A process for the preparation of a PEIT copolyester

Abstract

The application discloses a method for preparing PEIT copolyester, which comprises the following steps: A) first, performing an ester exchange reaction on bis2-hydroxyethyl terephthalate and isosorbide to generate terephthalate glycol isosorbide; B) then, performing a melt polycondensation reaction on the excess BHET monomer in the ester exchange reaction system and the generated terephthalate glycol isosorbide to obtain PEIT copolyester. The application not only realizes high conversion rate and high proportion of isosorbide, so that the prepared PEIT copolyester has excellent heat resistance, but also guarantees that the DEG content in the copolyester is lower than 1.2%, and the color value b value is less than 3, which can well meet the application requirements of food packaging; in particular, the BHET monomer can be sourced from chemical regeneration of waste polyester, which has important value for realizing resource recycling of waste polyester.

Description

Technical Field

[0001] This invention relates to a method for preparing PEIT copolyester, belonging to the field of specialty polyester preparation technology. Background Technology

[0002] Polyethylene terephthalate isosorbide copolyester, or PEIT copolyester for short, is a copolyester in which the rigid group isosorbide is embedded in the conventional PET molecule. Compared with conventional polyester PET, its glass transition temperature and thermal stability are significantly improved, and its pressure resistance is also enhanced. This makes it more applicable in daily life, such as for hot-fill bottles, heat-resistant containers, heat-resistant films, fibers, cosmetic packaging, etc.

[0003] In existing technologies, terephthalic acid, ethylene glycol, and isosorbide are mainly used as raw materials. Under the action of catalysts and stabilizers, esterification and polycondensation reactions are carried out to prepare polyethylene terephthalate isosorbide copolyester. In this preparation process, a large amount of diethylene glycol (DEG) byproducts are generated. The presence of diethylene glycol (DEG) will lead to a decrease in the Tg of the polymer. Therefore, in order to maximize the effect of isosorbide in increasing Tg, existing technologies require the addition of alkali (such as tetramethylammonium hydroxide TMAH) to inhibit DEG formation. However, this inhibitor is a toxic chemical reagent, and it will gradually precipitate during the use of polyester products, thus limiting its application in the food packaging field.

[0004] If a method can be developed to prepare non-toxic and heat-resistant PEIT copolyesters from waste polyester resources, it will be of great value and far-reaching significance for realizing the complete closed-loop recycling of waste polyester and establishing a sound green, low-carbon, and circular economic system. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the purpose of this invention is to provide a method for preparing non-toxic and heat-resistant PEIT copolyesters using waste polyester resources.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing PEIT copolyester includes the following reaction steps:

[0008] A) First, bis(2-hydroxyethyl) terephthalate (BHET) undergoes an exchange reaction with isosorbide to generate ethylene glycol terephthalate isosorbide ester. The specific reaction formula is shown below:

[0009]

[0010] B) The excess BHET monomer in the transesterification reaction system is then subjected to a melt polycondensation reaction with the generated ethylene glycol isosorbide terephthalate to obtain PEIT copolyester. The specific reaction formula is shown below:

[0011]

[0012] In the formula, m and n represent the number of the two unit segments shown in the PEIT copolyester, and are both natural numbers.

[0013] In one embodiment, m is a natural number from 1 to 160, and n is a natural number from 1 to 200.

[0014] In one embodiment, the transesterification reaction involves reacting BHET monomer and isosorbide in the presence of a transesterification catalyst at a reaction temperature of 190°C to 220°C and a reaction pressure of 70 kPa to 100 kPa for 20 to 60 minutes.

[0015] In a preferred embodiment, the molar ratio of isosorbide to BHET monomer is (5%–80%):1.

[0016] In a preferred embodiment, the transesterification catalyst is selected from at least one of the following: metal salt catalyst (e.g., zinc acetate, zinc oxide, tetrabutyl titanate, tetraisopropyl titanate, dibutyl zinc oxide, sodium methoxide, etc.), basic catalyst (e.g., NaOH, KOH, NaOCH3, organic bases and various solid bases, etc.), acidic catalyst (e.g., sulfuric acid, sulfonic acid and various solid acids, etc.), or biological enzyme catalyst.

