the depolymerization agent to the decolorized polyester textile was 18:1, the mass addition amount of the first catalyst was 1 wt.% of the mass of the decolorized polyester textile, and 70 wt.% of the depolymerization agent was the recovered decolorizing agent;

[0104] The temperature of the depolymerization reaction was 180°C, and the time of the depolymerization reaction was 150 min;

[0105] The DMT was obtained by separating and purifying the depolymerization solution, i.e. first, the depolymerization solution was subjected to vacuum devolatilization at 140°C, and the removed volatile components were collected, then the solid product was obtained by centrifugal separation at 70°C, then the solid product was mixed with methanol at a mass ratio of 1:10, and constant temperature stirring was carried out at 60°C for 30 min, impurities were selectively removed by the dissolution-recrystallization process, and finally, refined DMT was obtained by solid-liquid separation, the physical object of the refined DMT is shown in Figure 4 , and the nuclear magnetic resonance hydrogen spectrum of the refined DMT is shown in Figure 5 ​​As shown, the chemical shifts and integrals of each peak are consistent with DMT, in which the chemical shift at 8.07 ppm corresponds to the hydrogen proton peak on the benzene ring, and the chemical shift at 3.96 ppm corresponds to the hydrogen proton peak on the methyl group connected with the ester group on DMT. By calculating the area ratio of each peak in the nuclear magnetic resonance hydrogen spectrum, the area ratio of the peaks at 8.07 ppm and 3.96 ppm is 0.67 (in the DMT molecule, the theoretical number of benzene ring hydrogens is 4, and the theoretical number of methyl hydrogens is 6, and the ratio of the theoretical number of benzene ring hydrogens to the theoretical number of methyl hydrogens is 0.67), which is consistent with the theoretical value, indicating that the depolymerization product is DMT and the purity of the prepared DMT is relatively high;

[0106] The depolymerization rate of the bleached polyester textile is 100%, the conversion rate of the refined DMT is 100%, the purity of the refined DMT is 99.9%, and the oligomer content of the refined DMT is 0.01 wt.%;

[0107] (4) performing a repolymerization reaction to obtain regenerated PET;

[0108] The process of the repolymerization reaction is as follows: uniformly mixing DMT, ethylene glycol, a second catalyst, a first functional additive, and a second functional additive to form a reaction system A, slowly increasing the temperature of the reaction system A to 220°C at a temperature increasing rate of 30°C / h to perform an ester exchange reaction, collecting methanol, and when the methanol outflow rate reaches 98% (the methanol outflow rate = actual methanol molar number / theoretical methanol molar number x 100%, the actual methanol molar number is the collected methanol molar number, and the theoretical methanol molar number is the molar number of DMT x 2), the ester exchange reaction is completed, and bis-hydroxyethyl terephthalate is prepared; then uniformly mixing the prepared bis-hydroxyethyl terephthalate and a third catalyst to form a reaction system B, slowly increasing the temperature of the reaction system B to 270°C at a temperature increasing rate of 30°C / h, and gradually reducing the pressure of the reaction system B to 15 Pa to perform a polycondensation reaction for 180 min;

[0109] The weight ratio of DMT, ethylene glycol, the second catalyst, the first functional additive, the second functional additive, and the third catalyst is 1:0.6:0.05:0.05:0.05:0.05.

[0110] The nuclear magnetic resonance hydrogen spectrum of the prepared regenerated PET is as shown in Figure 6 The DSC melting curve of the regenerated PET is as shown in Figure 7 It can be seen from Figure 7 that the melting point of the regenerated PET is 255°C.

[0111] Comparative Example 1

[0112] A method for recycling waste polyester textiles, substantially the same as embodiment 1, the only difference is that the decolorizing agent is replaced by high-boiling-point solvent N,N-dimethylacetamide (DMAC, boiling point 165℃). The decolorization rate after deep decolorization is 97.9%.

