A low-temperature homogeneous depolymerization and regeneration method for waste PBT

Abstract

The present invention relates to a low-temperature homogeneous depolymerization and regeneration method for waste PBT. The method comprises dissolving the waste PBT polyester using a solvent and a co-solvent; then adding a diol and a catalyst to the dissolved waste PBT polyester for depolymerization to obtain a depolymerization liquid containing monomers; then adding methanol to the depolymerization liquid to produce a dimethyl terephthalate mixed liquid through an ester exchange reaction; then recrystallizing, filtering, and refining the dimethyl terephthalate mixed liquid to obtain high-purity dimethyl terephthalate; then subjecting the high-purity dimethyl terephthalate to an esterification and polycondensation reaction with the diol to produce fiber-grade regenerated polyester chips; and finally, melt spinning to obtain regenerated polyester fibers. Compared with the prior art, the present invention reduces equipment requirements, achieves low-temperature homogeneous depolymerization of polyester, and achieves high-quality regeneration. The intrinsic viscosity, color value, melting point, and other characteristics of the regenerated polyester chips all meet subsequent spinning requirements, and the fiber strength and elongation at break all meet those of virgin fibers.

Description

Technical Field

[0001] The present invention relates to a regeneration technology for waste PBT, in particular to a method for dissolving waste PBT and achieving low-temperature homogeneous depolymerization and high-quality regeneration of the waste PBT with the assistance of a co-solvent and a catalyst. Background Art

[0002] PBT, short for polybutylene terephthalate, is widely used in elastic textiles due to its excellent elasticity, dyeability, and ease of processing. However, with the surge in demand for these products and the sharp decline in their lifespan, the amount of PBT waste is also increasing. This large amount of discarded PBT fiber poses unforeseen risks to resources and the environment. Therefore, the recycling of waste PBT is of great significance for resource conservation and environmental protection.

[0003] Currently, the main methods for regenerating waste PBT include physical and chemical methods. Recycled PBT products produced using physical methods are of low quality and require downgrading. Compared to physical methods, chemical methods offer high-quality and efficient recycling of waste PBT and are currently a key research area in the textile industry.

[0004] Patent CN 1142123C uses methanol as a depolymerizing agent under high temperature and high pressure to produce regenerated dimethyl terephthalate, which is then used as a raw material to prepare regenerated polyester. The depolymerization reaction temperature is between 230 and 250°C, the pressure is between 2.0 and 20.0 MPa, and the depolymerization time is 0.5 to 10 hours.

[0005] Patent CN 114773668A uses 1,4-butanediol to depolymerize waste PBT and regenerate it into biodegradable aliphatic / aromatic polyesters. The depolymerization reaction begins by dissolving the solution at 180-200°C. Once the system is clarified, the temperature is gradually raised to 210-230°C and maintained at this temperature for 1.5-2 hours.

[0006] Patent CN 114805766A first melt-processes a waste PET-PBT mixture, then depolymerizes it with ethylene glycol / 1,4-butanediol. The resulting monomers are then transesterified with methanol to produce dimethyl terephthalate, achieving the recycling of waste PET-PBT. The depolymerization reaction temperature ranges from 190 to 240°C, the reaction pressure is 101 to 201 kPa, and the residence time is 1 to 2 hours.

[0007] In summary, current chemical regeneration methods for waste PBT are mostly based on high-temperature solid-liquid heterogeneous depolymerization reactions. During the depolymerization process, 1,4-butanediol undergoes side reactions such as cyclization, resulting in low recovery and depolymerization efficiency, and poor quality of the regenerated product. Therefore, the development of a low-temperature homogeneous depolymerization method for waste PBT regeneration is urgently needed to reduce or avoid cyclization of 1,4-butanediol during the reaction process, while simultaneously improving recovery, depolymerization efficiency, and regenerated product quality. This method has important scientific and practical value. Summary of the Invention

[0008] In response to the above problems, the present application provides a low-temperature homogeneous depolymerization and regeneration method for waste PBT. This method reduces the requirements for equipment, achieves low-temperature homogeneous alcoholysis of waste PBT through solvents, co-solvents and catalysts, and improves the recovery rate of PBT polyester; moreover, the characteristic viscosity, color value, melting point, etc. of the obtained recycled polyester product meet the subsequent spinning requirements.

