Polyester synthesis method based on titanium catalyst and spinning process using the polyester

Abstract

The application discloses a polyester synthesis method based on a titanium catalyst and a spinning process of the polyester. The synthesis method comprises the following steps: performing esterification reaction on purified terephthalic acid and ethylene glycol in an esterification reactor to generate an oligomer melt; then, the oligomer melt is sent to a pre-polycondensation reactor to perform pre-polycondensation reaction, so as to obtain a pre-polycondensation melt; then, the pre-polycondensation melt is sent to a final polycondensation reactor to perform final polycondensation reaction, so as to obtain a final polymer melt; a first injection point is arranged between a discharge pipeline of the esterification reactor and the pre-polycondensation reactor, and a titanium phosphine catalyst is injected in the form of a solution; and a second injection point is arranged between an outlet of the pre-polycondensation reactor and an inlet of the final polycondensation reactor, and a nano-silicon dioxide loaded titanium catalyst is added in the form of a solution. The application aims to guarantee the high-activity advantage of the titanium catalyst, effectively avoid the problems of high risk of hydrolysis inactivation and side reaction, and improve the spinning stability and quality.

Description

Technical Field

[0001] This application relates to the field of polyester materials, and in particular to a method for synthesizing polyester based on a titanium-based catalyst and a spinning process using the polyester. Background Technology

[0002] In the industrial synthesis of polyethylene terephthalate (PET), the catalyst is the core component driving the esterification and polycondensation reactions, and its performance directly affects the polymerization efficiency, product molecular weight distribution, and final spinning quality. Traditional antimony-based catalysts (such as antimony glycolate) exhibit good stability, but suffer from problems such as heavy metal residues, yellowish hue, and environmental toxicity, making it difficult to meet the increasingly stringent green requirements of high-end textiles and food-grade packaging. Titanium-based catalysts (such as tetrabutyl titanate) have become an ideal alternative due to their high catalytic activity, non-toxicity, and excellent polymerization rate; however, their strong Lewis acidity also brings significant drawbacks: on the one hand, they readily hydrolyze to form inactive TiO2 precipitates, and if added during the esterification stage in a conventional manner, the high water content in the system will lead to significant catalyst deactivation; on the other hand, excessively high reactivity easily triggers thermal degradation and side reactions, such as the dehydration of ethylene glycol to acetaldehyde, which in turn leads to polyester yellowing, gelation, and increased end-carboxyl group content. To mitigate these problems, existing technologies often employ ligands such as organophosphonic acids and alcohols to pre-complex with titanate esters to reduce their electron density and reactivity. However, such homogeneous complexes are still difficult to completely avoid hydrolysis and thermal degradation during high-temperature and long-term polycondensation. Especially under actual working conditions where moisture control is not perfect, residual active titanium species will continue to catalyze melt hydrolysis, causing molecular weight fluctuations and viscosity decreases, ultimately leading to increased spinning breakage rate and deterioration of fiber mechanical properties. Summary of the Invention

[0003] This application provides a method for synthesizing polyester based on a titanium-based catalyst and a spinning process using the polyester, aiming to ensure the high activity advantage of the titanium-based catalyst while effectively avoiding its hydrolysis deactivation and high risk of side reactions, thereby improving spinning stability and quality.

[0004] In a first aspect, this application provides a method for synthesizing polyester based on a titanium-based catalyst, comprising the following steps: Purified terephthalic acid and ethylene glycol are esterified in an esterification reactor to generate an oligomer melt. The oligomer melt is fed into a prepolymerization reactor for prepolymerization reaction to obtain prepolymerized melt; The prepolymer melt is fed into the final polymerization reactor for final polymerization reaction to obtain the final polymer melt. A first injection point is set between the discharge pipeline of the esterification reactor and the prepolymerization reactor, and a titanium phosphine catalyst accounting for 0.005 to 0.02 wt% of the PTA mass is injected in solution form. A second injection point is set between the outlet of the prepolymerization reactor and the inlet of the final polymerization reactor, and a co-catalyst of 0.001 to 0.005 wt% of the PTA mass is added in solution form. The co-catalyst is a titanium catalyst supported on nano-silica.

[0005] In any of the above technical solutions, the reaction temperature of the esterification reaction is 250-265℃ and the pressure is 0.05-0.3MPa.

[0006] In any of the above technical solutions, the esterification reaction takes 1.5 to 3.0 hours.

