Method for recovering flame-retardant polyester

Abstract

The present invention discloses a method for recovering flame-retardant polyester. The method includes determining whether the flame-retardant polyester is polyester A or polyester B based on the type of flame retardant. When the flame retardant is used, polyester A is one or more of decabromodiphenylethane, decabromodiphenyl ether, hexabromocyclododecane, and brominated epoxy. When the flame retardant is used, polyester B is one or more of phosphate flame retardants, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonate. In the case of polyester A, the flame retardant is recovered by microwave alcoholysis followed by extraction. In the case of polyester B, the flame retardant is recovered by extraction, followed by microwave alcoholysis to recover the polyester. The recovery method of the present invention not only efficiently recovers the flame retardant from the flame-retardant polyester, but also separates fillers and other impurities from the recovered resin, comprehensively recovering each component in the flame-retardant polyester and achieving efficient recycling of the flame-retardant polyester.

Description

[Technical Field]

[0001] The present invention relates to the technical field for recovering polymer compounds, and more specifically, to a method for recovering flame-retardant polyester. [Background technology]

[0002] Global waste electrical and electronic equipment (WEEE) amounts to 20 to 50 million tons annually, and approximately 26% of WEEE plastics contain flame retardants (FRs). Brominated flame retardants are currently the most effective flame retardants and are widely used to improve the fire resistance of plastic materials, with global production sometimes reaching 200,000 tons per year. Currently, the most consumed brominated flame retardants both in China and internationally are mainly tetrabromobisphenol A (TBBPA), decabromodiphenyl ether (DBDPO), hexabromocyclododecane (HBCD), decabromodiphenylethane (DBDPE), brominated epoxy resin (BEO), and brominated polystyrene (BPS). Bromine is a non-renewable resource. Since 2010, bromine prices have continued to rise globally. The main reason is the constant introduction of new end-product bromine products. Furthermore, the global extraction of bromine resources is making them increasingly scarce and difficult to extract, which is also exacerbating the rise in bromine prices. However, only about 9% of the world's plastic waste is recovered, 12% is incinerated, and 79% accumulates in landfills and the natural environment. By recovering and reusing flame retardants and resins from flame-retardant plastics, we can reduce the amount of waste flame-retardant plastic that ends up in landfills or is incinerated, mitigating the threat of pollution to the ecological environment, while also maximizing the use of waste and reducing the consumption of natural resources.

[0003] Currently, the processing method for flame-retardant plastics mainly involves first removing halogens and then mechanically recovering the dehalogenated plastic. Research on the debromination of waste plastics mainly focuses on technologies such as thermal decomposition, catalytic thermal decomposition, and hydrothermal treatment. These debromination technologies often require high-temperature decomposition of the flame retardant, but high-temperature decomposition also diminishes the value of recovering and reusing the plastic. Compared to dehalogenation technologies using heat treatment, using supercritical extraction of the flame retardant with carbon dioxide or solvent extraction of the flame retardant can reliably achieve dehalogenation without damaging the plastic itself.

[0004] For example, prior art has disclosed a method for recovering flame retardants from waste circuit boards. In this method, the waste circuit boards are first crushed, and then a supercritical CO2 fluid is used as an extractant to recover the flame retardant, namely triphenyl phosphate flame retardant. However, supercritical extraction is unsuitable for large-scale industrial applications due to its stringent operating conditions and high equipment requirements, and the resin portion is not recovered. Furthermore, Peng Shaohong et al. recovered flame retardants from waste electronic plastics using a poor solvent precipitation method. However, this method requires multiple dissolution, precipitation, extraction, and recovery of the flame retardant using large amounts of solvent and poor solvents, and even after desolvation, some polybrominated diphenyl ethers and unseparated fillers (antimony trioxide, glass fibers, carbon black, etc.) remain in the recycled plastic, affecting the use of the recycled plastic. [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide a method for recovering flame-retardant polyester in order to solve the defects and drawbacks of conventional methods, such as the retention of flame retardants in recycled plastics recovered from flame-retardant plastics and the difficulty in effectively separating fillers. This method employs separation and recovery methods corresponding to different flame-retardant polyesters and combines specific alcohol decomposition and extraction conditions with a separation sequence to efficiently recover flame retardants from flame-retardant polyesters, separate fillers and other impurities from the recovered resin, comprehensively recover various components in flame-retardant polyesters, and achieve efficient recycling of flame-retardant polyesters. [Means for solving the problem]

