Copolymerization preparation method of polyethylene glycol terephthalate polyester

Abstract

The invention relates to the technical field of copolymerization preparation of polyethylene glycol terephthalate polyester, and discloses a copolymerization preparation method of polyethylene glycol terephthalate polyester, which comprises an esterification reaction, the preparation method comprises the following steps: adding 100 parts of purified terephthalic acid, 40-60 parts of ethylene glycol, 3-15 parts of at least one dihydric alcohol comonomer except EG, and 0.03-0.08 part of a composite catalyst into a reaction kettle, gradually heating to 240-260 DEG C under the protection of nitrogen, and reacting until the esterification rate is greater than or equal to 96% under the pressure of 0.2-0.4 MPa; transferring the product to a pre-polycondensation kettle, adding a heat stabilizer, and reacting for 30-60 minutes at the temperature of 250-265 DEG C and the vacuum degree of less than or equal to 5kPa; according to the invention, through multi-dimensional process optimization, the technical bottlenecks of traditional copolymerized PET in the aspects of monomer synergy, catalytic efficiency, thermal stability and mass transfer efficiency are solved, and an efficient path is provided for industrial production of high-performance polyester materials.

Description

Technical Field

[0001] The present invention relates to the technical field of copolymerization preparation of polyethylene terephthalate polyester, and particularly to a method for copolymerization preparation of polyethylene terephthalate polyester. Background Art

[0002] Polyethylene terephthalate (PET), as an important thermoplastic polyester, is widely used in fields such as packaging, textiles, and electronics. However, traditional PET has defects such as slow crystallization rate, insufficient heat resistance, and limited flexibility. Introducing functional monomers through copolymer modification is a key way to improve its performance. In the prior art, the copolymerization preparation of PET mainly faces the following technical bottlenecks: Traditional copolymerization processes mostly use a single diol monomer (such as ethylene glycol mono-substitute), and it is difficult to achieve multi-dimensional performance optimization. For example, the single introduction of neopentyl glycol can improve the flexibility of the chain segment, but the improvement of heat resistance is limited; the single use of 1,4-cyclohexanedimethanol can enhance rigidity and heat resistance, but it may lead to difficulties in regulating the melt viscosity. In addition, the difference in the reactivity ratios of different monomers easily causes uneven composition distribution, affecting the uniformity of the product performance.

[0003] Conventional catalysts (such as single antimony-based or titanium-based catalysts) have problems of insufficient activity or poor selectivity. Although the antimony-based catalyst has high stability, its catalytic efficiency is relatively low, and high-temperature and long-time reactions are required; the titanium-based catalyst has high activity but is prone to side reactions (such as thermal oxidative degradation), resulting in yellowing of the product hue and wide molecular weight distribution. How to balance catalytic efficiency and side reaction control is one of the difficulties in the existing processes.

[0004] In the polycondensation stage, especially in a high-temperature and high-vacuum environment, the PET chain segments are prone to thermal oxidative degradation, resulting in a decrease in molecular weight and difficulty in meeting the target intrinsic viscosity. Traditional heat stabilizers (such as single phosphate esters) have insufficient dispersibility, and the addition timing has a significant impact on stability. In addition, the existing processes lack effective means for dynamically inhibiting degradation and are difficult to accurately control the stability of chain segments in the middle stage of polycondensation.

[0005] Traditional polycondensation reactors (such as tower or kettle reactors) have problems of long melt residence time and low mass transfer efficiency, resulting in incomplete removal of small molecule by-products (such as water and ethylene glycol), affecting the improvement of intrinsic viscosity. Especially in the final polycondensation stage, it is difficult to achieve uniform mixing under the high viscosity state of the melt, which is prone to local overheating or uneven molecular weight distribution.

[0006] In summary, we propose a method for copolymerization preparation of polyethylene terephthalate polyester to solve the above problems. Summary of the Invention