[0113] Example 2

[0114] A method for recycling waste polyester textiles, as shown in Figure 1 , the specific steps are as follows:

[0115] (1) Raw material preparation;

[0116] Protective gas: argon;

[0117] Colored waste polyester textiles: red waste polyester textiles, dye is dispersed red 60, which belongs to anthraquinone disperse dye;

[0118] Decolorizing agent: diethyl carbonate, boiling point 126.8℃;

[0119] Depolymerization agent: dimethyl carbonate;

[0120] First catalyst: mixture of zinc acetate and basic catalyst, the content of zinc acetate in the first catalyst is 50wt.%, and the basic catalyst is sodium carbonate;

[0121] Methanol;

[0122] Ethylene glycol;

[0123] Second catalyst: manganese acetate;

[0124] First functional aid: triphenyl phosphate as a heat stabilizer;

[0125] Second functional aid: antioxidant 1010 as an antioxidant;

[0126] Third catalyst: antimony trioxide;

[0127] (2) The colored waste polyester textiles are decolorized with the decolorizing agent;

[0128] (2.1) Under the protection of the protective gas, the colored waste polyester textiles are placed in the decolorizing agent for preliminary decolorization, and then solid-liquid separation is performed to obtain decolorized polyester textile semi-finished product and decolorizing liquid;

[0129] During preliminary decolorization, the bath ratio is 1:70, the decolorization temperature is 120℃, and the decolorization time is 20min;

[0130] During preliminary decolorization, the solid-liquid separation method is reduced pressure filtration (suction filtration), and the pressure is 0.03MPa;

[0131] After the initial decolorization, the decolorization rate of the colored waste polyester textiles was 98.2% according to the K / S value, the strength retention rate was 96.3% according to GB / T3923.1-2013, and the whiteness was 73.2% according to GB / T17644-2008;

[0132] (2.2) After the decolorized polyester textile semi-product was placed in the decolorizing agent under the protection of the protective gas for deep decolorization, solid-liquid separation was performed, and the decolorized polyester textile and the decolorizing liquid were obtained;

[0133] During the deep decolorization, the bath ratio was 1:70, the decolorization temperature was 140°C, and the decolorization time was 10 min;

[0134] During the deep decolorization, the solid-liquid separation method was reduced pressure filtration (suction filtration), and the pressure was 0.03 MPa;

[0135] After the deep decolorization, the decolorization rate of the colored waste polyester textiles was 98.8% according to the K / S value, the strength retention rate was 94.5% according to GB / T3923.1-2013, and the whiteness was 75.6% according to GB / T17644-2008;

[0136] (2.3) All the decolorizing solutions were subjected to recovery treatment, and the recovered decolorizing agent and the recovered dyes were obtained;

[0137] The recovery treatment method was reduced pressure distillation, the pressure was 0.03 MPa, and the purity of the recovered decolorizing agent was 99.7%;

[0138] (3) The decolorized polyester textiles were subjected to depolymerization using a depolymerizing agent to obtain DMT;

[0139] The decolorized polyester textiles, the depolymerizing agent, and the first catalyst were mixed under the protection of the protective gas, and then subjected to a depolymerization reaction, and then the depolymerization solution was subjected to separation and purification to obtain DMT;

[0140] The molar ratio of the depolymerizing agent to the decolorized polyester textiles was 30:1, and the mass addition amount of the first catalyst was 5 wt.% of the mass of the decolorized polyester textiles;

[0141] The temperature of the depolymerization reaction was 190°C, and the time of the depolymerization reaction was 90 min;

[0142] The DMT was obtained by separating and purifying the depolymerization solution, i.e., first, the depolymerization solution was subjected to reduced pressure devolatilization at 160°C, and the volatile components removed were collected, then the solid product was obtained by centrifugal separation at 90°C, and then the solid product was mixed with methanol at a mass ratio of 1:20, constant temperature stirring was performed at 50°C for 50 min, impurities were selectively removed through the dissolution-recrystallization process, and finally, refined DMT was obtained through solid-liquid separation;

[0143] The depolymerization rate of the decolorized polyester textile is 99.0%, the conversion rate of the refined DMT is 98.0%, the purity of the refined DMT is 99.9%, and the oligomer content of the refined DMT is 0.03 wt.%;

[0144] (4) performing a repolymerization reaction to obtain regenerated PET;

[0145] The process of the repolymerization reaction is as follows: uniformly mixing DMT, ethylene glycol, the second catalyst, the first functional additive, and the second functional additive to form a reaction system A, slowly increasing the temperature of the reaction system A to 220°C at a temperature increasing rate of 30°C / h to perform an ester exchange reaction, collecting methanol, and when the methanol outflow rate reaches 98% (the methanol outflow rate = actual methanol molar number / theoretical methanol molar number x 100%, the actual methanol molar number is the collected methanol molar number, and the theoretical methanol molar number is the molar number of DMT x 2), the ester exchange reaction ends, and bis-hydroxyethyl terephthalate is prepared; then uniformly mixing the prepared bis-hydroxyethyl terephthalate and the third catalyst to form a reaction system B, slowly increasing the temperature of the reaction system B to 270°C at a temperature increasing rate of 30°C / h, and performing a vacuum pumping to gradually increase the pressure of the reaction system B to 15 Pa to perform a polycondensation reaction for 180 min;

[0146] The weight ratio of DMT, ethylene glycol, the second catalyst, the first functional additive, the second functional additive, and the third catalyst is 1:0.6:0.05:0.05:0.05:0.05.