[0007] In any of the above technical solutions, the reaction temperature of the pre-condensation reaction is 265-275℃ and the pressure is 1-10kPa.

[0008] In any of the above technical solutions, the pre-condensation reaction time is 30 to 60 minutes.

[0009] In any of the above technical solutions, the reaction temperature of the final polycondensation reaction is 275-285℃ and the pressure is ≤50Pa.

[0010] In any of the above technical solutions, the time for the final polycondensation reaction is 60 to 120 minutes.

[0011] In any of the above technical solutions, the intrinsic viscosity of the prepolymer melt is 0.20 to 0.40 dL / g; the intrinsic viscosity of the final polymer is 0.62 to 0.68 dL / g, and the end carboxyl group content is ≤25 mol / t.

[0012] In any of the above technical solutions, the titanium phosphine catalyst is diluted with ethylene glycol to a solution of 50-200 ppm and injected into the first injection point in a pulsed or continuous manner using a metering pump.

[0013] This application effectively solves the balance between stability and activity in PET synthesis by controlling the addition site and morphology of titanium-based catalysts. Specifically, the main catalyst (titanium phosphine complex) is injected into the pipeline between the esterification outlet and the prepolymerization inlet. At this point, the moisture content of the system has dropped to a low level, and the melt is still in a low viscosity state, rich in terminal carboxyl and hydroxyl groups, providing an ideal environment for the rapid diffusion and efficient catalysis of the homogeneous titanium catalyst, thereby ensuring that the molecular weight steadily increases to 0.20–0.40 dL / g during the prepolymerization stage. At the same time, a second injection point is set between the prepolymerization outlet and the final polymerization inlet, introducing a titanium co-catalyst supported on nano-silica. This co-catalyst, due to its immobilization on an inorganic support, possesses excellent thermal stability and hydrolysis resistance, which can effectively compensate for the possible deactivation of the main catalyst in the high-temperature, high-viscosity melt, ensuring the efficient completion of the final polymerization reaction and obtaining high-quality PET with an intrinsic viscosity of 0.62–0.68 dL / g and terminal carboxyl groups ≤25 mol / t.

[0014] Crucially, the nano-silica particles are uniformly dispersed in the PET matrix after polymerization, which can serve as a highly efficient heterogeneous nucleating agent, significantly improving the crystallization rate and crystallinity. This overcomes the slow crystallization defect of traditional titanium-based PET, thereby improving fiber breaking strength and reducing fuzz and breakage.

[0015] In any of the above technical solutions, the titanium phosphine catalyst is a complex formed by titanate, aminophenylphosphonic acid ligand, and amino acid; the molar ratio of titanate to aminophenylphosphonic acid ligand and amino acid is 1:(1.0-1.5):(0.2-0.5).

[0016] In any of the above technical solutions, the aminophenylphosphonic acid ligand is 4-aminophenylphosphonic acid.

[0017] In any of the above technical solutions, the titanate ester is preferably tetrabutyl titanate.

[0018] In any of the above technical solutions, the amino acid is selected from at least one of glycine, alanine, or leucine.

[0019] The titanium phosphine catalyst used in this application employs 4-aminophenylphosphonic acid and small-molecule amino acids as composite ligands, exhibiting a synergistic effect. 4-Aminophenylphosphonic acid, with its aromatic ring structure, endows the complex with excellent hydrophobicity, effectively shielding the titanium center from water molecule attack and significantly enhancing the catalyst's resistance to hydrolysis in the early stages of polycondensation. However, the steric hindrance caused by its rigid benzene ring can prevent oligomer substrates such as BHET from approaching the titanium active center, leading to a decrease in catalytic efficiency. Therefore, this application introduces small-molecule amino acids such as glycine, alanine, or leucine as auxiliary ligands. Their small molecular size and high flexibility allow them to form additional coordination sites with titanium through amino and carboxyl groups without significantly increasing overall steric hindrance. This optimizes the electronic environment of the titanium center and opens up ligand space, providing channels for substrate molecules and effectively compensating for catalytic activity. More importantly, the combined participation of multiple coordination groups, including phosphonic acid, amino, and carboxyl groups, enables the titanium atoms to form a multidentate chelate structure, significantly enhancing the thermodynamic stability of the Ti-O bond, inhibiting ligand dissociation and titanium aggregation at high temperatures, and ensuring the catalyst's sustained high efficiency throughout the polycondensation process.