[0006] The above-mentioned objectives of the present invention are achieved by the following technical solutions.

[0007] A method for recovering flame-retardant polyester, comprising the step of determining the flame-retardant polyester to be polyester A or polyester B according to the type of flame retardant, wherein polyester A, when used as a flame retardant, is one or more polyesters selected from brominated polystyrene, polydibromostyrene, decabromodiphenylethane, decabromodiphenyl ether, hexabromocyclododecane, and brominated epoxy, and polyester B, when used as a flame retardant, is one or more polyesters selected from phosphate flame retardants, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonate. If the flame-retardant polyester is polyester A, Step S1 involves crushing polyester A, Step S2 involves performing microwave alcohol decomposition on polyester A, which has been crushed in S1, separating and filtering it to obtain filtrate X and residue a. Step S3 involves performing microwave alcohol decomposition on filtrate X in S2, then separating and purifying it to obtain monomers or oligomers and filtrate Y, and purifying filtrate Y to recover the alcohol-based substance. Step S4 includes extracting the residue a in S2 with the desired extractant, separating and purifying it to obtain the flame retardant and insoluble matter M, The alcohol decomposition agent used in the microwave alcohol decomposition in S2 and S3 is ethylene glycol or butanediol, and the target extractant in S4 is at least one of methanol, ethanol, isopropanol, acetone, chloroform, tetrahydrofuran, toluene, and limonene. If the flame-retardant polyester is polyester B, Step a1 involves crushing polyester B, Step a2 involves extracting and treating polyester B, which has been crushed in a1, with the desired extractant, separating and purifying it to obtain a flame retardant and insoluble matter N. Step a3 involves performing microwave alcohol decomposition on the insoluble matter N in a2, separating and filtering it to obtain the filtrate E and residue b. Step a4 includes performing microwave alcohol decomposition on filtrate E in a3, then separating and purifying it to obtain monomers or oligomers and filtrate F, and purifying filtrate F to recover the alcohol-based substance. The extractant for the purpose in a2 is at least one of methanol, ethanol, isopropanol, acetone, chloroform, tetrahydrofuran, toluene, and limonene, and the alcohol decomposition agent used in the microwave alcohol decomposition in a3 and a4 is ethylene glycol or butanediol.

[0008] Through numerous studies, the inventors discovered that by taking small samples, determining the type of flame retardant using conventional component analysis methods, and then using separation and recovery methods corresponding to different flame retardant polyesters according to the type of flame retardant in the flame retardant polyester, combined with specific microwave alcohol decomposition and extraction processes, it is possible to fully and efficiently recover the flame retardant in the flame retardant polyester while simultaneously separating fillers and other impurities from the recovered resin, thereby comprehensively recovering each component in the flame retardant polyester.

[0009] When the flame retardant in flame-retardant polyester is a flame retardant that is resistant to hydrolysis (one or more of the following: brominated polystyrene, polydibromostyrene, decabromodiphenylethane, decabromodiphenyl ether, hexabromocyclododecane, and brominated epoxy), the flame retardant has limited solubility in the desired extractant, making it difficult to directly extract the flame retardant from flame-retardant polyester. The only way to separate and recover the flame retardant and other components is to first release the flame retardant from the flame-retardant polyester by microwave alcohol decomposition, and then recover it by combining extraction with a specific extractant.

