Chemical regeneration method of waste polyester

Abstract

The invention discloses a chemical regeneration method of waste polyester, which comprises the following steps: adding waste polyester into ethylene glycol, carrying out a depolymerization reaction, carrying out filtering impurity removal, decoloration, cooling crystallization and separation on the obtained depolymerization reaction liquid to obtain a solid product which is a mixture of BHET and BHET dimer, and directly carrying out a condensation polymerization reaction to prepare regenerated polyester. According to the method disclosed by the invention, the solid impurities filtered and removed when the BHET is purified by adding water are found to be BHET dimers for the first time, and the mixture of the BHET and the BHET dimers is directly used as a raw material to prepare the RPET through polymerization without removing the solid impurities, so that the process is simplified, and the cost is saved. The post-treatment steps are simple, a large amount of water does not need to be added to purify BHET, and the solvent ethylene glycol can be recycled through simple treatment. The steps from waste polyester depolymerization to polymerization for preparation of rPET are few, the process is short, the energy consumption is low, the yield is high, and the method has important significance for high-efficiency recovery of PET and green economic technology popularization.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a chemical regeneration method for waste polyester. Background Art

[0002] Polyester is used in all aspects of life due to its excellent physical properties. As the application scope of polyester products continues to expand, its output is also rising year by year. On the one hand, polyester brings convenience to people's lives, but due to its excellent chemical stability, it also brings the problem of disposal of waste polyester. If it is left to be discarded in nature, it will cause white pollution and damage to the ecological environment. At present, many countries and regions around the world and multinational companies have formulated relevant policies for recycling and reuse. For example, the European Union proposed a new draft version of the "Food Contact Recycled Plastics Regulation" at the end of 2021, updating and refining the requirements for PET recycling technology; the European Union also passed the "Single Use Plastics Directive", setting a goal of 50% recycling rate for plastic packaging by 2025 and 65% by 2030.

[0003] At present, the recycling and reuse of polyester is still mainly physical recycling, because physical recycling is convenient, has low technical barriers and short cycles. However, physical recycling has an important disadvantage, which is that it cannot completely remove impurities or other components in the recycled materials, which also reduces viscosity and causes color difference. The recycled products are mainly used in low-end fields and are difficult to be applied to high-end or even food-grade fields.

[0004] Chemical recycling of polyester involves a deeper level, requiring polyester to be depolymerized and reduced to monomers, and then polymerized into polyester. The quality of the resulting recycled PET (RPET) is close to that of virgin polyester. Glycolysis is currently a mainstream PET chemical recycling technology in the industry. It uses ethylene glycol to depolymerize PET. Its reaction conditions are relatively milder than methanol depolymerization, but it is a reversible reaction and the conversion rate is limited. The product is generally a mixture of bis(2-hydroxyethyl) terephthalate (BHET) and other polymers, which makes separation difficult and costly.

[0005] Current research focuses on the effect of catalysts on the depolymerization rate of PET and the yield of BHET, such as ionic liquid catalysts, alkaloid catalysts, etc. Although new catalysts may slightly increase the yield of BHET, they have little effect on the cost of the entire polyester depolymerization and BHET extraction process. In the process of depolymerizing PET to prepare BHET, the separation and purification of the back-end products is actually the main part of the production cost, which is currently neglected.

[0006] Specifically, water is generally introduced as a solvent to dissolve BHET and separate it from other unreacted raw materials. For example, patents CN201510511713.9 and CN202310257181.5 both introduce water for multiple recrystallization purifications. The entire cycle is long, the efficiency is low, and a large amount of water is required, consuming resources. In addition, since the depolymerization product also contains ethylene glycol, after adding water, the separation of water and ethylene glycol in the later stage also requires higher energy consumption, resulting in huge costs. The high production cost leads to excessively high prices for recycled BHET products on the market, which makes general polyester plants and downstream customers discouraged.

[0007] It is necessary to develop a new recycling method that combines the convenience of physical methods with the high quality of chemical methods to reduce costs. Summary of the invention

[0008] In view of the technical problems of poor recycling efficiency and high cost of waste polyester in the prior art, the purpose of the present invention is to develop an efficient and low-cost chemical recycling and regeneration method for waste polyester.

