Continuous method for recycling of waste polyester textiles

Abstract

The present application relates to a continuous waste polyester textile regeneration method, which comprises the following steps: mixing waste polyester textiles, bis-hydroxyethyl terephthalate and ethylene glycol and performing continuous first alcoholysis to obtain a first alcoholysis solution; mixing the first alcoholysis solution, ethylene glycol and carboxylated zinc oxide and performing continuous second alcoholysis to obtain a second alcoholysis solution; sequentially performing continuous first filtration treatment, adsorption purification treatment and vacuum evaporation treatment on the second alcoholysis solution to obtain bis-hydroxyethyl terephthalate melt; sequentially performing continuous pre-polycondensation reaction and final polycondensation reaction on at least part of the bis-hydroxyethyl terephthalate melt to obtain polyester melt; directly spinning the polyester melt to prepare regenerated polyester fibers, and / or preparing regenerated polyester chips from the polyester melt. The regeneration method not only has simple process, high efficiency and low energy consumption, but also has high BHET purity, which can significantly improve the quality and production efficiency of the regenerated polyester product.

Description

Technical Field

[0001] This invention relates to the field of waste polyester textile recycling technology, and in particular to a continuous method for regenerating waste polyester textiles. Background Technology

[0002] Currently, the main recycling methods for waste polyester textiles include mechanical, physical, chemical, and thermal methods. Mechanical and physical methods result in recycled products with decreased molecular weight, unstable intrinsic viscosity, and altered terminal carboxyl group content, leading to poor fiber mechanical properties. These fibers can only be used at a lower grade and are unsuitable for high-end textiles. Furthermore, incomplete removal of impurities and colors limits their application. Thermal methods recover energy through high-temperature incineration, but this inherently wastes material resources and may generate harmful gases, causing secondary pollution. Chemical recycling methods decompose waste polyester into monomers or oligomers through chemical decomposition, followed by purification and repolymerization to regenerate polyester. This allows for a complete closed-loop cycle from textile to textile while maintaining high quality.

[0003] However, existing chemical recycling technologies still have the following drawbacks: First, a large amount of ethylene glycol is usually added during the alcoholysis process to promote the depolymerization reaction, resulting in extremely high energy consumption in the subsequent ethylene glycol recovery process and significantly increasing production costs; Second, recycled BHET still contains a lot of impurities, affecting the quality of subsequent recycled polyester products; Third, since a large amount of ethylene glycol is generated during the polymerization of recycled BHET, approximately 5 to 10 times that of virgin polymerization, incomplete removal can easily lead to low intrinsic viscosity of the product, affecting the quality of recycled polyester products. Summary of the Invention

[0004] Therefore, it is necessary to provide a continuous recycling method for waste polyester textiles to address the aforementioned problems. This recycling method is not only simple, efficient, and energy-saving, but also produces high-purity BHET, which can significantly improve the quality and production efficiency of recycled polyester products.

[0005] A continuous method for recycling waste polyester textiles includes the following steps:

[0006] Waste polyester textiles, diethyl terephthalate, and ethylene glycol are mixed and subjected to continuous first alcoholysis to obtain a first alcoholysis solution. The temperature of the first alcoholysis is ≥220℃, and the mass ratio of diethyl terephthalate to ethylene glycol is ≥1:4.

[0007] The first alcoholysis solution, ethylene glycol, and carboxylated zinc oxide are mixed and subjected to a continuous second alcoholysis to obtain a second alcoholysis solution, wherein the temperature of the second alcoholysis is lower than that of the first alcoholysis.

[0008] The second alcoholysis solution was subjected to a continuous first filtration process, an adsorption purification process, and a vacuum evaporation process to obtain a terephthalic acid diethyl ester melt. The adsorption purification process included an adsorption decolorization process and an ion adsorption process, and the adsorbent used in the adsorption decolorization process was acid / alkali activated alumina.

[0009] At least a portion of the bis(hydroxyethyl) terephthalate melt is subjected to a continuous pre-condensation reaction and a final condensation reaction to obtain a polyester melt. The pre-condensation reaction includes a first pre-condensation reaction, a second pre-condensation reaction, and a third pre-condensation reaction performed sequentially. The temperature of the first pre-condensation reaction is T1, and the vacuum degree is P1. The temperature of the second pre-condensation reaction is T2, and the vacuum degree is P2. The temperature of the third pre-condensation reaction is T3, and the vacuum degree is P3. T1 < T2 < T3, P3 < P2 < P1, and T1 < 260°C, P1 ≥ 25 kPa. The intrinsic viscosity of the polyester melt is ≥ 0.65 dL / g.

[0010] The polyester melt is directly spun to prepare recycled polyester fibers, and / or the polyester melt is used to prepare recycled polyester chips.

[0011] In one embodiment, the step of preparing the first alcoholysis solution further satisfies at least one of the following conditions:

[0012] (1) The mass ratio of the bis(hydroxyethyl) terephthalate to the ethylene glycol is 1:2-1:4;

[0013] (2) The molar ratio of the waste polyester textiles to the ethylene glycol is 1:0.5-1:1;

[0014] (3) The temperature of the first alcoholysis is 240℃-260℃, and the time is 1h-2h;

[0015] (4) Before mixing waste polyester textiles, bis(hydroxyethyl) terephthalate and ethylene glycol, the waste polyester textiles are also crushed.

[0016] In one embodiment, the step of preparing the second alcoholysis solution further satisfies at least one of the following conditions:

[0017] (1) The molar ratio of the waste polyester textiles to the ethylene glycol is 1:1-1:2;

[0018] (2) The mass of the carboxylated zinc oxide is 5%-10% of the mass of the waste polyester textiles;

[0019] (3) The particle size of the carboxylated zinc oxide is 5µm-10µm;

[0020] (4) The temperature of the second alcoholysis is 170℃-190℃ and the time is 3h-4h.

[0021] In one embodiment, the first filtration process includes a primary filtration and a secondary filtration performed sequentially, wherein the primary filtration uses a filter screen with a pore size of 30µm-50µm, and the secondary filtration uses a filter screen with a pore size of 2µm-4µm.

[0022] In one embodiment, the adsorption purification step further satisfies at least one of the following conditions:

[0023] (1) The adsorption purification treatment time is 4h-6h, of which the adsorption decolorization treatment time is 2h-4h;

[0024] (2) The adsorption decolorization treatment includes a first adsorption decolorization and a second adsorption decolorization performed sequentially, wherein the adsorbent used in the first adsorption decolorization is different from the adsorbent used in the second adsorption decolorization.

[0025] (3) The adsorbent used in ion adsorption treatment is at least one of ion exchange resin, macroporous adsorption resin or molecular sieve.

[0026] In one embodiment, the second alcoholysis solution after adsorption purification is subjected to a continuous second filtration process, wherein the second filtration process uses a filter screen with a pore size of 0.5µm-1.5µm.

[0027] In one embodiment, the vacuum evaporation process further satisfies at least one of the following conditions:

[0028] (1) The temperature of vacuum evaporation treatment is 130℃-150℃, the time is 8h-12h, and the vacuum degree is 8kPa-13kPa;

[0029] (2) In the vacuum evaporation process, ethylene glycol is obtained and is returned to the first alcoholysis or the second alcoholysis process for recycling.

[0030] In one embodiment, the pre-condensation reaction step satisfies at least one of the following conditions:

[0031] (1) In the first prepolymerization reaction step, a first prepolymer is obtained, and the intrinsic viscosity of the first prepolymer is 0.10 dL / g-0.15 dL / g;

[0032] (2) In the second prepolymerization reaction step, a second prepolymer is obtained, the intrinsic viscosity of which is 0.20 dL / g-0.25 dL / g;

[0033] (3) In the third prepolymerization reaction step, a third prepolymer is obtained, the intrinsic viscosity of which is 0.30 dL / g-0.35 dL / g;

[0034] (4) The temperature T1 of the first pre-condensation reaction is 240℃-250℃, the vacuum degree P1 is 30kPa-40kPa, and the time is 1h-1.5h;

[0035] (5) The temperature T2 of the second pre-condensation reaction is 260℃-265℃, the vacuum degree P2 is 10kPa-12kPa, and the time is 1h-1.5h;

[0036] (6) The temperature T3 of the third pre-condensation reaction is 270℃-275℃, the vacuum degree P3 is 1.0kPa-1.5kPa, and the time is 1.5h-2h.