[0009] The present application provides a low-temperature homogeneous depolymerization and regeneration method for waste PBT, comprising the following steps:

[0010] Step 1: Add 100 parts of waste PBT, 100-600 parts of solvent, and 50-400 parts of co-solvent to an autoclave, heat to 170-190°C, and stir for 10-30 minutes at a stirring speed of 15-50 r / min. Then, add 50-400 parts of diol and 0.5-5 parts of a first catalyst, and continue the reaction for 10-30 minutes to produce a PBT depolymerization solution, wherein the mass ratio of waste PBT, solvent, and co-solvent is 100:100-600:50-400. It should be noted that the parts per unit mass in each step may not be the same.

[0011] Step 2: Place 100 parts of the PBT depolymerization liquid prepared in Step 1, 100-300 parts of methanol, and 0.2-0.3 parts of a second catalyst in a reaction vessel and react at 60-70°C for 1-3 hours to produce a dimethyl terephthalate mixed liquid. The dimethyl terephthalate mixed liquid is recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, wherein the mass ratio of the PBT depolymerization liquid, methanol, and second catalyst is 100:100-300:0.2-0.3.

[0012] Step 3: placing 100 parts of high-purity dimethyl terephthalate obtained in step 2, 100 to 150 parts of glycol, and 0.5 parts of the third catalyst in a high-pressure reactor, and obtaining fiber-grade regenerated polyester chips after esterification and polycondensation reaction, that is, the mass ratio of high-purity dimethyl terephthalate, glycol, and the third catalyst is 100:100 to 150:0.5.

[0013] The fiber-grade regenerated polyester chips obtained in step three are melt-spun to obtain regenerated polyester fibers.

[0014] Preferably, the waste PBT in the depolymerization step is one or more of waste PBT plastics and waste PBT textiles.

[0015] Preferably, the solvent in the depolymerization step is one or more of dimethyl sulfoxide, N-methylpyrrolidone, aniline, and nitrobenzene.

[0016] Preferably, the co-solvent in the depolymerization step is one or more of acetonitrile, anisole, and dichloromethane.

[0017] Preferably, the diol in the depolymerization step is one of ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol.

[0018] Preferably, the first catalyst in the depolymerization step is one or more of an ionic liquid, a deep eutectic solvent and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0019] Preferably, the ionic liquid is one or more of 1,3-dimethylimidazolium chloride, 1,3-dimethylimidazolium bromide, and 1,3-dimethylimidazolium acetate.

[0020] Preferably, the deep eutectic solvent is one or more of 1,3-dimethylurea / zinc acetate and choline chloride / urea.

[0021] Preferably, the second catalyst is one or more of sodium hydroxide and potassium hydroxide.

[0022] Preferably, the third catalyst is one or more of tetrabutyl titanate, isopropyl titanate, antimony trioxide, and antimony ethylene glycol.

[0023] Preferably, the recycled polyester chips are one of recycled polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate chips.

[0024] Preferably, the regenerated polyester fiber is one of regenerated polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate fibers.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The present invention's low-temperature homogeneous depolymerization and regeneration method for waste PBT effectively reduces the reaction temperature during PBT depolymerization by optimizing the combination of solvent, co-solvent, and catalyst, thereby reducing the cyclization side reaction of 1,4-butanediol and significantly improving PBT recovery and depolymerization efficiency. This improvement not only enhances the chemical purity and physical properties of the regenerated product but also helps achieve high-value utilization of waste PBT, resulting in significant environmental and economic benefits.

[0027] 2) The present invention utilizes a low-temperature homogeneous depolymerization process, avoiding the energy waste and equipment loss that can occur in conventional high-temperature solid-liquid heterogeneous depolymerization processes, thereby reducing energy consumption and production costs throughout the depolymerization process. Furthermore, due to the improved depolymerization efficiency, high-quality recycled polyester products can be produced more quickly, meeting market demand for efficient, environmentally friendly materials and promoting the development of a circular economy.