[0009] The technical solution adopted by the present invention is:

[0010] A chemical regeneration method for waste polyester comprises the following steps: adding waste polyester into ethylene glycol to carry out depolymerization reaction; filtering the obtained depolymerization reaction liquid to remove impurities, decolorizing, cooling and crystallizing, and separating; the obtained solid product is a mixture of BHET and BHET dimer, and directly carrying out polycondensation reaction to prepare regenerated polyester.

[0011] Furthermore, the waste polyester includes but is not limited to packaging polyester bottles, polyester films and polyester fibers on the market.

[0012] Furthermore, the waste polyester includes PET and copolyesters obtained by copolymerization based on PET, specifically, polyesters obtained by copolymerization of terephthalic acid monomers with diols and dibasic acids, or terephthalic acid monomers with diols and dibasic acids.

[0013] The diol includes one or more of ethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, isosorbide, propylene glycol, and 1,4-butanediol; the dibasic acid includes one or more of naphthalene dicarboxylic acid, succinic acid, and adipic acid.

[0014] Preferably, the waste polyester mainly includes PET, PBT, PETG and PBAT.

[0015] Furthermore, the depolymerization reaction is carried out under the action of a depolymerization catalyst, which is generally an oxide, hydroxide, chloride or acetate of zinc, aluminum, antimony, manganese, cobalt, sodium or potassium, preferably an oxide or acetate of zinc, manganese or sodium.

[0016] More preferably, the depolymerization catalyst is zinc acetate or zinc oxide.

[0017] Furthermore, the amount of the depolymerization catalyst added is 0.01% to 1% of the mass of the waste polyester.

[0018] Furthermore, the mass ratio of waste polyester to ethylene glycol is 1:3-10, preferably 1:4-8.

[0019] Furthermore, the temperature of the depolymerization reaction is 180° C. to 195° C., preferably 185 to 190° C. The time of the depolymerization reaction is 2 h to 5 h, preferably 2.5 to 4 h.

[0020] Furthermore, the depolymerization reaction liquid is filtered to remove impurities, and the filter pore size is 1 to 15 μm. The filtration can remove unreacted PET (very small amount) and impurities, and at this time, BHET and BHET dimer are both dissolved in ethylene glycol solvent.

[0021] Furthermore, filtering and removing impurities is generally carried out at a temperature of 75°C to 120°C (preferably 75 to 100°C).

[0022] Furthermore, decolorization can be performed by using one or both of activated carbon and ion exchange resin.

[0023] Furthermore, the particle size of the activated carbon is preferably 100 to 500 meshes. The ion exchange resin is preferably a macroporous styrene-divinylbenzene anion exchange resin with a basic group, and the basic group is preferably a tertiary amine group or a quaternary ammonium group. More preferably, the ion exchange resin is D301 resin.

[0024] Furthermore, the added amount of activated carbon or ion exchange resin is 0.05% to 12% of the mass of the waste polyester.

[0025] Furthermore, the decolorization temperature is 50°C to 100°C (preferably 50 to 70°C), and the decolorization time is 0.5 to 5 hours.

[0026] Furthermore, the temperature during crystallization is 0°C to 25°C, preferably 0 to 10°C.

[0027] Furthermore, after cooling, crystallization and separation, the obtained solid product generally still contains a small amount of ethylene glycol solvent, and the solvent can be removed without drying. In the subsequent polycondensation reaction, the ethylene glycol will be vacuum extracted.

[0028] After crystallization and separation, the filtrate obtained is ethylene glycol solvent, which contains metal ions (catalyst of waste polyester itself and added depolymerization catalyst) and can be purified by chelating ion exchange resin. The purified ethylene glycol solvent obtained can be recycled.

[0029] The chelating ion exchange resin can be selected from macroporous styrene or acrylic acid cation exchange resins, preferably D401, D113 or 001*7 cation exchange resins.

[0030] The filtrate is purified by using a chelating ion exchange resin to remove metal ions and color. Since no water is added in the post-treatment of the present invention, the purified ethylene glycol can be directly recycled.

[0031] The polycondensation reaction is generally carried out under the action of a polycondensation catalyst, and the polycondensation catalyst is generally one or more of antimony trioxide, antimony glycol, antimony acetate, germanium oxide or germanium glycol.