[0037] In one embodiment, the step of preparing the polyester melt satisfies at least one of the following conditions:

[0038] (1) The final polycondensation reaction is carried out at a temperature of 280℃-282℃, a vacuum degree of 100Pa-150Pa, and a time of 2h-2.5h;

[0039] (2) The intrinsic viscosity of the polyester melt is 0.65 dL / g-0.70 dL / g;

[0040] (3) In the steps of pre-condensation reaction and final condensation reaction, the polyester catalyst used is selected from antimony glycolate and / or antimony trioxide, and the mass of the polyester catalyst is 0.05%-0.10% of the mass of bis(hydroxyethyl) terephthalate melt.

[0041] In one embodiment, the continuous waste polyester textile recycling method also satisfies at least one of the following conditions:

[0042] (1) A portion of the bis(hydroxyethyl) terephthalate melt is subjected to a continuous pre-condensation reaction and a final condensation reaction, while the other portion is returned to the first alcoholysis step for recycling.

[0043] (2) When preparing recycled polyester fiber by direct spinning of the polyester melt, the direct spinning process includes: the spinning temperature is 289℃-291℃, the cooling temperature is 22℃-25℃, the fiber oiling rate is 1.1wt%-1.3wt%, and the winding speed is 4200m / min-4500m / min.

[0044] In the continuous waste polyester textile recycling method of the present invention, the waste polyester textiles are treated by continuous first and second alcoholysis. The first alcoholysis is carried out at high temperature and the mass ratio of diethyl terephthalate (BHET) to ethylene glycol is limited, so that the high-boiling-point BHET is used as a solvent, realizing the rapid alcoholysis of waste polyester with low ethylene glycol usage. The second alcoholysis is carried out at a lower temperature and recyclable carboxylated zinc oxide is used as a catalyst. On the one hand, the lower temperature can effectively prevent the condensation reaction of BHET. On the other hand, the carboxyl groups on the carboxylated zinc oxide can form onium salt intermediates with ester bonds, so that it still maintains high activity at low temperature and achieves deep depolymerization. This not only improves the yield and purity of BHET, but also further reduces the unit consumption of ethylene glycol, so that the amount of ethylene glycol used in the entire alcoholysis process is very small, which greatly reduces the energy consumption of subsequent ethylene glycol recovery. Then, the second alcoholysis solution is subjected to a continuous first filtration treatment, adsorption purification treatment, and vacuum evaporation treatment. The adsorption purification treatment is limited to sequential adsorption decolorization treatment and ion adsorption treatment. The adsorbent used in the adsorption decolorization treatment is acid / alkali activated alumina, which not only achieves staged purification but also removes pigment components such as dyes and trace metal ions to the maximum extent, ensuring the high purity of the BHET melt and further improving the quality of recycled polyester products. Finally, the high-purity BHET melt is subjected to a continuous three-stage gradient pre-condensation reaction and final condensation reaction. The temperature and vacuum degree of each stage of the pre-condensation reaction are limited to meet specific gradient relationships and the temperature and vacuum degree conditions of the first pre-condensation reaction. This can effectively remove a large amount of ethylene glycol generated during BHET polymerization while gradually increasing the intrinsic viscosity of the prepolymer to obtain a polyester melt with an intrinsic viscosity ≥0.65 dL / g, thereby significantly improving the quality and production efficiency of recycled polyester products.

[0045] In addition, this invention enables continuous production from waste polyester textiles to recycled polyester products, avoiding the traditional processes of BHET cooling, crystallization, packaging, transportation, and reheating and melting polymerization, thus greatly saving energy and costs.

[0046] Therefore, the continuous waste polyester textile recycling method of the present invention is not only simple, efficient and energy-saving, but also produces BHET with high purity, which can significantly improve the quality and production efficiency of recycled polyester products. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 The high-performance liquid chromatogram of the BHET melt prepared in Example 1;

[0049] Figure 2 The differential scanning calorimetry (DSC) spectrum of the BHET melt prepared in Example 1. Detailed Implementation

[0050] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0052] The continuous recycling method for waste polyester textiles provided by this invention includes the following steps:

[0053] S1, waste polyester textiles, diethyl terephthalate and ethylene glycol are mixed and subjected to continuous first alcoholysis to obtain a first alcoholysis solution, wherein the temperature of the first alcoholysis is ≥220℃ and the mass ratio of diethyl terephthalate to ethylene glycol is ≥1:4.

[0054] S2, the first alcoholysis solution, ethylene glycol and carboxylated zinc oxide are mixed and subjected to a continuous second alcoholysis to obtain a second alcoholysis solution, wherein the temperature of the second alcoholysis is lower than the temperature of the first alcoholysis;

[0055] S3, the second alcoholysis liquid is subjected to a continuous first filtration treatment, adsorption purification treatment and vacuum evaporation treatment in sequence to obtain bis(hydroxyethyl) terephthalate melt. The adsorption purification treatment includes adsorption decolorization treatment and ion adsorption treatment in sequence, and the adsorbent used in the adsorption decolorization treatment is acid / alkali activated alumina.

[0056] S4, at least a portion of the diethyl terephthalate melt is subjected to a continuous pre-condensation reaction and a final condensation reaction to obtain a polyester melt. The pre-condensation reaction includes a first pre-condensation reaction, a second pre-condensation reaction, and a third pre-condensation reaction performed sequentially. The temperature of the first pre-condensation reaction is T1, and the vacuum degree is P1. The temperature of the second pre-condensation reaction is T2, and the vacuum degree is P2. The temperature of the third pre-condensation reaction is T3, and the vacuum degree is P3. T1 < T2 < T3, P3 < P2 < P1, and T1 < 260°C, P1 ≥ 25 kPa. The intrinsic viscosity of the polyester melt is ≥ 0.65 dL / g.

[0057] S5, the polyester melt is directly spun to prepare recycled polyester fibers, and / or the polyester melt is prepared to prepare recycled polyester chips.

[0058] In this invention, waste polyester textiles undergo continuous first and second alcoholyses sequentially. By limiting the temperature of the first alcoholysis to ≥220℃ and controlling the mass ratio of bis(hydroxyethyl) terephthalate (BHET) to ethylene glycol, the high-boiling-point BHET is ensured to fully transform from a solid state to a low-viscosity molten state, forming a homogeneous solvent system. This system, acting as the solvent for the first alcoholysis, allows the waste polyester product to fully swell and disperse in the molten BHET, and for the molecular chains to transform from an aggregated state to an extended state. This fully exposes the ester bond reaction sites, enabling ethylene glycol to precisely contact and react with the exposed ester bonds. Thus, rapid alcoholysis of waste polyester products can be achieved with a low ethylene glycol dosage. On the one hand, it can solve the problem; on the other hand, it can also create favorable conditions for the subsequent deep depolymerization of the second alcoholysis. By limiting the temperature of the second alcoholysis to be lower than that of the first alcoholysis, the second alcoholysis is carried out at a lower temperature, which effectively avoids the condensation reaction of BHET. At the same time, recyclable carboxylated zinc oxide is used as a catalyst. This catalyst still has high catalytic activity at low temperatures. The carboxyl groups on its surface can form onium salt intermediates with oxygen atoms of ester bonds, which enhances the efficiency of the catalyst in catalyzing alcoholysis and achieves deep depolymerization. This not only improves the yield and purity of BHET, but also further reduces the unit consumption of ethylene glycol. As a result, the amount of ethylene glycol used in the entire alcoholysis process is very small, which greatly reduces the energy consumption of subsequent ethylene glycol recovery.

[0059] Simultaneously, the second alcoholysis solution undergoes a continuous first filtration process, adsorption purification process, and vacuum evaporation process. The adsorption purification process includes sequential adsorption decolorization and ion adsorption treatments. The adsorbent used in the adsorption decolorization process is acid / alkali-activated alumina, which effectively removes insoluble matter, organic pigments, metal ions, and free ethylene glycol from the alcoholysis solution in stages, achieving graded purification of BHET. In particular, acid / alkali-activated alumina has a high specific surface area and activated surface characteristics, enabling efficient adsorption of residual dyes and other organic pigments in the alcoholysis solution. It also avoids the risk of BHET turning gray due to powder shedding, as is common with traditional activated carbon, thus ensuring the high purity of the BHET melt and further improving the quality of recycled polyester products.