[0007] The method for copolymerization preparation of polyethylene terephthalate polyester proposed by the present invention solves the problems in the background art.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A method for copolymerizing polyethylene terephthalate polyester, comprising the following steps: (1) Esterification reaction: By weight, 100 parts of purified terephthalic acid (PTA), 40 - 60 parts of ethylene glycol (EG), 3 - 15 parts of at least one diol comonomer other than EG, and 0.03 - 0.08 parts of a composite catalyst are added to a reaction kettle. Under nitrogen protection, the temperature is gradually raised to 240 - 260 °C, the pressure is 0.2 - 0.4 MPa, and the reaction is carried out until the esterification rate ≥ 96%; (2) Pre - polycondensation reaction: The product of step (1) is transferred to a pre - polycondensation kettle, and 0.01 - 0.05 parts by weight of a heat stabilizer is added. The reaction is carried out at a vacuum degree ≤ 5 kPa and a temperature of 250 - 265 °C for 30 - 60 min; The heat stabilizer is added in two times during the pre - polycondensation stage. 70% of the total amount is added for the first time, and the remaining 30% is added when the pre - polycondensation proceeds to 15 - 20 min; (3) Multi - stage polycondensation reaction: First - stage polycondensation: The reaction is carried out at a vacuum degree of 0.5 - 1.5 kPa and a temperature of 265 - 275 °C for 20 - 40 min. A gradient cooling program is started 10 min before the end of the reaction: The initial temperature T1 = 273 ± 2 °C, and the temperature is decreased to the final temperature T2 = 268 ± 2 °C at a rate of 3 - 5 °C / min. The vacuum degree is maintained at 0.8 - 1.2 kPa during the cooling process; Second - stage polycondensation: The reaction is carried out at a vacuum degree ≤ 0.3 kPa and a temperature of 275 - 285 °C. When the melt intrinsic viscosity reaches 0.68 - 0.72 dL / g, a trace amount of CO2 gas is introduced into the system at a flow rate of 0.5 - 2 L / min, and the reaction is carried out until the melt intrinsic viscosity ≥ 0.65 dL / g; (4) Final polycondensation and pelletizing: The melt is transported to a disk - ring reactor, and polycondensation is carried out at a vacuum degree ≤ 50 Pa and a temperature of 280 - 290 °C until the intrinsic viscosity ≥ 0.75 dL / g. After underwater pelletizing, crystallization and drying, a copolyester product is obtained.

[0009] Optionally, the diol comonomer other than ethylene glycol is selected from at least one of 1,4 - cyclohexanedimethanol, 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol, and neopentyl glycol.

[0010] Optionally, the comonomer comprises a combination of 1,4 - cyclohexanedimethanol and 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol, and the weight ratio of 1,4 - cyclohexanedimethanol to 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol in the comonomer is (1:2) - (2:1).

[0011] Optionally, the composite catalyst comprises the following raw materials by weight: Antimony glycolate: 0.015 - 0.056 parts Tetrabutyl titanate: 0.0045 - 0.020 parts Cobalt acetate: 0.0015 - 0.012 parts Sodium acetate: 0.0009 - 0.008 parts.

[0012] Optionally, the heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is (1:1) - (1:2).

[0013] Optionally, in the second - stage polycondensation of step (3), the introduced CO2 makes the volume concentration of CO2 in the reaction system reach 15 - 25%.

[0014] Optionally, in step (4), a rotating scraping film device is arranged in the disk - ring reactor, the rotation speed is 30 - 100 rpm, the melt film - forming thickness ≤ 0.5 mm, and the residence time is controlled within 15 - 25 min.

[0015] Optionally, in step (4), an on - line viscometer is arranged at the inlet of the disk - ring reactor to monitor the melt viscosity in real time and feedback to adjust the reactor temperature, and the temperature control accuracy is ±1℃.

[0016] The beneficial effects of the present invention are as follows: By compounding 1,4 - cyclohexanedimethanol and 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol, through the synergistic effect of the rigid ring structure and the steric hindrance group, the heat resistance (the glass transition temperature is increased by 10 - 15℃) and processing fluidity of the polyester are balanced, and at the same time, the crystallization rate is improved.

[0017] By adopting a quaternary catalyst system composed of antimony glycolate, tetrabutyl titanate, cobalt acetate and sodium acetate, significant advantages are shown in the preparation of polyester copolymerization. It can significantly optimize the product quality from multiple dimensions, effectively regulate the molecular structure, greatly reduce the product hue, make the product color more pure, at the same time reduce the content of diethylene glycol, improve the product purity and stability; in terms of reaction efficiency, the quaternary catalyst exerts strong catalytic activity, significantly shortens the esterification reaction time, accelerates the reaction process, greatly improves the production efficiency, reduces energy consumption and costs, and brings higher economic benefits and quality guarantee for the preparation of polyester copolymerization.

[0018] The compound of triphenyl phosphite and trimethyl phosphate is added in portions in the pre - polycondensation stage. In the initial stage, free radicals are quickly captured, and in the middle stage, the continuous oxidation in the polycondensation process is supplemented and inhibited; in the middle stage of the second - stage polycondensation, a small amount of CO2 is introduced. By inhibiting the thermal decomposition of the ester group through a weak acidic environment, the time for the intrinsic viscosity to reach the standard is shortened by 10 - 15 min, and at the same time, the yellowness index is reduced by 2 - 3 units.

[0019] The film thickness of the melt is controlled to be ≤0.5 mm by a rotating scraping film device, which greatly increases the gas-liquid interface area, improves the small molecule removal efficiency by 30%-40%, shortens the terminal polycondensation residence time to 15-25 min, and simultaneously realizes the precise regulation of the intrinsic viscosity.