[0032] Furthermore, the amount of the polycondensation catalyst added is 0.01%wt to 0.04%wt of the mass of the solid product.

[0033] Furthermore, the polycondensation reaction of the mixture of BHET and BHET dimer includes a prepolymerization step and a final polycondensation step.

[0034] In the prepolymerization step, the prepolymerization temperature is 200°C to 270°C (preferably 230 to 270°C), the prepolymerization reaction is carried out under a vacuum environment, the pressure drops from normal pressure to 1 to 3 kPa, and the prepolymerization time is 50 min to 120 min (preferably 90 to 120 min).

[0035] In the prepolymerization step, the ethylene glycol in the product and generated by the transesterification reaction is removed by vacuum.

[0036] In the final polycondensation step, the reaction temperature is 275 to 290° C., the absolute pressure is below 100 Pa, and the reaction time is 1 to 5 hours.

[0037] In the conventional PET depolymerization method, separation and purification are required after depolymerization. Generally, water is added to dissolve BHET, and the water-insoluble solid matter is removed as impurities. It is generally believed that solid impurities include impurities, a small amount of unreacted PET, and a mixture of various oligomers with different polymerization degrees. It is necessary to undergo multiple recrystallization purifications to obtain purer BHET, but it also causes a significant increase in cost. However, the present invention first discovered that in the process of ethylene glycol depolymerization of PET polyester, the products are BHET and BHET dimers. After removing impurities, the water-insoluble impurities obtained after adding water to the obtained solid product are actually BHET dimers, which are a single substance, rather than a mixture of oligomers with different polymerization degrees. The dimer of BHET is also an organic molecule like BHET, and can also be used as a final product and polymerized into rPET as a raw material. Therefore, as long as the product contains only BHET and pure BHET dimers, both raw materials can be used for polycondensation reactions, and the content of BHET in the mixture has no substantial effect on the quality of the final rPET. The BHET dimer that was previously removed as an impurity was discovered for the first time in the present invention to be used as a raw material without having to be removed at all, which not only simplifies the separation and purification steps but also greatly improves the recovery rate.

[0038] The molecular formulas of BHET and BHET dimer are shown below:

[0039]

[0040] Compared with the prior art inventions, the beneficial effects of the present invention are: solving the problems of cumbersome and high energy consumption in the separation process of BHET and its polymers (dimers), and discovering for the first time that the solid impurities filtered out when adding water to separate BHET are actually BHET dimers, so waste can be turned into treasure, and there is no need to remove the dimer impurities. Instead, BHET and its polymers (dimers) are used as raw materials to directly polymerize and prepare RPET, thereby simplifying the process and saving costs.

[0041] The present invention does not introduce other solvents such as water to highly purify BHET, thereby eliminating the high energy consumption separation step of water and ethylene glycol in the later stage, and the solvent ethylene glycol can be recycled after simple treatment.

[0042] During the decolorization and metal ion removal process, activated carbon or ion exchange resin has a good adsorption effect on the metal ions in the depolymerization solution. There are few metal ions in the product and it can be directly used as a raw material for polymerizing rPET.

[0043] The depolymerizing agent ethylene glycol can be directly reused after being purified by decolorization and ion adsorption; the ethylene glycol extracted under low vacuum during the prepolymerization process can also be reused.

[0044] The method of preparing rPET from depolymerization of waste polyester has fewer steps, shorter process, lower energy consumption and higher yield, and is of great significance for high-efficiency recycling of PET and promotion of green economic technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 IR spectra of BHET and BHET dimer.

[0046] Figure 2 This is the H NMR spectrum of BHET.

[0047] Figure 3 This is the H NMR spectrum of the BHET dimer.

[0048] Figure 4 These are photos of the depolymerization reaction and decolorization steps of waste polyester. Figure A shows the blue PET bottle flakes added to ethylene glycol solvent, Figure B shows the depolymerization reaction during heating, Figure C shows the completion of the depolymerization reaction, Figure D shows the decolorization after adding activated carbon, and Figure E shows the product after decolorization filtration, cooling crystallization and drying.

[0049] Figure 5 This is a photo of the undecolorized product of Comparative Example 2.

