High-quality polyester melt chemically regenerated from waste polyester and method for regenerating polyester textile by using high-quality polyester melt

Abstract

The invention provides a high-quality polyester melt chemically regenerated from waste polyester and a method for regenerating polyester textiles by using the high-quality polyester melt, which comprises the following steps: by taking non-polyester-containing waste polyester as a raw material, firstly, removing non-polyester components by using a chemical reagent; and regenerating a high-quality polyester melt through processes of chemical depolymerization, purification, polymerization and the like, and regenerating a polyester textile through processes of spinning, printing and dyeing and the like. The polyester melt prepared by the method is narrow in molecular weight distribution, low in diethylene glycol content, low in carboxyl content and excellent in color value, and regenerated polyester textiles are excellent in performance.

Description

Technical Field

[0001] The present invention relates to the technical field of waste polyester recycling, and particularly to a method for chemically recycling waste polyester into high-quality polyester melt and recycling polyester textiles using the same. Background Art

[0002] In the polyester industry, the treatment of waste polyester is an important issue. With the diversified application of polyester in various fields, a large amount of waste polyester containing non-polyester components from different sources has been generated. If these waste polyesters are directly discarded, it will cause resource waste and environmental pressure. From a resource perspective, polyester is synthesized from resources such as petroleum, and direct abandonment means wasting valuable raw materials.

[0003] In traditional treatment methods, physical recycling methods have certain limitations. For example, the quality of the recycled polyester decreases, making it unable to meet the production requirements of high-quality polyester. Chemical recycling methods, on the other hand, can treat waste polyester at the molecular level and better restore its performance. Under this process background, chemical recycling methods can accurately depolymerize the polyester components in waste polyester and then repolymerize them into high-quality polyester for the production of new polyester products, which is of great significance for the sustainable development of the polyester industry.

[0004] Patent CN109503818A (a production process of antimony-free recycled polyester chips) discloses a process method for producing polyester chips by alcoholysis refining and repolymerization using polyester-cotton waste as raw materials. After the polyester is alcoholyzed, cotton fibers are separated, which will cause the polyester-cotton separation device to become blocked quickly and have a high switching frequency. At the same time, this process requires transesterification of the polyester alcoholysis product with methanol to obtain DMT, and after DMT is refined, it is transesterified with ethylene glycol to obtain pure BHET. This process route is long, requires two transesterification reactions of methanol and ethylene glycol, and involves the use of methanol, a Class A chemical.

[0005] Patent CN114656684A (A method for preparing high-purity recycled PET polyester from waste PET polyester) discloses a process that uses waste polyester as raw material, obtains BHET through alcoholysis, and then purifies and repolymerizes BHET through vacuum concentration, vacuum evaporation, and short-path distillation. First, due to the presence of metal ions, esters, and trace amounts of acid-base compounds in the alcoholysis solution, the BHET alcoholysis solution in this process is extremely prone to oligomerization of BHET during concentration at 100 - 140 °C and 1 - 10 KPa. Second, the BHET disclosed in this process is purified through vacuum concentration, vacuum evaporation, and short-path distillation and then repolymerized, and various metal ions added during the manufacture of the waste polyester raw material cannot be removed during the purification stage of BHET, so it will cause a thermal degradation effect caused by metal ions during repolymerization, reducing the quality of the repolymerized polyester. Third, this process method first requires washing and drying the raw materials, generating sewage and consuming a large amount of heat for drying moisture. Finally, this process method is not applicable to waste PET polyester raw materials with a non-polyester component content exceeding a certain amount.

[0006] Patent CN118496092A (A method for producing high-purity BHET from waste polyester textiles and its application in the production of recycled polyester) discloses a process method that uses waste polyester textiles containing spandex as raw material, first removes the spandex, then performs decolorization and impurity removal, and finally alcoholysis and polymerization. In this process method, the decolorization process requires high pressure and extremely high requirements for equipment. Second, this process method can only remove impurities dissolved in N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide in the raw material, and the remaining impurities will be introduced into the recycled polyester. Summary of the Invention

[0007] In view of this, the present invention provides a method for chemically recycling waste polyester into high-quality polyester melt and a method for recycling polyester textiles using the same.

[0008] The method for chemically recycling waste polyester into high-quality polyester melt according to the present invention includes the following steps: (1) Pre-depolymerization Mix dry polyester chips with ethylene glycol and a depolymerization catalyst, carry out a pre-depolymerization reaction, and then filter to remove a small amount of non-polyester impurities to obtain a clear and transparent pre-depolymerization reaction solution; (2) Deep depolymerization Mix the pre-depolymerization reaction solution with ethylene glycol, carry out a deep depolymerization reaction, and then filter to obtain a deep depolymerization reaction solution; (3) Conditioning and concentration Mix the deep depolymerization reaction solution with ethylene glycol, cool down and perform conditioning and concentration, and then carry out solid-liquid separation to remove impurities with a particle size less than 3 μm to obtain a depolymerization product / ethylene glycol solution; (4) Purification of the depolymerization product The depolymerization product / ethylene glycol solution is refined and purified to obtain bis(2-hydroxyethyl) terephthalate (BHET); the refining and purification steps include one or more of a purification extraction process, a thermal stripping extraction process, and a crystalline aggregation process; (5)Pre-polycondensation The BHET is mixed with a polymerization catalyst, a heat stabilizer, and an antioxidant, and pre-polycondensation is carried out to obtain a pre-polycondensation product; (6)Final polycondensation The pre-polycondensation product is subjected to final polycondensation at a temperature of 270 - 290 °C to obtain a final polycondensation melt; (7)Melt filtration The final polycondensation melt is filtered to remove carbide and gel impurities generated in the previous processes to obtain a polyester melt.

[0009] Preferably, the waste polyester in step (1) includes at least one of waste polyester bottle chips, waste polyester-containing textiles, waste polyester fibers, waste polyester foam materials, waste polyester friction materials, and polyester chips; The waste polyester includes the following components by weight percentage: Polyester component 50 - 99.99%, non-polyester component 0 - 40%, dye 0 - 10%, pigment 0 - 10%, additive 0 - 10%; The non-polyester component is one or more of cotton, linen, wool, viscose fiber, acetate fiber, acrylic fiber, nylon fiber, polyolefin, and spandex.

[0010] Preferably, the mass ratio of ethylene glycol to polyester fragments in step (1) is 0.3:1 - 3:1; The mass addition amount of the depolymerization catalyst relative to the polyester fragments is 200 ppm - 2500 ppm; The depolymerization catalyst is a metal and metal composite oxide catalyst, a metal salt catalyst, or an ionic liquid catalyst; The temperature of the pre-depolymerization reaction is 180 °C - 240 °C, the reaction pressure is 100 Kpa - 400 Kpa(A), and the reaction time is 45 min - 120 min; The main component of the pre-depolymerization reaction solution is an oligomer of BHET, and the degree of polymerization is less than 40. Preferably, the mass ratio of ethylene glycol to polyester fragments in step (2) is 1:1 - 4:1; The reaction temperature of the deep depolymerization is 180 °C - 240 °C, the reaction pressure is 100 Kpa - 400 Kpa(A), and the reaction time is 90 min - 150 min; The main components of the depolymerization products in the deep depolymerization reaction solution are BHET and oligomers of BHET; the degree of polymerization of the oligomers is not more than 4.

[0011] Preferably, the mass ratio of ethylene glycol to polyester chips in step (3) is 3:1 - 7:1; The mass concentration of the depolymerization product in the depolymerization product / ethylene glycol solution is 9 - 24%; The temperature of the conditioned and concentrated depolymerization product / ethylene glycol solution is 60 - 100 °C.

[0012] Preferably, the refining and purification in step (4) includes one or more of a purification extraction process, a thermal stripping extraction process, and a crystalline aggregation process.

[0013] Preferably, after the refining and purification in step (4), it further includes a modification esterification and transesterification step, and the modification esterification and transesterification is to synthesize a modified polyester by flexibilizing BHET.