[0020] Through multi-dimensional process optimization, the present invention solves the technical bottlenecks of traditional copolyester PET in terms of monomer synergy, catalytic efficiency, thermal stability and mass transfer efficiency, and provides an efficient path for the industrial production of high-performance polyester materials. Detailed implementation mode

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0022] Example 1 A copolymerization preparation method of polyethylene terephthalate polyester, comprising the following steps: (1) Esterification reaction: By weight, 100 parts of purified terephthalic acid (PTA), 40 parts of ethylene glycol (EG), 3 parts of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), and a composite catalyst containing the following raw materials by weight: antimony glycolate: 0.015 parts, tetrabutyl titanate: 0.005 parts, cobalt acetate: 0.007 parts, sodium acetate: 0.003 parts are added to the reaction kettle, and gradually heated to 240 °C under nitrogen protection, with a pressure of 0.2 MPa, and reacted until the esterification rate reaches 96.2%; (2) Pre-polycondensation reaction: The product of step (1) is transferred to a pre-polycondensation kettle, 0.01 part by weight of a heat stabilizer is added, and the reaction is carried out at a vacuum degree of 5 kPa and a temperature of 255 °C for 30 min; the heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is (1:1). The heat stabilizer is added in two times during the pre-polycondensation stage, 70% of the total amount is added for the first time, and the remaining 30% is added in the middle stage of the pre-polycondensation; (3) Multi-stage polycondensation reaction: The first-stage polycondensation: The reaction is carried out at a vacuum degree of 1.5 kPa and a temperature of 270 °C for 20 min. 10 minutes before the end of the first-stage polycondensation, the reaction temperature is adjusted by a gradient cooling program: the initial temperature T1 = 273 °C, and the temperature is decreased at a rate of 5 °C / min, and the final temperature T2 = 268 °C. The vacuum degree is maintained at 0.8 kPa during the cooling process, so that the growth rate of the melt apparent viscosity is controlled at 0.01 dL / g·min -1 ; Second - stage polycondensation: React at a vacuum degree of 0.3 kPa and a temperature of 278 °C until the melt intrinsic viscosity reaches 0.68 dL / g; when the melt intrinsic viscosity reaches 0.68 dL / g, introduce a trace amount of CO2 gas into the system at a flow rate of 2 L / min for 5 min to inhibit thermal degradation, and the introduced CO2 makes the CO2 volume concentration in the reaction system reach 15%; (4) Final polycondensation and pelletizing: Transport the melt to a disk - ring reactor, and carry out polycondensation at a vacuum degree of 50 Pa and a temperature of 285 °C until the intrinsic viscosity reaches 0.75 dL / g. A rotating scraping film device is set in the disk - ring reactor with a rotation speed of 30 rpm, the melt film thickness is 0.5 mm, and the residence time is controlled at 15 min. After underwater pelletizing and crystallization drying, a copolyester product is obtained. The product indexes are: intrinsic viscosity 0.76 dL / g, Ð_M = 2.4, and terminal carboxyl group 28 mol / t.

[0023] Example 2 A method for copolymerizing and preparing polyethylene terephthalate polyester, comprising the following steps: (1) Esterification reaction: By weight, add 100 parts of purified terephthalic acid (PTA), 50 parts of ethylene glycol (EG), copolymer monomers: 3 parts of CHDM, 6 parts of TMCD, and a composite catalyst containing the following raw materials by weight: 0.050 parts of antimony glycolate, 0.01 part of tetrabutyl titanate, 0.012 parts of cobalt acetate, and 0.008 parts of sodium acetate into the reaction kettle. Gradually heat up to 250 °C under nitrogen protection, with a pressure of 0.3 MPa, and react until the esterification rate reaches 97.5%; (2) Pre - polycondensation reaction: Transfer the product of step (1) to a pre - polycondensation kettle, add 0.03 parts of heat stabilizer, and react at a vacuum degree of 0.3 kPa and a temperature of 260 °C for 45 min; the heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is 1:1.5. The heat stabilizer is added in two times during the pre - polycondensation stage. 70% of the total amount is added for the first time, and the remaining 30% is added in the middle of the pre - polycondensation; (3) Multi - stage polycondensation reaction: First - stage polycondensation: React at a vacuum degree of 1.0 kPa and a temperature of 272 °C for 30 min. 10 minutes before the end of the first - stage polycondensation, adjust the reaction temperature with a gradient cooling program: the initial temperature T1 = 271 °C, cool at a rate of 3 °C / min, and the final temperature T2 = 268 °C. The vacuum degree is maintained at 1.0 kPa during the cooling process; Second - stage polycondensation: React at a vacuum degree of 0.2 kPa and a temperature of 280 °C until the melt intrinsic viscosity reaches 70 dL / g, then introduce a trace amount of CO2 gas into the system at a flow rate of 1 L / min for 10 min to inhibit thermal degradation, and the introduced CO2 makes the CO2 volume concentration in the reaction system reach 18%; (4) Final polycondensation and pelletizing: The melt is transported to a disk-ring reactor and polycondensed to an intrinsic viscosity of 0.78 dL / g under a vacuum of 30 Pa and a temperature of 285 °C. A rotating scraping film device is installed in the disk-ring reactor with a rotation speed of 70 rpm. The melt forms a film with a thickness of 0.3 mm, and the residence time is controlled at 20 min. After underwater pelletizing and crystallization drying, a copolyester product is obtained. Product indicators: intrinsic viscosity 0.80 dL / g, Ð_M = 2.1, end carboxyl group 18 mol / t.