[0050] Figure 6 This is the BHET obtained by separating the product in Example 5. DETAILED DESCRIPTION

[0051] The method of the present invention is further described in detail below in conjunction with specific embodiments. The scope of the present invention includes but is not limited to the following implementation scope.

[0052] Examples 1 to 5 are laboratory depolymerization tests using colored bottle flakes. Examples 6 to 8 are preliminary laboratory amplifications and raw materials are prepared for recycled rPET. Due to the large demand for raw materials, PET slices are used instead. In addition, Examples 6 to 8 are depolymerized in a 20L reactor, and depolymerization products will remain on the reactor wall, the casting head and the pipeline, resulting in unavoidable losses. The actual product mass is greater than the weighed mass in the table. Example 9 is the preparation of recycled rPET by BHET and polymers. Comparative Example 1 uses the conventional BHET purification process of the prior art. Activated carbon is not used for decolorization in the step of Comparative Example 2. There is a drying and ethylene glycol removal process in Examples 1 to 8 in order to compare the product quality, but in normal production, there is no significant effect on excess ethylene glycol. When it is used to prepare recycled polyester later, ethylene glycol will be extracted under a long period of low vacuum in the prepolymerization step.

[0053] Example 1

[0054] In a 250mL beaker, add 20g blue PET bottle flakes (Wahaha activated beverage bottles, cut into 8*8mm pieces, the same below), 100g ethylene glycol, 0.04g zinc acetate (raw material photo as shown in the figure) Figure 4 A), put in a magnet, place on a magnetic stirring heating table, insert a thermocouple thermometer probe, seal with plastic wrap, and react at 195°C for 180 min (the depolymerization reaction process is shown in the photo Figure 4 As shown in Figure B, after the reaction is completed, the photo Figure 4 The mixture was cooled to 80°C and filtered (pore size 10 μm) to remove unreacted PET and impurities. 0.5 g of activated carbon (150 mesh) was added to the filtrate (the photo of activated carbon decolorization is shown in FIG. Figure 4 The mixture was stirred at 50-60°C for 1.5 hours, filtered again, cooled to 10°C, allowed to stand for 12 hours, filtered again, and a mixture of ethylene glycol, BHET and its polymers was obtained. The mixture was placed in a vacuum oven at 80°C for 8 hours and weighed. The product is shown in the photo. Figure 4 As shown in Figure E. Add 0.5g D113 resin to the filtrate, stir for 3h and filter. The filtrate is purified ethylene glycol and can be directly recycled.

[0055] Example 2

[0056] In a 250mL beaker, add 20g blue PET bottle flakes, 100g ethylene glycol, 0.04g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 150min, cool to 80℃, filter, add 0.5g activated carbon to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 10℃, let stand for 12h, filter again, get a mixture of ethylene glycol, BHET and its polymers, put it in a vacuum oven at 80℃ for 8h, weigh it. Add 0.5g D113 resin to the filtrate, stir for 3h, filter, and keep the filtrate.

[0057] Example 3

[0058] In a 250mL beaker, add 20g blue PET bottle flakes, 100g ethylene glycol, 0.04g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 120min, cool to 100℃, filter, add 2g D301 resin to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 10℃, let stand for 12h, filter again to obtain a mixture of ethylene glycol, BHET and its polymers. Place in a vacuum oven at 80℃ for 8h and weigh. Add 0.5g D113 resin to the filtrate, stir for 3h and filter, and keep the filtrate.

[0059] Example 4

[0060] In a 500mL three-necked flask, add 40g blue PET bottle flakes, 250g ethylene glycol, 0.08g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 180min, cool to 100℃, filter, add 1g activated carbon to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 10℃, let it stand for 12h, filter again, and obtain a mixture of ethylene glycol, BHET and its polymers. Place it in a vacuum oven at 80℃ for 8h and weigh it. Add 1g D113 resin to the filtrate, stir for 3h and filter, and keep the filtrate.

[0061] Example 5

[0062] In a 500mL three-necked flask, add 40g blue PET bottle flakes, 300g ethylene glycol, 0.1g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 180min, cool to 100℃, filter, add 1g activated carbon to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 10℃, let stand for 12h, filter again, and obtain a mixture of ethylene glycol, BHET and its polymers. Place in a vacuum oven at 80℃ for 8h and weigh. Add 1g D113 resin to the filtrate, stir for 3h and filter, and keep the filtrate.