[0014] Preferably, the polymerization catalyst in step (5) is one or more of an antimony-based catalyst, a titanium-based catalyst, and a germanium-based catalyst; the addition amount of the polymerization catalyst is 0.005 - 0.05% of the weight of BHET; The heat stabilizer is one or more of phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and triethyl phosphonoacetate; the addition amount of the heat stabilizer is 0.005 - 0.02% of the weight of BHET.

[0015] The antioxidant is one or more of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, tris(2,4-di-tert-butylphenyl)phosphite, and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite; the addition amount of the antioxidant is 0.03 - 0.15% of the weight of BHET.

[0016] The temperature of the prepolycondensation reaction is 250 - 290 °C, the reaction pressure is 0.1 - 30 KPa(A), and the reaction time is 60 - 240 min.

[0017] Preferably, the reaction temperature of the final polycondensation in step (6) is 270 - 290 °C, the reaction pressure is 20 - 500 Pa(A), and the reaction time is 120 - 240 min.

[0018] Preferably, the polyester melt is spun, woven, dyed, and post-finished to obtain a polyester textile.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for chemically regenerating high-quality polyester melt from waste polyester and applying the regenerated polyester to produce polyester textiles. Using waste polyester containing non-polyester components as raw materials, non-polyester components are first removed with chemical reagents, and then high-quality polyester textiles are regenerated through processes such as chemical depolymerization, purification, polymerization, spinning, and dyeing. The polyester melt prepared by the method of the present invention has a narrow molecular weight distribution, low diethylene glycol content, low carboxyl end group content, and excellent color value, and the regenerated polyester textiles have excellent properties. Description of the Drawings

[0020] Figure 1 1H-NMR spectrum of the depolymerization product obtained by thermal drive light boiling substance segregation extraction in Example 3; Figure 2 1H-NMR spectrum of BHET of the depolymerization product obtained by solid-liquid separation of the aqueous solution of the crystalline-enriched depolymerization product in Example 3; Figure 3 1H-NMR spectrum of the liquid obtained by solid-liquid separation of the aqueous solution of the crystalline-enriched depolymerization product in Example 3. Detailed Embodiments

[0021] The present invention provides a method for chemically regenerating high-quality polyester melt from waste polyester, and the steps are as follows: (1) Pre-depolymerization Mix the dried polyester chips with ethylene glycol and a depolymerization catalyst, carry out a pre-depolymerization reaction, and then filter to remove a small amount of non-polyester impurities to obtain a clear and transparent pre-depolymerization reaction solution; (2) Deep depolymerization Mix the pre-depolymerization reaction solution with ethylene glycol, carry out a deep depolymerization reaction, and then filter to obtain a deep depolymerization reaction solution; (3) Conditioning and concentration Mix the deep depolymerization reaction solution with ethylene glycol, cool down and carry out conditioning and concentration, and then carry out solid-liquid separation to remove impurities with a particle size less than 3 μm to obtain a depolymerization product / ethylene glycol solution; (4) Purification of the depolymerization product Refine and purify the depolymerization product / ethylene glycol solution to obtain BHET; the refining and purification steps include one or more of a purification extraction process, a thermal drive segregation extraction process, and a crystalline condensation process; (5) Pre-polycondensation Mix the BHET with a polymerization catalyst, a heat stabilizer, and an antioxidant, and carry out pre-polycondensation to obtain a pre-polycondensation product; (6) Final polycondensation Carry out final polycondensation on the pre-polycondensation product at a temperature of 270-290 °C to obtain a final polycondensation melt; (7) Melt filtration Filter the end condensation melt to remove carbide and gel impurities generated in the previous process to obtain a polyester melt.

[0022] Preferably, the waste polyester in step (1) includes at least one of waste polyester bottle chips, waste polyester-containing textiles, waste polyester fibers, waste polyester foam materials, waste polyester friction materials, and polyester chips; The waste polyester includes the following components in weight percentages: Polyester component 50 - 99.99%, non-polyester component 0 - 40%, dye 0 - 10%, pigment 0 - 10%, additive 0 - 10%; The non-polyester component is one or more of cotton, linen, wool, viscose fiber, acetate fiber, acrylic fiber, nylon fiber, polyolefin, and spandex.

[0023] In a specific embodiment of the present invention, when the waste polyester is waste polyester-containing textiles or waste polyester fibers, it further includes a pretreatment step for the waste polyester, and the steps of the pretreatment are as follows: S1 Waste polyester crushing Crush the recycled waste polyester to ≤100 mm to obtain waste polyester fragments; S2 Removal of non-polyester components Add the waste polyester fragments to a reaction reagent to remove non-polyester components; S3 Decolorization Mix the waste polyester fragments after removing non-polyester components with a decolorizing agent for decolorization until the nitrogen atom content in the waste polyester is below 100 ppm; S4 Drying Dry the decolorized polyester fragments until the content of the decolorizing agent in the polyester fragments is below 25 ppm.

[0024] The reaction reagent in step S2 is one or more of sodium hypochlorite, formic acid aqueous solution, sulfuric acid aqueous solution, hydrochloric acid aqueous solution, trichloroacetic acid, sodium hydroxide - methanol solution, dichloromethane, trichloroethane, dimethyl sulfoxide, dimethylpyrrolidone, cyclohexanone, and dimethyl ester of mixed dibasic acids; The order of removing non-polyester components can be arbitrary. However, in order to better recycle various non-polyester components and the reaction reagent for removing non-polyester components, in a specific embodiment of the present invention, the order is to first remove nylon fiber and cotton, then remove viscose fiber and spandex, then remove wool, acrylic fiber, and linen fiber, then remove acetate fiber, and finally remove polyolefin.

[0025] The mass ratio of the reaction reagent to the waste polyester-containing textiles is 2:1 - 7:1, preferably 3:1 - 5:1; The reaction temperature for removing non-polyester components is 20°C - 120°C, preferably 40°C - 60°C; the reaction pressure is 100KPa - 300KPa(A), preferably 100KPa - 150KPa(A); the reaction time is 5min - 90min, preferably 10min - 60min.

[0026] When the reaction reagent is an aqueous sulfuric acid solution or an aqueous hydrochloric acid solution, after the reaction, it is discharged as industrial sewage after flocculation, COD reduction, and BOD reduction. When the reaction reagent is other components, after the reaction, it enters the rectification recovery system and is reused after removing impurities by rectification. The flocculation, COD reduction, BOD reduction, and rectification are all carried out by conventional methods in the art.

[0027] The decolorizing agent in step S3 is one or more of dimethyl sulfoxide, dimethylpyrrolidone, dichloroacetic acid, straight-chain diol, and dimethylformamide; The mass ratio of the decolorizing agent to the waste polyester textile fragments is 5:1 - 15:1; preferably 7:1 - 10:1; The temperature for decolorization is 70°C - 150°C, preferably 100°C - 120°C; the decolorization time is 30min - 90min, preferably 50min - 60min.

[0028] The used decolorizing agent can be recovered by rectification using conventional methods.

[0029] The pressure for drying in step S4 is normal pressure or negative pressure. Considering the vaporization latent heat of the decolorizing agent, reducing energy consumption, reducing waste gas, increasing drying efficiency, while not destroying the chemical structure of polyester and avoiding thermal degradation, in the specific embodiments of the present invention, the drying pressure is negative pressure.

[0030] The temperature for drying is 40 - 120°C, preferably 60 - 100°C; the drying pressure is 0.5 - 10KPa(A), preferably 2 - 5KPa(A); Preferably, the mass ratio of ethylene glycol to polyester fragments in step (1) is 0.3:1 - 3:1, preferably 1:1 - 2:1; The mass addition amount of the depolymerization catalyst relative to the polyester textile fragments is 200ppm - 2500ppm, preferably 500ppm - 1500pmm; The depolymerization catalyst is a metal oxide catalyst, a metal composite oxide catalyst, a metal salt catalyst, or an ionic liquid catalyst; preferably a metal salt catalyst; The metal salt catalysts are any one or more of zinc acetate, zinc acetate dihydrate, sodium carbonate, potassium carbonate, and zinc acetate; The temperature of the pre-depolymerization reaction is 180°C - 240°C, preferably 195 - 200°C; the reaction pressure is 100Kpa - 400Kpa(A), preferably 100Kpa - 200Kpa(A); the reaction time is 45min - 120min, preferably 60min - 90min; The main component of the pre-depolymerization reaction solution in step (1) is the oligomer of BHET, with a degree of polymerization less than 40, preferably less than 25.