[0010] If the flame retardant in flame-retardant polyester is a flame retardant that is easily hydrolyzed (one or more of the following: phosphate flame retardants, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonates), it is necessary to first extract and recover the flame retardant from the flame-retardant polyester, and then recover the resin by microwave alcohol decomposition. The reason for this is that if microwave alcohol decomposition is performed first when recovering a flame retardant that is easily hydrolyzed, the flame retardant will be destroyed during the microwave alcohol decomposition process, affecting not only the quality of the recovered flame retardant but also the recovery rate of the flame retardant.

[0011] In a specific embodiment, when the alcohol decomposition agent of the present invention is butanediol, the microwave alcohol decomposition temperature in S2 and S3 is 220-230°C, and the microwave alcohol decomposition time is 10-30 min.

[0012] In a specific embodiment, when the alcohol decomposition agent of the present invention is ethylene glycol, the microwave alcohol decomposition temperature in a3 and a4 is 200 to 210°C, and the microwave alcohol decomposition time is 5 to 10 minutes.

[0013] In a specific embodiment, when the flame-retardant polyester is polyester A, the insoluble matter M is dissolved with aqueous ammonia, and antimony trioxide is separated and recovered; when the flame-retardant polyester is polyester B, the filter residue b in step a3 is treated with a zinc chloride solution to recover antimony trioxide.

[0014] Specifically, the catalyst used for the microwave alcoholysis in S2 and S3 of the present invention is any one of zinc acetate, butyl titanate, titanate nanotubes, titanium glycolate, 1,3-dimethylimidazole iron(III) chloride ionic liquid, 1-allyl-3-methylimidazolium ionic liquid, and iron chloride.

[0015] Specifically, the catalyst used for the microwave alcoholysis in a3 and a4 of the present invention is one or more of zinc acetate, butyl titanate, titanate nanotubes, titanium glycolate, 1,3-dimethylimidazole iron(III) chloride ionic liquid, 1-allyl-3-methylimidazolium ionic liquid, and iron chloride.

[0016] Specifically, the addition amount of the catalyst in the present invention is 0.05% to 1% of the mass of the flame-retardant polyester.

[0017] In a specific embodiment, the extraction in step S4 of the present invention is microwave extraction, the extraction temperature is 35 to 160°C, and the extraction time is 10 to 120 min.

[0018] In a specific embodiment, the extraction in step a2 of the present invention is microwave extraction, the extraction temperature is 35 to 160°C, and the extraction time is 10 to 120 min.

[0019] This invention employs a microwave heating method. Compared to other heating methods, microwave heating can heat the inside and outside of the material simultaneously, and because the heating rate is fast and uniform, not only is the reaction time significantly reduced, but the impact on the thermal stability of the bromine-containing flame retardant during extraction can also be effectively reduced. If the extraction temperature is too high, boiling will occur, and if the extraction temperature is too low, the extraction efficiency will decrease. If the extraction time is too long, it will affect the thermal stability of the recovered flame retardant, and if the extraction time is too short, it will be difficult to sufficiently recover the flame retardant in the polyester.

[0020] Specifically, in S1 of the present invention, the average particle size of polyester A after the crushing treatment is 2 to 10 mm, and in a1, the average particle size of polyester B after the crushing treatment is 0.02 to 1 mm. In actual production processes, the smaller the average particle size, whether polyester A or polyester B, the easier subsequent processing becomes. However, if the particle size is too small, energy consumption increases. Considering all factors, the requirements for use can be met if the average particle size of flame-retardant polyester A particles is 10 mm or less, and the average particle size of flame-retardant polyester B particles is 1 mm or less. [Effects of the Invention]

[0021] Compared to the prior art, the present invention has the following beneficial effects.