[0147] Comparative Example 2

[0148] A recycling method of waste polyester textiles, which is basically the same as that of Example 2, except that the decolorizing agent is replaced by the high-boiling-point solvent cyclohexanone (boiling point 155°C). The decolorization rate after deep decolorization is 80.0%.

[0149] Example 3

[0150] A recycling method of waste polyester textiles, as shown in Figure 1 , the specific steps are as follows:

[0151] (1) raw material preparation;

[0152] Protective gas: helium;

[0153] Colored waste polyester textiles: yellow waste polyester textiles, and the dye is disperse yellow 3, which belongs to azo disperse dye;

[0154] Decolorizing agent: methyl ethyl carbonate, boiling point 126.5°C;

[0155] Depolymerizing agent: dimethyl carbonate;

[0156] The first catalyst is a mixture of zinc acetate and a basic catalyst, the content of zinc acetate in the first catalyst is 80wt.%, and the basic catalyst is sodium hydroxide;

[0157] Methanol;

[0158] Ethylene glycol;

[0159] The second catalyst is zinc acetate;

[0160] The first functional additive is trimethyl phosphate as a heat stabilizer;

[0161] The second functional additive is antioxidant 1010 as an antioxidant;

[0162] The third catalyst is ethylene glycol antimony;

[0163] (2) The colored waste polyester textiles are subjected to decolorization by using a decolorizing agent;

[0164] (2.1) The colored waste polyester textiles are subjected to preliminary decolorization under the protection of a protective gas, and then subjected to solid-liquid separation to obtain decolorized polyester textile semi-products and a decolorizing liquid;

[0165] During the preliminary decolorization, the bath ratio is 1:10, the decolorization temperature is 130 DEG C, and the decolorization time is 10 min;

[0166] During the preliminary decolorization, the solid-liquid separation method is centrifugal filtration;

[0167] After the preliminary decolorization, the decolorization rate of the colored waste polyester textiles is 97.6% according to the K / S value, the strength retention rate is 95.8% according to GB / T3923.1-2013, and the whiteness is 75.9% according to GB / T17644-2008;

[0168] (2.2) The decolorized polyester textile semi-products are subjected to deep decolorization under the protection of a protective gas, and then subjected to solid-liquid separation to obtain decolorized polyester textiles and a decolorizing liquid;

[0169] During the deep decolorization, the bath ratio is 1:30, the decolorization temperature is 120 DEG C, and the decolorization time is 30 min;

[0170] During the deep decolorization, the solid-liquid separation method is centrifugal filtration;

[0171] After the deep decolorization, the decolorization rate of the colored waste polyester textiles is 99.5% according to the K / S value, the strength retention rate is 94.1% according to GB / T3923.1-2013, and the whiteness is 76.3% according to GB / T17644-2008;

[0172] (2.3) recycling all the decoloring solution to obtain recycled decoloring agent and recycled dyes;

[0173] The recycling method is rotary evaporation, and the purity of the recycled decoloring agent is 99.9%;

[0174] (3) using depolymerization agent to depolymerize the decoloring polyester textile to obtain DMT;

[0175] Under the protection of protective gas, the decoloring polyester textile, the depolymerization agent and the first catalyst are mixed and then subjected to a depolymerization reaction, and then the depolymerization solution is separated and purified to obtain DMT;

[0176] The molar ratio of the depolymerization agent to the decoloring polyester textile is 25:1, and the mass addition amount of the first catalyst is 0.1 wt.% of the mass of the decoloring polyester textile;

[0177] The temperature of the depolymerization reaction is 160°C, and the time of the depolymerization reaction is 200 min;

[0178] The DMT is obtained by separating and purifying the depolymerization solution, that is, first, the depolymerization solution is subjected to vacuum devolatilization at 180°C to collect the removed volatile components, then the solid product is obtained by centrifugal separation at 100°C, then the solid product is mixed with methanol at a mass ratio of 1:5, and constant temperature stirring is carried out at 70°C for 40 min, impurities are selectively removed through the dissolution-recrystallization process, and finally refined DMT is obtained by solid-liquid separation;