[0031] There is no special limitation on the pre-depolymerization reactor in the present invention. To enhance mass transfer and heat transfer, in the specific embodiments of the present invention, a continuous stirred tank reactor is used.

[0032] Preferably, the mass ratio of ethylene glycol to polyester fragments in step (2) is 1:1 - 4:1, preferably 2:1 - 3:1; The temperature of the deep-depolymerization reaction is 180°C - 240°C, preferably 195 - 200°C; the reaction pressure is 100Kpa - 400Kpa(A), preferably 100Kpa - 200Kpa(A); the reaction time is 90min - 150min, preferably 90min - 120min; The main component of the depolymerization product in the deep-depolymerization reaction solution is BHET and its oligomers; the degree of polymerization of the oligomers is not more than 4. The oligomers with a degree of polymerization not more than 4 account for 3% - 7% of the total mass of the depolymerization product.

[0033] There is no special limitation on the deep-depolymerization reactor in the present invention. To reduce the content of oligomers in the depolymerization product, in the specific embodiments of the present invention, a plug flow reactor is used.

[0034] Preferably, the mass ratio of ethylene glycol to polyester fragments in step (3) is 3:1 - 7:1, preferably 4:1 - 6:1; The mass concentration of the depolymerization product / ethylene glycol solution is 9 - 24%, preferably 10 - 20%; The temperature of the depolymerization product / ethylene glycol solution after conditioning and concentration should be maintained at 60 - 100°C, preferably 70 - 90°C.

[0035] Preferably, the refining and purification in step (4) includes one or more of a purification extraction process, a thermal stripping extraction process, and a crystalline aggregation process; The purification extraction process includes a molecular adsorption purification extraction process and an ion purification extraction process; Specifically, the purification extraction process sequentially includes a molecular adsorption purification extraction process and an ion purification extraction process; The adsorption and purification medium used in the molecular adsorption purification extraction process is one or more of bentonite, diatomite, silica gel, and activated carbon. Diatomite and activated carbon are preferred, and more preferably, it is first purified by diatomite to adsorb and extract some impurities and pigments in the depolymerization product / ethylene glycol solution; then purified by activated carbon to adsorb and extract non-polar or weakly polar organic substances by van der Waals force, adsorb and extract small-diameter molecules by size screening effect, and adsorb and extract molecules with stronger polarity by chemical bond action; The reaction temperature of the molecular adsorption purification extraction is 60-90°C, the reaction pressure is atmospheric pressure, and the reaction time is 30-90 min, preferably 45-60 min; After the molecular adsorption purification extraction reaction, the small molecules in the depolymerization product / ethylene glycol solution are reduced from 1000 ppm to less than 10 ppm; Specifically, the media used in the ion purification extraction process are cation exchange resin and anion exchange resin. The cation exchange resin is a weakly acidic cation exchange resin, including acrylic cation exchange resin, phenolic cation exchange resin, styrene cation exchange resin, and urea formaldehyde cation exchange resin. Styrene cation exchange resin and acrylic cation exchange resin are preferred, including D113, D101, D152, HP336, CXO-5MP, and D113 or HP336 are preferred. The anion exchange resin is a strongly basic anion exchange resin, including styrene anion exchange resin and acrylic anion exchange resin. Styrene anion exchange resin is preferred, including D201, 201*7 / 201*4, IRA402 / 420, etc., and IRA402 / 420 is preferred.

[0036] When the depolymerization product / ethylene glycol solution reacts and extracts with the weakly acidic cation exchange resin, the pH value of the depolymerization product / ethylene glycol solution system is weakly acidic. BHET and BHET oligomers undergo ester bond hydrolysis reaction to generate mono(2-hydroxyethyl) terephthalate. There will be exposed carboxyl groups at the end of mono(2-hydroxyethyl) terephthalate, which will exacerbate the acidity of the depolymerization product / ethylene glycol solution, further affecting the quality deterioration of BHET and BHET oligomers and generating more mono(2-hydroxyethyl) terephthalate. In addition, because the depolymerization product / ethylene glycol solution is acidic, it will promote the transesterification reaction between the by-produced diethylene glycol and BHET and BHET oligomers during the depolymerization of waste polyester textile fragments, forming bis(2-hydroxyethyl) terephthalate, resulting in the quality deterioration of BHET and BHET oligomers. Therefore, the ion purification extraction process should be carried out in the order of first reacting and extracting through the weakly acidic cation exchange resin and then reacting and extracting through the strongly basic anion exchange resin. It should be noted that after the depolymerization product / ethylene glycol solution reacts and extracts with the weakly acidic cation exchange resin, it should react and extract with the strongly basic anion exchange resin as soon as possible to quickly adjust the acidity and alkalinity of the depolymerization product / ethylene glycol solution and keep the depolymerization product / ethylene glycol solution neutral or weakly basic.

[0037] The temperature of the ion purification extraction reaction is 70 - 80 °C, the reaction pressure is 100 KPa, and the reaction time is 1 - 3 min; After the ion purification extraction reaction, the ionic impurities in the depolymerization product / ethylene glycol solution are reduced from 2000 ppm to less than 5 ppm.

[0038] The thermal drive segregation extraction mainly uses a heat source to drive the removal of all substances other than BHET in the depolymerization product / ethylene glycol solution, including the thermal drive segregation extraction of light-boiling substances and the thermal drive segregation extraction of heavy-boiling substances. Considering process economy and the quality of BHET, the preferred order is to first perform the thermal drive segregation extraction of light-boiling substances and then perform the thermal drive segregation extraction of heavy-boiling substances.

[0039] Among them, the thermal drive segregation extraction of light-boiling substances is to separate and extract the light-boiling substances in the depolymerization product / ethylene glycol solution from BHET and BHET oligomers through the drive of a heat source. The light-boiling substances undergo a phase transformation and leave the thermal drive segregation extraction reactor of light-boiling substances in a gaseous state, while BHET and BHET oligomers do not undergo a phase transformation and leave the thermal drive segregation extraction reactor of light-boiling substances in a liquid state.

[0040] The light-boiling substances include acetaldehyde, ethylene glycol, diethylene glycol, oil agent, additives, etc. After the thermal drive segregation extraction of light-boiling substances, the mass fraction of light-boiling substances in the liquid-phase BHET and BHET oligomers is reduced to less than 1%.

[0041] The reaction temperature of the thermal drive segregation extraction of light-boiling substances is 120 - 180 °C, preferably 130 - 150 °C.

[0042] The reaction pressure of the thermal drive segregation extraction of light-boiling substances is 0.3 - 5 KPa, preferably 0.5 - 2 KPa.

[0043] During the thermal drive segregation extraction of light-boiling substances, the time for the light-boiling substances to undergo a phase transformation and leave the thermal drive segregation extraction reaction should be less than 60 s, preferably less than 30 s.

[0044] The structure of the thermal drive segregation extraction reactor of light-boiling substances is not particularly limited, but it should meet the above reaction time, otherwise it will cause the self-polymerization of BHET to generate more BHET oligomers under high-temperature and high-vacuum conditions.

[0045] The number of thermal drive segregation extraction reactors of light-boiling substances is not particularly limited. Considering process economy, the number of thermal drive segregation extraction reactors of light-boiling substances should not be less than 2 to utilize the reaction waste heat and reduce energy consumption.

[0046] The gaseous light-boiling substances leaving the thermal drive light-boiling substance separation and extraction reactor should also be purified through a rectification device. The light-boiling substances include acetaldehyde, ethylene glycol, diethylene glycol, sizing agent, and additive. High-purity ethylene glycol is recycled to the processes of pre-depolymerization, deep depolymerization, and conditioning and concentration of waste polyester textile fragments, and the remaining substances such as acetaldehyde, diethylene glycol, sizing agent, and additive are sold as commodities.