[0020] In any of the above technical solutions, the titanium catalyst supported on nano-silica is prepared by the following method: Using silicate compounds and epoxy-based silane coupling agents in a molar ratio of 1:(0.1–0.3) as raw materials, epoxy-based nano-silica was prepared by sol-gel method. Carboxyl-grafted nano-silica was prepared by ring-opening reaction of epoxy-containing nano-silica and carboxylic acid-containing ligands under an alkaline catalyst. The carboxyl-grafted nano-silica is obtained by coordinating it with titanate; The molar ratio of the carboxylic acid ligand to the epoxy group is (0.8-1.2):1, and the molar ratio of the titanate to the carboxylic acid ligand is 1:(1.0-1.3).

[0021] In any of the above technical solutions, the epoxy-based silane coupling agent is selected from... In any of the above technical solutions, the carboxylic acid ligand is selected from at least one of citric acid, oxalic acid, and gluconic acid.

[0022] This application further constructs a synergistic mechanism between the main catalyst and the co-catalyst. Specifically, during the preparation of the titanium catalyst supported on nano-silica, epoxy groups are introduced onto the surface through an epoxy-silane coupling agent, followed by the grafting of carboxylic acid ligands via a ring-opening reaction. This not only provides stable coordination sites for titanium but also constructs a reactive long-chain structure on the particle surface. Under the high-temperature, high-shear environment of the final polycondensation stage, the epoxy or hydroxyl groups on the surface of this co-catalyst can undergo ring-opening addition or coordination interactions with the free phosphonic acid groups, carboxyl groups, or amino groups retained in the titanium phosphine complex of the main catalyst due to excess ligands, forming extended long-chain segments on the surface of nano-silica. As the PET melt cools and crystallizes, these long-chain segments interweave and entangle with each other in the amorphous region, forming a slip-like network structure. When the fiber is stretched by external force, controllable slippage can occur between the interwoven segments, dissipating energy and significantly improving the elongation at break and toughness of the material. This achieves a good balance between rigidity and flexibility, effectively reducing the breakage rate during high-speed spinning and improving production efficiency and product quality.

[0023] Secondly, this application provides a spinning process that uses the final polymer melt described in any of the first aspects as raw material for melt direct spinning.

[0024] In summary, this application has the following beneficial effects: This application achieves a balance between high activity and high stability by segmenting the injection of a main titanium catalyst and a co-catalyst system. The main catalyst efficiently initiates polymerization in the low-moisture, low-viscosity stage, while the co-catalyst supplements activity and also functions as a nucleator in the high-viscosity stage, significantly improving polymerization stability and crystallization performance. Furthermore, the composite ligands used in the titanium phosphine catalyst balance hydrolysis resistance and catalytic efficiency, and the dynamic interpenetration structure between the two types of catalysts further endows the polyester fibers with excellent flexibility and spinning processability. Detailed Implementation

[0025] Preparation Example Preparation Example 1-1, titanium phosphine catalyst, was prepared according to the following steps: Under nitrogen protection, 10.0 g of tetrabutyl titanate (27.8 mmol), 150 mL of anhydrous ethylene glycol, and 6.32 g of 4-aminophenylphosphonic acid (33.4 mmol) were added to a three-necked flask equipped with a stirrer, reflux condenser, and thermometer. The temperature was raised to 80 °C, and the reaction was stirred for 1 hour to allow the phosphonic acid and titanate ester to fully coordinate and form a preliminary complex. Subsequently, 1.05 g of glycine (13.9 mmol) was added, and the reaction was continued at 80 °C for 2 hours. The system remained clear and transparent during the reaction. After cooling to room temperature, the solution was removed by vacuum distillation at 40 °C and ≤10 kPa. The product was filtered out, washed three times with deionized water, and then dried under vacuum at room temperature, pulverized, and ground to obtain the titanium phosphine catalyst.