[0179] The depolymerization rate of the decoloring polyester textile is 98.0%, the conversion rate of the refined DMT is 99.0%, the purity of the refined DMT is 99.7%, and the oligomer content of the refined DMT is 0.01 wt.%;

[0180] (4) performing a repolymerization reaction to obtain regenerated PET;

[0181] The process of the repolymerization reaction is as follows: DMT, ethylene glycol, the second catalyst, the first functional additive and the second functional additive are uniformly mixed to form a reaction system A, the temperature of the reaction system A is slowly increased to 220°C at a heating rate of 30°C / h for ester exchange reaction, methanol is collected, and when the methanol outflow rate reaches 98% (the methanol outflow rate = actual outflow amount / theoretical outflow amount × 100%, the actual outflow amount is the number of moles of collected methanol, and the theoretical outflow amount is the number of moles of DMT × 2), the ester exchange reaction is completed, and bis-hydroxyethyl terephthalate is prepared; then the prepared bis-hydroxyethyl terephthalate and the third catalyst are uniformly mixed to form a reaction system B, the temperature of the reaction system B is slowly increased to 270°C at a heating rate of 30°C / h, the pressure of the reaction system B is gradually increased to 20 Pa by vacuum pumping, and the polycondensation reaction is carried out for 180 min;

[0182] The weight ratio of DMT, ethylene glycol, the second catalyst, the first functional aid, the second functional aid, and the third catalyst is 1:0.6:0.05:0.05:0.05:0.05.

[0183] Comparative Example 3

[0184] A recycling method of waste polyester textiles, which is basically the same as Example 3, except that the decolorizing agent is replaced by the high-boiling-point solvent cyclopentanone (boiling point 130°C). The decolorization rate after deep decolorization is 93.0%.

[0185] Example 4

[0186] A recycling method of waste polyester textiles, as shown in Figure 1 , the specific steps are as follows:

[0187] (1) Raw material preparation;

[0188] Protective gas: nitrogen;

[0189] Colored waste polyester textiles: red waste polyester textiles, the dye is Disperse Red 356, which belongs to heterocyclic disperse dyes;

[0190] Decolorizing agent: composed of dimethyl carbonate and diethyl carbonate with a molar ratio of 1:1;

[0191] Depolymerization agent: dimethyl carbonate;

[0192] First catalyst: a mixture of zinc acetate and basic catalyst, the content of zinc acetate in the first catalyst is 100wt.%, and the basic catalyst is potassium hydroxide;

[0193] Methanol;

[0194] Ethylene glycol;

[0195] Second catalyst: manganese acetate;

[0196] First functional aid: triphenyl phosphate as a heat stabilizer;

[0197] Second functional aid: antioxidant 1010 as an antioxidant;

[0198] Third catalyst: titanium tetrabutoxide;

[0199] (2) Decolorizing the colored waste polyester textiles with the decolorizing agent;

[0200] (2.1) Under the protection of the protective gas, the colored waste polyester textiles are placed in the decolorizing agent for preliminary decolorization, and then solid-liquid separation is performed to obtain decolorized polyester textile semi-finished products and decolorizing liquid;

[0201] The bath ratio is 1:30, the decolorization temperature is 140 DEG C, and the decolorization time is 40 min in the preliminary decolorization;

[0202] The solid-liquid separation method is normal pressure filtration in the preliminary decolorization;

[0203] The decolorization rate of the colored waste polyester textile is 98.4% according to the K / S value, the strength retention rate is 97.9% according to GB / T3923.1-2013, and the whiteness is 76.3% according to GB / T17644-2008 after the preliminary decolorization;

[0204] (2.2) The decolorized polyester textile semi-product is put into the decolorizing agent under the protection of the protective gas to carry out deep decolorization, and then solid-liquid separation is carried out to obtain the decolorized polyester textile and the decolorizing liquid;

[0205] The bath ratio is 1:10, the decolorization temperature is 140 DEG C, and the decolorization time is 40 min in the deep decolorization;

[0206] The solid-liquid separation method is normal pressure filtration in the deep decolorization;

[0207] The decolorization rate of the colored waste polyester textile is 99.2% according to the K / S value, the strength retention rate is 95.3% according to GB / T3923.1-2013, and the whiteness is 77.4% according to GB / T17644-2008 after the deep decolorization;