[0028] 3) The recycled polyester product of this invention achieves key indicators such as intrinsic viscosity, color, and melting point that meet or exceed the requirements of subsequent spinning processes. This ensures that the performance indicators of the recycled polyester fiber, such as fiber strength and elongation at break, are comparable to those of virgin petroleum-based fibers. This achieves a chemical closed-loop recycling of waste PBT into recycled polyester. This not only broadens the application range of waste PBT and enhances its market competitiveness, but also provides a sustainable raw material option for the textile industry, helping to reduce dependence on fossil fuels and achieve green manufacturing. DETAILED DESCRIPTION

[0029] Overall, the technical solution provides a process for the low-temperature homogeneous alcoholysis regeneration of waste PBT polyester. The present invention first dissolves waste PBT (polybutylene terephthalate), then adds glycol to depolymerize it through alcoholysis to form a depolymerization liquid containing BHBT (bis-hydroxybutyl terephthalate), BHPT (bis-hydroxypropyl terephthalate), and BHET (bis-hydroxyethyl terephthalate) monomers; then, an ester exchange reaction is carried out with methanol to produce crude DMT (dimethyl terephthalate); the resulting crude DMT is purified to produce refined regenerated DMT; the refined regenerated DMT is subjected to an ester exchange reaction with glycol to produce polyester monomers; and then, the monomers are subjected to a polycondensation reaction to prepare regenerated polyester. The intrinsic viscosity, color value, melting point, etc. of the regenerated polyester chips produced by the process of the present invention meet the requirements for subsequent spinning. The fiber strength and elongation at break of the regenerated polyester fibers meet the performance requirements of petroleum-based virgin fibers.

[0030] The present invention is described in detail below with reference to specific embodiments, but is by no means intended to limit the present invention. Any features, such as preparation methods, materials, structures, or composition ratios, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0031] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0032] Unless otherwise specified, the number of portions described in the present invention refers to the value under the condition of equal unit mass. The unit mass is the mass of each portion. If each portion is 1g, the unit mass is 1g / portion, and 100 portions are equal to 100g.

[0033] The testing steps for the intrinsic viscosity in each embodiment of the present invention are as follows:

[0034] Dissolve 0.25±0.005g of sample in 96.00±0.2% concentrated sulfuric acid and measure its viscosity at 25°C using an Ubbelohde viscometer. Specific test principles and methods are described in GBT 12006.1-2009. The intrinsic viscosity is calculated using the following formula:

[0035]

[0036] Wherein, [η] is the intrinsic viscosity, η sp is the specific viscosity, η r is the relative viscosity, C is the sample concentration, and the unit is g / dl.

[0037] Example 1

[0038] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0039] Step 1: Add 50g of waste PBT, 50g of dimethyl sulfoxide (DMSO) solvent, and 25g of acetonitrile co-solvent to a 500mL autoclave. Heat to 170°C and stir at 15 rpm for 10 minutes. Then, add 25g of ethylene glycol and 0.25g of 1,3-dimethylimidazolium chloride catalyst. Stir at 100 rpm for 10 minutes to produce a PBT depolymerization solution.

[0040] Step 2: 150 g of the PBT depolymerization solution prepared in Step 1, 150 g of methanol, and 0.3 g of sodium hydroxide were placed in a reaction vessel and reacted at 60°C for 1 hour to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.1%.

[0041] Step 3: 42 g of high-purity dimethyl terephthalate obtained in step 2, 42 g of ethylene glycol, and 0.21 g of tetrabutyl titanate were placed in a high-pressure reactor for ester exchange at 190° C. and reacted for 2 hours to obtain the monomer BHET. The temperature was gradually raised to 275° C. and the pressure in the reactor was gradually reduced to below 50 Pa and reacted for 3 hours to carry out a condensation reaction of the monomer BHET to obtain a macromolecular chain polymer PET with an intrinsic viscosity of 0.65 dl / g.

[0042] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 280° C. to obtain regenerated PET polyester fibers with a breaking elongation of 19.3% and a fiber strength of 4.42 cN / dtex.

[0043] Example 2

[0044] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0045] Step 1: Add 40g of waste PBT, 80g of N-methylpyrrolidone solvent, and 40g of acetonitrile co-solvent to a 500mL autoclave. Heat to 180°C and stir at 30 rpm for 15 minutes. Then, add 80g of 1,4-butanediol and 0.4g of 1,3-dimethylurea / zinc acetate catalyst. Stir at 100 rpm for 15 minutes to produce a PBT depolymerization solution.

[0046] Step 2: 240 g of the PBT depolymerization solution prepared in Step 1, 480 g of methanol, and 0.48 g of sodium hydroxide were placed in a reaction vessel and reacted at 65°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.3%.