[0060] Furthermore, at least a portion of the bis(hydroxyethyl) terephthalate melt undergoes a continuous pre-polymerization and final polymerization reaction sequentially. The pre-polymerization reaction includes a first, second, and third pre-polymerization reaction performed sequentially. A specific gradient relationship is defined between the temperature T1 and vacuum P1 of the first pre-polymerization reaction and the temperature T2 and vacuum P2 and temperature T3 and vacuum P3 of the second and third pre-polymerization reactions, respectively. This, along with the temperature and vacuum conditions of the first pre-polymerization reaction, enables precise control of the regenerated BHET polymerization process. The first pre-polymerization reaction is carried out at a lower temperature and vacuum, effectively removing BHET polymers. The first prepolymerization reaction generates a large amount of ethylene glycol during the process, effectively preventing BHET from being extracted and clogging the vacuum system, and avoiding thermal degradation side reactions. The second prepolymerization reaction, by increasing the temperature and vacuum level, moderately increases the viscosity of the prepolymer, facilitating its adhesion to the reactor surface (such as a disc agitator), and significantly increasing the ash exchange area. The third prepolymerization reaction, carried out at high temperature and high vacuum, can deeply remove residual ethylene glycol, further increasing the intrinsic viscosity of the prepolymer. Simultaneously, it prevents the less reactive prepolymer from being extracted under the high vacuum of the subsequent final polymerization reaction, which could lead to vacuum system blockage. This allows the prepolymer to continue the final polymerization reaction in a stable state, obtaining a polyester melt with an intrinsic viscosity ≥0.65 dL / g. Therefore, through the above three-stage gradient control and synergistic final polymerization reaction, it is possible to effectively remove a large amount of ethylene glycol generated during BHET polymerization while gradually increasing the intrinsic viscosity of the prepolymer, obtaining a high intrinsic viscosity polyester melt, thereby significantly improving the quality and production efficiency of recycled polyester products.

[0061] In addition, this invention enables continuous production from waste polyester textiles to recycled polyester products, avoiding the traditional processes of BHET cooling, crystallization, packaging, transportation, and reheating and melting polymerization, thus greatly saving energy and costs.

[0062] Therefore, the continuous waste polyester textile recycling method of the present invention is not only simple, efficient and low energy consumption, but also produces BHET with high purity, which can significantly improve the quality and production efficiency of recycled polyester products.

[0063] In step S1, the mass ratio of bis(hydroxyethyl) terephthalate to ethylene glycol is 1:2-1:4; this setting can achieve rapid alcoholysis of waste polyester products while effectively reducing the amount of ethylene glycol used, and at the same time reduce production costs.

[0064] Optionally, the molar ratio of the waste polyester textiles to the ethylene glycol is 1:0.5-1:1; this setting is beneficial to further improve the alcoholysis efficiency of the first alcoholysis.

[0065] Optionally, the temperature of the first alcoholysis is 240℃-260℃, and the time is 1h-2h. This setting can better ensure that diethyl terephthalate (BHET) is fully melted to form a low-viscosity, high-flow homogeneous solvent system, which is conducive to the full swelling and dispersion of waste polyester textiles in molten BHET, the full extension of molecular chains, and the exposure of more ester bond reaction sites, thereby improving the alcoholysis efficiency.

[0066] Optionally, before mixing the waste polyester textiles, diethyl terephthalate, and ethylene glycol, the waste polyester textiles may be shredded; this arrangement helps to increase the alcoholysis rate of the waste polyester textiles.

[0067] It should be noted that the source of waste polyester textiles is not particularly required in this invention. Specifically, in one embodiment, waste polyester textiles are selected from discarded clothing or chemical fiber fabric scraps.

[0068] In step S2, the molar ratio of the waste polyester textiles to the ethylene glycol is 1:1-1:2, preferably 1:1.5-1:2; this setting is beneficial to further improve the efficiency of the second alcoholysis.

[0069] Optionally, the mass of the carboxylated zinc oxide is 5%-10% of the mass of the waste polyester textiles; this setting is beneficial to further improve the alcoholysis efficiency, achieve deep depolymerization, and increase the productivity of the alcoholysis product BHET.

[0070] Optionally, the particle size of the carboxylated zinc oxide is 5µm-10µm; this setting ensures that the carboxylated zinc oxide has high catalytic activity, while the large particles of carboxylated zinc oxide are easy to separate and recover, and can be recycled, which is beneficial to further improve the purity of BHET and greatly reduces the production cost.

[0071] Optionally, the temperature of the second alcoholysis is 170℃-190℃, and the time is 3h-4h. This setting can effectively prevent BHET from undergoing condensation reaction, while further improving the catalytic activity of carboxylated zinc oxide, thereby improving the alcoholysis efficiency and thus increasing the BHET yield, while reducing the amount of ethylene glycol used and reducing the energy consumption for ethylene glycol recovery.

[0072] It should be noted that the carboxylated zinc oxide in this invention can be purchased from the market or prepared by conventional methods.

[0073] In one embodiment, carboxylated zinc oxide can be prepared by the following method: Zinc oxide nanoparticles are dried at a temperature of 90°C-120°C, preferably 105°C, for 3-6 hours, preferably 4 hours; the dried zinc oxide nanoparticles are then dispersed in anhydrous toluene and ultrasonically treated to obtain a dispersion; under stirring and a protective atmosphere, 3-aminopropyltriethoxysilane is added to the dispersion to obtain a mixture, wherein the 3-aminopropyltriethoxysilane reacts with the zinc oxide nanoparticles... The mass ratio of rice particles is 3:100-8:100, preferably 5:100; then the mixture is heated to 110℃-130℃, preferably 120℃, and then reacted under reflux for 10h-15h, preferably 12h. Then maleic anhydride powder is added to the reaction solution and the reaction is stirred for another 10h-15h, preferably 12h. Finally, after cooling, washing and drying, carboxylated zinc oxide is obtained, wherein the molar ratio of maleic anhydride to 3-aminopropyltriethoxysilane is 1:1-2:1, preferably 1.5:1.

[0074] In one embodiment, the specific steps of washing and drying are as follows: centrifugation washing is performed using an organic solvent such as acetone or ethanol, followed by vacuum drying.

[0075] It should be noted that in this invention, the form in which ethylene glycol and carboxylated zinc oxide are added in step S2 is not particularly limited. Ethylene glycol and carboxylated zinc oxide can be added directly in their original form, or they can be added in the form of an ethylene glycol dispersion of carboxylated zinc oxide.

[0076] In step S3, the first filtration process includes a primary filtration and a secondary filtration performed sequentially. The primary filtration uses a filter screen with a pore size of 30µm-50µm, preferably 35µm-45µm, and the secondary filtration uses a filter screen with a pore size of 2µm-4µm, preferably 2µm-3µm. It can be understood that the primary filtration using a filter screen with a specific pore size is mainly used to remove impurities that have not been hydrolyzed, while the secondary filtration using a filter screen with a specific pore size is mainly used to separate and recover the carboxylated zinc oxide catalyst for reuse.

[0077] In one embodiment, the catalyst carboxylated zinc oxide recovered after secondary filtration can be directly reused.

[0078] Optionally, the adsorption purification treatment time is 4h-6h, preferably 5h-6h, wherein the adsorption decolorization treatment time is 2h-4h; this setting can better remove a large number of dyes and other colored components and metal ions in the second alcoholysis solution, thereby improving the adsorption purification effect.

[0079] Considering that waste polyester textiles typically contain various dyes with different acidity and alkalinity, traditional adsorbents such as activated carbon and activated alumina are insufficient for complete adsorption. Therefore, in this invention, the adsorption decolorization process includes a first adsorption decolorization and a second adsorption decolorization performed sequentially. The adsorbent used in the first adsorption decolorization is different from that used in the second adsorption decolorization. Specifically, when the adsorbent used in the first adsorption decolorization is acid-activated activated alumina, the adsorbent used in the second adsorption decolorization is alkali-activated activated alumina, and vice versa. This configuration allows for better dye removal, further improving the adsorption and purification effect and increasing the purity of BHET.

[0080] It should be noted that, in this invention, the acid-activated activated alumina and the alkali-activated activated alumina can be purchased from the market or prepared by conventional methods.