[0063] Example 6

[0064] In a 20L reactor, add 2kg PET chips, 8kg ethylene glycol, 3.5g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 180min, cool to 100℃, filter, add 40g activated carbon to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 15℃, let it stand for 12h, filter again to obtain a mixture of ethylene glycol, BHET and its polymers. Place it in a stainless steel tray, put it in a vacuum oven, 80℃, 8h, weigh it. Add 60g D113 resin to the filtrate, stir for 3h, filter, and keep the filtrate.

[0065] Example 7

[0066] In a 20L reactor, add 2.5kg PET chips, 12kg ethylene glycol, 4.4g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 180min, cool to 100℃, filter, add 50g activated carbon to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 15℃, let it stand for 12h, filter again to obtain a mixture of ethylene glycol, BHET and its polymers. Place it in a stainless steel tray, put it in a vacuum oven, 80℃, 8h, weigh it. Add 70g D113 resin to the filtrate, stir for 3h, filter, and keep the filtrate.

[0067] Example 8

[0068] In a 20L reactor, add 2kg PET chips, 12kg ethylene glycol, 4.4g zinc acetate, put it on a magnetic stirring heating table, react at 195℃ for 150min, cool to 100℃, filter, add 50g activated carbon to the filtrate, stir at 50-60℃ for 1h, filter again, cool the solution to 15℃, let it stand for 12h, filter again to obtain a mixture of ethylene glycol, BHET and its polymers. Place it in a stainless steel tray, put it in a vacuum oven, 80℃, 8h, weigh it. Add 70g D113 resin to the filtrate, stir for 3h, filter, and keep the filtrate.

[0069] Example 9

[0070] The mixture of BHET and BHET dimer obtained in Examples 6 to 8 was weighed 7.5 kg and placed in a 20L reactor, 1.65 g of antimony trioxide catalyst was added, the kettle temperature was controlled at 35 to 60 ° C, nitrogen was introduced to replace the air, and the vacuum pump was started to slowly evacuate to 1 kPa, and repeated 3 times. The kettle temperature was raised to 150 ° C, and after 35 minutes of constant temperature, all the reactants melted (judged by the stirring current), and the temperature was continued to rise to 230 ° C, and low vacuum was started. Within 2 hours, the pressure was gradually reduced from normal pressure to 1 kPa, and the temperature of the reactor was controlled to rise slowly to 265 ° C, so that the excess ethylene glycol in the kettle was extracted after the ester exchange, and the temperature was prevented from rising too fast to cause BHET to be extracted. After the low vacuum was completed, the kettle temperature was raised to 275 ° C for polycondensation, the pressure was below 100 Pa, and after 118 minutes, the current reached the target value, the reaction was terminated, the material was discharged, and the pellets were cut.

[0071] Comparative Example 1

[0072] In a 500mL three-necked flask, add 40g of blue PET bottle flakes, 250g of ethylene glycol, and 0.08g of zinc acetate, place on a magnetic stirring heating table, and react at 195°C for 180min;

[0073] Cool to 100°C, filter, add 600 g of pure water to the filtrate, stir for 30 min, cool to 15°C, keep constant temperature for 12 h, filter to obtain crude BHET;

[0074] The crude BHET was dissolved in 600g pure water at 80°C, 1g D113 resin was added to the solution, stirred and dissolved for 60min, filtered, and then the filtrate was cooled to 15°C, allowed to stand for 12h, and filtered again to obtain refined BHET.

[0075] Place the refined BHET in a vacuum oven at 80°C for 8 h and weigh it.

[0076] Comparative Example 2

[0077] In a 500mL three-necked flask, add 40g blue PET bottle flakes, 300g ethylene glycol, and 0.1g zinc acetate, place on a magnetic stirring heating table, react at 195°C for 180min, cool to 100°C, filter, cool the solution to 10°C, let stand for 12h, filter again, and obtain a mixture of ethylene glycol, BHET and its polymers. Place in a vacuum oven at 80°C for 8h, weigh, and the resulting product is shown in the photo. Figure 5 Add 1 g of D113 resin to the filtrate, stir for 3 h, filter, and keep the filtrate.