[0017] In a further preferred embodiment, the transesterification catalyst is zinc acetate.

[0018] In a preferred embodiment, the amount of the transesterification catalyst is 10 to 1000 ppm (preferably 50 to 100 ppm) of the BHET monomer mass.

[0019] In one embodiment, the BHET monomer is obtained by purifying the ethylene glycol alcoholysis solution of waste polyester.

[0020] In a preferred embodiment, the purification process includes a secondary thin-film evaporation process and a primary molecular distillation process.

[0021] A further preferred embodiment includes the following specific steps in the purification process:

[0022] a) The ethylene glycol alcoholysis solution of waste polyester is decolorized and then fed into the first thin film evaporator for a thin film evaporation process at 140℃~180℃ and 100Pa~10000Pa.

[0023] b) The remaining alcoholysis product after the first thin-film evaporation treatment is fed into the second thin-film evaporator and subjected to a second thin-film evaporation treatment at 140℃~180℃ and a pressure of 10Pa~1000Pa.

[0024] c) Input the melt obtained by the secondary thin-film evaporation process into a molecular distillation apparatus and perform molecular distillation at 180℃~250℃ and 1Pa~100Pa.

[0025] d) Collect BHET monomer melt from the light component outlet of the molecular distillation apparatus.

[0026] In one embodiment, the ethylene glycol alcoholysis solution of the waste polyester is prepared by adding ethylene glycol and waste polyester particles that have been pretreated by crushing, washing and drying into an alcoholysis reactor at a mass ratio of (1-3):1, and then carrying out the alcoholysis reaction for 2-6 hours at 190℃-230℃ and an internal pressure of 0.1MPa-0.5MPa under the action of zinc acetate catalyst.

[0027] One embodiment of the invention includes waste polyester production materials and waste polyester products, specifically including at least one of waste PET bottles, PET packaging sheets, PET fibers, PET textiles, and PET bubble materials.

[0028] In one embodiment, the melt polycondensation reaction involves subjecting an excess of BHET monomer in the transesterification reaction system to a pre-polycondensation reaction with the generated ethylene glycol isosorbide terephthalate (PEG) under the action of a polycondensation catalyst and a stabilizer. The reaction is first carried out at 250°C–265°C and a pressure of 1 kPa–50 kPa for 40–100 minutes, followed by a final polycondensation reaction at 270°C–280°C and a pressure of 50 Pa–500 Pa to obtain PEIT melt.

[0029] In one embodiment, the polycondensation catalyst is a metal compound, including, but not limited to, any one or a mixture of several metal compounds based on Al, Co, Ge, Mn, Mg, Pb, Ti, Sb, and Zn.

[0030] In a preferred embodiment, the polycondensation catalyst is selected from at least one of zinc-based metal compounds, titanium-based metal compounds, or zinc-titanium complexes formed by zinc-based metal compounds and titanium-based metal compounds.

[0031] In a further preferred embodiment, the mass ratio of zinc-based metal compound to titanium-based metal compound in the zinc-titanium composite is 1:9 to 9:1 (7:3 being optimal), the zinc-based metal compound is zinc oxide, and the titanium-based metal compound is tetrabutyl titanate or tetraisopropyl titanate.

[0032] In a preferred embodiment, the amount of the polycondensation catalyst is 20 to 200 ppm (preferably 20 to 30 ppm) of the BHET monomer mass.

[0033] In a preferred embodiment, the stabilizer is a phosphoric acid compound.

[0034] In a further preferred embodiment, the stabilizer is selected from any one or a mixture of several of the following: phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and ethylene glycol phosphate.

[0035] In a preferred embodiment, the amount of stabilizer is 50 to 500 ppm (preferably 50 to 100 ppm) of the BHET monomer mass.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] Experiments have demonstrated that this invention, through the innovative transesterification reaction of BHET monomer with isosorbide to generate ethylene glycol terephthalate isosorbide ester, and then the excess BHET monomer in the transesterification system undergoes a melt polycondensation reaction with the generated ethylene glycol terephthalate isosorbide ester, achieves not only a high conversion rate (up to 96%) and a high proportion of isosorbide addition (up to 80% of the molar amount of BHET monomer), but also results in a glass transition temperature (Tg) of up to 133℃ for the prepared PEIT copolyester, exhibiting excellent heat resistance. Furthermore, without the addition of any inhibitors, the DEG content in the copolyester can be guaranteed to be below 1.2%, and the color value b value can be less than 3, perfectly meeting the requirements for food packaging applications. In particular, the BHET monomer used can be derived from the chemical regeneration of waste polyester, which is of great value for realizing the resource recycling of waste polyester and has profound significance and value for establishing and improving a green, low-carbon, and circular economy. Therefore, this invention represents a significant advancement compared to existing technologies and is of great value for achieving large-scale production of PEIT copolyester. Attached Figure Description