[0022] The flame retardant polyester recovery method according to the present invention employs a separation and recovery method corresponding to different flame retardant polyesters, and by combining specific alcohol decomposition and extraction conditions with the separation sequence, it efficiently recovers the flame retardant in the flame retardant polyester, separates fillers and other impurities from the recovered resin, comprehensively recovers various components in the flame retardant polyester, and achieves efficient recycling of flame retardant polyester, with a recovery rate of 80% to 92% for the flame retardant and a recovery rate of 80% to 95% for the polyester resin. [Brief explanation of the drawing]

[0023] [Figure 1] This is a flowchart of the recovery of waste flame-retardant polyester in Example 1. [Figure 2] This is a flowchart for the recovery of waste flame-retardant polyester in Example 6. [Figure 3] These are the infrared spectra of waste flame-retardant PBT (a) and microwave alcohol decomposition products (b) in Example 1. [Figure 4] These are the infrared spectra of the brominated epoxy resin flame retardant (a) and the original brominated epoxy sample (b) recovered in Example 1. [Modes for carrying out the invention]

[0024] The present invention will be further described below with reference to embodiments for carrying out the invention, but these embodiments do not limit the present invention in any way. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are commonly purchased raw materials and reagents.

[0025] 1. Main raw materials and reagents Waste flame-retardant polyester 1 is flame-retardant PBT, and its main components are PBT, brominated epoxy, EVA, antimony trioxide, glass fiber, and other additives. Waste flame-retardant polyester 2 is flame-retardant PET, and its main components are PET, brominated polystyrene, antimony trioxide, glass fiber, and other additives. Waste flame-retardant polyester 3 is flame-retardant PBT / PET, and its main components are PBT / PET, tetrabromobisphenol A, antimony trioxide, glass fiber, and other additives. Waste flame-retardant polyester 4 is flame-retardant PC, and its main components are PC, triphenyl phosphate (BDP), antimony trioxide, glass fiber, and other additives. The target extractant is methanol. ethanol, Chloroform, tetrahydrofuran, or It's acetone. Alcohol decomposing agent 1 is ethylene glycol, and alcohol decomposing agent 2 is butanediol. Catalyst 1 is zinc acetate, and catalyst 2 is butyl titanate.

[0026] 2. Characteristic Testing

[0027] (1) Infrared Spectrum Testing As can be seen from Figure 3, curve a is the infrared spectrum of waste flame-retardant PBT, and at 1717.52 cm -1 , the absorption peak is the characteristic absorption peak of an ester group. Curve b is the infrared spectrum of the product obtained by microwave alcoholysis, and at 3370.45 cm -1 , there is a strong and broad peak, which is the stretching vibration absorption peak of a hydroxyl group (-OH). It can be inferred that hydroxyl groups may be present in the polyester depolymerization product. In addition, in curve b, at 2932.15 cm -1 , there is an absorption peak of methylene, which indicates that methylene is present in the microwave alcoholysis product. At 2960.12 cm -1 , there is a characteristic absorption peak of C-H stretching vibration on the benzene ring, which indicates that the microwave alcoholysis product contains a benzene ring. At 750.24 cm -1 , there is a strong absorption peak corresponding to para-substitution on the benzene ring, which indicates that the structure of the microwave alcoholysis product contains not only benzene rings but also para-substituted benzene rings. Curves a and b in Figure 3 clearly show that the waste polyester has been completely depolymerized into monomers. As shown in Figure 4, curve a is the recovered brominated epoxy resin, and curve b is the original sample of brominated epoxy resin. Among them, at 910.33 cm -1 , 870.55 cm -1 , and 797.99 cm -1 , there are asymmetric stretching vibration peaks of -C-O-C- in epoxy groups, and at 1738 cm -1 , there is a stretching vibration peak of C=O in the ester group, and the assignments of the remaining absorption peaks are as follows. 3081 cm -1, 1583cm -1 , and 1536cm -1 It has a characteristic absorption peak of the benzene ring, at 1467 cm⁻¹. -1 There is a characteristic absorption peak for methylene at 2967.52 cm⁻¹. -1 and 2929.25cm -1 There is a characteristic absorption peak for methine in epoxy, at 1065 cm⁻¹. -1 , 1127cm -1 , 1250cm -1 This is the antisymmetric stretching vibration of the ether bond. 1386 cm -1 There is a characteristic methyl peak at 641 cm⁻¹. -1 , 659cm -1 , 738cm -1 This sample exhibits a characteristic absorption peak for C-Br, which almost perfectly overlaps with the original sample of brominated epoxy.