[0024] Example 3 A copolymerization preparation method of polyethylene terephthalate polyester, comprising the following steps: (1) Esterification reaction: By weight, 100 parts of purified terephthalic acid (PTA), 60 parts of ethylene glycol (EG), a comonomer: 15 parts of neopentyl glycol (NPG), and a composite catalyst containing the following raw materials by weight: antimony glycolate: 0.036 parts, tetrabutyl titanate: 0.012 parts, cobalt acetate: 0.007 parts, sodium acetate: 0.005 parts are added to a reaction kettle. Under nitrogen protection, the temperature is gradually raised to 260 °C and the pressure is 0.2 MPa, and the reaction proceeds until the esterification rate reaches 98.1%; catalyst: 0.04 parts of antimony glycolate + 0.01 parts of tetrabutyl titanate.

[0025] (2) Pre-polycondensation reaction: The product of step (1) is transferred to a pre-polycondensation kettle, and 0.05 parts of a heat stabilizer is added. The reaction is carried out at a vacuum of 1 kPa and a temperature of 265 °C for 60 min; the heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is 1:2. The heat stabilizer is added in two times during the pre-polycondensation stage. 70% of the total amount is added for the first time, and the remaining 30% is added in the middle of the pre-polycondensation; (3) Multi-stage polycondensation reaction: First-stage polycondensation: The reaction is carried out at a vacuum of 0.5 kPa and a temperature of 275 °C for 40 min. 10 minutes before the end of the first-stage polycondensation, the reaction temperature is adjusted by a gradient cooling program: the initial temperature T1 = 275 °C, and the temperature is decreased at a rate of 4 °C / min, and the final temperature T2 = 270 °C. The vacuum is maintained at 1.2 kPa during the cooling process; Second-stage polycondensation: When the melt reaches an intrinsic viscosity of 0.72 dL / g at a vacuum of 0.1 kPa and a temperature of 285 °C, a trace amount of CO2 gas is introduced into the system at a flow rate of 0.5 / min for 15 min to inhibit thermal degradation. The introduced CO2 makes the CO2 volume concentration in the reaction system reach 20%; (4) Final polycondensation and pelletizing: The melt is transported to a disk-ring reactor and polycondensed to an intrinsic viscosity of 0.82 dL / g under a vacuum of 10 Pa and a temperature of 290 °C. A rotating scraping film device is provided in the disk-ring reactor with a rotation speed of 30 rpm. The film thickness of the melt is 0.2 mm, and the residence time is controlled at 25 min. After underwater pelletizing, crystallization and drying, a copolyester product is obtained with an intrinsic viscosity of 0.83 dL / g, Ð_M = 2.3, and T_g = 92 °C.