[0038] Figure 1 The image shows the HPLC chromatogram of the BHET monomer obtained in Example 1; in the figure, the peak at a retention time of 3.465 min represents the BHET monomer.

[0039] Figure 2The image shows the NMR spectrum of the BHET monomer obtained in Example 1. In the image: δ = 0 ppm is the solvent peak of the internal standard tetramethylsilane, δ = 7.26 ppm is the solvent peak of deuterated chloroform, δ = 8.13 ppm is the proton peak corresponding to the hydrogen on the benzene ring in BHET, δ = 4.51 ppm is the proton peak of the four hydrogen atoms on the two methylene groups connected to the oxygen atom, and δ = 4.00 ppm is the proton peak of the four hydrogen atoms on the two methylene groups connected to the hydroxyl group.

[0040] Figure 3 The image shows the FTIR spectrum of the BHET monomer obtained in Example 1; in the image: 3446 cm⁻¹ -1 The absorption peak corresponding to the stretching vibration of -OH is at 2963 cm⁻¹. -1 and 2880cm -1 The absorption peak corresponding to the stretching vibration of -CH2- is at 1716 cm⁻¹. -1 The characteristic absorption peak corresponding to the stretching vibration of C=O in the ester group is 1411 cm⁻¹. -1 The peak near 1134 cm⁻¹ is an absorption peak due to the vibration of the benzene ring skeleton. -1 and 1282cm -1 The characteristic peak corresponding to the CO stretching vibration in the ester group is 874 cm⁻¹. -1 This is a characteristic absorption peak for para-substitution of the benzene ring. Detailed Implementation

[0041] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments. The detection methods involved in the following embodiments and comparative examples are described as follows:

[0042] 1) HPLC purity analysis of BHET monomer:

[0043] An Agilent-1100 high-performance liquid chromatograph was used, with a Benetnach C18 column (5 μm, 4.6 x 150 mm), acetonitrile as the solvent, a detection wavelength of 254 nm, an acetonitrile-water mobile phase (70:30, V / V), a flow rate of 0.5 mL / min, and an injection volume of 20 μL.

[0044] 2) Nuclear magnetic resonance analysis of BHET monomer: The product was analyzed by 1H NMR using an AVANCEⅢHD 400 nuclear magnetic resonance spectrometer at 400MHz.

[0045] 3) FTIR analysis of BHET monomers: After pressing the sample powder into pellets with potassium bromide, the sample was scanned using a Nicolet IS5 Fourier transform infrared spectrometer at wavelengths of 400-4000 cm⁻¹. -1 ;

[0046] 4) Intrinsic viscosity of PEIT copolyester: It shall be performed in accordance with the capillary viscometer method in GB / T 14190. The unit of intrinsic viscosity is dL / g, wherein the mass ratio of phenol to 1,1,2,2-tetrachloroethane is 50:50 or 60:40.

[0047] 5) Glass transition temperature of PEIT copolyester: Differential scanning calorimetry (DSC) was used. Under a nitrogen atmosphere, the sample was first heated from 30℃ to 280℃ at a rate of 10℃ / min, held at 280℃ for 3 min, then heated from 280℃ to 30℃ at a rate of 10℃ / min, and held at 30℃ for 1 min to eliminate thermal history. The sample was then heated from 30℃ to 280℃ at a rate of 10℃ / min for the second time. The DSC curve of the sample was recorded during the test.

[0048] 6) DEG content in PEIT copolyester: The sample was subjected to a degradation reaction under high temperature and methanol conditions using gas chromatography, which resulted in the release of diethylene glycol. The diethylene glycol content in the filtrate was then detected by gas chromatography.