[0081] In one embodiment, the method for preparing the acid-activated alumina includes the following steps: drying the activated alumina at a temperature of 110℃-130℃ for 3h-5h, preferably 4h; then immersing it in 2mol / L hydrochloric acid at room temperature for 10h-15h, filtering to obtain a filter cake; washing the filter cake with deionized water until neutral, and then drying it at 110℃-130℃ for 10h-15h to obtain a precursor; calcining the precursor in a muffle furnace at a programmed temperature to obtain acid-activated alumina, wherein the calcination temperature is 450℃-550℃ and the calcination time is 4h-6h.

[0082] In one embodiment, the method for preparing the alkali-activated alumina includes the following steps: drying the activated alumina at a temperature of 110℃-130℃ for 3-5 hours; then immersing it in a 1 mol / L sodium hydroxide solution at room temperature for 10-15 hours, filtering to obtain a filter cake; washing the filter cake with deionized water until neutral, and then drying it at 110℃-130℃ for 10-15 hours to obtain a precursor; and calcining the precursor in a muffle furnace at a programmed temperature to obtain alkali-activated alumina at a calcination temperature of 450℃-550℃ for 4-6 hours.

[0083] Optionally, the adsorbent used in the ion adsorption treatment is at least one of ion exchange resin, macroporous adsorption resin, or molecular sieve, preferably an ion exchange resin. This configuration can better remove trace metal ions, further improve the adsorption and purification effect, and increase the purity of BHET.

[0084] Optionally, the second alcoholysis solution after adsorption purification is subjected to a continuous second filtration process. Further, the second filtration process uses a filter screen with a pore size of 0.5µm-1.5µm, preferably 0.5µm-1µm. This setting can further remove extremely small impurities in the second alcoholysis solution and further improve the purity of BHET.

[0085] Optionally, the vacuum evaporation process is performed at a temperature of 130℃-150℃ for 8h-12h and a vacuum degree of 8kPa-13kPa; this setting can better remove ethylene glycol.

[0086] Furthermore, in the vacuum evaporation process, ethylene glycol is obtained, which is then returned to the first or second alcoholysis step for recycling. This arrangement enables the internal recycling of ethylene glycol, reduces the amount of ethylene glycol used, and thus lowers costs.

[0087] In step S4, the first prepolymerization reaction yields a first prepolymer with an intrinsic viscosity of 0.10 dL / g-0.15 dL / g; the second prepolymerization reaction yields a second prepolymer with an intrinsic viscosity of 0.20 dL / g-0.25 dL / g; and the third prepolymerization reaction yields a third prepolymer with an intrinsic viscosity of 0.30 dL / g-0.35 dL / g. This configuration, by controlling the intrinsic viscosity of the prepolymers in each prepolymerization reaction within a suitable range, facilitates a better improvement in the intrinsic viscosity of the polyester melt, thereby enhancing the performance of the recycled polyester product.

[0088] Optionally, the temperature T1 of the first prepolymerization reaction is 240℃-250℃, the vacuum degree P1 is 30kPa-40kPa, and the time is 1h-1.5h. This setting can better remove the ethylene glycol produced during the polymerization reaction, control the intrinsic viscosity of the first prepolymer in the first prepolymerization reaction within a suitable range, and ensure the smoothness of the vacuum system and the purity of the prepolymer.

[0089] Optionally, the temperature T2 of the second prepolymerization reaction is 260℃-265℃, the vacuum degree P2 is 10kPa-12kPa, and the time is 1h-1.5h. This setting can effectively improve the intrinsic viscosity of the second prepolymer within a suitable range, while allowing the second prepolymer to adhere to the agitator of the prepolymerization reactor, thereby better increasing the ash exchange area and further improving the purity and quality of the second prepolymer.

[0090] Optionally, the temperature T3 of the third prepolymerization reaction is 270℃-275℃, the vacuum degree P3 is 100Pa-150Pa, and the time is 1.5h-2h. This setting can effectively improve the intrinsic viscosity of the third prepolymer within a suitable range, while effectively preventing the prepolymer with a lower degree of reaction from being released in the subsequent high-vacuum final polymerization reaction, which would cause the vacuum system to be blocked.

[0091] Optionally, the intrinsic viscosity of the polyester melt is 0.65 dL / g-0.70 dL / g; this setting can better ensure the quality of recycled polyester products.

[0092] Optionally, the final polycondensation reaction is carried out at a temperature of 280℃-282℃, a vacuum degree of 100Pa-150Pa, and a time of 2h-2.5h. This setting can better improve the intrinsic viscosity of the polyester melt and control it within a suitable range, thereby improving the quality of recycled polyester products.

[0093] In this invention, the polyester catalyst used in the pre-condensation reaction and the final condensation reaction steps is selected from antimony-based catalysts, preferably antimony glycolate and / or antimony trioxide, and more preferably antimony glycolate.

[0094] Optionally, the mass of the polyester catalyst is 0.05%-0.10% of the mass of the bis(hydroxyethyl) terephthalate melt, preferably 0.07%-0.10%; this setting is beneficial to better improve the polycondensation effect.

[0095] In this invention, the entire bis(hydroxyethyl) terephthalate melt can be subjected to a continuous pre-condensation reaction and a final condensation reaction sequentially. Alternatively, a portion of the bis(hydroxyethyl) terephthalate melt can be subjected to a continuous pre-condensation reaction and a final condensation reaction sequentially, while the other portion is returned to the first alcoholysis step for recycling. Preferably, a portion of the bis(hydroxyethyl) terephthalate melt is subjected to a continuous pre-condensation reaction and a final condensation reaction sequentially, while the other portion is returned to the first alcoholysis step for recycling. This arrangement enables internal recycling of bis(hydroxyethyl) terephthalate, reducing production costs.

[0096] Furthermore, when a portion of the diethyl terephthalate melt undergoes a continuous pre-condensation reaction and a final condensation reaction, and another portion is returned to the first alcoholysis step for recycling, the mass ratio of the diethyl terephthalate melt undergoing the continuous pre-condensation reaction and the final condensation reaction to the diethyl terephthalate melt returned to the first alcoholysis step for recycling is 10:1-16:1.

[0097] It is understood that in step S5, all of the polyester melt can be directly spun to prepare recycled polyester fibers, or all of the polyester melt can be used to prepare recycled polyester chips, or a portion of the polyester melt can be directly spun to prepare recycled polyester fibers and another portion of the polyester melt can be used to prepare recycled polyester chips.

[0098] Optionally, when preparing recycled polyester fibers by directly spinning the polyester melt, the direct spinning process includes: a spinning temperature of 289℃-291℃, a cooling temperature of 22℃-25℃, an oiling rate of 1.1wt%-1.3wt% for the fibers, and a winding speed of 4200m / min-4500m / min; such settings are beneficial for obtaining better recycled polyester fibers.

[0099] It should be noted that the specific steps of directly spinning the polyester melt to prepare recycled polyester fibers in this invention are existing technologies, and therefore will not be described in detail here.

[0100] The continuous waste polyester textile recycling method will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0101] It should also be noted that the intrinsic viscosity of the first prepolymer, the intrinsic viscosity of the second prepolymer, the intrinsic viscosity of the third prepolymer, and the intrinsic viscosity of the polyester melt involved in the embodiments and comparative examples of this invention were all tested using the method of national standard GB / T14190-2017.

[0102] Example 1

[0103] Zinc oxide with a particle size of 5 µm was placed in an oven and vacuum dried at 105 °C for 4 h. It was then dispersed in anhydrous toluene and sonicated to obtain a zinc oxide dispersion. 3-Aminopropyltriethoxysilane was added to the zinc oxide dispersion under stirring and a nitrogen atmosphere to obtain a mixture, wherein the mass ratio of 3-aminopropyltriethoxysilane to zinc oxide was 5:100. The mixture was then heated to 120 °C and reacted under reflux for 1 h. Maleic anhydride was added, and the reaction was continued with stirring for 12 h to obtain a reaction solution, wherein the molar ratio of maleic anhydride to 3-aminopropyltriethoxysilane was 1.5:1. The reaction solution was cooled, then centrifuged and washed with acetone, and finally vacuum dried to obtain carboxylated zinc oxide with a particle size of 5 µm.

