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 of recovering polymeric compounds, and more particularly to a method for recovering flame-retardant polyester. [Background technology]

[0002] Global waste electrical and electronic equipment (WEEE) reaches 20-50 million tons per year, of which approximately 26% of WEEE plastics contain flame retardants (FRs). Brominated flame retardants, currently the most effective flame retardants, are widely used to improve the fire performance of plastic materials, with global production reaching 200,000 tons per year. Currently, the most commonly consumed brominated flame retardants in China and abroad 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 been rising globally, primarily due to the constant development of new end-use bromine products. Furthermore, due to the mining of bromine resources worldwide, bromine resources are becoming increasingly scarce and increasingly difficult to mine, further exacerbating the rise in bromine prices. However, only about 9% of plastic waste worldwide is recovered, 12% is incinerated, and 79% accumulates in landfills and the natural environment. Recovering and reusing flame retardants and resins from flame-retardant plastics not only reduces the amount of waste flame-retardant plastics landfilled or incinerated, thereby mitigating the threat of ecological pollution, but also maximizes the use of waste and reduces the consumption of natural resources.

[0003] Currently, the primary method for treating flame-retardant plastics is to first remove the halogens and then mechanically recover the dehalogenated plastic. Research into debromination of waste electronic plastics has focused primarily on techniques such as pyrolysis, catalytic pyrolysis, and hydrothermal treatment. These debromination techniques often require high-temperature decomposition of the flame retardants, which also reduces the value of the plastic for recycling. Compared to thermal dehalogenation techniques, supercritical extraction of flame retardants using carbon dioxide or solvent extraction of flame retardants can reliably dehalogenate the plastic without damaging it.

[0004] For example, the prior art discloses a method for recovering flame retardants from waste circuit boards. This method involves first crushing the waste circuit boards and then using CO2 supercritical fluid as an extractant to recover the flame retardant, i.e., triphenyl phosphate flame retardant. However, supercritical extraction requires strict operating conditions and high equipment requirements, making it unsuitable for large-scale industrial applications, and the resin portion is not recovered. Furthermore, Peng Shaohong et al. used anti-solvent precipitation to recover flame retardants from waste electronic plastics. However, this method not only requires multiple dissolution, precipitation, extraction, and recovery steps using large amounts of solvent and anti-solvent, but also leaves some polybrominated diphenyl ethers and unseparated fillers (such as antimony trioxide, glass fiber, and carbon black) remaining in the recycled plastic after desolventization, which affects the usability of the recycled plastic. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a method for recovering flame-retardant polyesters to solve the problems and drawbacks of flame retardants remaining in recycled plastics recovered from conventional flame-retardant plastics and the difficulty of effectively separating fillers. This method employs separation and recovery methods suited to different flame-retardant polyesters, and combines specific alcoholysis and extraction conditions with the separation order to efficiently recover the flame retardants in the flame-retardant polyesters, separate the fillers and other impurities from the recovered resin, and comprehensively recover the various components in the flame-retardant polyesters, thereby achieving efficient recycling of flame-retardant polyesters. [Means for solving the problem]

[0006] The above object of the present invention is achieved by the following technical solutions.