[0049] 7) Color value of PEIT copolyester: After drying the sample at 140℃ for 30 min, the color value of the sample was tested by an automatic colorimeter, and the result was expressed as the b value of the HunterLab color system.

[0050] 8) Isosorbide conversion rate: Using nuclear magnetic resonance spectroscopy, the percentage of isosorbide relative to BHET in PEIT copolyester was calculated by utilizing the integral area occupied by the characteristic hydrogen atom proton peaks in isosorbide and BHET, and then divided by the percentage of isosorbide relative to BHET at the time of feeding. The conditions for nuclear magnetic resonance analysis were as follows: PEIT copolyester was dissolved in deuterated trifluoroacetic acid, tetramethylsilane was used as an internal standard, and 1H NMR was performed using an AVANCEⅢ400 nuclear magnetic resonance spectrometer at 400MHz.

[0051] Example 1:

[0052] I. Preparation of BHET Monomer Melt

[0053] A) Waste polyester (including polyester production waste and / or waste polyester products) is crushed, washed and dehydrated in sequence to obtain waste polyester particles with a moisture content of 1% to 3%.

[0054] B) Measure 1 ton of pretreated waste polyester particles and transport them to the alcoholysis reactor. Then add 2 tons of ethylene glycol (EG) and 3 kg of zinc acetate catalyst. Heat the mixture to 200°C and control the pressure inside the alcoholysis reactor to 0.1 MPa. Allow the alcoholysis reaction to proceed for 3 hours to obtain ethylene glycol alcoholysis liquid from the waste polyester.

[0055] C) Purify the glycol alcoholysis solution of waste polyester, i.e.:

[0056] C1) The ethylene glycol alcoholysis solution of waste polyester obtained in step B) is filtered using a 50-150 mesh filter to remove insoluble matter, and then decolorized by activated carbon adsorption.

[0057] C2) The decolorized filtrate is added to the first thin-film evaporator and the first thin-film evaporation process is carried out at a temperature of 140℃~180℃ and a pressure of 100Pa~10KPa.

[0058] C3) The remaining alcoholysis product after the first thin-film evaporation treatment in step C2) is fed into the second thin-film evaporator and subjected to a second thin-film evaporation treatment at a temperature of 140℃~180℃ and a pressure of 10Pa~1KPa.

[0059] C4) The melt obtained from the secondary thin-film evaporation treatment in step C3) is fed into a molecular distillation apparatus and subjected to molecular distillation at a temperature of 180 ℃~250 ℃ and a pressure of 1 Pa~100 Pa. The BHET monomer melt is collected from the light component outlet of the molecular distillation apparatus. The collected distillate is a colorless and transparent liquid that crystallizes into a white solid at room temperature. Analysis shows that the HPLC purity of the obtained BHET monomer is 99.8%. (See details...) Figure 1 The spectrum shown; and the color value b is 1.21; in addition, by Figure 2 The nuclear magnetic resonance analysis spectrum shown is as follows: Figure 3 The FTIR analysis spectrum shown proves that the obtained colorless fraction is the BHET monomer.

[0060] II. Transesterification reaction of bis(2-hydroxyethyl) terephthalate (BHET) with isosorbide.

[0061] BHET monomer (which can be directly obtained from the liquid fraction collected from the light component outlet of a molecular distillation apparatus, thus enabling continuous production and saving energy), isosorbide, and zinc acetate are added to the reactor in a certain proportion, wherein: the molar amount of isosorbide is 10% of the molar amount of BHET monomer, and the amount of zinc acetate is 70 ppm of the mass of BHET monomer; the reaction is controlled at a reaction temperature of 190℃~220℃ and a reaction pressure of 70kPa~100kPa (preferably 80kPa) for 20~60 minutes (preferably 50 minutes) to generate ethylene glycol isosorbide terephthalate, and the byproduct ethylene glycol is removed and collected during the reaction.

[0062] III. Perform melt polycondensation to prepare PEIT copolyester.