[0104] Activated alumina was dried at 120℃ for 4 hours, then immersed in 2 mol / L hydrochloric acid at room temperature for 12 hours, and filtered to obtain a filter cake. The filter cake was washed with deionized water until neutral and then dried at 120℃ for 12 hours to obtain a precursor. The precursor was calcined in a muffle furnace with programmed temperature rise to obtain acid-activated activated alumina, wherein the calcination temperature was 500℃ and the calcination time was 5 hours.

[0105] Activated alumina was dried at 120℃ for 4 hours, then immersed in a 1 mol / L sodium hydroxide solution at room temperature for 12 hours, and filtered to obtain a filter cake. The filter cake was washed with deionized water until neutral and then dried at 120℃ for 12 hours to obtain a precursor. The precursor was calcined in a muffle furnace with programmed temperature rise to obtain alkali-activated activated alumina, wherein the calcination temperature was 500℃ and the calcination time was 5 hours.

[0106] 1000 kg of waste polyester textiles were shredded to obtain waste polyester scraps. The waste polyester scraps were then fed into a first alcoholysis reactor containing diethyl terephthalate (BHET), and ethylene glycol was continuously added for continuous first alcoholysis, yielding a first alcoholysis solution. The molar ratio of waste polyester scraps to ethylene glycol was 1:0.75, the mass ratio of BHET to ethylene glycol was 1:3, the first alcoholysis temperature was 240℃, and the time was 2 hours. The first alcoholysis solution was then continuously fed into a second alcoholysis reactor, and carboxylated zinc oxide and ethylene glycol were continuously added for second alcoholysis, yielding a second alcoholysis solution. The mass of carboxylated zinc oxide was 10% of the mass of the waste polyester scraps, the molar ratio of waste polyester scraps to ethylene glycol was 1:1.5, the second alcoholysis temperature was 170℃, and the time was 4 hours.

[0107] The second alcoholysis solution obtained above was subjected to continuous primary and secondary filtration to obtain filtrate and recovered carboxylated zinc oxide. The primary filtration used a filter with a pore size of 30µm, and the secondary filtration used a filter with a pore size of 2µm. The recovered carboxylated zinc oxide was washed and reused. The filtrate obtained above was subjected to continuous adsorption purification treatment for 5 hours to obtain purified solution. The adsorption purification treatment included adsorption decolorization and ion adsorption treatment. The adsorption decolorization treatment included a first adsorption decolorization treatment and a second adsorption decolorization treatment. The adsorbent for the first adsorption decolorization treatment is acid-activated activated alumina, the adsorbent for the second adsorption decolorization treatment is alkali-activated activated alumina, and the adsorbent for the ion adsorption treatment is ion exchange resin, with an adsorption decolorization treatment time of 3 hours. Then, the purified solution is subjected to a second filtration treatment using a filter screen with a pore size of 0.5µm to obtain a second filtrate. The second filtrate is then placed at 130℃ for vacuum evaporation to obtain 1203.9 kg of BHET melt and recovered ethylene glycol. The recovered ethylene glycol is returned to the first alcoholysis reactor for recycling.

[0108] The BHET melt obtained above is continuously fed into a first prepolymerization reactor, and antimony glycolate is continuously added, wherein the mass of antimony glycolate is 0.075% of the mass of the BHET melt. A first prepolymerization reaction is then carried out to obtain a first prepolymer. The temperature of the first prepolymerization reaction is 240°C, the vacuum degree is 30 kPa, and the time is 1 hour. The intrinsic viscosity of the first prepolymer is 0.1 dL / g. The first prepolymer is then continuously fed into a second prepolymerization reactor to carry out a second prepolymerization reaction to obtain a second prepolymer. The temperature of the second prepolymerization reaction is 260°C, and the vacuum degree is 10 kPa. The reaction time is 1 hour, and the intrinsic viscosity of the second prepolymer is 0.2 dL / g. The second prepolymer is continuously fed into a third prepolymerization reactor for a third prepolymerization reaction to obtain a third prepolymer. The temperature of the third prepolymerization reaction is 270°C, the vacuum degree is 1.0 kPa, the time is 1.5 hours, and the intrinsic viscosity of the third prepolymer is 0.3 dL / g. The third prepolymer is continuously fed into a final polymerization reactor for a final polymerization reaction to obtain a polyester melt. The temperature of the final polymerization reaction is 280°C, the vacuum degree is 100 Pa, the time is 2 hours, and the intrinsic viscosity of the polyester melt is 0.65 dL / g.

[0109] One part of the polyester melt obtained above is used for drawing, cooling and pelletizing to prepare recycled polyester chips, and the other part is used for melt direct spinning to prepare recycled polyester fibers. The melt direct spinning process parameters are: spinning temperature of 289℃, cooling temperature of 22℃, fiber oiling rate of 1.1wt%, and winding speed of 4200m / min.

[0110] from Figures 1 to 2As can be seen, the high performance liquid chromatogram shows a single main peak, which is a characteristic peak of BHET. At the same time, the differential scanning calorimetry shows a single peak shape with a low melting point of about 113℃, indicating that the main component of BHET melt is monomer, with very little content of other impurities or polymers, and the purity is very high.

[0111] Example 2

[0112] Carboxylated zinc oxide with a particle size of 7 µm was prepared using the method of Example 1; acid-activated activated alumina and alkali-activated activated alumina were prepared using the method of Example 1, respectively.

[0113] 1000 kg of waste polyester textiles were shredded to obtain waste polyester scraps. The waste polyester scraps were then fed into a first alcoholysis reactor containing diethyl terephthalate (BHET), and ethylene glycol was continuously added for continuous first alcoholysis, yielding a first alcoholysis solution. The molar ratio of waste polyester scraps to ethylene glycol was 1:1, the mass ratio of BHET to ethylene glycol was 1:4, the first alcoholysis temperature was 245°C, and the time was 1.5 h. The first alcoholysis solution was then continuously fed into a second alcoholysis reactor, and carboxylated zinc oxide and ethylene glycol were continuously added for second alcoholysis, yielding a second alcoholysis solution. The mass of carboxylated zinc oxide was 8% of the mass of the waste polyester scraps, the molar ratio of waste polyester scraps to ethylene glycol was 1:2, the second alcoholysis temperature was 175°C, and the time was 3.5 h.

[0114] The second alcoholysis solution obtained above was subjected to continuous primary and secondary filtration to obtain filtrate and recovered carboxylated zinc oxide. The primary filtration used a filter with a pore size of 40µm, and the secondary filtration used a filter with a pore size of 3µm. The recovered carboxylated zinc oxide was washed and reused. The filtrate obtained above was subjected to continuous adsorption purification treatment for 5 hours to obtain purified solution. The adsorption purification treatment included adsorption decolorization treatment and ion adsorption treatment. The adsorption decolorization treatment included a first adsorption decolorization treatment and a second adsorption decolorization treatment. The adsorbent for the first adsorption decolorization treatment was acid-activated activated alumina, and the adsorbent for the second adsorption decolorization treatment was alkali-activated activated alumina. The adsorbent for the ion adsorption treatment was ion exchange resin, and the adsorption decolorization treatment time was 3 hours. Then, the purified solution was subjected to a second filtration treatment using a filter with a pore size of 1µm to obtain a second filtrate. The second filtrate was placed at 140°C for vacuum evaporation to obtain 1166.8 kg of BHET melt and recovered ethylene glycol. The recovered ethylene glycol was returned to the first alcoholysis reactor for recycling.

[0115] The BHET melt obtained above is continuously fed into a first prepolymerization reactor, and antimony glycolate is continuously added, wherein the mass of antimony glycolate is 0.05% of the mass of the BHET melt. A first prepolymerization reaction is then carried out to obtain a first prepolymer. The temperature of the first prepolymerization reaction is 245℃, the vacuum degree is 35 kPa, and the time is 1.5 h. The intrinsic viscosity of the first prepolymer is 0.12 dL / g. The first prepolymer is then continuously fed into a second prepolymerization reactor to carry out a second prepolymerization reaction to obtain a second prepolymer. The temperature of the second prepolymerization reaction is 262℃, the vacuum degree is 11 kPa, and the time is... The second prepolymer is continuously fed to a third prepolymerization reactor for a third prepolymerization reaction at a temperature of 272°C, a vacuum of 1.2 kPa, and a time of 1.7 h, and the intrinsic viscosity of the third prepolymer is 0.32 dL / g. The third prepolymer is then continuously fed to a final polycondensation reactor for a final polycondensation reaction to obtain a polyester melt at a temperature of 281°C, a vacuum of 120 Pa, and a time of 2.2 h, and the intrinsic viscosity of the polyester melt is 0.67 dL / g.

