Preparation method of polyester with low diethylene glycol content and obtained polyester

Abstract

The invention provides a preparation method of polyester with low diethylene glycol content and the obtained polyester, and the method comprises the following steps: taking components including dicarboxylic acid and dihydric alcohol as raw materials, and reacting under the condition of adding a diethylene glycol inhibitor to obtain the polyester with low diethylene glycol content. A proper amount of diethylene glycol inhibitor is added into a reaction system, so that the content of diethylene glycol in the polyester material is reduced, and further application of the polyester material is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyester, further relates to a method for preparing polyester with low diethylene glycol content and polyester obtained by the method. BACKGROUND

[0002] Polyester has excellent mechanical properties, wear resistance, wrinkle resistance and other properties, and is widely used in the fields of film, resin and fiber. For example, polyethylene terephthalate (PET) has excellent mechanical, mechanical and chemical properties, has the advantages of heat resistance, chemical resistance, high mechanical strength, good transparency and other advantages, and is widely used in the fields of fiber, film and bottle sheet.

[0003] Diethylene glycol (DEG) is an important indicator of the degree of etherification side reaction in the production of polyester. The presence of diethylene glycol to some extent destroys the regularity of the arrangement of polyester macromolecular chains, thereby reducing the strength of the macromolecular chains and leading to a decrease in the mechanical strength, melting point and ultraviolet resistance of the polyester. Therefore, reducing the diethylene glycol content in the polyester is one of the problems that the polyester industry needs to overcome.

[0004] Chinese patent CN109206596A discloses a method for preparing polyester with low diethylene glycol content, in which ethylene glycol terephthalate is used as a polyester raw material to reduce the diethylene glycol content in the polyester. The disadvantage is that the obtained polyester product has insufficient activity, and the cost of ethylene glycol terephthalate raw material is relatively high.

[0005] Chinese patent CN106459389A discloses a polyester and a method for preparing the polyester, in which an additive such as an alkaline compound or an alkaline alkali metal salt is added during the esterification of the polyester. The presence of metal ions can affect the crystallization properties of the polyester, thereby limiting subsequent applications, and the metal ions can also affect the polycondensation process of the polyester. SUMMARY

[0006] To solve the above problems, the present application provides a method for preparing polyester with low diethylene glycol content. The present application adds an appropriate amount of diethylene glycol inhibitor to the reaction system, which on the one hand solves the problem that the high diethylene glycol content in the polyester material affects the performance of the polyester material and is not conducive to the further application of the polyester material, and on the other hand ensures the activity and color of the polyester material, so that the polyester product has good quality.

[0007] First, one of the objects of the present application is to provide a method for preparing polyester with low diethylene glycol content.

[0008] Specifically, the method comprises the following steps: using components including a dicarboxylic acid and a dihydric alcohol as raw materials, and reacting under the condition of adding a diethylene glycol inhibitor to obtain the polyester with low diethylene glycol content, wherein the diethylene glycol inhibitor is an acetal compound.

[0009] It is worth mentioning that by introducing a diethylene glycol inhibitor into the reaction system for generating polyester, this invention effectively inhibits the etherification side reaction, reduces the content of etherification byproducts in polyester products, and significantly improves the performance and quality of polyester materials.

[0010] Preferably, the dicarboxylic acid is at least one of an aromatic dicarboxylic acid or a heterocyclic dicarboxylic acid.

[0011] More preferably, the aromatic dicarboxylic acid is an aromatic dicarboxylic acid containing 8 to 16 carbon atoms. It should be noted that the carbon atom number mentioned here refers to the carbon atom number of the entire aromatic dicarboxylic acid. Particularly preferably, the aromatic dicarboxylic acid is at least one selected from terephthalic acid, isophthalic acid, phthalic acid, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 2,2'-biphenyldicarboxylic acid.