[0078] The weights of the products obtained in Examples 1 to 8 and the comparative example are shown in the following table: The products of Examples 1 to 8 are mixtures of BHET and dimer, and the product of the comparative example is BHET.

[0079]

[0080] It can be seen from the yield data that the product of the present invention has a higher yield. In addition, the separation step is simple, and no additional water needs to be added, so there is no need to separate ethylene glycol and water, the purification steps are few, and the production efficiency is high.

[0081] The yield of Example 3 is relatively low, which may be because the reaction time is only 120 minutes and the depolymerization reaction is not complete. Therefore, the reaction time of the present invention is preferably 150 to 180 minutes.

[0082] The product prepared in Example 5 was separated and water was added. BHET was soluble in water, but the dimer was insoluble in water. After the two were separated, infrared detection was performed. The spectrum was as follows: Figure 1 shown. Figure 1 In the figure, the upper figure is the dimer spectrum, and the lower figure is the BHET spectrum.

[0083] In Example 5, after separation, the masses of BHET and dimer were 42.5944 g and 6.5875 g respectively (loss in the separation process, BHET loss is greater), and it can be seen that the mass ratio of BHET and dimer is about 6:1. Figure 6 .

[0084] The H NMR spectrum of BHET is shown in Figure 2 , the hydrogen spectrum is consistent with the BHET literature data.

[0085] The H NMR spectrum of BHET dimer is shown in Figure 3 , the hydrogen shift peak area ratio is close to 4:2:2:2:1, which is the same as the hydrogen ratio of the BHET dimer. Figure 1 , Figure 3 It can be seen that the polymer product is actually a pure dimer, not a mixture.

[0086] The regenerated PET slices of Example 9 were tested, and the test results are shown in the following table.

[0087] Intrinsic viscosity dL / g Terminal carboxyl group mmol / kg DEG% Color value L Color value b 0.653 32.34 1.092 73.16 4.6

Claims

1. A chemical regeneration method for waste polyester, characterized in that The method comprises the following steps: waste polyester is added into ethylene glycol to carry out depolymerization reaction; the obtained depolymerization reaction liquid is filtered to remove impurities, decolorized, cooled for crystallization, and separated; the obtained solid product is a mixture of BHET and BHET dimer, which is directly subjected to polycondensation reaction to prepare recycled polyester.

2. The method according to claim 1, characterized in that The depolymerization reaction is carried out under the action of a depolymerization catalyst, and the depolymerization catalyst is an oxide, hydroxide, chloride or acetate of zinc, aluminum, antimony, manganese, cobalt, sodium or potassium.

3. The method according to claim 1, characterized in that The mass ratio of waste polyester to ethylene glycol is 1:3-10.

4. The method according to claim 1, characterized in that The temperature of the depolymerization reaction is 180° C. to 195° C., and the time of the depolymerization reaction is 2 h to 5 h.

5. The method according to claim 1, characterized in that The decolorization is carried out by using one or both of activated carbon and ion exchange resin, and the temperature during decolorization is 50°C to 100°C.

6. The method according to claim 1, characterized in that The temperature during crystallization is 0°C to 25°C.

7. The method according to claim 1, characterized in that After cooling, crystallization and separation, the obtained filtrate is ethylene glycol solvent, which is purified by chelating ion exchange resin, and the obtained purified ethylene glycol solvent is recovered for reuse.

8. The method according to claim 1, characterized in that The polycondensation reaction is carried out under the action of a polycondensation catalyst, and the polycondensation catalyst is one or more of antimony trioxide, antimony glycol, antimony acetate, germanium oxide or germanium glycol.

9. The method according to claim 1, characterized in that The polycondensation reaction of the mixture of BHET and BHET dimer includes a prepolymerization step and a final polycondensation step; in the prepolymerization step, the prepolymerization temperature is 200°C to 270°C, the prepolymerization reaction is carried out in a vacuum environment, the pressure drops from normal pressure to 1 to 3 kPa, and the prepolymerization time is 50 min to 120 min.

10. The method according to claim 9, characterized in that In the final polycondensation step, the reaction temperature is 275 to 290° C., the absolute pressure is below 100 Pa, and the reaction time is 1 to 5 hours.

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