[0116] A portion of the polyester melt obtained above was used for drawing, cooling and pelletizing to prepare recycled polyester chips, and another portion was used for melt direct spinning to prepare recycled polyester fibers. The melt direct spinning process parameters were: spinning temperature of 290℃, cooling temperature of 23℃, fiber oiling rate of 1.2wt%, and winding speed of 4300m / min.

[0117] Example 3

[0118] Carboxylated zinc oxide with a particle size of 10 µm was prepared using the method of Example 1; acid-activated activated alumina and alkali-activated activated alumina were prepared using the method of Example 1, respectively.

[0119] 1000 kg of waste polyester textiles were shredded to obtain waste polyester scraps. The waste polyester scraps were then fed into a first alcoholysis reactor containing diethyl terephthalate (BHET), and ethylene glycol was continuously added for continuous first alcoholysis, yielding a first alcoholysis solution. The molar ratio of waste polyester scraps to ethylene glycol was 1:0.5, the mass ratio of BHET to ethylene glycol was 1:2, the first alcoholysis temperature was 260℃, and the time was 1 hour. The first alcoholysis solution was then continuously fed into a second alcoholysis reactor, and carboxylated zinc oxide and ethylene glycol were continuously added for second alcoholysis, yielding a second alcoholysis solution. The mass of carboxylated zinc oxide was 5% of the mass of the waste polyester scraps, the molar ratio of waste polyester scraps to ethylene glycol was 1:1, the second alcoholysis temperature was 190℃, and the time was 4 hours.

[0120] The second alcoholysis solution obtained above was subjected to continuous primary and secondary filtration to obtain filtrate and recovered carboxylated zinc oxide. The primary filtration used a 50µm pore size filter, and the secondary filtration used a 3µm pore size filter. The recovered carboxylated zinc oxide was washed and reused. The filtrate obtained above was subjected to continuous adsorption purification treatment for 6 hours to obtain purified solution. The adsorption purification treatment included adsorption decolorization and ion adsorption treatment. The adsorption decolorization treatment included a first adsorption decolorization treatment and a second adsorption decolorization treatment. The adsorbent for the first adsorption decolorization treatment is acid-activated activated alumina, the adsorbent for the second adsorption decolorization treatment is alkali-activated activated alumina, and the adsorbent for the ion adsorption treatment is ion exchange resin, with an adsorption decolorization treatment time of 4 hours. Then, the purified solution is subjected to a second filtration treatment using a filter screen with a pore size of 1.5µm to obtain a second filtrate. The second filtrate is then placed at 150°C for vacuum evaporation to obtain 1184.0 kg of BHET melt and recovered ethylene glycol. The recovered ethylene glycol is returned to the first alcoholysis reactor for recycling.

[0121] The BHET melt obtained above is continuously fed into a first prepolymerization reactor, and antimony glycolate is continuously added, wherein the mass of antimony glycolate is 0.1% of the mass of the BHET melt. A first prepolymerization reaction is then carried out to obtain a first prepolymer. The temperature of the first prepolymerization reaction is 250°C, the vacuum degree is 40 kPa, and the time is 1.5 h. The intrinsic viscosity of the first prepolymer is 0.15 dL / g. The first prepolymer is then continuously fed into a second prepolymerization reactor to carry out a second prepolymerization reaction to obtain a second prepolymer. The temperature of the second prepolymerization reaction is 265°C, the vacuum degree is 12 kPa, and the time is... The second prepolymer is continuously fed to a third prepolymerization reactor for a third prepolymerization reaction at a temperature of 275°C, a vacuum of 1.5 kPa, and a time of 2 hours, and the intrinsic viscosity of the third prepolymer is 0.35 dL / g. The third prepolymer is then continuously fed to a final polycondensation reactor for a final polycondensation reaction to obtain a polyester melt at a temperature of 282°C, a vacuum of 150 Pa, and a time of 2.5 hours, and the intrinsic viscosity of the polyester melt is 0.7 dL / g.

[0122] One part of the polyester melt obtained above is used for drawing, cooling and pelletizing to prepare recycled polyester chips, and the other part is used for melt direct spinning to prepare recycled polyester fibers. The melt direct spinning process parameters are: spinning temperature of 291℃, cooling temperature of 25℃, fiber oiling rate of 1.3wt%, and winding speed of 4500m / min.

[0123] Example 4

[0124] Example 4 differs from Example 1 only in that the particle size of the carboxylated zinc oxide is 4µm, and the mass of the BHET melt obtained is 1206.5kg; all other conditions are the same.

[0125] Example 5

[0126] The only difference between Example 5 and Example 1 is that the particle size of the carboxylated zinc oxide is 12µm, and the mass of the BHET melt obtained is 1168.1kg; all other conditions are the same.

[0127] Example 6

[0128] The only difference between Example 6 and Example 1 is that the temperature of the first alcoholysis was 220°C and the time was 2 hours, and the mass of the BHET melt obtained was 1156.2 kg; all other conditions were the same.

[0129] Example 7

[0130] The only difference between Example 7 and Example 1 is that the second alcoholysis temperature was 160°C and the time was 4 hours, during which the mass of BHET melt obtained was 1154.9 kg; all other conditions were the same.

[0131] Example 8

[0132] The only difference between Example 8 and Example 1 is that the mass of the carboxylated zinc oxide is 4% of the mass of the waste polyester shreds, and the mass of the BHET melt obtained is 1132.4 kg; all other conditions are the same.

[0133] Example 9

[0134] The only difference between Example 9 and Example 1 is that the mass of the carboxylated zinc oxide is 12% of the mass of the waste polyester shreds, and the mass of the BHET melt obtained is 1206.5 kg; all other conditions are the same.

[0135] Example 10

[0136] Example 10 differs from Example 1 only in that it does not include a secondary filtration step. That is, the second alcoholysis solution obtained above is subjected to continuous primary filtration to obtain a filtrate, wherein the mass of the BHET melt obtained is 1197.2 kg; all other conditions are the same.

[0137] Example 11

[0138] Example 11 differs from Example 1 only in that it does not include the step of using a filter with a pore size of 1µm to perform a second filtration of the purified solution. Instead, the purified solution is directly placed at 140°C for vacuum evaporation to obtain 1185.3 kg of BHET melt and recovered ethylene glycol; all other conditions are the same.

[0139] Example 12

[0140] Example 12 differs from Example 1 only in that a portion of the BHET melt obtained above is returned to the first alcoholysis reactor for recycling, while the other portion is continuously fed to the first pre-polymerization reactor. The mass of the BHET melt obtained is 1198.6 kg. All other conditions are the same.

[0141] Example 13

[0142] The only difference between Example 13 and Example 1 is that in the step of preparing the first alcoholysis solution, the mass ratio of BHET to ethylene glycol is 1:1, and the mass of BHET melt obtained is 1197.2 kg; all other conditions are the same.

[0143] Comparative Example 1

[0144] The only difference between Comparative Example 1 and Example 1 is that ethylene glycol was used instead of BHET in the step of preparing the first alcoholysis solution, and the mass of BHET melt obtained was 799.0 kg; all other conditions were the same.

[0145] Comparative Example 2

[0146] Compared with Example 1, Comparative Example 2 differs only in that ethylene glycol is used instead of BHET in the step of preparing the first alcoholysis solution, and the molar ratio of waste polyester shreds to ethylene glycol is 1:5.75, in which the mass of BHET melt obtained is 1153.6 kg; all other conditions are the same.

[0147] Comparative Example 3

[0148] Comparative Example 3 differs from Example 1 only in that the zinc oxide is not modified with carboxyl groups; that is, zinc oxide with a particle size of 5µm is used instead of carboxylated zinc oxide with a particle size of 5µm. The mass of BHET melt obtained is 906.2kg. All other conditions are the same.