[0047] Among them, thermal drive heavy-boiling substance separation and extraction is driven by a heat source to separate and extract BHET from the heavy-boiling substances in the liquid phase obtained after thermal drive light-boiling substance separation and extraction. BHET undergoes a phase transformation and leaves the thermal drive heavy-boiling substance separation and extraction reactor in a gaseous state, while the heavy-boiling substances do not undergo a phase transformation and leave the thermal drive light-boiling substance separation and extraction reactor in a liquid state.

[0048] After thermal drive heavy-boiling substance separation and extraction, the mass fraction of heavy-boiling substances in the gaseous BHET is reduced to less than 0.01%. The heavy-boiling substances include BHET oligomers, mono-hydroxyethyl terephthalate, bis-diethylene glycol terephthalate, and carbon black powder.

[0049] The reaction temperature for thermal drive heavy-boiling substance separation and extraction is 180 - 240 °C, preferably 180 - 210 °C.

[0050] The reaction pressure for thermal drive heavy-boiling substance separation and extraction is 3 - 60 Pa, preferably 10 - 30 Pa.

[0051] During the process of thermal drive heavy-boiling substance separation and extraction, the time for the light-boiling substances to undergo a phase transformation and leave the thermal drive heavy-boiling substance separation and extraction reaction should be less than 10 s, preferably less than 5 s.

[0052] There is no special restriction on the structure of the thermal drive heavy-boiling substance separation and extraction reactor, but it should meet the above reaction time, otherwise self-polymerization of BHET will occur under high-temperature and high-vacuum conditions to generate more BHET oligomers.

[0053] There is no special restriction on the number of thermal drive heavy-boiling substance separation and extraction reactors.

[0054] The liquid-phase heavy-boiling substances leaving the thermal drive heavy-boiling substance separation and extraction reactor contain some BHET oligomers. Therefore, the liquid-phase heavy-boiling substances should be selectively recycled to the waste polyester textile pre-depolymerization reactor and participate in the pre-depolymerization reaction as the pre-depolymerization mother liquor, and the recycling amount should be adjusted in a timely manner according to the process.

[0055] The crystalline condensation is to continuously feed the BHET purified by thermal drive separation and extraction into the crystalline condensation device. BHET undergoes a microscopic dynamic process from a molten liquid to a solution and then to crystalline condensation, further removing water-soluble impurities, and the obtained BHET purity reaches over 99.99%.

[0056] The crystalline condensation described above includes conditioning and concentration adjustment, centrifugal separation, crystalline enrichment, and solid-liquid separation.

[0057] There is no particular limitation on the number of stages of the crystalline condensation described above. To minimize the content of water-soluble impurities, it is preferably not less than 2 stages.

[0058] The water-soluble impurities described above are carboxylates formed by the reaction of metal ions with trace amounts of acidic substances generated during the previous pre-depolymerization and deep depolymerization processes.

[0059] Among them, the solvents for conditioning and concentration adjustment are water, ethanol, tetrahydrofuran, acetone, ethyl acetate, etc. Considering the solubility of BHET and water-soluble impurities in the solvent and indicators such as crystal particle size and optical purity during the subsequent crystalline enrichment process, the preferred solvent for conditioning and concentration adjustment is water. During the multi-stage crystalline aggregation process, the solvent for conditioning and concentration adjustment in the subsequent stage of crystalline aggregation is used as the solvent for conditioning and concentration adjustment in the previous stage of crystalline aggregation, thereby further increasing the concentration of water-soluble impurities in the solvent for conditioning and concentration adjustment until it approaches saturation, which is beneficial to reducing the dosage of the solvent for conditioning and concentration adjustment and improving the economy of the entire process method.

[0060] The mass ratio of the solvent added relative to BHET is 4:1 - 10:1, preferably 6:1 - 8:1; The reaction temperature for conditioning and concentration adjustment is 40 - 90°C, preferably 65 - 75°C; The reaction time for conditioning and concentration adjustment is 20 - 50 min, preferably 30 - 40 min; There is no particular limitation on the reactor for conditioning and concentration adjustment. To enhance the mass transfer and heat transfer of the material flow, a continuous stirred-tank reactor is preferably used.

[0061] Among them, there is no particular limitation on the centrifugal separation device, and the separation accuracy of centrifugal separation is less than 5 μm, preferably less than 3 μm.

[0062] Among them, crystalline enrichment and solid-liquid separation are a dynamic process. Therefore, the structure of the crystalline enrichment reactor is designed by balancing the continuous stirred-tank structure and the plug-flow structure. During the process from the conditioning and concentration adjustment of the depolymerization product and centrifugal separation to cooling to the appropriate temperature for crystalline enrichment, the material flow of the conditioned and concentrated solution of the depolymerization product is in a continuous stirred-tank state, thereby achieving better mass transfer and heat transfer. During the process from the appropriate temperature for crystalline enrichment to solid-liquid separation, the crystalline enrichment liquid of the depolymerization product is in a plug-flow state, thereby ensuring the stability of the purity and mass yield of BHET crystals. There is no special limitation on the structure of the solid-liquid separator, and the separation accuracy is less than 30 μm, preferably less than 10 μm.

[0063] The temperature for crystalline enrichment is 10 - 30°C, preferably 15 - 20°C; if the temperature for crystalline enrichment is too high, the solubility of BHET will be large, and the mass yield will be uneconomical. If the temperature for crystalline enrichment is too low, the solubility of water-soluble impurities will be too small, affecting the crystal purity of BHET.

[0064] The time for crystalline enrichment is 60 min - 240 min, preferably 90 min - 150 min; if the time for crystalline enrichment is too long or too short, the optical purity and particle size of BHET crystals are not good. In addition, if the time for crystalline enrichment is too short, both the mass yield and purity of BHET are not good.

[0065] Preferably, step (4) further includes the steps of modified esterification and transesterification of BHET, and the modified esterification and transesterification are used to synthesize modified polyester fibers by making BHET flexible.

[0066] The modified esterification and transesterification are applicable to synthesizing modified polyester fibers by making BHET flexible obtained through the previous process, and then reprocessing to manufacture polyester textiles. The modified polyester fibers include water-soluble polyester fibers, cationic flame-retardant polyester fibers, low-melting-point polyester fibers, etc. If pure polyester fibers need to be synthesized for spinning polyester textiles, the BHET after the previous process treatment is directly subjected to the subsequent process of pre-polycondensation.

[0067] Among them, the modified esterification is mainly the esterification of the three monomers. The three monomers are the modified monomers of the modified polyester fibers, including one or several of polyethylene glycol, sodium 5-sulfoisophthalate, diethylene glycol, isophthalic acid, succinic acid, adipic acid, 1,4-butanediol, pentaerythritol, ethylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, isosorbide.

[0068] The temperature of the modified esterification reaction is 140 - 250 °C, preferably 160 - 240 °C; The pressure of the modified esterification reaction is 100 - 400 KPa(A), preferably 250 - 350 KPa(A); The time of the modified esterification reaction is 90 - 240 min, preferably 120 - 180 min.

[0069] There is no special limitation on the reactor for the modified esterification. To improve the reaction efficiency, enhance mass transfer and heat transfer, and ensure the esterification rate of the modified three monomers, an inner and outer chamber structure is preferably used.

[0070] Among them, the modified transesterification is mainly to carry out a transesterification reaction between BHET and the reaction product of the above-mentioned modified esterification to form an esterified product with uniform distribution of each unit structure in the chain segment.

[0071] The temperature of the modified transesterification reaction is 190 - 250 °C, preferably 220 - 240 °C; The pressure of the modified transesterification reaction is 100 - 400 KPa(A), preferably 250 - 350 KPa(A); The time of the modified transesterification reaction is 45 - 120 min, preferably 60 - 90 min.

[0072] There are no special restrictions on the reactor for modified transesterification. To improve the reaction efficiency and enhance mass and heat transfer, a continuous stirred tank reactor is preferably used.