[0007] A method for recovering flame-retardant polyesters, comprising the step of classifying the flame-retardant polyesters as polyester A or polyester B according to the type of flame retardant, wherein the polyester A is one or more polyesters selected from the group consisting of brominated polystyrene, polydibromostyrene, decabromodiphenylethane, decabromodiphenylether, hexabromocyclododecane, and brominated epoxy when the flame retardant is used, and the polyester B is one or more polyesters selected from the group consisting of phosphate flame retardants, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonate when the flame retardant is used; If the flame-retardant polyester is Polyester A, Step S1 of crushing polyester A; Step S2: microwave alcoholyzing the polyester A crushed in step S1, separating and filtering the polyester A to obtain a filtrate X and a residue a; Step S3: subjecting the filtrate X in S2 to microwave alcoholysis, followed by separation and purification to obtain a monomer or oligomer, filtrate Y, and purifying the filtrate Y to recover an alcohol-based substance; and step S4 of extracting the residue a in S2 with a target extractant, separating and purifying it to obtain a flame retardant and an insoluble matter M; The alcoholysis agent used in the microwave alcoholysis 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 of crushing polyester B; Step a2: extracting, treating, separating and purifying the polyester B crushed in step a1 with a target extractant to obtain a flame retardant and insoluble matter N; Step a3: subjecting the insoluble matter N in a2 to microwave alcoholysis, separating and filtering the insoluble matter N to obtain a filtrate E and a residue b; and step a4 of subjecting the filtrate E in step a3 to microwave alcoholysis, followed by separation and purification to obtain a monomer or oligomer, a filtrate F, and purifying the filtrate F to recover an alcohol-based substance; The target extractant in a2 is at least one of methanol, ethanol, isopropanol, acetone, chloroform, tetrahydrofuran, toluene, and limonene, and the alcoholysis agent used in the microwave alcoholysis in a3 and a4 is ethylene glycol or butanediol.

[0008] Through extensive research, the inventors have discovered that by taking a small amount of sample and determining the type of flame retardant through conventional component analysis methods, and then using a separation and recovery method corresponding to the different flame retardant polyesters depending on the type of flame retardant in the flame retardant polyester, in combination with a specific microwave alcoholysis and extraction process, the flame retardant in the flame retardant polyester can be fully and efficiently recovered, while at the same time, fillers and other impurities can be separated from the recovered resin, and each component in the flame retardant polyester can be comprehensively recovered.

[0009] When the flame retardant in flame-retardant polyester is one or more of the following flame retardants that are difficult to hydrolyze (brominated polystyrene, polydibromostyrene, decabromodiphenylethane, decabromodiphenyl ether, hexabromocyclododecane, and brominated epoxies), the flame retardant has limited solubility in the target extractant, making it difficult to directly extract the flame retardant from the 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 using microwave alcoholysis, and then recover it by combining extraction with the specific target extractant.

[0010] When the flame retardant in the flame-retardant polyester is one or more of a hydrolyzable flame retardant (phosphate flame retardant, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonate), the flame retardant must first be extracted and recovered from the flame-retardant polyester, and then microwave alcoholysis must be performed to recover the resin. This is because if microwave alcoholysis is performed first to recover a hydrolyzable flame retardant, the flame retardant will be destroyed during the microwave alcoholysis process, which will not only affect the quality of the recovered flame retardant but also its recovery rate.

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

[0012] In a specific embodiment, when the alcoholysis agent of the present invention is ethylene glycol, the microwave alcoholysis temperature in a3 and a4 is 200 to 210° C., and the microwave alcoholysis 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 ammonia water to separate and recover antimony trioxide; 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 in 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 in 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 amount of the catalyst of the present invention added 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, and the extraction temperature is 35 to 160°C, and the extraction time is 10 to 120 minutes.

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

[0019] The present invention uses microwave heating. Compared with other heating methods, microwave heating can simultaneously heat both the inside and outside of the material, resulting in a fast and uniform heating rate, which not only significantly shortens the reaction time but also effectively reduces the impact on the thermal stability of the bromine-containing flame retardant during extraction. If the extraction temperature is too high, boiling will occur, and if the extraction temperature is too low, the extraction efficiency will be reduced. If the extraction time is too long, the thermal stability of the recovered flame retardant will be affected, and if the extraction time is too short, it will be difficult to fully recover the flame retardant from the polyester.

[0020] Specifically, in the present invention, the average particle size of polyester A after the crushing treatment in S1 is 2 to 10 mm, and the average particle size of polyester B after the crushing treatment in a1 is 0.02 to 1 mm. In actual production processes, the smaller the average particle size, whether polyester A particles or polyester B particles, the easier the subsequent processing. 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] The present invention has the following advantageous effects compared to the prior art.