[0047] Step 3: 33 g of high-purity dimethyl terephthalate obtained in step 2, 33 g of ethylene glycol, and 0.165 g of isopropyl titanate were placed in a high-pressure reactor for ester exchange at 190° C. and reacted for 2 hours to obtain the monomer BHET. The temperature was gradually raised to 275° C. and the pressure in the reactor was gradually reduced to below 50 Pa and reacted for 3 hours to carry out a condensation reaction of the monomer BHET to obtain a macromolecular chain polymer PET with an intrinsic viscosity of 0.67 dl / g.

[0048] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 280° C. to obtain regenerated PET polyester fibers with a breaking elongation of 20.2% and a fiber strength of 4.59 cN / dtex.

[0049] Example 3

[0050] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0051] Step 1: Add 25g of waste PBT, 100g of aniline solvent, and 75g of anisole co-solvent to a 500mL autoclave. Heat to 180°C and stir at 40 rpm for 20 minutes. Then, add 75g of 1,3-propylene glycol and 1.25g of choline chloride / urea catalyst. Stir at 100 rpm for 25 minutes to produce a PBT depolymerization solution.

[0052] Step 2: 275 g of the PBT depolymerization solution prepared in Step 1, 275 g of methanol, and 0.825 g of potassium hydroxide were placed in a reaction vessel and reacted at 70°C for 2 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.7%.

[0053] Step 3: 21 g of high-purity dimethyl terephthalate obtained in step 2, 31.5 g of ethylene glycol, and 0.105 g of antimony trioxide were placed in a high-pressure reactor for ester exchange at 190° C. and reacted for 2 hours to obtain monomer BHET. The temperature was gradually raised to 275° C. and the pressure in the reactor was gradually reduced to below 50 Pa and reacted for 3 hours to carry out a condensation reaction of the monomer BHET to obtain a macromolecular chain polymer PET with an intrinsic viscosity of 0.69 dl / g.

[0054] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 280° C. to obtain regenerated PET polyester fibers with a breaking elongation of 22.4% and a fiber strength of 4.63 cN / dtex.

[0055] Example 4

[0056] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0057] Step 1: Add 15g of waste PBT, 90g of nitrobenzene solvent, and 60g of dichloromethane co-solvent to a 500mL autoclave. Heat to 190°C and stir at 50 rpm for 30 minutes. Then, add 60g of ethylene glycol and 0.6g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst. Stir at 100 rpm for 30 minutes to produce a PBT depolymerization solution.

[0058] Step 2: 225 g of the PBT depolymerization solution prepared in Step 1, 675 g of methanol, and 0.675 g of potassium hydroxide were placed in a reaction vessel and reacted at 70°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 99.1%.

[0059] Step 3: 13 g of high-purity dimethyl terephthalate obtained in step 2, 19.5 g of ethylene glycol, and 0.065 g of ethylene glycol antimony are placed in a high-pressure reactor at 190° C. for ester exchange. The reaction is performed for 2 hours to obtain the monomer BHET. The temperature is gradually increased to 275° C. and the pressure in the reactor is gradually reduced to below 50 Pa for 3 hours to carry out a condensation reaction of the monomer BHET to obtain a macromolecular chain polymer PET with an intrinsic viscosity of 0.71 dl / g.

[0060] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 280° C. to obtain regenerated PET polyester fibers with a breaking elongation of 24.3% and a fiber strength of 4.75 cN / dtex.

[0061] Example 5

[0062] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0063] Step 1: Add 50g of waste PBT, 50g of nitrobenzene solvent, and 25g of dichloromethane co-solvent to a 500mL polymerization autoclave. Heat to 170°C and stir at 15 rpm for 30 minutes. Then, add 25g of 1,3-propylene glycol and 0.25g of 1,3-dimethylimidazolium bromide catalyst. Stir at 100 rpm for 30 minutes to produce a PBT depolymerization solution.

[0064] Step 2: 150 g of the PBT depolymerization solution prepared in Step 1, 150 g of methanol, and 0.3 g of sodium hydroxide were placed in a reaction vessel and reacted at 60°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.2%.