[0149] Comparative Example 4

[0150] Compared with Example 1, Comparative Example 4 differs only in that, in the adsorption decolorization treatment step, the adsorbent for the first adsorption decolorization treatment and the adsorbent for the second adsorption decolorization treatment are both ordinary activated alumina, and the mass of the BHET melt obtained is 1178.7 kg; all other conditions are the same.

[0151] Comparative Example 5

[0152] Compared with Example 1, Comparative Example 5 differs only in that the adsorption purification process does not include ion adsorption treatment, and the mass of BHET melt obtained is 1174.8 kg; all other conditions are the same.

[0153] Comparative Example 6

[0154] Comparative Example 6 differs from Example 1 only in that it does not include the step of continuously feeding the obtained BHET melt into the first prepolymerization reactor. Instead, the obtained BHET melt is directly fed into the second prepolymerization reactor, and antimony glycol is continuously added. The intrinsic viscosity of the polyester melt is 0.61 dL / g, and the mass of the obtained BHET melt is 1165.5 kg. All other conditions are the same.

[0155] Comparative Example 7

[0156] The only difference between Comparative Example 7 and Example 1 is that the vacuum degree of the first pre-condensation reaction was 10 kPa, and the mass of the BHET melt obtained was 1181.4 kg; all other conditions were the same.

[0157] Comparative Example 8

[0158] Compared with Example 1, Comparative Example 8 differs only in that the temperature of the first prepolymerization reaction is 265°C, the intrinsic viscosity of the first prepolymer is 0.12 dL / g, the intrinsic viscosity of the polyester melt is 0.66 dL / g, and the mass of the BHET melt obtained is 1194.6 kg; all other conditions are the same.

[0159] Comparative Example 9

[0160] Compared with Example 1, Comparative Example 9 is only different in that it does not contain the step of continuously feeding the second prepolymer to the third prepolymerization reactor for the third prepolymerization reaction. Instead, the second prepolymer is directly fed to the final polymerization reactor for the final polymerization reaction, and the mass of the BHET melt obtained is 1176.1 kg. All other conditions are the same.

[0161] Comparative Example 10

[0162] The only difference between Comparative Example 10 and Example 1 is that in the step of preparing the first alcoholysis solution, the mass ratio of BHET to ethylene glycol is 1:5, and the mass of BHET melt obtained is 959.1 kg; all other conditions are the same.

[0163] Comparative Example 11

[0164] The only difference between Comparative Example 11 and Example 1 is that the temperature of the second alcoholysis in the step of preparing the second alcoholysis solution is 240°C, and the mass of the BHET melt obtained is 1166.9 kg; all other conditions are the same.

[0165] Comparative Example 12

[0166] Compared with Example 1, Comparative Example 12 differs only in that, in the adsorption purification process, the first adsorption decolorization process uses activated carbon as the adsorbent, and the second adsorption decolorization process uses unactivated alumina without acid / alkali activation as the adsorbent. The mass of BHET melt obtained is 1198.6 kg; all other conditions are the same.

[0167] The yield, purity, and color of the BHET melts prepared in Examples 1 to 13 and Comparative Examples 1 to 12, as well as the intrinsic viscosity and color of the polyester melts, were tested. The test results are shown in Table 1. The specific test methods are as follows:

[0168] BHET melt yield: calculated based on the ratio of actual obtained BHET melt mass to theoretically calculated BHET melt mass. Using 1000kg of waste polyester textiles as a benchmark, the theoretically calculated BHET melt mass is 1323kg.

[0169] The purity of BHET melt is calculated based on the ratio of the BHET peak area to the total peak area in the high-performance liquid chromatography (HPLC) chromatogram.

[0170] The color value of BHET melt, intrinsic viscosity and color of polyester melt were determined according to the method of national standard GB / T14190-2017.

[0171] Table 1

[0172]

[0173] Based on the data in Table 1, compared to Examples 1 and 4 to 5, it is evident that controlling the particle size of carboxylated zinc oxide within a suitable range is beneficial for synergistically improving the yield and purity of BHET, and preventing zinc oxide residue in the BHET melt, thereby further improving the color and mechanical properties of the recycled polyester product. Compared to Examples 1 and 6, it is evident that an excessively low first alcoholysis temperature leads to a slower alcoholysis rate, resulting in incomplete second alcoholysis and affecting the yield and purity of BHET. Compared to Examples 1 and 7, it is evident that an excessively low second alcoholysis temperature, although capable of preventing BHET shrinkage to some extent, can still contribute to improving the yield and purity of BHET. Polymerization improves the purity of BHET, but it reduces the efficiency of the second alcoholysis, affecting the yield of BHET. Compared with Examples 1 and 8 to 9, it is evident that controlling the amount of carboxylated zinc oxide within a suitable range is beneficial for improving the yield and purity of BHET, enhancing the quality of recycled polyester products, and reducing raw material costs. Compared with Examples 1 and 10, it is evident that using two-stage filtration before adsorption purification is beneficial for further improving the purity of BHET. Compared with Examples 1 and 11, it is evident that filtration after adsorption purification is beneficial for further improving the purity of BHET.

[0174] Compared to Example 1 and Comparative Examples 1 to 3, it can be seen that the use of BHET as a solvent in the first alcoholysis of the present invention can synergistically work with the carboxylated zinc oxide in the second alcoholysis, significantly improving the alcoholysis efficiency and increasing the yield of BHET while reducing the amount of ethylene glycol used. In contrast to Comparative Examples 1 to 2, without BHET as a solvent, a large amount of ethylene glycol is required to achieve comparable performance between the prepared BHET melt and the polyester melt, resulting in a significant increase in the energy consumption for ethylene glycol recovery. Compared to Example 1 and Comparative Examples 4 to 5, it can be seen that the active oxidation used in the first adsorption decolorization treatment and the second adsorption decolorization treatment in Comparative Example 4... The aluminum in the original samples was not acidified / alkalized, and Comparative Example 5 did not include ion adsorption treatment, resulting in a significant amount of residual dye or trace metal ion impurities in the prepared BHET, leading to poor color of the BHET and consequently causing the recycled polyester products to appear dark and yellow. In contrast, this invention uses acid- and alkali-activated alumina as adsorbents for the first and second adsorption decolorization treatments, respectively. This alumina has a large specific surface area, is filled with nanoscale micropores and channels, and its surface groups can interact with different types of dye molecules for effective decolorization. Furthermore, the ion adsorption treatment following the adsorption decolorization further removes trace metal ions, improving the color retention. The quality of BHET; compared with Examples 1 and Comparative Examples 6 to 9, it can be seen that Comparative Example 6 does not contain the first pre-polymerization reaction step, which easily leads to the inability to quickly remove ethylene glycol, resulting in low viscosity of polyester melt and recycled polyester chips; while in Comparative Example 7, the vacuum degree of the first pre-polymerization reaction is too high, which will cause BHET with low molecular weight and good melt flowability to be extracted, resulting in blockage of the vacuum system and failure to obtain polyester melt; in Comparative Example 8, the temperature of the first pre-polymerization reaction is too high, which makes the prepolymer produced by polymerization prone to degradation side reactions, resulting in a yellowish color of recycled polyester product; Comparative Example 9 does not contain the third pre-polymerization reaction step, resulting in low intrinsic viscosity. The lower prepolymer content was extracted during the subsequent high-vacuum final polycondensation reaction, causing blockage of the vacuum system and preventing the production of polyester melt. Compared to Example 1 and Comparative Example 10, controlling the mass ratio of BHET to ethylene glycol ensures that BHET serves as the solvent for the first alcoholysis while improving the efficiency of the first alcoholysis and minimizing the amount of ethylene glycol used. Compared to Example 1 and Comparative Example 11, since the temperature of the second alcoholysis in Comparative Example 11 was the same as that of the first alcoholysis (both were high-temperature treatments), BHET underwent a polycondensation reaction, resulting in lower purity and poorer decolorization of BHET, which in turn affected the quality of the recycled polyester product prepared from it.Compared to Example 1 and Comparative Example 12, it can be seen that the use of activated carbon and ordinary activated alumina as adsorbents in the adsorption and decolorization process in Comparative Example 12 not only makes it difficult to remove a large amount of dyes and other colored components, but also causes the activated carbon to easily detach, forming fine black impurities that are difficult to separate and contaminate the BHET product. This results in low purity and poor color of BHET, and consequently, poor quality of the recycled polyester product.