[0028] (2) XRF test The test was performed using the goniometric method (Gonio), with a LiF 200 diffraction crystal, a 150 μm collimator, a scintillation counter detector, and an Al (750 μm) filter. In this invention, an external standard method was used for the quantitative analysis of bromine. In Example 1, Table 1 shows the bromine content of the original samples of waste flame-retardant polyester, recovered brominated epoxy flame retardant, and brominated epoxy. It was found that the bromine content of the recovered brominated epoxy flame retardant was the same as the bromine content of the original sample of brominated epoxy.

[0029] [Table 1]

[0030] (3) TGA Test The TGA test temperature range is 30°C to 750°C, the heating rate is 10 to 20°C / min, the test atmosphere is nitrogen, and the initial decomposition temperature is determined by referring to the ISO 11358-1:2014 standard analysis.

[0031] (4) Recovery rate of flame retardants and resin monomers Flame retardant recovery rate = Mass of recovered flame retardant / Mass of flame retardant in flame retardant polyester × 100%

[0032] Specific test method: First, a small amount of flame-retardant polyester is taken, and the type of flame retardant contained is determined using XRF analysis. Next, the bromine or phosphorus content per unit flame retardant component is determined according to the type of flame retardant. Then, the total bromine or phosphorus content in the flame-retardant polyester is analyzed and determined, and these are divided by the bromine or phosphorus content per unit flame retardant component to determine the mass of flame retardant in the flame-retardant polyester. The mass of the recovered flame retardant can be directly weighed, and the flame retardant recovery rate can be calculated using the above formula.

[0033] Polyester monomer recovery rate = (Mass of recovered monomers / Relative molecular mass of monomers) / (Mass of polyester in flame-retardant polyester / Relative molecular mass of polyester repeating units) * 100%

[0034] Here, the mass of polyester in flame-retardant polyester = mass of flame-retardant polyester - mass of flame retardant in flame-retardant polyester - mass of insoluble matter. The mass of flame retardant in flame-retardant polyester can be obtained by the above calculation method, and the mass of insoluble matter can be measured directly. Example 1

[0035] A method for recovering flame-retardant polyester, comprising the following steps (shown in Figure 1): S1. Waste flame-retardant polyester 1 was crushed, and the average particle size of the obtained particles was set to 10 mm. S2. 1150 parts by weight of the crushed waste flame-retardant polyester from S1, 150 parts of butanediol, and 0.3 parts of zinc acetate were added to a microwave reactor, and microwave alcohol decomposition was carried out at 220°C for 30 minutes. The mixture was separated and filtered to obtain filtrate X and residue a. The filtrate X from S3 and S2 was subjected to a second secondary microwave alcohol decomposition at 220°C for 30 minutes. After separation, the clarified liquid was obtained, and the clarified liquid was purified by repeated crystallization in hot water (100°C) to obtain hydroxybutyl terephthalate. The remaining solution was azeotropically distilled under reduced pressure to recover butanediol. After washing the filtration residue a in S4.S2 with ethanol, tetrahydrofuran was added to remove the EVA, and the mixture was filtered. Next, the filtered cake was added to the target extractant 2 (chloroform), extracted at 50°C for 20 minutes, separated, and purified to obtain a flame retardant (brominated epoxy resin) and insoluble matter M. Insoluble matter M was dissolved in ammonia water to obtain antimony trioxide as a soluble substance and glass fibers as an insoluble substance. The glass fibers were washed with acetone and recovered. Example 2