[0063] A polycondensation catalyst (a zinc-titanium complex, wherein the mass ratio of zinc metal compound to titanium metal compound is 7:3, wherein the zinc metal compound is zinc oxide, and the titanium metal compound is tetrabutyl titanate or tetraisopropyl titanate) and a stabilizer (triethyl phosphate) are added to the transesterification reaction system. The amount of the polycondensation catalyst is 20 ppm of the mass of BHET monomer, and the amount of the stabilizer is 50 ppm of the mass of BHET monomer.

[0064] The above reaction system is first subjected to a pre-condensation reaction at 250℃~265℃ and a pressure of 1kPa~50kPa for 40~100 minutes (60 minutes is preferred), and then subjected to a final condensation reaction at 270℃~280℃ and a pressure of 50Pa~500Pa. The reaction is terminated when the stirring motor of the reactor reaches the specified current, and PEIT final condensation melt is obtained. During the reaction, the by-product ethylene glycol is removed, collected and recovered.

[0065] High-purity nitrogen gas is introduced into the reactor and the pressure inside the reactor is controlled at 0.3 MPa. After the PEIT final shrinkage melt passes through the casting head, it becomes multiple copolyester melt strips. After being cooled by the guide plate of the pelletizer, it becomes solid and can then be cut into PEIT copolyester chips in the pelletizer cutting chamber.

[0066] Examples 2-4

[0067] The only difference between Examples 2-4 and Example 1 is the ratio of the materials involved in the reaction, as shown in Table 1; all other contents are the same as those in Example 1.

[0068] Comparative Examples 1-2

[0069] The difference between Comparative Examples 1 and 2 and Examples 1 and 2 is that isosorbide was not subjected to a transesterification reaction with the BHET monomer beforehand, but instead directly underwent a melt polycondensation reaction with the BHET monomer in the presence of antimony glycolate and triethyl phosphate. The specific operation was as follows:

[0070] First, add BHET monomer, antimony glycol, and triethyl phosphate to the reactor according to the proportions shown in Table 1. Then, heat the reactor to 240°C and add isosorbide in the proportions shown in Table 1. Apply a pressure of 0.25 MPa and maintain the temperature for 30–40 min. Then, perform the polycondensation operation as described in Example 1, i.e., first carry out a pre-polycondensation reaction at 250°C–265°C and a pressure of 1 kPa–50 kPa for 40–100 min (60 min is preferred), and then carry out a final polycondensation reaction at 270°C–280°C and a pressure of 50 Pa–500 Pa. Stop the reaction when the reactor stirring motor reaches the specified current to obtain the PEIT final polycondensation melt.

[0071] High-purity nitrogen gas is introduced into the reactor and the pressure inside the reactor is controlled at 0.3 MPa. After the PEIT final shrinkage melt passes through the casting head, it becomes multiple copolyester melt strips. After being cooled by the guide plate of the pelletizer, it becomes solid and can then be cut into PEIT copolyester chips in the pelletizer cutting chamber.

[0072] Table 1. Material proportions of Examples 1-4 and Comparative Examples 1-2

[0073]

[0074]

[0075] Table 2. Performance test results of PEIT copolyester chips obtained in Examples 1-4 and Comparative Examples 1-2

[0076]

[0077] By comparing the above examples and comparative examples, it can be seen that the present invention creatively first performs an ester exchange reaction between BHET monomer and isosorbide to generate ethylene glycol terephthalate isosorbide ester, and then performs a melt polycondensation reaction between the excess BHET monomer in the ester exchange reaction system and the generated ethylene glycol terephthalate isosorbide ester. This not only achieves a high conversion rate of isosorbide (up to 96%, while with the same molar amount of isosorbide added, if BHET monomer is directly subjected to a melt polycondensation reaction with isosorbide, such as in Comparative Example 1 corresponding to Example 1, only a 70% reaction conversion rate can be achieved; furthermore, Example 2 of the present invention can achieve a reaction conversion rate of up to 95%, while the corresponding Comparative Example 2 can only achieve a 68% reaction conversion rate) but also a high proportion of addition (the present invention can achieve BHET monomer isosorbide ester ... The PEIT copolyester prepared by using 80% of the molar amount of ET monomer (as in Example 4) can achieve a glass transition temperature (Tg) as high as 133°C, exhibiting excellent heat resistance. Furthermore, without the addition of any inhibitors, the DEG content in the copolyester can be guaranteed to be below 1.2% (significantly reducing DEG content compared to Comparative Examples 1 and 2 under the same conditions of direct melt polycondensation), and the color value b-value can be less than 3 (while the b-values ​​in Comparative Examples 1 and 2 under the same conditions of direct melt polycondensation are both greater than 3). This demonstrates that the PEIT copolyester prepared by this invention can well meet the needs of food packaging applications. In particular, the BHET monomer used in this invention can be derived from the chemical regeneration of waste polyester, which is of great value for realizing the resource recycling of waste polyester and has profound significance and value for establishing and improving a green, low-carbon, and circular economy. Therefore, this invention represents a significant advancement compared to the prior art and is of great value for realizing the large-scale production of PEIT copolyester.