[0065] Step 3: 42 g of high-purity dimethyl terephthalate obtained in step 2, 42 g of 1,3-propylene glycol, and 0.21 g of tetrabutyl titanate were placed in a high-pressure reactor and subjected to ester exchange at 190° C. The reaction was performed for 2 h to obtain the monomer BHPT. The temperature was gradually raised to 245° C. and the pressure in the reactor was gradually reduced to below 50 Pa for 3 h to carry out a condensation reaction of the monomer BHPT to obtain a macromolecular chain polymer PTT with an intrinsic viscosity of 0.88 dl / g.

[0066] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 260° C. to obtain regenerated PTT polyester fibers with a breaking elongation of 45.6% and a fiber strength of 3.37 cN / dtex.

[0067] Example 6

[0068] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0069] Step 1: Add 40g of waste PBT, 80g of N-methylpyrrolidone solvent, and 40g of acetonitrile co-solvent to a 500mL autoclave. Heat to 175°C and stir at 25 rpm for 15 minutes. Then, add 80g of 1,4-butanediol and 0.4g of choline chloride / urea catalyst. Stir at 100 rpm for 15 minutes to produce a PBT depolymerization solution.

[0070] Step 2: 240 g of the PBT depolymerization solution prepared in Step 1, 480 g of methanol, and 0.48 g of sodium hydroxide were placed in a reaction vessel and reacted at 65°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.6%.

[0071] Step 3: 34 g of high-purity dimethyl terephthalate obtained in step 2, 34 g of 1,3-propylene glycol, and 0.17 g of isopropyl titanate were placed in a high-pressure reactor and subjected to ester exchange at 190° C. The reaction was carried out for 2 h to obtain the monomer BHPT. The temperature was gradually raised to 245° C. and the pressure in the reactor was gradually reduced to below 50 Pa for 3 h to carry out a condensation reaction of the monomer BHPT to obtain a macromolecular chain polymer PTT with an intrinsic viscosity of 0.91 dl / g.

[0072] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 260° C. to obtain regenerated PTT polyester fibers with a breaking elongation of 47.9% and a fiber strength of 3.43 cN / dtex.

[0073] Example 7

[0074] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0075] Step 1: Add 35g of waste PBT, 70g of aniline solvent, and 35g of anisole co-solvent to a 500mL autoclave. Heat to 185°C and stir at 50 rpm for 25 minutes. Then, add 70g of ethylene glycol and 0.4g of 1,3-dimethylimidazolium acetate catalyst. Stir at 100 rpm for 10 minutes to produce a PBT depolymerization solution.

[0076] Step 2: 210 g of the PBT depolymerization solution prepared in Step 1, 420 g of methanol, and 0.42 g of potassium hydroxide were placed in a reaction vessel and reacted at 70°C for 2 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.9%.

[0077] Step 3: 30 g of high-purity dimethyl terephthalate obtained in step 2, 30 g of 1,3-propylene glycol, and 0.15 g of antimony trioxide were placed in a high-pressure reactor and subjected to ester exchange at 190° C. for 2 h to obtain the monomer BHPT. The temperature was gradually raised to 245° C. and the pressure in the reactor was gradually reduced to below 50 Pa for 3 h to carry out a condensation reaction of the monomer BHPT to obtain a macromolecular chain polymer PTT with an intrinsic viscosity of 0.98 dl / g.

[0078] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 260° C. to obtain regenerated PTT polyester fibers with a breaking elongation of 50.3% and a fiber strength of 3.51 cN / dtex.

[0079] Example 8

[0080] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0081] Step 1: Add 20g of waste PBT, 80g of dimethyl sulfoxide (DMSO) solvent, and 80g of acetonitrile co-solvent to a 500mL autoclave. Heat to 190°C and stir at 50 rpm for 30 minutes. Then, add 60g of ethylene glycol and 1g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst. Stir at 100 rpm for 30 minutes to produce a PBT depolymerization solution.

[0082] Step 2: 240 g of the PBT depolymerization solution prepared in Step 1, 720 g of methanol, and 0.72 g of potassium hydroxide were placed in a reaction vessel and reacted at 70°C for 1 hour to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 99.3%.

[0083] Step 3: 17 g of high-purity dimethyl terephthalate obtained in step 2, 25.5 g of 1,3-propylene glycol, and 0.085 g of antimony trioxide were placed in a high-pressure reactor and subjected to ester exchange at 190° C. The reaction was carried out for 2 h to obtain the monomer BHPT. The temperature was gradually raised to 245° C. and the pressure in the reactor was gradually reduced to below 50 Pa for 3 h to carry out a condensation reaction of the monomer BHPT to obtain a macromolecular chain polymer PTT with an intrinsic viscosity of 1.07 dl / g.