[0012] More preferably, the heterocyclic dicarboxylic acid is a heterocyclic dicarboxylic acid containing 4 to 7 carbon atoms. It should be noted that the carbon atom number mentioned here refers to the total number of carbon atoms in the entire heterocyclic dicarboxylic acid. Particularly preferably, the heterocyclic dicarboxylic acid is furanyl dicarboxylic acid.

[0013] Preferably, the diol is an alkylene glycol; more preferably, it is at least one of ethylene glycol and propylene glycol.

[0014] Preferably, the diethylene glycol inhibitor is a cyclic acetal compound; particularly preferably, it is at least one of 1,3-dioxane-2-methanol and 2-methyl-1,3-dioxolane. It is worth mentioning that the cyclic acetal compound used in this invention undergoes hydrolysis under the action of hydrogen ions during the esterification stage of the polyester reaction, reducing the acidity of the reaction system, inhibiting the activity of the etherification side reaction, and reducing the formation of etherification products.

[0015] Preferably, the molar ratio of dicarboxylic acid to diol is 1:1.3 to 1.8; more preferably, it is 1:1.4 to 1.6. The two raw materials need to be kept within an appropriate ratio range. If the alcohol-acid ratio is too high, it will lead to a higher content of etherification side reactions; if it is too low, it will affect the activity of the polyester esterification reaction.

[0016] Preferably, the amount of diethylene glycol inhibitor added is 0.1 to 3‰ based on the weight of the polyester produced, more preferably 0.1 to 2‰, and particularly preferably 0.5 to 1‰.

[0017] Furthermore, the reaction system for preparing polyester also includes a catalyst.

[0018] Specifically, the preparation method of low diethylene glycol content polyester includes the following steps: using components including dicarboxylic acids and diols as raw materials, carrying out an esterification reaction in the presence of a catalyst and a diethylene glycol inhibitor to obtain an esterification product; and then carrying out a polycondensation reaction to obtain the low diethylene glycol content polyester.

[0019] Preferably, the catalyst is at least one of antimony-based catalysts and titanium-based catalysts; more preferably, it is at least one of antimony glycolate, antimony acetate, antimony trioxide, tetraisopropyl titanate, and tetrabutyl titanate.

[0020] The amount of catalyst added in the technical solution of the present invention is determined based on the amount of active metal in the catalyst.

[0021] Specifically, when using an antimony-based catalyst, the weight of antimony atoms in the added antimony-based catalyst is 50 to 500 ppm based on the weight of the polyester produced; preferably 200 to 250 ppm. When using a titanium-based catalyst, the weight of titanium atoms in the added titanium-based catalyst is 2 to 20 ppm based on the weight of the polyester produced; preferably 5 to 10 ppm.

[0022] Furthermore, the esterification reaction conditions are as follows: reaction temperature is 240–260℃, preferably 250–255℃; reaction pressure is 0.1–0.35 MPa, preferably 0.2–0.28℃; and reaction time is 90–130 min, preferably 100–120 min.

[0023] Furthermore, the conditions for the polycondensation reaction are as follows: the reaction temperature is 230–280℃, preferably 250–280℃; the reaction pressure is 0–0.5 MPa, preferably 0–150 Pa; and the reaction time is 60–180 min, preferably 100–120 min.

[0024] Secondly, a second objective of this invention is to provide a polyester with low diethylene glycol content obtained by the preparation method of one objective of this invention. The polyester provided by this invention has a diethylene glycol content of less than or equal to 5%; preferably less than or equal to 3.5%; more preferably less than or equal to 2.5%.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention effectively inhibits the etherification side reaction during polyester production by adding a special compound, namely a diethylene glycol inhibitor, to the reaction system for polyester production. This reduces the content of etherification byproducts in the polyester product, effectively improving the thermodynamic properties of the polyester material. At the same time, it also ensures the intrinsic viscosity and color of the polyester material, giving it better quality. This solves the problem that the poor thermodynamic properties and color differences of polyester limit the application of polyester products.