[0073] Preferably, the pre-polycondensation in step (5) is to continuously feed the BHET or its modified transesterification product obtained in step (4) into the pre-polycondensation reactor, and a polymerization catalyst, a heat stabilizer, and an antioxidant are added into the pre-polycondensation reactor; The polymerization catalyst includes antimony-based catalysts, such as one or more of antimony trioxide, antimony acetate, and antimony glycolate; titanium-based catalysts, such as one or more of isopropyl titanate, tetrabutyl titanate, titanium dioxide, supported titanium-based catalysts, and composite titanium-based catalysts; germanium-based catalysts, such as germanium dioxide; preferably one or more of antimony glycolate, tetrabutyl titanate, and germanium dioxide. The addition amount of the catalyst is 0.005-0.05% based on the weight of BHET or the modified transesterification product, preferably 0.015-0.035%; The heat stabilizer includes one or more of phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and triethyl phosphonoacetate. Preferably, it is triethyl phosphonoacetate. The addition amount of the heat stabilizer is 0.005-0.02% based on the weight of BHET or the modified transesterification product, preferably 0.008-0.015%; The antioxidant includes one or more of pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine, tris(2,4-di-tert-butylphenyl) phosphite, and bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite. Preferably, they are pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and tris(2,4-di-tert-butylphenyl) phosphite. The addition amount of the antioxidant is 0.03-0.15% based on the weight of BHET or the modified transesterification product, preferably 0.05-0.1%. The mass ratio of pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] to tris(2,4-di-tert-butylphenyl) phosphite is 1:1, which has the best effect.

[0074] The temperature of the pre-polycondensation reaction is 250-290°C, preferably 255-275°C; The pressure of the pre-polycondensation reaction is 100-100000 Pa(A), preferably 200-3000 Pa(A); The time of the pre-polycondensation reaction is 60-240 min, preferably 120-180 min.

[0075] There are no special restrictions on the structure of the pre-polycondensation reactor. To increase mass and heat transfer and ensure the uniformity of the degree of polymerization of the chain segments, a plug flow structure is preferably used.

[0076] Preferably, the final polycondensation is to continuously feed the prepolycondensation product into the final polycondensation reactor.

[0077] The temperature of the final polycondensation reaction is 275 - 290 °C, preferably 280 - 285 °C; The pressure of the final polycondensation reaction is 20 - 200 Pa(A), preferably 50 - 150 Pa(A); The time of the final polycondensation reaction is 120 - 240 min, preferably 120 - 210 min.

[0078] The structure of the final polycondensation reactor has no special limitation. To ensure that the molecular weight distribution of the polymer is as narrow as possible, a plug flow structure is preferred.

[0079] Preferably, the melt filtration is to continuously feed the final polycondensation melt into the melt filter through a melt pump to remove impurities such as carbides and gels generated in the previous process. The filtration accuracy is 20 - 100 μm, preferably 20 - 40 μm.

[0080] The present invention also provides a method for regenerating polyester textiles using the polyester melt, which involves spinning, weaving, dyeing, and post - finishing the polyester melt to obtain polyester textiles.

[0081] In the specific embodiments of the present invention, the spinning, weaving, dyeing, and post - finishing are all conventional methods in the art.

[0082] The present invention will be further described below with reference to the embodiments. Example 1

[0083] A method for chemically regenerating high - quality polyester melt from waste polyester and applying it to regenerate polyester textiles is as follows: (1) Crushing of waste polyester The recycled polyester - containing textile (waste polyester / viscose fiber / spandex waste cloth with 15% viscose fiber content and 5% spandex content) is crushed to 80 mm to obtain waste polyester - containing textile fragments; (2) Removal of non - polyester components According to 1000 kg / h of waste polyester - containing textile fragments and 1400 kg / h of dimethyl sulfoxide, the waste polyester - containing textile fragments and the reaction reagent dimethyl sulfoxide are put into the reactor, and reacted at 60 °C, 100 KPa(A) for 45 min to remove non - polyester components (viscose fiber, spandex), obtaining waste polyester - containing textile fragments with non - polyester components removed; (3) Decolorization According to 840 kg / h of waste polyester-containing textile fragments after removing non-polyester components and 1400 kg / h of dimethyl sulfoxide, the waste polyester-containing textile fragments after removing non-polyester components and the decolorizing agent dimethyl sulfoxide are put into a reactor, and reacted at a temperature of 120 °C for 50 min for decolorization until the nitrogen atom content in the waste polyester-containing textile fragments reaches 70 ppm; (4)Drying The decolorized waste polyester-containing textile fragments are dried. After drying, the content of the decolorizing agent in the waste polyester-containing textile fragments is 20 ppm; the drying temperature is 90 °C; the drying pressure is 2 KPa(A); (5)Pre-depolymerization 760 Kg / h of the dried waste polyester-containing textile fragments, 1540 kg / h of ethylene glycol, and 1.54 kg / h of the depolymerization catalyst anhydrous zinc acetate are mixed and reacted at 197 °C and 100 Kpa (A) for 90 min for the pre-depolymerization reaction of the waste polyester-containing textiles, and then filtered (filtration accuracy is 35 μm) to remove a small amount of non-polyester impurities to obtain a clear and transparent pre-depolymerization reaction solution; the main component of the pre-depolymerization reaction solution is the oligomer of BHET with a degree of polymerization of 20; (6)Deep depolymerization Continue to add 1540 kg / h of ethylene glycol to the pre-depolymerization reaction solution and react at 195 °C and 100 Kpa (A) for 120 min for the deep depolymerization reaction, and then filter (filtration accuracy is 3 μm) to remove trace impurities of non-BHET and oligomer products to obtain a deep depolymerization reaction solution; the oligomers in the deep depolymerization reaction solution account for 2.2% of the total mass of the depolymerization products, the BHET oligomers with a degree of polymerization of 4 account for 3.6% of the total oligomer content, the BHET oligomers with a degree of polymerization of 3 account for 5.4% of the total mass of the oligomers, and the oligomers with a degree of polymerization of 2 account for 91% of the total mass of the oligomers.

[0084] (7)Conditioning and concentration adjustment Continue to add 3850 kg / h of ethylene glycol to the pre-depolymerization reaction solution, keep the temperature at 80 °C, and then perform centrifugal separation to remove impurities with a particle size less than 3 μm to obtain a depolymerization product / ethylene glycol solution with a mass concentration of 14.78% of the depolymerization product; the content of small molecule impurities in the depolymerization product / ethylene glycol solution is 920 ppm, the content of ionic impurities is 1530 ppm, the content of light boiling substances is 8.3%, and the content of heavy boiling substances is 4.7%.

[0085] (8)Purification of the depolymerization product The depolymerization product / ethylene glycol solution is successively subjected to molecular adsorption purification extraction process, ion purification extraction process, and thermal stripping extraction process; The molecular adsorption purification extraction process first uses 500 kg of diatomaceous earth (purchased from Hebei Runhuabang New Materials Technology Co., Ltd.; model: ZBS200#) to perform molecular adsorption purification extraction on 8131.9 kg / h of depolymerized product / ethylene glycol solution. The purification temperature is 80 °C, the pressure is atmospheric pressure, and the time is 20 min. Then, 800 kg of activated carbon (purchased from Shanghai Junpeng Environmental Protection Technology Co., Ltd.; model: JPWT-200) is used to perform molecular adsorption purification extraction on the depolymerized product / ethylene glycol solution. The temperature is 80 °C, the pressure is 100 KPa(A), and the passing time is 30 min. After molecular adsorption purification extraction, the content of small molecule impurities in the depolymerized product / ethylene glycol solution is 8 ppm; The ion purification extraction process is to first adsorb the depolymerized product / ethylene glycol solution that has undergone molecular adsorption purification extraction through 200 kg of cation exchange resin (purchased from Shenzhen Sanyang Environmental Protection Technology Co., Ltd.; model: IMAC HP336), and then adsorb it through 200 kg of anion exchange resin (purchased from Shenzhen Sanyang Environmental Protection Technology Co., Ltd.; model: AMBERLITE IRA402Cl). The ion purification extraction temperature is 80 °C, the pressure is 100 KPa(A), and the passing time is 3 min. After ion purification extraction, the content of ion impurities in the depolymerized product / ethylene glycol solution is 2.5 ppm; The thermal drive separation extraction process is to react the depolymerized product / ethylene glycol solution that has undergone ion purification extraction at 140 °C and 1.5 KPa for 20 s. At this time, the content of low-boiling substances in the depolymerized product is 0.68%; then react at 200 °C and 15 Pa for 3 s to make the content of high-boiling substances in the depolymerized BHET 0.007%. The thermal drive separation extraction process is to vaporize a large amount of ethylene glycol in the depolymerized product / ethylene glycol solution. At the same time, the low-boiling substances in it will also vaporize. Through the process of a large amount of ethylene glycol vaporization-condensation, the low-boiling substances are extracted from the depolymerized product; after removing the low-boiling substances, under the process conditions of high-boiling substance removal, BHET escapes from the surface of the material system. During the escape process, high-boiling substances will be carried out. At this time, BHET is the extractant for high-boiling substances. Considering from the molecular level, the average free paths of various substances are different, so as to separate BHET and high-boiling substances.