[0084] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 260° C. to obtain regenerated PTT polyester fibers with a breaking elongation of 53.6% and a fiber strength of 3.56 cN / dtex.

[0085] Example 9

[0086] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0087] Step 1: Add 50g of waste PBT, 50g of dimethyl sulfoxide (DMSO) solvent, and 50g of acetonitrile co-solvent to a 500mL autoclave. Heat to 175°C and stir at 50 rpm for 30 minutes. Then, add 50g of ethylene glycol and 2.5g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst. Stir at 100 rpm for 30 minutes to produce a PBT depolymerization solution.

[0088] Step 2: 200 g of the PBT depolymerization solution prepared in Step 1, 600 g of methanol, and 0.6 g of sodium hydroxide were placed in a reaction vessel and reacted at 65°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.4%.

[0089] Step 3: 42 g of high-purity dimethyl terephthalate obtained in step 2, 42 g of 1,4-butanediol, and 0.21 g of tetrabutyl titanate were placed in a high-pressure reactor and subjected to ester exchange at 190° C. The reaction was performed for 2 hours to obtain the monomer BHBT. The temperature was gradually raised to 255° C. and the pressure in the reactor was gradually reduced to below 50 Pa to react for 3 hours to carry out a condensation reaction of the monomer BHBT to obtain a macromolecular chain polymer PBT with an intrinsic viscosity of 1.15 dl / g.

[0090] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 265° C. to obtain regenerated PBT polyester fibers with a breaking elongation of 47.8% and a fiber strength of 2.87 cN / dtex.

[0091] Example 10

[0092] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0093] Step 1: Add 40g of waste PBT, 40g of N-methylpyrrolidone solvent, and 40g of dichloromethane co-solvent to a 500mL autoclave. Heat to 180°C and stir at 40 rpm for 15 minutes. Then, add 80g of 1,4-butanediol and 1.2g of choline chloride / urea catalyst. Stir at 100 rpm for 30 minutes to produce a PBT depolymerization solution.

[0094] Step 2: 200 g of the PBT depolymerization solution prepared in Step 1, 400 g of methanol, and 0.4 g of sodium hydroxide were placed in a reaction vessel and reacted at 60°C for 1 hour to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.6%.

[0095] Step 3: 33 g of high-purity dimethyl terephthalate obtained in step 2, 49.5 g of 1,4-butanediol, and 0.165 g of tetrabutyl titanate were placed in a high-pressure reactor and subjected to ester exchange at 190° C. The reaction was performed for 2 hours to obtain the monomer BHBT. The temperature was gradually raised to 255° C. and the pressure in the reactor was gradually reduced to below 50 Pa to react for 3 hours to carry out a condensation reaction of the monomer BHBT to obtain a macromolecular chain polymer PBT with an intrinsic viscosity of 0.93 dl / g.

[0096] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 265° C. to obtain regenerated PBT polyester fibers with a breaking elongation of 44.5% and a fiber strength of 2.96 cN / dtex.

[0097] Example 11

[0098] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0099] Step 1: Add 30g of waste PBT, 90g of aniline solvent, and 60g of anisole co-solvent to a 500mL autoclave. Heat to 185°C and stir at 50 rpm for 30 minutes. Then, add 60g of 1,3-propylene glycol and 0.6g of 1,3-dimethylimidazolium acetate catalyst. Stir at 100 rpm for 20 minutes to produce a PBT depolymerization solution.

[0100] Step 2: 240 g of the PBT depolymerization solution prepared in Step 1, 480 g of methanol, and 0.48 g of potassium hydroxide were placed in a reaction vessel and reacted at 70°C for 1 hour to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 98.8%.

[0101] Step 3: Take 25g of high-purity dimethyl terephthalate obtained in step 2, 25g of 1,4-butanediol, and 0.125g of tetrabutyl titanate, place them in a high-pressure reactor at 190°C for ester exchange, react for 2h to obtain monomer BHBT, gradually increase the temperature to 255°C, and gradually reduce the pressure in the reactor to below 50Pa for 3h to carry out condensation reaction of monomer BHBT to obtain a macromolecular chain polymer PBT with an intrinsic viscosity of 0.89dl / g.