[0027] 2. This invention obtains high-quality polyester products by adding a special compound, namely a diethylene glycol inhibitor, to the reaction system for generating polyester. The process is simple and easy to implement. At the same time, it avoids the problem of adding additives to the system, which affects the crystallization performance of polyester and the quality of the product, thus limiting the application of polyester materials. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0029] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] In the polyester reaction system of the present invention, the amounts of the diethylene glycol inhibitor, the catalyst, and other components are all based on the weight of the generated polyester. It should be noted that the weight of the generated polyester refers to the weight of the polyester theoretically generated by the esterification of dicarboxylic acid and diol, and this theoretically generated polyester weight is determined based on the amount of raw materials.

[0031] In the embodiments and comparative examples of the invention, the raw materials are all derived from commercially available products.

[0032] The methods used in the performance tests of the embodiments and comparative examples in the invention are as follows:

[0033] Colorimetric analysis: The colorimetric properties of the polyester chips were tested according to the 5.5 colorimetric test method in GB / T 14190-2017, the analytical method for fiber-grade polyester chips. The dried polyester chips were heated at 135±5℃ for 60 min to crystallize them. After cooling, the L, a, and b values ​​were measured using a color-view colorimeter from BYK Gardner, Germany.

[0034] Intrinsic viscosity: The intrinsic viscosity of polyester chips was analyzed according to the test method of 5.1 intrinsic viscosity in GB / T 14190-2017, the analytical method for fiber-grade polyester chips. The solvent was a mixture of phenol and tetrachloroethane (chemically pure) (mass ratio 1:1), the test temperature was 25℃, and the polyester solution concentration was 0.005 g / mL.

[0035] Melting point: DSC testing of the mixture was performed using a Discovery DSC-type TA instrument. 3-10 mg of sample was taken and heated from 40°C to 300°C at a rate of 10°C / min. The heating process was conducted in an N2 atmosphere at a flow rate of 50 mL / min. Temperature (or time) curves corresponding to the heat flow at the respective heating rates were collected for each sample.

[0036] Diethylene glycol content: The diethylene glycol content of polyester chips is analyzed according to the test method for diethylene glycol in section 5.2 of GB / T 14190-2017.

[0037] Example 1

[0038] 500 g (3 mol) of terephthalic acid, 316 g (5.1 mol, 1.7 eq) of ethylene glycol, 0.207 g of antimony glycolate catalyst (based on the weight of the generated polyester, the weight of antimony atoms is 200 ppm), and 0.0578 g of 1,3-dioxane-2-methanol (based on 0.1‰ of the weight of the generated polyester, purchased from Beijing Wokai Biotechnology Co., Ltd.) were mixed to form a slurry, which was then added to a polymerization reactor for esterification. The esterification temperature was 255℃, the pressure was 0.25 MPa, and the time was 120 min. The water generated in the reaction was discharged through a distillation apparatus. After esterification, the pressure was reduced to atmospheric pressure, and then vacuumed until the system pressure was below 150 Pa. At the same time, the reaction temperature was gradually increased to 280℃. The reaction was stopped after 120 min. The reaction product was then extruded from the bottom of the polymerization reactor, cooled, and pelletized to obtain the polyester product.

[0039] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0040] Example 2

[0041] In this embodiment, the polyester preparation method is basically the same as that in Example 1, except that 0.1156g of 1,3-dioxane-2-methanol (based on 0.2‰ of the weight of the polyester produced) is added.

[0042] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0043] Example 3

[0044] In this embodiment, the polyester preparation method is basically the same as that in Example 1, except that 0.289 g of 1,3-dioxane-2-methanol (based on 0.5‰ of the weight of the polyester produced) was added.

[0045] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0046] Example 4

[0047] In this embodiment, the polyester preparation method is basically the same as that in Example 1, except that 0.578g of 1,3-dioxane-2-methanol (based on 1‰ of the weight of the polyester produced) is added.