[0022] The method for recovering flame-retardant polyester according to the present invention employs separation and recovery methods suited to different flame-retardant polyesters, and by combining specific alcoholysis and extraction conditions with the separation order, the flame retardant in the flame-retardant polyester can be efficiently recovered, and fillers and other impurities can be separated from the recovered resin, comprehensively recovering various components in the flame-retardant polyester, realizing efficient recycling of flame-retardant polyester, with a flame retardant recovery rate of 80% to 92% and a polyester resin recovery rate of 80% to 95%. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a flowchart of the recovery of waste flame-retardant polyester in Example 1. [Figure 2] 1 is a flowchart of the recovery of waste flame-retardant polyester in Example 6. [Figure 3] 1 shows infrared spectra of the waste flame-retardant PBT (a) and the microwave alcohol decomposition product (b) in Example 1. [Figure 4] 1A and 1B are infrared spectra of the brominated epoxy resin flame retardant recovered in Example 1 (a) and the original sample of brominated epoxy (b). DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be further described below with reference to the following examples, but these examples are not intended to limit the present invention in any way. Raw materials and reagents used in the examples of the present invention are commonly purchased raw materials and reagents unless otherwise specified.

[0025] 1. Main raw materials and reagents Waste flame-retardant polyester 1 is flame-retardant PBT, whose main components are PBT, brominated epoxy, EVA, antimony trioxide, glass fiber, and other auxiliaries. Waste flame-retardant polyester 2 is a flame-retardant PET, whose main components are PET, brominated polystyrene, antimony trioxide, glass fiber, and other auxiliaries. Waste flame-retardant polyester 3 is flame-retardant PBT / PET, whose main components are PBT / PET, tetrabromobisphenol A, antimony trioxide, glass fiber, and other auxiliaries. Waste flame-retardant polyester 4 is a flame-retardant PC, whose main components are PC, triphenyl phosphate (BDP), antimony trioxide, glass fiber, and other auxiliaries. Extractants of interest are methanol, chloroform, tetrahydrofuran, and acetone. Alcoholyzing agent 1 is ethylene glycol and alcoholyzing agent 2 is butanediol. Catalyst 1 is zinc acetate and catalyst 2 is butyl titanate.

[0026] 2. Testing Characteristics

[0027] (1) Infrared spectrum test As can be seen from Figure 3, curve a is the infrared spectrum of the waste flame-retardant PBT, and the curve a is the infrared spectrum of the waste flame-retardant PBT at 1717.52 cm -1 The absorption peak at 3370.45 cm is the characteristic absorption peak of the ester group. Curve b is the infrared spectrum of the microwave alcoholysis product, and -1 There is a strong and broad peak at 2932.15 cm, which is the stretching vibration absorption peak of hydroxyl (-OH). It can be inferred that hydroxyl may be present in the polyester depolymerization product. -1 There is a methylene absorption peak at 2960.12 cm, which indicates the presence of methylene in the microwave alcoholysis product. -1 There is a characteristic absorption peak of the CH stretching vibration on the benzene ring at 750.24 cm, which indicates that the microwave alcoholysis product contains a benzene ring. -1 There is a strong absorption peak of the para-substituted benzene ring in the graph, which indicates that the structure of the microwave alcoholysis product contains not only the benzene ring but also the para-substituted benzene ring. 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. Of these, the peak at 910.33 cm for curve a -1 , 870.55cm -1 , 797.99cm -1 There is an asymmetric stretching vibration peak of -C-O-C- of epoxy at 1738 cm -1 The C=O ester group stretching vibration peak is present at 3081 cm. The remaining absorption peaks are assigned as follows: -1 , 1583cm -1 , and 1536 cm -1has a characteristic absorption peak of the benzene ring at 1467 cm -1 There is a characteristic absorption peak of methylene at 2967.52 cm -1 and 2929.25 cm -1 has a characteristic absorption peak of methine in epoxy, at 1065 cm -1 , 1127cm -1 , 1250cm -1 is the antisymmetric stretching vibration of the ether bond. 1386cm -1 has a characteristic methyl peak at 641 cm -1 , 659cm -1 , 738cm -1 has a characteristic absorption peak of C-Br, which overlaps almost perfectly with the original sample of brominated epoxy.