[0102] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 265° C. to obtain regenerated PBT polyester fibers with a breaking elongation of 40.9% and a fiber strength of 3.05 cN / dtex.

[0103] Example 12

[0104] In this embodiment, a low-temperature homogeneous depolymerization and regeneration method for waste PBT is provided, and the specific steps are as follows:

[0105] Step 1: Add 20g of waste PBT, 40g of dimethyl sulfoxide (DMSO) solvent, and 80g of acetonitrile co-solvent to a 500mL autoclave. Heat to 190°C and stir at 50 rpm for 30 minutes. Then, add 80g of ethylene glycol and 1g of 1,3-dimethylurea / zinc acetate catalyst. Stir at 100 rpm for 30 minutes to produce a PBT depolymerization solution.

[0106] Step 2: 220 g of the PBT depolymerization solution prepared in Step 1, 440 g of methanol, and 0.66 g of potassium hydroxide were placed in a reaction vessel and reacted at 70°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 99.4%.

[0107] Step 3: 17 g of high-purity dimethyl terephthalate obtained in step 2, 17 g of 1,4-butanediol, and 0.085 g of tetrabutyl titanate were placed in a high-pressure reactor and subjected to ester exchange at 190°C. The reaction was performed for 2 hours to obtain the monomer BHBT. The temperature was gradually raised to 255°C, and the pressure in the reactor was gradually reduced to below 50 Pa. The reaction was performed for 3 hours to carry out a condensation reaction of the monomer BHBT to obtain a macromolecular chain polymer PBT with an intrinsic viscosity of 0.87 dl / g.

[0108] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 265° C. to obtain regenerated PBT polyester fibers with a breaking elongation of 38.8% and a fiber strength of 3.28 cN / dtex.

[0109] Comparative Example 1

[0110] In this comparative example, a method for depolymerizing and regenerating waste PBT is described, and the specific steps are as follows:

[0111] Step 1: Add 70g of waste PBT, 140g of ethylene glycol and 0.35g of zinc acetate catalyst into a 500mL polymerization kettle, react at 200℃ for 2h at a stirring speed of 100r / min to obtain a PBT depolymerization liquid.

[0112] Step 2: 210 g of the PBT depolymerization solution prepared in Step 1, 630 g of methanol, and 0.63 g of sodium hydroxide were placed in a reaction vessel and reacted at 65°C for 3 hours to produce a dimethyl terephthalate mixed solution. The dimethyl terephthalate mixed solution was recrystallized, filtered, and refined to obtain high-purity dimethyl terephthalate, with a dimethyl terephthalate recovery rate of 95.2%.

[0113] Step 3: 56 g of high-purity dimethyl terephthalate obtained in step 2, 56 g of 1,4-butanediol, and 0.28 g of tetrabutyl titanate were placed in a high-pressure reactor and subjected to ester exchange at 190°C. The reaction was performed for 2 hours to obtain the monomer BHBT. The temperature was gradually raised to 255°C, and the pressure in the reactor was gradually reduced to below 50 Pa. The reaction was performed for 3 hours to carry out a condensation reaction of the monomer BHBT to obtain a macromolecular chain polymer PBT with an intrinsic viscosity of 0.78 dl / g.

[0114] Step 4: The fiber-grade regenerated polyester chips obtained in step 3 are melt-spun at a spinning temperature of 265° C. to obtain regenerated PBT polyester fibers with a breaking elongation of 32.4% and a fiber strength of 3.31 cN / dtex.

[0115] Analysis of Comparative Example 1 and Examples of the present invention shows that:

[0116] In Comparative Example 1, the depolymerization reaction of waste PBT was carried out at 200°C, while in the Examples of the present invention, the depolymerization reaction temperature ranged from 170°C to 190°C, demonstrating a lower reaction temperature. The depolymerization reaction time in Comparative Example 1 was 2 hours, while the depolymerization reaction times in the Examples of the present invention ranged from 10 minutes to 30 minutes, demonstrating that the Examples of the present invention may have a faster reaction rate.

[0117] The recovery rate of dimethyl terephthalate in Comparative Example 1 was 95.2%, while the recovery rates in the examples of the present invention ranged from 98.1% to 99.4%, indicating that the examples of the present invention have a higher monomer recovery rate.