[0036] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 1, but differing in the following respects: The microwave alcohol decomposition temperature in steps S2 and S3 is 230°C, and the alcohol decomposition time is 10 min. Example 3

[0037] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 1, but differing in the following respects: The microwave alcohol decomposition temperature in steps S2 and S3 is 210°C, and the alcohol decomposition time is 150 min. Example 4

[0038] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 1, but differing in the following respects: The microwave alcohol decomposition temperature in steps S2 and S3 is 215°C, and the alcohol decomposition time is 60 min. Example 5

[0039] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 1, but differing in the following respects: the alcohol decomposing agent in steps S2 and S3 is ethylene glycol, and the waste flame-retardant polyester in step S1 is waste flame-retardant polyester 2. S1. Waste flame-retardant polyester 2 was crushed, and the average particle size of the resulting particles was set to 10 mm. S2. 150 parts by weight of the crushed waste flame-retardant polyester 2 from S1, 300 parts of ethylene glycol, and 0.3 parts of zinc acetate were added to a microwave reactor, and microwave alcohol decomposition was carried out at 195°C for 30 minutes. The mixture was separated and filtered to obtain filtrate X and residue a. The filtrate X from S3 and S2 was subjected to a second microwave alcohol decomposition at 195°C for 30 minutes. After separation, the clarified liquid was obtained, and the clarified liquid was purified by repeated crystallization in hot water (100°C) to obtain hydroxyethyl terephthalate. The remaining solution was azeotropically distilled under reduced pressure to recover ethylene glycol. After washing the filtration residue a in S4.S2 with ethanol, tetrahydrofuran was added to remove the EVA, and the mixture was filtered. Next, the filtered cake was added to the target extractant 2 (chloroform), extracted at 50°C for 20 minutes, separated, and purified to obtain a flame retardant (brominated epoxy resin) and insoluble matter M. Insoluble matter M was dissolved in ammonia water to obtain antimony trioxide as a soluble substance and glass fibers as an insoluble substance. The glass fibers were washed with acetone and recovered. Example 6

[0040] A method for recovering flame-retardant polyester, comprising the following steps (shown in Figure 2). a1. Waste flame-retardant polyester 3 was crushed, and the average particle size of the resulting particles was set to 1 mm. a2. The waste flame-retardant polyester 3, which was pulverized in a1, was microwave-extracted with the target extractant acetone at 50°C for 30 minutes, separated, and purified to obtain the flame retardant (tetrabromobisphenol A) and insoluble matter N. a3. Add 150 parts by weight of the insoluble N from a2, 300 parts of ethylene glycol, and 0.15 parts of butyl titanate to a microwave reactor, and microwave alcohol decomposition is carried out at 195°C for 20 minutes. The mixture is separated and filtered to obtain filtrate E and residue b. For filtrate E in a4.a3, a second microwave alcohol decomposition was performed at 195°C for 20 minutes, then separated to obtain a clarified solution. The clarified solution was purified by repeated crystallization in hot water (100°C) to obtain hydroxyethyl terephthalate, and the remaining solution was azeotropically distilled under reduced pressure. Ethylene glycol The material was recovered. In addition, the residue b in S3 was added to a zinc chloride solution and separated by flotation to obtain antimony trioxide and glass fibers, and the glass fibers were washed with acetone and recovered. Example 7

[0041] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 6, but differing in the following respects: The microwave alcohol decomposition temperature in steps a3 and a4 is 210°C, and the alcohol decomposition time is 5 min. Example 8

[0042] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 6, but differing in the following respects: The microwave alcohol decomposition temperature in steps a3 and a4 is 190°C, and the alcohol decomposition time is 150 min. Example 9

[0043] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 6, but differing in the following respects: The microwave alcohol decomposition temperature in steps a3 and a4 is 200°C, and the alcohol decomposition time is 10 min. Example 10