[0086] (9) Pre-polycondensation Mix 1020 kg / h of the purified depolymerized product with 0.3 kg / h of ethylene glycol antimony as a polymerization catalyst, 0.08 kg / h of triethyl phosphonoacetate as a heat stabilizer, 0.25 kg / h of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, and 0.25 kg / h of tris(2,4-di-tert-butylphenyl) phosphite, and react at 265 °C and 5 KPa(A) for 150 min for pre-polycondensation to obtain a pre-polycondensed product; (10) Final polycondensation The pre-polycondensate is further reacted for 180 min at 278 °C and 100 Pa(A) for final polycondensation to obtain a final polycondensate melt; (11)Melt filtration and spinning The final polycondensate melt is filtered (filtration accuracy: 30 μm) to remove carbide and gel impurities generated in the previous process to obtain a polyester melt; The polyester melt is spun, woven, dyed and post-finished by conventional methods to obtain polyester textiles.

[0087] After the drying step of the present invention, in every 1 kg of polyester textile fragments obtained, the residual amount of viscose fiber is 0.0002 kg, and the residual amount of dimethyl sulfoxide is 0.0017 kg. Example 2

[0088] A method for chemically recycling waste polyester into high-quality polyester melt and recycling polyester textiles using the same, the steps are as follows (1)Crushing of waste polyester The recycled polyester-containing textiles (waste polyester / cotton / nylon waste cloth fragments with 10% cotton content and 5% nylon content) are crushed to 80 mm to obtain waste polyester-containing textile fragments; (2)Removal of non-polyester components According to 1000 kg / h of waste polyester-containing textile fragments and 1400 kg / h of sodium hydroxide-methanol solution, the waste polyester fragments and the reaction reagent sodium hydroxide-methanol solution are put into a reactor, and reacted at 60 °C, 100 KPa(A) for 60 min to remove non-polyester components (cotton, nylon); (3)Decolorization According to 892 kg / h of waste polyester-containing textile fragments after removing non-polyester components and 1800 kg / h of dimethyl sulfoxide, the waste polyester-containing textile fragments after removing non-polyester components and the decolorizing agent dimethyl sulfoxide are put into a reactor, and reacted at a temperature of 120 °C for 50 min for decolorization until the nitrogen atom content in the waste polyester-containing textiles reaches 63 ppm; (4)Drying The decolorized waste polyester-containing textile fragments are dried, and the content of the decolorizing agent in the dried polyester textile fragments is 27 ppm; the drying temperature is 90 °C; the drying pressure is 2 KPa(A); (5)Pre-depolymerization 800 Kg / h of dried waste polyester-containing textile fragments are mixed with 1600 kg / h of ethylene glycol and 1.6 kg / h of depolymerization catalyst anhydrous zinc acetate, and reacted at 197 °C and 100 Kpa (A) for 90 min for the pre-depolymerization reaction of waste polyester-containing textiles. Then, filtration (filtration accuracy is 35 μm) is carried out to remove a small amount of non-polyester impurities, and a clarified and transparent pre-depolymerization reaction solution is obtained; the main component of the pre-depolymerization reaction solution is the oligomer of BHET, with a degree of polymerization of 18; (6) Deep depolymerization Continue to add 1600 kg / h of ethylene glycol to the pre-depolymerization reaction solution, and react at 195 °C and 100 Kpa (A) for 120 min for the deep depolymerization reaction. Then, filtration (filtration accuracy is 3 μm) is carried out to remove trace impurities of non-BHET and oligomer products, and a deep depolymerization reaction solution is obtained; the oligomers in the deep depolymerization reaction solution account for 2.25% of the total mass of the depolymerization products. The BHET oligomer with a degree of polymerization of 4 accounts for 3.5% of the total oligomer content, the BHET oligomer with a degree of polymerization of 3 accounts for 3.1% of the total mass of the oligomers, and the oligomers with a degree of polymerization of 2 account for 93.4% of the total mass of the oligomers.

[0089] (7) Conditioning and concentration adjustment Continue to add 3200 kg / h of ethylene glycol to the pre-depolymerization reaction solution, keep the temperature at 80 °C, and then carry out centrifugal separation to remove impurities with a particle size less than 3 μm, obtaining a depolymerization product / ethylene glycol solution with a mass concentration of the depolymerization product of 16.63%; the content of small molecule impurities in the depolymerization product / ethylene glycol solution is 740 ppm, the content of ionic impurities is 1280 ppm, the content of light boiling substances is 6.9%, and the content of heavy boiling substances is 3.2%.

[0090] (8) Purification of depolymerization products The depolymerization product / ethylene glycol solution is successively subjected to molecular adsorption purification extraction process, ionic purification extraction process, and thermal drive separation extraction process; the specific method is the same as that in Example 1; After the molecular adsorption purification extraction, the content of small molecule impurities in the depolymerization product / ethylene glycol solution is 5 ppm; after the ionic purification extraction, the content of ionic impurities is 1.7 ppm.

[0091] After the thermal drive separation extraction, the content of light boiling substances in the depolymerization product is 0.41%, and the content of heavy boiling substances is 0.006%; (9) Pre-polycondensation Mix the purified depolymerized product at 1059 kg / h with 0.31 kg / h of the polymerization catalyst antimony glycolate, 0.08 kg / h of the heat stabilizer triethyl phosphonoacetate, 0.26 kg / h of the antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.26 kg / h of tris(2,4-di-tert-butylphenyl) phosphite, and react at 265 °C and 5 KPa(A) for 150 min for pre-polycondensation to obtain a pre-polycondensed product; Steps (10)-(11) are the same as in Example 1. Example 3

[0092] A method for chemically recycling waste polyester into high-quality polyester melt and applying the recycled polyester to produce polyester textiles, the steps are as follows (1) Pre-depolymerization Mix 1000 Kg / h of dried recycled polyester bottle chips (containing 3.2% isophthalic acid and the rest is polyester) with 500 kg / h of ethylene glycol and 1.5 kg / h of the depolymerization catalyst anhydrous zinc acetate, and react at 240 °C and 300 Kpa(A) for 90 min for the pre-depolymerization reaction of the polyester bottle chips, and then filter (filter accuracy is 35 μm) to remove a small amount of non-polyester impurities to obtain a clear and transparent pre-depolymerization reaction solution; the main component of the pre-depolymerization reaction solution is an oligomer of BHET with a degree of polymerization of 15; (2) Deep depolymerization Continue to add 2500 kg / h of ethylene glycol to the pre-depolymerization reaction solution, and react at 195 °C and 100 Kpa(A) for 120 min for the deep depolymerization reaction, and then filter (filter accuracy is 3 μm) to remove trace impurities of non-BHET and oligomer products to obtain a deep depolymerization reaction solution; the oligomers in the deep depolymerization reaction solution account for 1.93% of the total mass of the depolymerized product, the BHET oligomer with a degree of polymerization of 4 accounts for 2.59% of the total oligomer content, the BHET oligomer with a degree of polymerization of 3 accounts for 4.15% of the total mass of the oligomers, and the oligomers with a degree of polymerization of 2 account for 93.26% of the total mass of the oligomers.