[0026] Example 4 A method for copolymerizing poly(ethylene terephthalate) polyester, comprising the following steps: (1) Esterification reaction: By weight, 100 parts of purified terephthalic acid (PTA), 45 parts of ethylene glycol (EG), comonomers: 4 parts of CHDM and 4 parts of TMCD, and a composite catalyst containing the following raw materials by weight: 0.056 parts of antimony glycolate, 0.0112 parts of tetrabutyl titanate, 0.016 parts of cobalt acetate, and 0.008 parts of sodium acetate are added to a reaction kettle. Under nitrogen protection, the temperature is gradually raised to 240 °C and the pressure is 0.35 MPa, and the reaction proceeds until the esterification rate reaches 96.8%; (2) Pre-polycondensation reaction: The product of step (1) is transferred to a pre-polycondensation kettle, and 0.02 parts by weight of a heat stabilizer is added. The reaction is carried out at a vacuum of 4 kPa and a temperature of 250 °C for 45 min; the heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is 1:1. The heat stabilizer is added in two times during the pre-polycondensation stage. 70% of the total amount is added for the first time, and the remaining 30% is added in the middle of the pre-polycondensation; (3) Multi-stage polycondensation reaction: First-stage polycondensation: The reaction is carried out at a vacuum of 1.2 kPa and a temperature of 265 °C for 25 min. 10 minutes before the end of the first-stage polycondensation, the reaction temperature is adjusted by a gradient cooling program: the initial temperature T1 = 270 °C, and the temperature is decreased at a rate of 5 °C / min, and the final temperature T2 = 266 °C. The vacuum of 1.2 kPa is maintained during the cooling process, and CO2 is introduced to make the volume concentration of CO2 in the reaction system reach 22%; Second-stage polycondensation: When the melt reaches an intrinsic viscosity of 0.69 dL / g at a vacuum of 0.25 kPa and a temperature of 275 °C, a trace amount of CO2 gas is introduced into the system at a flow rate of 1.5 L / min and continued for 8 min to inhibit thermal degradation; (4) Final polycondensation and pelletizing: The melt is transported to a disk-ring reactor and polycondensed to an intrinsic viscosity of 0.77 dL / g under a vacuum of 40 Pa and a temperature of 280 °C. A rotating scraping film device is provided in the disk-ring reactor with a rotation speed of 50 rpm. The film thickness of the melt is 0.4 mm, and the residence time is controlled at 18 min. After underwater pelletizing, crystallization and drying, a copolyester product is obtained. Product indexes: intrinsic viscosity 0.79 dL / g, Ð_M = 2.0, YI = 1.8.

[0027] Example 5 A copolymerization preparation method of polyethylene terephthalate polyester, comprising the following steps: (1) Esterification reaction: By weight, 100 parts of purified terephthalic acid (PTA), 55 parts of ethylene glycol (EG), comonomers: 8 parts of CHDM + 4 parts of TMCD, and a composite catalyst comprising the following raw materials by weight: 0.04 parts of antimony glycolate, 0.009 parts of tetrabutyl titanate, 0.01 parts of cobalt acetate, and 0.001 parts of sodium acetate are added to the reaction kettle, and the temperature is gradually raised to 255 °C under nitrogen protection, the pressure is 0.25 MPa, and the reaction is carried out until the esterification rate reaches 97.9%; (2) Pre-polycondensation reaction: The product of step (1) is transferred to a pre-polycondensation kettle, and 0.04 parts by weight of a heat stabilizer is added, and the reaction is carried out at a vacuum degree of 2 kPa and a temperature of 263 °C for 50 min; the heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is 1:1.8. The heat stabilizer is added in two times during the pre-polycondensation stage, 70% of the total amount is added for the first time, and the remaining 30% is added in the middle of the pre-polycondensation; (3) Multi-stage polycondensation reaction: First-stage polycondensation: The reaction is carried out at a vacuum degree of 0.8 kPa and a temperature of 268 °C for 35 min. 10 minutes before the end of the first-stage polycondensation, the reaction temperature is adjusted by a gradient cooling program: the initial temperature T1 = 274 °C, the temperature is decreased at a rate of 3 °C / min, and the final temperature T2 = 270 °C. The vacuum degree of 0.8 kPa is maintained during the cooling process; Second-stage polycondensation: When the reaction is carried out at a vacuum degree of 0.15 kPa and a temperature of 282 °C until the melt intrinsic viscosity reaches 0.71 dL / g, a trace amount of CO2 gas is introduced into the system at a flow rate of 0.8 L / min and continued for 12 min to inhibit thermal degradation. The introduced CO2 makes the CO2 volume concentration in the reaction system reach 25%; (4) Final polycondensation and pelletizing: The melt is transported to a disk-ring reactor, and polycondensation is carried out at a vacuum degree of 20 Pa and a temperature of 288 °C until the intrinsic viscosity reaches 0.81 dL / g. A rotating scraping film device is arranged in the disk-ring reactor, the rotation speed is 90 rpm, the melt film thickness is 0.35 mm, and the residence time is controlled at 22 min. After underwater pelletizing, crystallization and drying, a copolyester product is obtained. Product indexes: intrinsic viscosity 0.83 dL / g, Ð_M = 1.9, [COOH] = 14 mol / t.

[0028] The following designs 4 groups of comparative examples and 5 examples for comparative experiments. Experimental design principle: Controlled variables: Fix the basic formula (100 parts of PTA, 50 parts of EG, 8 parts of TMCD) Testing standards: Intrinsic viscosity: ISO 1628-5 Molecular weight distribution (Ð_M): GPC (Waters 1515) Terminal carboxyl content: ISO 2114 Yellowness Index (YI): ASTM E31 Comparative Example 1: This comparative example differs from Example 2 only in that there is no composite catalyst (only 0.05 parts of antimony glycolate); Comparative Example 2: The difference between this comparative example and Example 2 is that the heat stabilizer is added at one time.

[0029] Comparative Example 3: The difference between this comparative example and Example 2 is that the gradient cooling is cancelled (constant 275° C.).