[0118] The intrinsic viscosity of the PBT polymer obtained in Comparative Example 1 was 0.78 dl / g, the elongation at break of the regenerated PBT fiber was 32.4%, and the fiber strength was 3.31 cN / dtex. In the embodiments of the present invention, the intrinsic viscosity of the PET polymer is 0.65 dl / g to 0.71 dl / g, the elongation at break of the recycled PET fiber is 19.3% to 24.3%, and the fiber strength is 4.42 cN / dtex to 4.75 cN / dtex; the intrinsic viscosity of the PTT polymer is 0.88 dl / g to 1.07 dl / g, the elongation at break of the recycled PTT fiber is 45.6% to 53.6%, and the fiber strength is 3.37 cN / dtex to 3.56 cN / dtex; the intrinsic viscosity of the PBT polymer is 0.87 dl / g to 1.15 dl / g, the elongation at break of the recycled PBT fiber is 38.8% to 47.8%, and the fiber strength is 2.87 cN / dtex to 3.28 cN / dtex. The intrinsic viscosity, fiber strength, elongation at break, etc. of the recycled polymer are more in line with the required ranges of each virgin polyester.

[0119] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A low-temperature homogeneous depolymerization and regeneration method for waste PBT, characterized in that: The following steps are involved: Step 1: Add waste PBT, solvent, and co-solvent into a high-pressure reactor, heat to 170-190°C, and treat for 10-30 minutes at a stirring speed of 15-50 r / min. Then, add 50-400 parts of diol and 0.5-5 parts of the first catalyst, and continue the reaction for 10-30 minutes to prepare a PBT depolymerization liquid, wherein the mass ratio of waste PBT, solvent, and co-solvent is 100:100-600:50-400; Step 2: placing the PBT depolymerization liquid, methanol, and a second catalyst obtained in step 1 in a reaction vessel, reacting at a temperature of 60-70° C. for 1-3 hours to obtain a dimethyl terephthalate mixed liquid, and then recrystallizing, filtering, and refining the dimethyl terephthalate mixed liquid to obtain high-purity dimethyl terephthalate, wherein the mass ratio of the PBT depolymerization liquid, methanol, and the second catalyst is 100:100-300:0.2-0.3; Step 3: placing the high-purity dimethyl terephthalate, glycol, and third catalyst obtained in step 2 into a high-pressure reactor, and subjecting them to esterification and polycondensation reactions to obtain fiber-grade regenerated polyester chips, wherein the mass ratio of high-purity dimethyl terephthalate, glycol, and third catalyst is 100:100 to 150:0.5; Step 4: melt-spinning the fiber-grade regenerated polyester chips obtained in step 3 to obtain regenerated polyester fibers; In step 1, the solvent is one or more of dimethyl sulfoxide, N-methylpyrrolidone, aniline, and nitrobenzene; In step 1, the co-solvent is one or more of acetonitrile, anisole, and dichloromethane; The first catalyst is one or more of an ionic liquid, a deep eutectic solvent, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene; The ionic liquid is one or more of 1,3-dimethylimidazolium chloride, 1,3-dimethylimidazolium bromide, and 1,3-dimethylimidazolium acetate; The deep eutectic solvent is one or more of 1,3-dimethylurea / zinc acetate and choline chloride / urea; In step 2, the second catalyst is one or more of sodium hydroxide and potassium hydroxide; In step three, the third catalyst is one or more of tetrabutyl titanate, isopropyl titanate, antimony trioxide, and antimony ethylene glycol.

2. The low-temperature homogeneous depolymerization and regeneration method of waste PBT according to claim 1, characterized in that: In step 1, the waste PBT is one or more of waste PBT plastics, waste PBT fibers, and waste PBT textiles.

3. The low-temperature homogeneous depolymerization and regeneration method of waste PBT according to claim 1, characterized in that: In step 1 and step 3, the diol is one of ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol.

4. The low-temperature homogeneous depolymerization and regeneration method of waste PBT according to claim 1, characterized in that: In step 3 and step 4, the recycled polyester chips are one of recycled polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate chips.

5. The low-temperature homogeneous depolymerization and regeneration method of waste PBT according to claim 1, characterized in that: In step 4, the regenerated polyester fiber is one of regenerated polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate fibers.

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