[0093] (3)Conditioning and concentration adjustment Continue to add 5500 kg / h of ethylene glycol to the pre-depolymerization reaction solution, keep the temperature at 80 °C, and then perform centrifugal separation to remove impurities with a particle size less than 3 μm to obtain a depolymerized product / ethylene glycol solution with a mass concentration of 10.5% of the depolymerized product; the content of small molecule impurities in the depolymerized product / ethylene glycol solution is 360 ppm, the content of ionic impurities is 880 ppm, the content of light boiling substances is 4.2%, and the content of heavy boiling substances is 2.8%.

[0094] (4)Purification of the depolymerized product Thermal drive separation extraction of light-boiling substances: React the depolymerized product / ethylene glycol solution at 140 °C and 1.5 KPa for 20 s. At this time, the content of light-boiling substances in the depolymerized product is 0.22%. The H-NMR spectrum (nuclear magnetic resonance frequency 400 MHZ) of the depolymerized product obtained by thermal drive separation extraction of light-boiling substances is as Figure 1 ; Crystalline condensation: Mix 1330 kg / h of the depolymerized product after thermal drive separation extraction of light-boiling substances and 8000 kg / h of water, and then send them into a conditioning and concentration device. The conditioning and concentration temperature is 70 °C, and the conditioning and concentration time is 40 min. Centrifuge the conditioned and concentrated aqueous solution of the depolymerized product with a separation accuracy of 3 μm to remove trace impurities and oligomers insoluble in water, and obtain a clear and transparent aqueous solution of the depolymerized product; then perform crystalline enrichment at 15 °C for 120 min, and then perform solid-liquid separation (separation accuracy 5 μm) to obtain the depolymerized product BHET with a purity greater than 99.99%. Through nuclear magnetic resonance analysis, no isophthalic acid component is detected. The crystalline enrichment is carried out using a DTB crystallizer. During the process, some BHET in the aqueous solution of the depolymerized product forms small crystals, and the subsequent hot saturated aqueous solution of the depolymerized product is continuously added and mixed with the solution containing small crystals. Part of the BHET in the solution heated during the conditioning and concentration process deposits on the surface of the suspended crystal particles, causing the crystals to grow.

[0095] The H-NMR (nuclear magnetic resonance frequency 400 MHZ) of the depolymerized product BHET obtained by solid-liquid separation of the aqueous solution of the depolymerized product with crystalline enrichment is as Figure 2 ; The H-NMR (nuclear magnetic resonance frequency 400 MHZ) of the liquid obtained by solid-liquid separation of the aqueous solution of the depolymerized product with crystalline enrichment is as Figure 3 ; (5) Pre-polycondensation Mix 1285 kg / h of the depolymerized product BHET with 0.38 kg / h of the polymerization catalyst antimony glycolate, 0.1 kg / h of the heat stabilizer triethyl phosphonoacetate, 0.31 kg / h of the antioxidant pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.31 kg / h of tris(2,4-di-tert-butylphenyl) phosphite, and react at 265 °C and 5 KPa(A) for 150 min for pre-polycondensation to obtain a pre-polycondensed product; Steps (6) to (7) are the same as steps (10) to (11) in Example 1; Through Figure 1 、 Figure 2 、 Figure 3 It shows that the crystalline condensation process of the present invention can effectively remove the isophthalic acid component in waste bottle chips. Example 4

[0096] A method for chemically regenerating high-quality polyester melt from waste polyester and applying the regenerated polyester to polyester textiles, the steps are as follows (1)Pre-depolymerization 1000 Kg / h of variegated polyester bottle chip powder (polyolefin content 0.84%, the rest is polyester) was mixed and reacted with 500 kg / h of ethylene glycol and 1.5 kg / h of depolymerization catalyst zinc acetate anhydrous. The reaction conditions were the same as those in Example 3, and the main component of the pre-depolymerization reaction liquid was an oligomer of BHET with a degree of polymerization of 15; (2)Deep depolymerization The reaction conditions were the same as those in Example 3 to obtain a deep depolymerization reaction liquid; in the deep depolymerization reaction liquid, the oligomers accounted for 1.93% of the total mass of the depolymerization products. The BHET oligomers with a degree of polymerization of 4 accounted for 2.7% of the total oligomer content, the BHET oligomers with a degree of polymerization of 3 accounted for 4.2% of the total oligomer mass, and the oligomers with a degree of polymerization of 2 accounted for 93.1% of the total oligomer mass.

[0097] (3)Conditioning and concentration adjustment The reaction conditions were the same as those in Example 3 to obtain a depolymerization product / ethylene glycol solution with a mass concentration of 15.5% of the depolymerization product; the content of small molecule impurities in the depolymerization product / ethylene glycol solution was 388 ppm, the content of ionic impurities was 907 ppm, the content of light boiling substances was 6.1%, and the content of heavy boiling substances was 3.5%.

[0098] (4)Purification of depolymerization products The depolymerization product / ethylene glycol solution was successively subjected to a molecular adsorption purification extraction process, an ion purification extraction process, a thermal stripping extraction process, and a crystalline aggregation process; The molecular adsorption purification extraction process was the same as that in Example 1; after the molecular adsorption purification extraction, the content of small molecule impurities in the depolymerization product / ethylene glycol solution was 3 ppm; The ion purification extraction process was the same as that in Example 1; after the ion purification extraction, the content of ionic impurities in the depolymerization product / ethylene glycol solution was 1.1 ppm; The thermal stripping extraction process was the same as that in Example 1, and the content of light boiling substances in the depolymerization product was 0.22%; the content of heavy boiling substances in the depolymerization product was 0.004%; The crystalline aggregation process was the same as that in Example 3 to obtain BHET with a purity greater than 99.99%. Through nuclear magnetic resonance analysis, no isophthalic acid component was detected; Steps (5) to (7) were the same as those in Example 1. Example 5

[0099] A method for chemically regenerating high-quality polyester melt from waste polyester and applying the regenerated polyester to produce polyester textiles, the steps are as follows Steps (1) to (8) were the same as those in Example 1; (9)Modification Mix the purified depolymerized product at 1020 kg / h with the modified trimonomer 1,4 - cyclohexanedimethanol at 102 kg / h and tetrabutyl titanate as the transesterification catalyst at 0.1 kg / h, and react at 250 °C and 350 KPa(A) for 90 min to obtain the modified transesterification product.

[0100] Steps (10) - (11) are the same as steps (9) - (10) in Example 1; (11) Melt filtration and spinning Filter the final polycondensation melt (filtration accuracy 30 μm) to remove carbide and gel impurities generated in the previous process to obtain the modified polyester melt PETG; Example 6

[0101] A method for chemically recycling waste polyester into high - quality polyester melt and applying the recycled polyester melt to produce polyester textiles, the steps are as follows Steps (1) - (8) are the same as those in Example 1; (9) Modification Mix the modified trimonomer sodium 5 - sulfoisophthalate - 1,3 - diol at 25 kg / h and ethylene glycol at 9 kg / h, and react at 220 °C and 250 KPa for 180 min to obtain sodium 5 - sulfoisophthalate - 1,3 - diol ethylene glycol ester at 33.35 kg / h.

[0102] Mix the purified depolymerized product at 1020 kg / h with sodium 5 - sulfoisophthalate - 1,3 - diol ethylene glycol ester at 33.35 kg / h, and react at 250 °C and 350 KPa(A) for 90 min to obtain the modified transesterification product.