[0044] A method for recovering flame-retardant polyester, comprising substantially the same steps as in Example 6, but differing in the following respects: the waste flame-retardant polyester in step a1 is waste flame-retardant polyester 4, and the target extractant in step a2 is ethanol. Comparative Example 1

[0045] A method for recovering flame-retardant polyester, comprising the following steps (shown in Figure 2). a1. Waste flame-retardant polyester 1 was crushed, and the average particle size of the resulting particles was set to 1 mm. a2. The waste flame-retardant polyester 1, which was pulverized in a1, was microwave-extracted with the target extractant chloroform at 50°C for 30 minutes, separated, and purified to obtain the flame retardant (brominated epoxy resin) and insoluble matter N. a3. Add 150 parts by weight of the insoluble N from a2, 150 parts of butanediol, and 0.15 parts of butyl titanate to a microwave reactor, and microwave alcohol decomposition is carried out at 220°C for 20 minutes. The mixture is separated and filtered to obtain filtrate E and residue b. a4.a3 filtrate E was subjected to a second microwave alcohol decomposition at 220°C for 20 minutes, then separated to obtain a clarified solution. The clarified solution was purified by repeated crystallization in hot water (100°C) to obtain bishydroxybutyl terephthalate. The remaining solution was azeotropically distilled under reduced pressure to recover butanediol. In addition, the residue b from a3 was added to a zinc chloride solution and separated by flotation to obtain antimony trioxide and glass fibers. The glass fibers were washed with acetone and recovered. Comparative Example 2

[0046] A method for recovering flame-retardant polyester, comprising the following steps (shown in Figure 1): S1. Waste flame-retardant polyester 3 was crushed, and the average particle size of the resulting particles was set to 10 mm. S2. Add 150 parts by weight of the crushed waste flame-retardant polyester 3 from S1, 150 parts of ethylene glycol, and 0.75 parts of zinc acetate to a microwave reactor, and microwave alcohol decomposition is carried out at 195°C for 30 minutes. The mixture is separated and filtered to obtain filtrate X and residue a. The filtrate X from S3 and S2 was subjected to a second microwave alcohol decomposition at 195°C for 30 minutes. After separation, the clarified liquid was obtained, and the clarified liquid was purified by repeated crystallization in hot water (100°C) to obtain hydroxyethyl terephthalate. The remaining solution was azeotropically distilled under reduced pressure to recover ethylene glycol. After washing the filtration residue a in S4.S2 with ethanol, it was added to the target extractant (chloroform), extracted at 50°C for 20 minutes, separated and purified to obtain a flame retardant (tetrabromobisphenol A) and insoluble matter M. Insoluble matter M was dissolved in ammonia water to obtain antimony trioxide as a soluble substance and glass fibers as an insoluble substance. The glass fibers were washed with acetone and recovered. Table 2 shows the results of testing the properties of the product obtained by the flame-retardant polyester recovery method described above.

[0047] [Table 2]