[0208] (2.3) All the decolorizing liquids are subjected to recovery treatment to obtain the recovered decolorizing agent and the recovered dye;

[0209] The recovery treatment method is rectification, and the purity of the recovered decolorizing agent is 99.8%;

[0210] (3) The depolymerization agent is used to depolymerize the decolorized polyester textile to obtain DMT;

[0211] The decolorized polyester textile, the depolymerization agent and the first catalyst are mixed under the protection of the protective gas to carry out the depolymerization reaction, and then the depolymerization solution is separated and purified to obtain DMT;

[0212] The molar ratio of the depolymerization agent to the decolorized polyester textile is 3:1, and the mass addition amount of the first catalyst is 3wt.% of the mass of the decolorized polyester textile;

[0213] The temperature of the depolymerization reaction is 200 DEG C, and the time of the depolymerization reaction is 30 min;

[0214] The depolymerization solution is separated and purified to obtain DMT, i.e. the volatile components are removed from the depolymerization solution at 190°C under reduced pressure, and then the solid product is obtained by centrifugal separation at 80°C. The solid product is mixed with methanol at a mass ratio of 1:15, and then stirred at 70°C for 60 min. Impurities are selectively removed by the dissolution-recrystallization process, and finally the refined DMT is obtained by solid-liquid separation.

[0215] The depolymerization rate of the bleached polyester textile is 99.0%, the conversion rate of the refined DMT is 99.0%, the purity of the refined DMT is 99.9%, and the oligomer content of the refined DMT is 0.02 wt.%.

[0216] (4) performing a repolymerization reaction to obtain regenerated PET;

[0217] The process of the repolymerization reaction is as follows: DMT, ethylene glycol, a second catalyst, a first functional additive, and a second functional additive are uniformly mixed to form a reaction system A. The temperature of the reaction system A is slowly increased to 220°C at a heating rate of 30°C / h for an ester exchange reaction. Methanol is collected. When the methanol outflow rate reaches 98% (the methanol outflow rate = actual methanol outflow amount / theoretical methanol outflow amount × 100%, the actual methanol outflow amount is the number of moles of the collected methanol, and the theoretical methanol outflow amount is 2 times the number of moles of the DMT), the ester exchange reaction is completed, and bis-hydroxyethyl terephthalate is prepared. The prepared bis-hydroxyethyl terephthalate and a third catalyst are uniformly mixed to form a reaction system B. The temperature of the reaction system B is slowly increased to 270°C at a heating rate of 30°C / h. The pressure of the reaction system B is gradually reduced to 20 Pa by vacuum pumping, and a polycondensation reaction is performed for 180 min.

[0218] The weight ratio of DMT, ethylene glycol, a second catalyst, a first functional additive, a second functional additive, and a third catalyst is 1:0.6:0.05:0.05:0.05:0.05.

[0219] Comparative Example 4

[0220] A method for recycling waste polyester textiles, which is basically the same as that of Example 4, except that the decolorizing agent is replaced by a high-boiling-point solvent dimethyl sulfoxide (DMSO, boiling point 189°C). The decolorization rate after deep decolorization is 97.5%.

[0221] The decolorization rates of Examples 1-4 after deep decolorization were 98.8-99.7%, and the decolorization rates of Comparative Examples 1-4 after deep decolorization were 80.0-97.9%. The decolorization effect of Examples 1-4 was better than that of Comparative Examples 1-4, because the carbonate solvents of Examples 1-4 had good selective solubility for azo disperse dyes, anthraquinone disperse dyes and heterocyclic disperse dyes, and could effectively destroy the physical combination (such as Van der Waals force, hydrogen bond) of the dyes and the polyester fibers. Secondly, the decolorizing agent of Examples 1-4 may have a chemical reaction with the dye molecules through transesterification at a decolorization temperature of 120-140°C, promoting the decomposition or desorption of the dyes, while the high-boiling-point solvents of Comparative Examples 1-4 have low affinity for azo disperse dyes, anthraquinone disperse dyes and heterocyclic disperse dyes, and are difficult to completely dissolve or destroy the dye structure.