[0103] (9) Pre - polycondensation Mix the modified transesterification product at 1054 kg / h with germanium dioxide as the polymerization catalyst at 0.38 kg / h, triethyl phosphonoacetate as the heat stabilizer at 0.08 kg / h, pentaerythritol tetra[β - (3,5 - di - tert - butyl - 4 - hydroxyphenyl)propionate] as the antioxidant at 0.25 kg / h, and tris(2,4 - di - tert - butylphenyl) phosphite at 0.25 kg / h, and react at 260 °C and 5 KPa(A) for 150 min for pre - polycondensation to obtain the pre - polycondensation product; Steps (10) - (11) are the same as steps (9) - (10) in Example 1; (12) Melt filtration and spinning Filter the final polycondensation melt (filtration accuracy 30 μm) to remove carbide and gel impurities generated in the previous process to obtain the cation - dyeable polyester melt CDP; Comparative Example 1

[0104] A method for chemically recycling waste polyester into high-quality polyester melt and applying the recycled polyester melt to produce polyester textiles, the steps are the same as those in Example 1, except that Comparative Example 1 does not include steps (2) removing non-polyester components, (3) decolorization, (4) drying, (7) conditioning and concentration adjustment, and (8) depolymerization product purification. Comparative Example 2

[0105] A method for chemically recycling waste polyester into high-quality polyester melt and applying the recycled polyester melt to produce polyester textiles, the steps are the same as those in Example 1, except that Comparative Example 2 does not include steps (7) conditioning and concentration adjustment and (8) depolymerization product purification. Comparative Example 3

[0106] A method for chemically recycling waste polyester into high-quality polyester melt and applying the recycled polyester melt to produce polyester textiles, the steps are the same as those in Example 1, except that step (8) of Comparative Example 3 only includes molecular adsorption purification extraction process and ion purification extraction process.

[0107] The polyester melt is spun, woven, dyed and post-finished by conventional methods to obtain polyester textiles.

[0108] The performance of the depolymerization product BHET obtained after purifying the depolymerization product of Example 1 was compared and analyzed with the depolymerization products in Comparative Examples 1-3, and the results are shown in Table 1. Table 1

[0109] From the comparison of the performance of the depolymerization product BHET obtained after purifying the depolymerization product of Example 1 and the depolymerization products of Comparative Examples 1-3 in Table 1, it was found that through the removal of non-polyester components, purification extraction, and thermal stripping extraction of the present invention, the quality indicators of the obtained depolymerization product BHET fully meet the requirements for downstream polymerization processes.

[0110] The performance indicators of the polyester melts of Example 1 and Comparative Examples 1-3 are shown in Table 2. Table 2

[0111] The results in Table 2 show that the performance of the polyester melt prepared by using the process technology of the present invention has been greatly improved.

[0112] Fibers (1.5 dtex < dpf ≤ 2.9 dtex) were prepared using the polyester melts of Example 1 and Comparative Examples 1-3. The specific method was as follows: The melt was fed into a spinning box (spinning box temperature 280 °C, pressure 10 MPa), and a filament bundle was formed through a melt spinning spinneret; the filament bundle was cooled and formed by ring blowing (temperature 25 °C, wind speed 0.5 m / s, relative humidity 70%); the cooled and formed filament bundle was collected and oiled through a godet frame, and then obtained fibers through drawing and setting and winding and setting. The performance indicators of the fibers are shown in Table 3.

[0113] Table 3

[0114] As can be seen from Table 3, Comparative Example 1 cannot spin the polyester melt by conventional methods and no specific data can be provided. It is illustrated by Table 3 that the textile fibers of the process technology of the present invention can all reach first-class products.

[0115] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for chemically regenerating high-quality polyester melt from waste polyester, characterized in that: The following steps are involved: (1) Pre-depolymerization The dried polyester fragments are mixed with ethylene glycol and a depolymerization catalyst to perform a pre-depolymerization reaction, and then a small amount of non-polyester impurities are removed by filtration to obtain a clear and transparent pre-depolymerization reaction liquid; (2) Deep disaggregation The pre-depolymerization reaction liquid is mixed with ethylene glycol to perform a deep depolymerization reaction, and then filtered to obtain a deep depolymerization reaction liquid; (3) Adjusting the quality and concentration The deep depolymerization reaction liquid and ethylene glycol are mixed, cooled, tempered and concentrated, and then solid-liquid separated to remove impurities with a particle size of less than 3 μm to obtain a depolymerization product / ethylene glycol solution; (4) Purification of depolymerization products The depolymerization product / ethylene glycol solution is refined and purified to obtain bis(hydroxyethyl) terephthalate; the refining and purification step comprises one or more of a purification extraction process, a heat-driven separation extraction process, and a crystalline condensation process; (5) Precondensation The bis(hydroxyethyl) terephthalate is mixed with a polymerization catalyst, a heat stabilizer, and an antioxidant to perform pre-polycondensation to obtain a pre-polycondensation product; (6) Final polycondensation The pre-polycondensation product is subjected to final polycondensation at a temperature of 270-290° C. to obtain a final polycondensation melt; (7) Melt filtration The final polycondensation melt is filtered to remove carbide and gel impurities produced in the previous process to obtain a polyester melt.

2. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The waste polyester in step (1) includes at least one of waste polyester bottle flakes, waste polyester-containing textiles, waste polyester fibers, waste polyester foams, waste polyester friction materials, and polyester chips; The waste polyester comprises the following components in percentage by weight: Polyester component 50-99.99%, non-polyester component 0-40%, dye 0-10%, pigment 0-10%, additive 0-10%; The non-polyester component is one or more of cotton, linen, wool, viscose fiber, acetate fiber, acrylic fiber, nylon fiber, polyolefin, and spandex.

3. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The mass ratio of ethylene glycol to polyester fragments in step (1) is 0.3:1-3:1; The depolymerization catalyst is added in an amount of 200ppm-2500ppm relative to the mass of the polyester fragments; The depolymerization catalyst is a metal and metal composite oxide catalyst, a metal salt catalyst or an ionic liquid catalyst; The temperature of the pre-depolymerization reaction is 180°C-240°C, the reaction pressure is 100Kpa-400Kpa(A), and the reaction time is 45min-120min; The main component of the pre-depolymerization reaction liquid is oligomers of bis(hydroxyethyl) terephthalate, and the degree of polymerization is less than 40.

4. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The mass ratio of ethylene glycol to polyester fragments in step (2) is 1:1-4:1; The reaction temperature of the deep depolymerization is 180°C-240°C, the reaction pressure is 100Kpa-400Kpa(A), and the reaction time is 90min-150min; The main components of the depolymerization product in the deep depolymerization reaction liquid are bis(hydroxyethyl) terephthalate and oligomers of bis(hydroxyethyl) terephthalate; and the polymerization degree of the oligomers is not greater than 4.

5. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The mass ratio of ethylene glycol to polyester fragments in step (3) is 3:1-7:1; The mass concentration of the depolymerization product in the depolymerization product / ethylene glycol solution is 9-24%; The temperature of the depolymerization product / ethylene glycol solution that is being tempered and concentrated is 60-100°C.

6. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The refining and purification in step (4) includes one or more of a purification extraction process, a heat-driven separation extraction process, and a crystal condensation process.

7. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: After the refining and purification in step (4) is completed, it also includes a modification esterification and ester exchange step, wherein the modification esterification and ester exchange are to flexibly synthesize the dihydroxyethyl terephthalate into modified polyester.

8. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The polymerization catalyst in step (5) is one or more of an antimony catalyst, a titanium catalyst, and a germanium catalyst; the amount of the polymerization catalyst added is 0.005-0.05% by weight of bis(hydroxyethyl) terephthalate; The heat stabilizer is one or more of phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and triethyl phosphonoacetate; the addition amount of the heat stabilizer is 0.005-0.02% of the weight of BHET; The antioxidant is one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl alcohol ester, N, N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, and the added amount of the antioxidant is 0.03-0.15% of the weight of bis(hydroxyethyl) terephthalate; The pre-polycondensation reaction temperature is 250-290° C., the reaction pressure is 0.1-30 KPa(A), and the reaction time is 60-240 min.

9. The method for chemically regenerating high-quality polyester melt from waste polyester according to claim 1, characterized in that: The reaction temperature of the final polycondensation in step (6) is 270-290° C., the reaction pressure is 20-500 Pa(A), and the reaction time is 120-240 min.

10. A method for regenerating polyester textiles using the polyester melt according to any one of claims 1 to 9, characterized in that: The polyester melt is spun, woven, printed, dyed and post-finished to obtain polyester textiles.

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