[0048] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0049] Example 5

[0050] In this embodiment, the polyester preparation method is basically the same as that in Example 1, except that 1.156g of 1,3-dioxane-2-methanol (based on 2‰ of the weight of the polyester produced) was added.

[0051] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0052] Example 6

[0053] In this embodiment, the preparation method of polyester is basically the same as that of polyester in Example 1. The difference is that in this embodiment, 1.734g of 1,3-dioxane-2-methanol (3‰ of the polyester weight) is added as an inhibitor to obtain the polyester product.

[0054] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0055] Example 7

[0056] In this embodiment, the polyester preparation method is basically the same as that in Example 1, except that 0.578g of 2-methyl-1,3-dioxolane (purchased from Beijing Wokai Biotechnology Co., Ltd., based on 1‰ of the weight of the polyester produced) was added.

[0057] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0058] Example 8

[0059] In this embodiment, the polyester preparation method is basically the same as that in Example 4, except that 0.259g of antimony glycol catalyst is added (based on the weight of the generated polyester, the weight of antimony atoms is 250ppm).

[0060] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0061] Example 9

[0062] In this embodiment, the polyester preparation method is basically the same as that in Example 4, except that the esterification temperature is 260°C and the pressure is 0.28 MPa.

[0063] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0064] Example 10

[0065] In this embodiment, the polyester preparation method is basically the same as that in Example 4, except that the polycondensation temperature in this embodiment is 270°C.

[0066] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0067] Example 11

[0068] In this embodiment, the polyester preparation method is basically the same as that in Example 4, except that the raw materials added in this embodiment are furan dicarboxylic acid and ethylene glycol (molar ratio 1:1.4).

[0069] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0070] Example 12

[0071] 500 g (3 mol) of terephthalic acid, 316 g (5.1 mol, 1.7 eq) of ethylene glycol, 1.435 g of a tetraisopropyl titanate catalyst solution in ethylene glycol (tetraisopropyl titanate concentration 1 wt%, titanium atom weight 5 ppm based on the weight of the generated polyester), and 0.578 g of 1,3-dioxane-2-methanol (1.0‰ based on the weight of the generated polyester, purchased from Beijing Wokai Biotechnology Co., Ltd.) were mixed to form a slurry, which was then added to a polymerization reactor for esterification. The esterification temperature was 255℃, the pressure was 0.25 MPa, and the time was 120 min. The water generated in the reaction was discharged through a distillation apparatus. After esterification, the pressure was reduced to atmospheric pressure, and then vacuumed until the system pressure was below 150 Pa. At the same time, the reaction temperature was gradually increased to 280℃. The reaction was stopped after 120 min. The reaction product was then extruded from the bottom of the polymerization reactor, cooled, and pelletized to obtain the polyester product.

[0072] The performance of the polyester material prepared in this embodiment was tested, and the test results are detailed in Table 1.

[0073] Comparative Example 1

[0074] In this comparative example, the polyester preparation method is basically the same as that in Example 1, except that the inhibitor 1,3-dioxane-2-methanol was not added in this comparative example.

[0075] The performance of the polyester material prepared in this comparative example was tested, and the test results are detailed in Table 1.

[0076] Comparative Example 2

[0077] In this comparative example, the preparation method of the polyester is basically the same as that of the polyester preparation method in Example 1. The difference is that the inhibitor added in this comparative example is 0.112g of sodium acetate (based on 0.2‰ of the weight of the polyester produced, purchased from Beijing Wokai Biotechnology Co., Ltd.).

[0078] The performance of the polyester material prepared in this comparative example was tested, and the test results are detailed in Table 1.

[0079] Comparative Example 3

[0080] In this comparative example, the polyester preparation method is basically the same as that in Example 11, except that the inhibitor 1,3-dioxane-2-methanol was not added in this comparative example.

[0081] The performance of the polyester material prepared in this comparative example was tested, and the test results are detailed in Table 1.

[0082] The intrinsic viscosity, hue (Lb), melting point, and diethylene glycol content of the polyester materials prepared in Examples 1-12 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1 below.