[0175] Therefore, the continuous waste polyester textile recycling method of the present invention employs continuous first and second alcoholysis to treat waste polyester textiles, and limits the temperature of the first alcoholysis, the mass ratio of diethyl terephthalate (DHT) to ethylene glycol, and the use of carboxylated zinc oxide as a catalyst at a lower temperature. This results in a very low amount of ethylene glycol used throughout the alcoholysis process, significantly reducing the energy consumption for subsequent ethylene glycol recovery while synergistically improving the purity and yield of BHET. Simultaneously, the adsorption purification process is limited to sequential adsorption decolorization and ion adsorption treatments. Furthermore, the adsorbent used in the adsorption decolorization treatment is acid / alkali activated alumina, which further improves the purity and good color of BHET; and the three-stage gradient prepolymerization reaction is adopted, and the temperature and vacuum degree of each stage of the prepolymerization reaction are limited to meet specific gradient relationships and the temperature and vacuum degree conditions of the first prepolymerization reaction. This can effectively remove a large amount of ethylene glycol generated during the BHET polymerization process, while gradually increasing the intrinsic viscosity of the prepolymer to obtain polyester melt with intrinsic viscosity ≥0.65dL / g, thereby significantly improving the quality and production efficiency of recycled polyester products.

[0176] In addition, compared with the traditional waste polyester recycling process, the present invention realizes the continuous production from waste polyester textiles to recycled polyester products, avoiding the BHET cooling, crystallization, packaging, transportation and reheating melting polymerization processes in the traditional process, which greatly saves energy consumption and costs while improving the quality of recycled polyester products.

[0177] Therefore, the continuous waste polyester textile recycling method of the present invention is not only simple, efficient and energy-saving, but also produces BHET with high purity, which can significantly improve the quality and production efficiency of recycled polyester products.

[0178] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0179] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A continuous method for recycling waste polyester textiles, characterized in that, Includes the following steps: Waste polyester textiles, diethyl terephthalate, and ethylene glycol are mixed and subjected to continuous first alcoholysis to obtain a first alcoholysis solution. The temperature of the first alcoholysis is ≥220℃, and the mass ratio of diethyl terephthalate to ethylene glycol is ≥1:

4. The first alcoholysis solution, ethylene glycol, and carboxylated zinc oxide are mixed and subjected to a continuous second alcoholysis to obtain a second alcoholysis solution, wherein the temperature of the second alcoholysis is lower than the temperature of the first alcoholysis. The second alcoholysis solution was subjected to a continuous first filtration process, an adsorption purification process, and a vacuum evaporation process to obtain a terephthalic acid diethyl ester melt. The adsorption purification process included an adsorption decolorization process and an ion adsorption process, and the adsorbent used in the adsorption decolorization process was acid / alkali activated alumina. At least a portion of the bis(hydroxyethyl) terephthalate melt is subjected to a continuous pre-condensation reaction and a final condensation reaction to obtain a polyester melt. The pre-condensation reaction includes a first pre-condensation reaction, a second pre-condensation reaction, and a third pre-condensation reaction performed sequentially. The temperature of the first pre-condensation reaction is T1, and the vacuum degree is P1. The temperature of the second pre-condensation reaction is T2, and the vacuum degree is P2. The temperature of the third pre-condensation reaction is T3, and the vacuum degree is P3. T1 < T2 < T3, P3 < P2 < P1, and T1 < 260°C, P1 ≥ 25 kPa. The intrinsic viscosity of the polyester melt is ≥ 0.65 dL / g. The polyester melt is directly spun to prepare recycled polyester fibers, and / or the polyester melt is used to prepare recycled polyester chips.

2. The continuous waste polyester textile recycling method according to claim 1, characterized in that, The preparation of the first alcoholysis solution must also satisfy at least one of the following conditions: (1) The mass ratio of the bis(hydroxyethyl) terephthalate to the ethylene glycol is 1:2-1:4; (2) The molar ratio of the waste polyester textiles to the ethylene glycol is 1:0.5-1:1; (3) The temperature of the first alcoholysis is 240℃-260℃, and the time is 1h-2h; (4) Before mixing waste polyester textiles, bis(hydroxyethyl) terephthalate and ethylene glycol, the waste polyester textiles are also crushed.

3. The continuous waste polyester textile recycling method according to claim 1, characterized in that, The step of preparing the second alcoholysis solution also satisfies at least one of the following conditions: (1) The molar ratio of the waste polyester textiles to the ethylene glycol is 1:1-1:2; (2) The mass of the carboxylated zinc oxide is 5%-10% of the mass of the waste polyester textiles; (3) The particle size of the carboxylated zinc oxide is 5µm-10µm; (4) The temperature of the second alcoholysis is 170℃-190℃ and the time is 3h-4h.

4. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, The first filtration process includes a primary filtration and a secondary filtration performed sequentially, wherein the primary filtration uses a filter screen with a pore size of 30µm-50µm, and the secondary filtration uses a filter screen with a pore size of 2µm-4µm.

5. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, The adsorption purification process also requires at least one of the following conditions to be met: (1) The adsorption purification treatment time is 4h-6h, of which the adsorption decolorization treatment time is 2h-4h; (2) The adsorption decolorization treatment includes a first adsorption decolorization and a second adsorption decolorization performed sequentially, wherein the adsorbent used in the first adsorption decolorization is different from the adsorbent used in the second adsorption decolorization. (3) The adsorbent used in ion adsorption treatment is at least one of ion exchange resin, macroporous adsorption resin or molecular sieve.

6. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, The second alcoholysis solution after adsorption purification is subjected to a continuous second filtration process, wherein the second filtration process uses a filter screen with a pore size of 0.5µm-1.5µm.

7. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, The vacuum evaporation process also requires at least one of the following conditions to be met: (1) The temperature of vacuum evaporation treatment is 130℃-150℃, the time is 8h-12h, and the vacuum degree is 8kPa-13kPa; (2) In the vacuum evaporation process, ethylene glycol is obtained, and the ethylene glycol is returned to the first alcoholysis or the second alcoholysis process for recycling.

8. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, In the pre-condensation reaction step, at least one of the following conditions is met: (1) In the first prepolymerization reaction step, a first prepolymer is obtained, and the intrinsic viscosity of the first prepolymer is 0.10 dL / g-0.15 dL / g; (2) In the second prepolymerization reaction step, a second prepolymer is obtained, the intrinsic viscosity of which is 0.20 dL / g-0.25 dL / g; (3) In the third prepolymerization reaction step, a third prepolymer is obtained, the intrinsic viscosity of which is 0.30 dL / g-0.35 dL / g; (4) The temperature T1 of the first pre-condensation reaction is 240℃-250℃, the vacuum degree P1 is 30kPa-40kPa, and the time is 1h-1.5h; (5) The temperature T2 of the second pre-condensation reaction is 260℃-265℃, the vacuum degree P2 is 10kPa-12kPa, and the time is 1h-1.5h; (6) The temperature T3 of the third pre-condensation reaction is 270℃-275℃, the vacuum degree P3 is 1.0kPa-1.5kPa, and the time is 1.5h-2h.

9. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, In the steps of preparing polyester melt, at least one of the following conditions must be met: (1) The final polycondensation reaction is carried out at a temperature of 280℃-282℃, a vacuum degree of 100Pa-150Pa, and a time of 2h-2.5h; (2) The intrinsic viscosity of the polyester melt is 0.65 dL / g-0.70 dL / g; (3) In the steps of pre-condensation reaction and final condensation reaction, the polyester catalyst used is selected from antimony glycolate and / or antimony trioxide, and the mass of the polyester catalyst is 0.05%-0.10% of the mass of bis(hydroxyethyl) terephthalate melt.

10. The continuous recycling method for waste polyester textiles according to claim 1, characterized in that, A continuous method for recycling waste polyester textiles also meets at least one of the following conditions: (1) A portion of the bis(hydroxyethyl) terephthalate melt is subjected to a continuous pre-condensation reaction and a final condensation reaction, while the other portion is returned to the first alcoholysis step for recycling. (2) When preparing recycled polyester fiber by direct spinning of the polyester melt, the direct spinning process includes: the spinning temperature is 289℃-291℃, the cooling temperature is 22℃-25℃, the fiber oiling rate is 1.1wt%-1.3wt%, and the winding speed is 4200m / min-4500m / min.

Images