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

[0029] [Table 1]

[0030] (3) TGA test The temperature range of the TGA test 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 reference 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 sampled and the type of flame retardant contained is determined using XRF analysis. The bromine or phosphorus content per unit of flame retardant is then determined based on the type of flame retardant. The total bromine or phosphorus content in the flame-retardant polyester is then analyzed and divided by the corresponding bromine or phosphorus content per unit of flame retardant to determine the mass of flame retardant in the flame-retardant polyester. The mass of the recovered flame retardant is then directly weighed, and the flame retardant recovery rate can be calculated using the above formula.

[0033] Recovery rate of polyester monomer = (mass of recovered monomer / relative molecular mass of monomer) / (mass of polyester in flame-retardant polyester / relative molecular mass of polyester repeat unit)*100%

[0034] Here, the mass of polyester in the flame-retardant polyester = mass of flame-retardant polyester - mass of flame retardant in the flame-retardant polyester - mass of insoluble matter. The mass of the flame retardant in the flame-retardant polyester can be obtained by the above calculation method, and the mass of the insoluble matter can be directly measured. 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 to obtain particles with an average particle size of 10 mm. In S2, 1,150 parts by weight of the waste flame-retardant polyester crushed in S1, 150 parts of butanediol, and 0.3 parts of zinc acetate were added to a microwave reactor, and microwave alcoholysis was carried out at 220°C for 30 minutes. The mixture was then separated and filtered to obtain filtrate X and residue a. S3. The filtrate X from S2 was subjected to a second microwave alcoholysis at 220°C for 30 minutes, and then separated to obtain a clear liquid. The clear liquid was then added to hot water (100°C) and repeatedly crystallized to obtain hydroxybutyl terephthalate. The remaining solution was azeotropically distilled under reduced pressure to recover butanediol. S4. After washing the filter residue a in S2 with ethanol, tetrahydrofuran was added to remove EVA and filtered. The filter cake was then added to the target extractant 2 (chloroform) and extracted at 50°C for 20 minutes, followed by separation and purification to obtain a flame retardant (brominated epoxy resin) and insoluble matter M. The insoluble matter M was added to ammonia water and dissolved to obtain antimony trioxide as a soluble matter and glass fiber as an insoluble matter. The glass fiber was then washed with acetone and recovered. Example 2

[0036] This method for recovering flame-retardant polyester includes almost the same steps as in Example 1, but differs in the following respects: the microwave alcoholysis temperature in steps S2 and S3 is 230°C, and the alcoholysis time is 10 minutes. Example 3

[0037] This method for recovering flame-retardant polyester includes almost the same steps as in Example 1, but differs in the following respects: the microwave alcoholysis temperature in steps S2 and S3 is 210°C, and the alcoholysis time is 150 minutes. Example 4

[0038] This method for recovering flame-retardant polyester includes almost the same steps as in Example 1, but differs in the following respects: the microwave alcoholysis temperature in steps S2 and S3 is 215°C, and the alcoholysis time is 60 minutes. Example 5