[0078] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing PEIT copolyester, characterized in that, The reaction steps include the following: A) First, bis(2-hydroxyethyl) terephthalate (BHET) undergoes an exchange reaction with isosorbide to generate ethylene glycol terephthalate isosorbide ester. The specific reaction formula is shown below: ； B) The excess BHET monomer in the transesterification reaction system is then subjected to melt polycondensation with the generated ethylene glycol isosorbide terephthalate to obtain PEIT copolyester. The specific reaction formula is shown below: ； In the formula, m and n represent the number of the two unit segments shown in the PEIT copolyester, respectively, where m is a natural number from 1 to 160 and n is a natural number from 1 to 200.

2. The method for preparing PEIT copolyester according to claim 1, characterized in that: The transesterification reaction involves reacting BHET monomer and isosorbide in the presence of a transesterification catalyst at a reaction temperature of 190℃~220℃ and a reaction pressure of 70kPa~100kPa for 20~60 minutes.

3. The method for preparing PEIT copolyester according to claim 2, characterized in that: The molar ratio of isosorbide to BHET monomer is (5%–80%):

1.

4. The method for preparing PEIT copolyester according to claim 2, characterized in that: The transesterification catalyst is zinc acetate, and the amount of the transesterification catalyst is 10 to 1000 ppm of the mass of BHET monomer.

5. The method for preparing PEIT copolyester according to claim 1 or 2, characterized in that: The BHET monomer is obtained by purifying the ethylene glycol alcoholysis solution of waste polyester.

6. The method for preparing PEIT copolyester according to claim 5, characterized in that: The purification process includes a secondary thin-film evaporation process and a primary molecular distillation process.

7. The method for preparing PEIT copolyester according to claim 6, characterized in that, The purification process includes the following specific steps: a) The ethylene glycol alcoholysis solution of waste polyester is decolorized and then fed into the first thin film evaporator for a thin film evaporation process at 140℃~180℃ and 100Pa~10000Pa. b) The remaining alcoholysis product after the first thin-film evaporation treatment is fed into the second thin-film evaporator and subjected to a second thin-film evaporation treatment at 140℃~180℃ and a pressure of 10Pa~1000Pa. c) The melt obtained by the secondary thin-film evaporation process is fed into a molecular distillation apparatus and subjected to molecular distillation at 180℃~250℃ and 1Pa~100Pa. d) Collect the BHET monomer melt from the light component outlet of the molecular distillation apparatus.

8. The method for preparing PEIT copolyester according to claim 1, characterized in that: The melt polycondensation reaction involves pre-polymerizing excess BHET monomer in the transesterification reaction system with the generated ethylene glycol isosorbide terephthalate under the action of a polycondensation catalyst and stabilizer at 250℃~265℃ and 1kPa~50kPa for 40~100 minutes, followed by a final polycondensation reaction at 270℃~280℃ and 50Pa~500Pa to obtain PEIT melt.

9. The method for preparing PEIT copolyester according to claim 8, characterized in that: The condensation catalyst is selected from at least one of zinc-based metal compounds, titanium-based metal compounds, or zinc-titanium complexes formed by zinc-based metal compounds and titanium-based metal compounds, and the stabilizer is selected from phosphoric acid compounds.

10. The method for preparing PEIT copolyester according to claim 8 or 9, characterized in that: The amount of the polycondensation catalyst is 20 to 200 ppm of the BHET monomer mass, and the amount of the stabilizer is 50 to 500 ppm of the BHET monomer mass.

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