[0083] Table 1:

[0084] Auxiliaries Addition amount in ‰ Diethylene glycol content in % Intrinsic viscosity in dL / g Hue L b ]] Melting point in °C Example 1 1,3-dioxolane-2-methanol 0.1 3.4 0.676 2.9 244.4 Example 2 1,3-dioxolane-2-methanol 0.2 3.2 0.697 2.4 245.9 Example 3 1,3-dioxolane-2-methanol 0.5 2.6 0.685 2.8 248.8 Example 4 1,3-dioxolane-2-methanol 1.0 1.8 0.671 2.8 250.7 Example 5 1,3-dioxolane-2-methanol 2.0 2.9 0.661 3.1 247.3 Example 6 1,3-dioxolane-2-methanol 3.0 2.5 0.513 3.2 249.2 Example 7 2-methyl-1,3-dioxolane 1.0 3.0 0.632 3.0 246.7 Example 8 1,3-dioxolane-2-methanol 1.0 1.9 0.732 3.4 250.2 Example 9 1,3-dioxolane-2-methanol 1.0 2.2 0.680 3.2 249.5 Example 10 1,3-dioxolane-2-methanol 1.0 1.9 0.608 2.8 249.8 Example 11 1,3-dioxolane-2-methanol 1.0 4.8 0.532 18.3 214.2 Example 12 1,3-dioxolane-2-methanol 1.0 1.4 0.676 5.8 253.2 Comparative Example 1 / / 5.4 0.678 3.0 239.8 Comparative Example 2 Sodium acetate 0.2 2.6 0.711 4.1 249.6 Comparative Example 3 / / 5.6 0.522 17.6 210.8

[0085] According to the data in Table 1, in the preparation of polyester materials, the reaction system using aromatic dicarboxylic acids and ethylene glycol as raw materials, after adding a diethylene glycol inhibitor, resulted in polyester materials with a diethylene glycol content of only 1.8-3.4% (Examples 1-10), while the polyester materials prepared without the addition of a diethylene glycol inhibitor contained 5.4% diethylene glycol (Comparative Example 1). It is evident that the diethylene glycol inhibitor provided by this invention can significantly inhibit the etherification side reaction in the above reaction system, reducing the diethylene glycol content in the polyester materials. The melting point data shows that the reduction in diethylene glycol content improves the thermodynamic properties of the polyester materials. Simultaneously, the intrinsic viscosity and color data indicate that the above polyester materials possess good activity and color.

[0086] Furthermore, comparing the polyester materials obtained in Examples 1-10 with those obtained in Comparative Example 2, it can be seen that when sodium acetate is added as a diethylene glycol inhibitor to the reaction system of Comparative Example 2, although the diethylene glycol content in the polyester material can be significantly reduced (2.6%), the color data shows that even adding only 0.2‰ sodium acetate will significantly affect the color of the polyester material. Therefore, the diethylene glycol inhibitor provided by this invention can better preserve the color of the polyester material and will not affect the quality of the polyester product.

[0087] Furthermore, as shown in Table 1, in the preparation of polyester materials, the reaction system using heterocyclic dicarboxylic acids and ethylene glycol as raw materials, after adding a diethylene glycol inhibitor, resulted in a diethylene glycol content of 4.8% in the obtained polyester material (Example 11), while the polyester material prepared without adding a diethylene glycol inhibitor contained 5.6% diethylene glycol (Comparative Example 3). This demonstrates that when the raw material is a heterocyclic dicarboxylic acid, the diethylene glycol inhibitor provided by this invention can also inhibit the etherification side reaction in the above reaction system, reduce the diethylene glycol content in the polyester material, and improve the thermodynamic properties of the polyester material. Furthermore, due to the high hue value of furanyl dicarboxylic acid itself, the hue value of the polyester material after preparation is also high.