[0039] This is a method for recovering flame-retardant polyester, and includes almost the same steps as in Example 1, but differs in the following points: the alcohol decomposition 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 to obtain particles with an average particle size of 10 mm. In S2, 150 parts by weight of the waste flame-retardant polyester 2 crushed in S1, 300 parts of ethylene glycol, and 0.3 parts of zinc acetate were added to a microwave reactor, and microwave alcoholysis was carried out at 195°C for 30 minutes. The mixture was then separated and filtered to obtain filtrate X and residue a. The filtrate X from S3.S2 was subjected to a second microwave alcoholysis at 195°C for 30 minutes, after which it was separated to obtain a clear liquid. The clear liquid was then placed in hot water (100°C) and repeatedly crystallized to obtain hydroxyethyl terephthalate, and the remaining solution was azeotropically distilled under reduced pressure to recover ethylene glycol. S4. After washing the filter residue a in S2 with ethanol, tetrahydrofuran was added to remove EVA and filtered. The filter cake was then added to the target extractant 2 (chloroform) and extracted at 50°C for 20 minutes, followed by separation and purification to obtain a flame retardant (brominated epoxy resin) and insoluble matter M. The insoluble matter M was added to ammonia water and dissolved to obtain antimony trioxide as a soluble matter and glass fiber as an insoluble matter. The glass fiber was then 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 pulverized to obtain particles with an average particle size of 1 mm. a2. The waste flame-retardant polyester 3 crushed in a1 was subjected to microwave extraction with the target extractant acetone at 50°C for 30 minutes, followed by separation and purification to obtain the flame retardant (tetrabromobisphenol A) and insoluble matter N. In a3. parts by weight, 150 parts of the insoluble matter N in a2, 300 parts of ethylene glycol, and 0.15 parts of butyl titanate were added to a microwave reactor, and microwave alcoholysis was carried out at 195°C for 20 minutes, followed by separation and filtration to obtain filtrate E and residue b. The filtrate E from a4.a3 was subjected to a second microwave alcoholysis at 195°C for 20 minutes, after which it was separated to obtain a clear liquid, which was then added to hot water (100°C) and repeatedly crystallized to obtain hydroxyethyl terephthalate, and the remaining solution was azeotropically distilled under reduced pressure to recover butanediol. The residue b from S3 was added to a zinc chloride solution and separated by flotation to obtain antimony trioxide and glass fiber, which was then washed with acetone and recovered. Example 7

[0041] This method for recovering flame-retardant polyester includes almost the same steps as in Example 6, but differs in the following points: In steps a3 and a4, the microwave alcoholysis temperature is 210°C, and the alcoholysis time is 5 minutes. Example 8

[0042] This method for recovering flame-retardant polyester includes almost the same steps as in Example 6, but differs in the following points: In steps a3 and a4, the microwave alcoholysis temperature is 190°C, and the alcoholysis time is 150 minutes. Example 9

[0043] This method for recovering flame-retardant polyester includes almost the same steps as in Example 6, but differs in the following points: In steps a3 and a4, the microwave alcoholysis temperature is 200°C, and the alcoholysis time is 10 minutes. Example 10

[0044] The method for recovering flame-retardant polyester includes almost the same steps as in Example 6, but differs in the following points: 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 pulverized to obtain particles with an average particle size of 1 mm. a2. The waste flame-retardant polyester 1 crushed in a1 was extracted with the target extractant chloroform at 50°C for 30 minutes using microwaves, separated and purified to obtain a flame retardant (brominated epoxy resin) and insoluble matter N. In a3. parts by weight, 150 parts of the insoluble matter N in a2, 150 parts of butanediol, and 0.15 parts of butyl titanate were added to a microwave reactor, and microwave alcoholysis was carried out at 220°C for 20 minutes, followed by separation and filtration to obtain filtrate E and residue b. The filtrate E from a4.a3 was subjected to a second microwave alcoholysis at 220°C for 20 minutes, after which it was separated to obtain a clear liquid, which was then added to hot water (100°C) for repeated crystallization and purification to obtain bishydroxybutyl terephthalate, and the remaining solution was azeotropically distilled under reduced pressure to recover butanediol. The residue b from a3 was added to a zinc chloride solution and separated by flotation to obtain antimony trioxide and glass fiber, which was then 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 pulverized to obtain particles with an average particle size of 10 mm. In S2, 150 parts by weight of the waste flame-retardant polyester 3 crushed in S1, 150 parts of ethylene glycol, and 0.75 parts of zinc acetate were added to a microwave reactor, and microwave alcoholysis was carried out at 195°C for 30 minutes. The mixture was then separated and filtered to obtain filtrate X and residue a. The filtrate X from S3.S2 was subjected to a second microwave alcoholysis at 195°C for 30 minutes, after which it was separated to obtain a clear liquid. The clear liquid was then placed in hot water (100°C) and repeatedly crystallized to obtain hydroxyethyl terephthalate, and the remaining solution was azeotropically distilled under reduced pressure to recover ethylene glycol. S4. The filter residue a in S2 was washed with ethanol, then added to the target extractant (chloroform) and extracted for 20 minutes at 50°C, followed by separation and purification to obtain a flame retardant (tetrabromobisphenol A) and insoluble matter M. Insoluble matter M was added to ammonia water and dissolved to obtain antimony trioxide as a soluble matter and glass fiber as an insoluble matter, which was then washed with acetone and recovered. The properties of the product obtained by the above-described method for recovering flame-retardant polyester were tested and the results are shown in Table 2.