[0048] The above embodiments of the present invention are merely examples to clearly illustrate the present invention and do not limit its embodiments. Those skilled in the art can make various other forms of variations or modifications based on the above description. It is not necessary, nor is it possible, to limit all embodiments here. Any modifications, equivalent substitutions, and improvements made without departing from the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for recovering flame-retardant polyester, The process includes the step of determining whether the flame-retardant polyester is polyester A or polyester B depending on the type of flame retardant, wherein the flame-retardant polyester is determined to be polyester A when the flame retardant is one or more of brominated polystyrene, decabromodiphenylethane, decabromodiphenyl ether, hexabromocyclododecane, and brominated epoxy, and the flame-retardant polyester is determined to be polyester B when the flame retardant is one or more of phosphate flame retardants, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonate. If the flame-retardant polyester is polyester A, Step S1 involves crushing polyester A, Step S2 involves performing microwave alcohol decomposition on polyester A crushed in S1, separating and filtering to obtain filtrate X and residue a, Step S3 involves performing microwave alcohol decomposition on the filtrate X in S2, then separating and purifying it to obtain monomers or oligomers and filtrate Y, and purifying filtrate Y to recover the alcohol-based substance. Step S4 includes extracting the residue a in S2 with the desired extractant, separating and purifying it to obtain a flame retardant and an insoluble substance M, The alcohol decomposition agent used in the microwave alcohol decomposition in S2 and S3 is ethylene glycol or butanediol, and the target extractant in S4 is at least one of methanol, ethanol, isopropanol, acetone, chloroform, tetrahydrofuran, toluene, and limonene. If the flame-retardant polyester is polyester B, Step a1 involves crushing polyester B, Step a2 involves extracting the polyester B crushed in a1 with the desired extractant, separating and purifying it to obtain a flame retardant and insoluble matter N. Step a3 involves performing microwave alcohol decomposition on the insoluble matter N in a2, separating and filtering it to obtain the filtrate E and residue b. The process includes step a4, in which microwave alcohol decomposition is performed on filtrate E in a3, followed by separation and purification to obtain monomers or oligomers and filtrate F, and filtrate F is purified to recover the alcohol-based substance. A method for recovering flame-retardant polyester, characterized in that the target extractant in a2 is at least one of methanol, ethanol, isopropanol, acetone, chloroform, tetrahydrofuran, toluene, and limonene, and the alcohol decomposition agent used in the microwave alcohol decomposition in a3 and a4 is ethylene glycol or butanediol.

2. The method for recovering flame-retardant polyester according to claim 1, characterized in that, when the alcohol decomposition agent is butanediol, the temperature of the microwave alcohol decomposition in S2 and S3 is 220°C to 230°C, and the microwave alcohol decomposition time is 10 min to 30 min.

3. The method for recovering flame-retardant polyester according to claim 1, characterized in that, when the alcohol decomposition agent is ethylene glycol, the temperature of the microwave alcohol decomposition in a3 and a4 is 200°C to 210°C, and the microwave alcohol decomposition time is 5 min to 10 min.

4. The method for recovering flame-retardant polyester according to claim 1, characterized in that the insoluble substance M is dissolved in ammonia water, and antimony trioxide is separated and recovered.

5. The method for recovering flame-retardant polyester according to claim 1, characterized in that the catalyst used in the microwave alcohol decomposition in S2 and S3 is one or more of zinc acetate, butyl titanate, titanium nanotube, titanium glycolate, 1,3-dimethylimidazole iron(III) chloride ionic liquid, 1-allyl-3-methylimidazolium ionic liquid, and iron chloride.

6. The method for recovering flame-retardant polyester according to claim 1, characterized in that the catalyst used in the microwave alcohol decomposition in a3 and a4 is one or more of zinc acetate, butyl titanate, titanium nanotube, titanium glycolate, 1,3-dimethylimidazole iron(III) chloride ionic liquid, 1-allyl-3-methylimidazolium ionic liquid, and iron chloride.

7. The method for recovering flame-retardant polyester according to claim 5 or 6, characterized in that the amount of catalyst added is 0.05% to 1% of the mass of the flame-retardant polyester.

8. The method for recovering flame-retardant polyester according to claim 1, characterized in that the extraction in S4 is microwave extraction, the extraction temperature is 35°C to 160°C, and the extraction time is 10 min to 120 min.

9. The method for recovering flame-retardant polyester according to claim 1, characterized in that the extraction in a2 is microwave extraction, the extraction temperature is 35°C to 160°C, and the extraction time is 10 min to 120 min.

10. The method for recovering flame-retardant polyester according to claim 1, characterized in that the average particle size of polyester A after crushing in S1 is 2 mm to 10 mm, and the average particle size of polyester B after crushing in a1 is 0.02 mm to 1 mm.

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