[0030] Comparative Example 4: This comparative example differs from Example 2 only in that there is no CO2 protection.

[0031] Comparative Example 5: The only difference between this comparative example and Example 2 is that the composite catalyst does not contain cobalt acetate and sodium acetate (only 0.05 parts of antimony ethylene glycol + 0.01 parts of tetrabutyl titanate).

[0032] Comparative Example 6: The only difference between this comparative example and Example 2 is that the composite catalyst does not contain cobalt acetate (0.05 parts of antimony ethylene glycol + 0.01 parts of tetrabutyl titanate + 0.008 parts of sodium acetate).

[0033] The experimental data are shown in the following table:

[0034] The present invention achieves a breakthrough optimization of polyester copolymerization preparation through the deep synergy of four core innovations: composite catalyst system, gradient cooling program, CO2 protection technology and stabilizer segmented addition. Its technical effect is significantly better than that of traditional processes, which is specifically reflected in the following aspects: 1. Revolutionary upgrade of catalytic system The four-way catalytic system composed of antimony glycol, tetrabutyl titanate, cobalt acetate and sodium acetate solves the industry problem that traditional antimony / titanium catalysts are difficult to balance activity and product quality: Hue optimization: Cobalt acetate chelates quinone chromophores, reducing the b value of the product from 6.2 in comparative example 5 to 3.8 (a decrease of 38.7%), breaking through the bottleneck of yellowing of copolyester; Side reaction inhibition: Sodium acetate selectively neutralizes the acidic byproducts, reducing the content of diethylene glycol (DEG) from 1.5wt% in Comparative Example 6 to 1.0wt% (a decrease of 33.3%), significantly reducing the risk of hydrolysis; Synergistic Catalytic Enhancement: The quaternary system shortens the esterification time to 135 minutes (a 25.8% reduction compared to the antimony / titanium binary system), the terminal carboxyl group content is as low as 18 mol / t (a 57% reduction compared to single-antimony catalysis), and the thermal weight loss rate is only 0.32% / h (an optimization of 54.3% compared to the binary system), achieving triple breakthroughs of "high activity - low side reactions - excellent stability".

[0035] II. Precise Synergy in Process Control. Four major process innovation points form a degradation inhibition network through sequential linkage: Gradient cooling program (at the end of the first-stage polycondensation): Under precise temperature control from 273°C to 268°C, high-activity short chains selectively terminate, and long chains continue to grow, narrowing the molecular weight distribution (Ð_M) from 2.7 in Comparative Example 3 to 2.1 (a 22.2% reduction), reaching the medical-grade polyester level; introducing CO2 to form a weak acidic microenvironment, significantly reducing the thermal weight loss rate from 0.85% / h in Comparative Example 4 to 0.32% / h (a 62.4% reduction) and shortening the polycondensation time by 12 minutes; Stabilizer added in stages (in the pre-polycondensation stage): 70% initially added to capture free radicals, 30% added in the middle to block oxidation, reducing the b value by 27% (from 5.2 to 3.8) compared to one-time addition (Comparative Example 2) and reducing the terminal carboxyl group by 31%; When the four processes are implemented simultaneously (Example 2), the product simultaneously achieves: Ð_M ≤ 2.1 (↑ molecular weight uniformity), thermal weight loss rate ≤ 0.32% / h (↑ thermal stability), b value ≤ 3.8 (↑ color quality), breaking through the traditional paradox of "the increase in molecular weight must be accompanied by increased degradation".

[0036] It should be noted that the composite catalytic system (antimony glycolate / tetrabutyl titanate) reduces the terminal carboxyl group content by 57% (from 42 to 18 mol / t) compared to single-antimony catalysis, and the yellowness index decreases by 78%; The gradient cooling program suppresses local overheating at the end of polycondensation, optimizing the molecular weight distribution Ð_M from 2.7 at a constant temperature to 2.1, and reducing the GPC half-peak width by 35%; The CO2 protection technology is introduced in the critical viscosity range (0.68 - 0.72 dL / g), reducing the high-temperature thermal weight loss rate from 0.85% / h to 0.32% / h and blocking the oxidative degradation chain reaction; Adding the stabilizer in stages reduces the yellowness index by 53% (from 3.2 to 1.5) compared to one-time addition, and simultaneously reduces the terminal carboxyl group by 31%. Each technical feature has a strict sequential correlation and non-linear synergistic effect - When the four elements are implemented simultaneously, the molecular weight uniformity (Ð_M ≤ 2.1), thermal stability (thermal weight loss rate ≤ 0.32% / h), and color (YI ≤ 1.5) of the product all break through the bottlenecks of the existing technology (industry premium product standard: Ð_M < 2.5, thermal weight loss rate < 0.8% / h), proving that the process design of the present invention has outstanding creativity and industrial practicality.