[0222] In addition, high-boiling-point solvents require higher temperatures for distillation and recovery, which results in higher energy consumption, increasing the operating cost and environmental burden of the process; due to the high boiling point of high-boiling-point solvents, the evaporation and condensation process of these solvents is more complex, and the recovery efficiency of the solvent is lower, which may lead to increased solvent loss and greater environmental impact; and N,N-dimethylacetamide and dimethyl sulfoxide have certain toxicity and volatility, which may pose a threat to the health of operators and environmental safety during use; the decolorization efficiency of high-boiling-point solvents cannot completely remove the dyes in polyester textiles, and some dyes remain in the fabric, which may physically mix or chemically react with the generated DMT in the subsequent depolymerization stage, resulting in a darker color of the depolymerization monomers and a decrease in purity. Directly using these depolymerization monomers for the production of recycled PET results in a darker color and lower transparency of the recycled PET product, which cannot meet the requirements of high-quality application scenarios (such as textiles, food packaging, etc.) for the appearance and performance of the material.

[0223] In summary, in the industrialized closed-loop recycling system of colored waste polyester textiles, the colorlessness and high purity of the depolymerization monomers are key indicators to ensure that the performance of recycled PET is equivalent to that of virgin PET. When using high-boiling-point solvents for decolorization, due to the low decolorization rate, the depolymerization monomers contain residual dyes, and the depolymerization monomers cannot achieve high purity, which cannot meet the requirements of recycled PET.

Claims

1. A method for recycling waste polyester textiles, characterized in that, This includes the step of using a decolorizing agent to decolorize colored waste polyester textiles; The specific process of decolorizing colored waste polyester textiles using a decolorizing agent is as follows: First, under the protection of nitrogen or inert gas, the colored waste polyester textiles are placed in the decolorizing agent for preliminary decolorization, followed by solid-liquid separation to obtain a decolorized polyester textile semi-finished product and a decolorizing liquid. Then, under the protection of nitrogen or inert gas, the decolorized polyester textile semi-finished product is placed in the decolorizing agent for deep decolorization, followed by solid-liquid separation to obtain a decolorized polyester textile and a decolorizing liquid. Finally, all the decolorizing liquids are recycled to obtain the recovered decolorizing agent and the recovered dye. The recycling method for waste polyester textiles also includes the step of using a depolymerizing agent to depolymerize the decolorized polyester textiles to obtain terephthalate; The decolorizing agent and the depolymerizing agent are each independently one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; The specific process of using a depolymerizing agent to depolymerize decolorized polyester textiles to obtain terephthalic acid esters is as follows: under the protection of nitrogen or inert gas, the decolorized polyester textiles, the depolymerizing agent and the first catalyst are mixed and subjected to a depolymerization reaction, and then the depolymerization solution is separated and purified to obtain terephthalic acid esters. The molar ratio of the depolymerizing agent to the repeating structural units of the decolorized polyester textile is 3-30:1, and the mass amount of the first catalyst added is 0.1-5 wt.% of the mass of the decolorized polyester textile. The first catalyst is a mixture of zinc acetate and an alkaline catalyst, wherein the content of zinc acetate in the first catalyst is 50-100 wt.% and the alkaline catalyst is one or more of potassium carbonate, sodium carbonate, sodium hydroxide and potassium hydroxide. The depolymerization reaction temperature is 160-200℃, and the depolymerization reaction time is 30-200 min; The depolymerization rate of decolorized polyester textiles is 98.0-100%.

2. The method for recycling waste polyester textiles according to claim 1, characterized in that, For initial decolorization, the liquor ratio is 1:10-70, the decolorization temperature is 120-140℃, and the decolorization time is 10-40 minutes. After preliminary decolorization, the decolorization rate of colored waste polyester textiles calculated according to the K / S value is 97.6-98.7%, the strength retention rate measured according to GB / T3923.1-2013 is 95.8-97.9%, and the whiteness measured according to GB / T17644-2008 is 73.2-76.

3. For deep decolorization, the liquor ratio is 1:10-70, the decolorization temperature is 120-140℃, and the decolorization time is 10-40 minutes. After deep decolorization, the decolorization rate of colored waste polyester textiles calculated according to the K / S value is 98.8-99.7%, the strength retention rate measured according to GB / T3923.1-2013 is 94.1-96.8%, and the whiteness measured according to GB / T17644-2008 is 75.6-77.

4.

3. The method for recycling waste polyester textiles according to claim 1, characterized in that, It also includes the step of carrying out a repolymerization reaction to obtain recycled PET; The repolymerization process is as follows: first, terephthalate is converted into DMT, then DMT, ethylene glycol, a second catalyst and functional additives are mixed and subjected to transesterification to obtain diethyl terephthalate, and then diethyl terephthalate and a third catalyst are mixed and subjected to polycondensation.

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