[0088] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a polyester with low diethylene glycol content, comprising the following steps: The polyester with low diethylene glycol content is obtained by reacting components including dicarboxylic acids and diols under the condition of adding a diethylene glycol inhibitor; the diethylene glycol inhibitor is an acetal compound.

2. The method for preparing low diethylene glycol content polyester according to claim 1, characterized in that, The dicarboxylic acid is at least one of an aromatic dicarboxylic acid or a heterocyclic dicarboxylic acid; and / or The diol is an alkylene glycol; and / or, The diethylene glycol inhibitor is a cyclic acetal compound.

3. The method for preparing low diethylene glycol content polyester according to claim 2, characterized in that, The aromatic dicarboxylic acid is an aromatic dicarboxylic acid containing 8 to 16 carbon atoms; and / or, The heterocyclic dicarboxylic acid is a heterocyclic dicarboxylic acid containing 4 to 7 carbon atoms.

4. The method for preparing low diethylene glycol content polyester according to claim 3, characterized in that, The aromatic dicarboxylic acid is at least one selected from terephthalic acid, isophthalic acid, phthalic acid, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenylenedicarboxylic acid, and 2,2'-biphenylenedicarboxylic acid; and / or, The heterocyclic dicarboxylic acid is furanyl dicarboxylic acid; and / or... The diol is at least one of ethylene glycol and propylene glycol; and / or, The diethylene glycol inhibitor is at least one of 1,3-dioxane-2-methanol and 2-methyl-1,3-dioxolane.

5. The method for preparing low diethylene glycol content polyester according to claim 1, characterized in that, The molar ratio of the added dicarboxylic acid to diol is 1:1.3 to 1.8; preferably 1:1.4 to 1.

6.

6. The method for preparing low diethylene glycol content polyester according to claim 1, characterized in that, The weight of the added diethylene glycol inhibitor is 0.1 to 3‰ based on the weight of the polyester produced; preferably 0.1 to 2‰; more preferably 0.5 to 1‰.

7. The method for preparing low diethylene glycol content polyester according to any one of claims 1 to 6, characterized in that, The reaction system also includes a catalyst; preferably, the method includes the following steps: using components including dicarboxylic acids and diols as raw materials, carrying out an esterification reaction in the presence of a catalyst and a diethylene glycol inhibitor to obtain an esterified product; and then carrying out a polycondensation reaction to obtain the polyester with low diethylene glycol content.

8. The method for preparing low diethylene glycol content polyester according to claim 7, characterized in that, The catalyst is at least one of antimony-based catalysts and titanium-based catalysts.

9. The method for preparing low diethylene glycol content polyester according to claim 8, characterized in that, The catalyst is at least one of antimony glycolate, antimony acetate, antimony trioxide, tetraisopropyl titanate, and tetrabutyl titanate.

10. The method for preparing low diethylene glycol content polyester according to claim 8, characterized in that, Based on the weight of the generated polyester, The added antimony catalyst contains 50–500 ppm of antimony atoms by weight; preferably 200–250 ppm; and / or, The titanium-based catalyst added contains titanium atoms in a weight of 2 to 20 ppm; preferably 5 to 10 ppm.

11. The method for preparing low diethylene glycol content polyester according to claim 7, characterized in that, The esterification reaction conditions are: a reaction temperature of 240–260°C, a reaction pressure of 0.1–0.35 MPa, and a reaction time of 90–130 min; preferably: a reaction temperature of 250–255°C, a reaction pressure of 0.2–0.28 MPa, and a reaction time of 100–120 min; and / or, The conditions for the polycondensation reaction are: reaction temperature of 230-280℃, reaction pressure of 0-0.5MPa, and reaction time of 60-180min; preferably: reaction temperature of 250-280℃, reaction pressure of 0-150Pa, and reaction time of 100-120min.

12. The polyester obtained by the preparation method according to any one of claims 1 to 11, wherein the weight percentage of diethylene glycol in the polyester is less than or equal to 5%; preferably less than or equal to 3.5%, more preferably less than or equal to 2.5%.