[0037] In the present invention, 1,4-cyclohexanedimethanol (CHDM) and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBT) are compounded in a specific ratio (weight ratio 1:2-2:1), and the rigid alicyclic structure and steric hindrance group of the two form "molecular synergy": the cyclohexyl ring of CHDM improves the rigidity of the chain segment, so that the glass transition temperature (Tg) of the copolyester is 12-15℃ higher than that of traditional PET, and the heat deformation resistance is enhanced; the tetramethylcyclobutyl of CBT inhibits the excessive stacking of the chain segment through the steric hindrance effect, while improving the crystallization rate (half crystallization time is shortened by 25%), avoiding the problem of a sudden increase in melt viscosity caused by a single rigid monomer, so that the processing fluidity of the copolyester (melt flow rate increased by 15%) and dimensional stability are balanced. This "rigid and flexible complementary" molecular design breaks through the performance ceiling of traditional single monomer modification, especially the creep resistance in high temperature environment is improved by more than 30% compared with commercially available copolymer PET.

[0038] The composite catalyst formed by compounding ethylene glycol antimony and tetrabutyl titanate at a ratio of 3:1-5:1 cleverly combines the stability of antimony catalysts with the high activity of titanium catalysts: ethylene glycol antimony provides stable esterification catalytic sites, inhibits the formation of side reactions (ether bond content is 60% lower than that of single titanium catalyst), and ensures that the esterification rate quickly exceeds 96%; the Lewis acid sites of tetrabutyl titanate accelerate the transesterification reaction, shortening the esterification reaction time by 20% compared with the traditional single antimony catalyst. Under the synergistic effect of the two, the catalytic efficiency is improved while achieving "selective catalysis" - the selectivity of ester bond formation reaches 98.5%, which is 5 percentage points higher than the existing technology, reducing the interference of impurity segments on subsequent polycondensation reactions from the source, laying the foundation for uniform molecular weight growth.

[0039] Among them, 70% triphenyl phosphite and trimethyl phosphate compound stabilizer was added for the first time in the pre-condensation stage to quickly capture the free radicals generated by the initial high temperature and inhibit the yellowing of the melt; the remaining 30% stabilizer was added in the middle stage to continuously neutralize the trace oxygen caused by the increase in vacuum during the condensation process, reducing the degree of thermal oxidation degradation in the entire condensation stage by 40%. More importantly, when the intrinsic viscosity of the melt reaches 0.68-0.72dL / g, a trace amount of CO2 (0.5-2L / min) is introduced, and the weak acidic environment of CO2 (local pH value drops by 0.3-0.5) is used to reversibly inhibit the thermal decomposition of ester groups. This "gas-liquid interface microenvironment regulation" method was unexpectedly found to shorten the time to reach the intrinsic viscosity standard by 12 minutes, and at the same time reduce the product yellowness index (b value) from 8-10 in the traditional process to 5-6, solving the long-standing contradiction of "molecular weight growth and color control are difficult to achieve at the same time" in the high-temperature condensation process.

[0040] In addition, gradient cooling is implemented 10 minutes before the end of the first-stage polycondensation (initially at 273 ± 2 °C, cooled to 268 ± 2 °C at a rate of 4 °C / min, and the vacuum degree is maintained at 0.8 - 1.2 kPa). This seemingly "counterintuitive" operation (usually, the polycondensation reaction requires heating to increase activity) unexpectedly achieves "narrowing of the molecular weight distribution": during the cooling process, the highly active short-chain segments preferentially terminate the reaction, and the long-chain segments continue to grow due to the kinetic energy advantage, reducing the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) (PDI) from 2.5 - 3.0 in the traditional process to 1.8 - 2.0, approaching the narrow distribution level of biodegradable polyesters. This mechanism of "screening chain segments through kinetic differences" provides a low-cost solution for preparing polyesters for high-end fibers (requiring PDI ≤ 2.0).

[0041] Furthermore, the rotary scraping film device (rotation speed 30 - 100 rpm, film-forming thickness ≤ 0.5 mm) converts the "melt mass mixing" in the traditional kettle reactor into "thin-film state high-efficiency mass transfer", increasing the removal efficiency of small-molecule by-products (water, EG) in the final polycondensation stage by 40%, and shortening the residence time of the melt in the reactor from 40 - 60 min in the traditional process to 15 - 25 min. More importantly, the contact area between the thin-film state melt and the vacuum environment expands by more than 3 times, stably increasing the intrinsic viscosity (η) from 0.70 - 0.75 dL / g in the traditional process to 0.75 - 0.85 dL / g, and the fluctuation range ≤ ±0.02 dL / g, which is especially suitable for preparing high-viscosity polyesters for bottles (requiring η ≥ 0.78 dL / g), solving the long-standing industry problem of "difficult coexistence of high viscosity and uniformity". Through in-depth innovation in four dimensions: molecular structure, catalytic efficiency, process control, and equipment mass transfer, the present invention not only breaks through the performance bottleneck of traditional PET copolymer modification, but also achieves a leap-forward progress in industrial production efficiency, product quality stability, and adaptability to high-end applications.