[0047] [Table 2]

[0048] The above examples of the present invention are merely examples for clearly explaining the present invention and do not limit the embodiments of the present invention. Those skilled in the art can make various other changes or modifications based on the above description. It is not necessary or possible to list all embodiments here in a restrictive manner. Any modifications, equivalent replacements, improvements, etc. 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, comprising: a step of determining the flame-retardant polyester as polyester A or polyester B according to the type of flame retardant, wherein the polyester A is one or more polyesters selected from the group consisting of brominated polystyrene, polydibromostyrene, decabromodiphenylethane, decabromodiphenylether, hexabromocyclododecane, and brominated epoxy when the flame retardant is used, and the polyester B is one or more polyesters selected from the group consisting of phosphate flame retardants, tetrabromobisphenol A, tetrabromobisphenol S, and brominated polycarbonate when the flame retardant is used; When the flame-retardant polyester is Polyester A, Step S1 of crushing polyester A; Step S2: microwave alcoholyzing the polyester A pulverized in step S1, separating and filtering the polyester A to obtain a filtrate X and a residue a; Step S3: subjecting the filtrate X in S2 to microwave alcoholysis, separating and purifying it to obtain a monomer or oligomer, filtrate Y, and purifying the filtrate Y to recover an alcohol-based substance; and step S4 of extracting the residue a in S2 with a target extractant, separating and purifying the residue a to obtain a flame retardant and an insoluble matter M. The alcoholysis agent used in the microwave alcoholysis 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; When the flame-retardant polyester is Polyester B, Step a1 of crushing polyester B; Step a2 of extracting the polyester B crushed in step a1 with a target extractant, separating and purifying the polyester B to obtain a flame retardant and an insoluble matter N; Step a3 of subjecting the insoluble matter N in a2 to microwave alcoholysis, separating and filtering the insoluble matter N to obtain a filtrate E and a residue b; and step a4 of subjecting the filtrate E in step a3 to microwave alcoholysis, followed by separation and purification to obtain a monomer or oligomer and a filtrate F, and purifying the filtrate F to recover an alcohol-based substance; The method for recovering flame-retardant polyester in a2 is characterized in that the target extractant is at least one of methanol, ethanol, isopropanol, acetone, chloroform, tetrahydrofuran, toluene, and limonene, and the alcoholysis agent used in the microwave alcoholysis in a3 and a4 is ethylene glycol or butanediol.

2. 2. The method for recovering flame-retardant polyester according to claim 1, wherein when the alcoholyzing agent is butanediol, the microwave alcoholysis temperature in steps S2 and S3 is 220°C to 230°C, and the microwave alcoholysis time is 10 minutes to 30 minutes.

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

4. 2. The method for recovering flame-retardant polyester according to claim 1, wherein the insoluble matter M is dissolved in aqueous ammonia to separate and recover antimony trioxide.

5. 2. The method for recovering flame-retardant polyester according to claim 1, wherein the catalyst used in the microwave alcoholysis in steps S2 and S3 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.

6. The method for recovering flame-retardant polyester according to claim 1, wherein the catalyst used in the microwave alcoholysis in a3 and a4 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.

7. 7. The method for recovering flame-retardant polyester according to claim 5, wherein the amount of the 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 minutes to 120 minutes.

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

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

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