[0042] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for copolymerizing polyethylene terephthalate polyester, characterized in that, It includes the following steps: (1) Esterification reaction: By weight, 100 parts of purified terephthalic acid (PTA), 40 - 60 parts of ethylene glycol (EG), 3 - 15 parts of at least one diol comonomer other than EG, and 0.03 - 0.08 parts of a composite catalyst are added to a reaction kettle. Under nitrogen protection, the temperature is gradually raised to 240 - 260 °C, the pressure is 0.2 - 0.4 MPa, and the reaction proceeds until the esterification rate ≥ 96%; (2) Pre - polycondensation reaction: The product of step (1) is transferred to a pre - polycondensation kettle, and 0.01 - 0.05 parts by weight of a heat stabilizer is added. The reaction is carried out at a vacuum degree ≤ 5 kPa and a temperature of 250 - 265 °C for 30 - 60 min; The heat stabilizer is added in two times during the pre - polycondensation stage. 70% of the total amount is added for the first time, and the remaining 30% is added when the pre - polycondensation proceeds to 15 - 20 min; (3) Multi - stage polycondensation reaction: The first - stage polycondensation: The reaction is carried out at a vacuum degree of 0.5 - 1.5 kPa and a temperature of 265 - 275 °C for 20 - 40 min. A gradient cooling program is started 10 min before the end of the reaction: The initial temperature T1 = 273 ± 2 °C, and the temperature is decreased to the final temperature T2 = 268 ± 2 °C at a rate of 3 - 5 °C / min. The vacuum degree is maintained at 0.8 - 1.2 kPa during the cooling process; The second - stage polycondensation: The reaction is carried out at a vacuum degree ≤ 0.3 kPa and a temperature of 275 - 285 °C. When the melt intrinsic viscosity reaches 0.68 - 0.72 dL / g, a trace amount of CO2 gas is introduced into the system at a flow rate of 0.5 - 2 L / min, and the reaction proceeds until the melt intrinsic viscosity ≥ 0.65 dL / g; (4) Final polycondensation and pelletizing: The melt is transported to a disk - ring reactor and polycondensed at a vacuum degree ≤ 50 Pa and a temperature of 280 - 290 °C until the intrinsic viscosity ≥ 0.75 dL / g. After underwater pelletizing, crystallization and drying, a copolyester product is obtained.

2. The copolymerization preparation method of the polyethylene terephthalate polyester according to claim 1, characterized in that, The diol comonomer other than ethylene glycol is selected from at least one of 1,4 - cyclohexanedimethanol, 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol, and neopentyl glycol.

3. The copolymerization preparation method of polyethylene terephthalate polyester according to claim 1, characterized in that, The comonomer contains a combination of 1,4 - cyclohexanedimethanol and 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol, and the weight ratio of 1,4 - cyclohexanedimethanol to 2,2,4,4 - tetramethyl - 1,3 - cyclobutanediol in the comonomer is (1:2) - (2:1).

4. The copolymerization preparation method of polyethylene terephthalate polyester according to claim 1, characterized in that, The composite catalyst contains the following raw materials by weight: Antimony glycolate: 0.015 - 0.056 parts Tetrabutyl titanate: 0.0045 - 0.020 parts Cobalt acetate: 0.0015 - 0.012 parts Sodium acetate: 0.0009 - 0.008 parts.

5. The copolymerization preparation method of the polyethylene terephthalate polyester according to claim 1, characterized in that, The heat stabilizer is a compound of triphenyl phosphite and trimethyl phosphate, and the compounding weight ratio is (1:1) - (1:2).

6. The copolymerization preparation method of the polyethylene terephthalate polyester according to claim 1, characterized in that, In the second - stage polycondensation of step (3), the introduced CO2 makes the volume concentration of CO2 in the reaction system reach 15 - 25%.

7. The copolymerization preparation method of the polyethylene terephthalate polyester according to claim 1, characterized in that, In step (4), a rotating scraping film device is arranged in the disk - ring reactor, the rotation speed is 30 - 100 rpm, the film thickness of the melt is ≤ 0.5 mm, and the residence time is controlled within 15 - 25 min.

8. The method for copolymerizing and preparing polyethylene terephthalate polyester according to claim 1, characterized in that, In step (4), an on-line viscometer is set at the inlet of the disk-ring reactor to monitor the melt viscosity in real time and feedback to adjust the reactor temperature.

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