[0026] Preparation Examples 1-2, titanium phosphine catalysts, were prepared according to the following steps: Under nitrogen protection, 15.0 g of tetrabutyl titanate (41.7 mmol), 90 mL of anhydrous ethylene glycol, and 4.21 g of 4-aminophenylphosphonic acid (22.2 mmol) were added to a three-necked flask equipped with a stirrer, reflux condenser, and thermometer. The temperature was raised to 75 °C, and the reaction was stirred for 1.5 hours to allow the phosphonic acid and titanate ester to fully coordinate and form a preliminary complex. Subsequently, 0.25 g of alanine (2.8 mmol) was added, and the reaction was continued at 75 °C for another 2.5 hours. The system remained clear and transparent during the reaction. After cooling to room temperature, the solution was removed by vacuum distillation at 50 °C and ≤15 kPa. The product was filtered out, washed three times with deionized water, and then dried under vacuum at room temperature, pulverized, and ground to obtain the titanium phosphine catalyst.

[0027] Preparation Examples 1-3, titanium phosphine catalysts, were prepared according to the following steps: Under nitrogen protection, 15.0 g of tetrabutyl titanate (41.7 mmol), 200 mL of anhydrous ethylene glycol, and 9.48 g of 4-aminophenylphosphonic acid (50.0 mmol) were added to a three-necked flask equipped with a stirrer, reflux condenser, and thermometer. The temperature was raised to 85 °C, and the reaction was stirred for 1 hour to allow the phosphonic acid and titanate ester to fully coordinate and form a preliminary complex. Subsequently, 1.05 g of glycine (13.9 mmol) was added, and the reaction was continued at 80 °C for 2 hours. The system remained clear and transparent during the reaction. After cooling to room temperature, the solution was removed by vacuum distillation at 40 °C and ≤10 kPa. The product was filtered out, washed three times with deionized water, and then dried under vacuum at room temperature, pulverized, and ground to obtain the titanium phosphine catalyst.

[0028] Preparation Examples 1-4, titanium phosphine catalysts, differ from Preparation Example 1-1 in that glycine is replaced with an equimolar amount of 4-aminophenylphosphonic acid.

[0029] Preparation Examples 1-5, titanium phosphine catalysts, differ from Preparation Example 1-1 in that 4-aminophenylphosphine is replaced with an equimolar amount of glycine.

[0030] Preparation Example 2-1: Nano-silica supported titanium catalyst, prepared by the following method: Under nitrogen protection, 20.8 g of tetraethyl orthosilicate (100 mmol), 150 mL of anhydrous ethanol, and 18 mL of deionized water were added to a three-necked flask. 5 mL of ammonia (25 wt%) was slowly added dropwise as an alkaline catalyst with stirring, and the reaction was carried out at 25 °C for 2 hours to form a primary SiO2 sol. Subsequently, 4.47 g of 3-glycidyl etheroxypropyltrimethoxysilane (20 mmol) was added, and the temperature was raised to 50 °C, and the reaction continued for 4 hours to allow the epoxy-containing silanes to co-hydrolyze and condense into the SiO2 network, yielding an epoxy-containing nano-silica dispersion (average particle size approximately 22 nm). The solid was collected by centrifugation, washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 12 hours to obtain epoxy-containing nano-silica powder.

[0031] The epoxy-containing nano-silica powder prepared above was dispersed in 80 mL of deionized water, 2.10 g of citric acid (10.9 mmol) was added, and sodium hydroxide was added to adjust the pH of the system to 9-10. The mixture was stirred at 70 °C for 4 hours. After the reaction was completed, the mixture was centrifuged, washed with deionized water until neutral (pH≈7), and dried at 60 °C to obtain carboxyl-grafted nano-silica powder.

[0032] The carboxyl-grafted nano-silica powder prepared above was dispersed in 100 mL of anhydrous ethylene glycol, and 1.79 g of tetrabutyl titanate (5.0 mmol) was slowly added dropwise under a nitrogen atmosphere. The mixture was heated to 85 °C and reacted for 2 hours. After cooling, the product was filtered out, washed three times with deionized water, and then vacuum dried, pulverized, and ground at room temperature to obtain the final product.

[0033] Preparation Example 2-2: Nano-silica supported titanium catalyst, prepared by the following method: Under nitrogen protection, 10.4 g of tetraethyl orthosilicate (50 mmol), 100 mL of anhydrous ethanol, and 10 mL of deionized water were added to a three-necked flask. 2.5 mL of ammonia (25 wt%) was slowly added dropwise as an alkaline catalyst with stirring, and the reaction was carried out at 25 °C for 1.5 hours to form a primary SiO2 sol. Subsequently, 1.12 g of 3-glycidyl etheroxypropyltrimethoxysilane (5 mmol) was added, and the temperature was raised to 50 °C, and the reaction continued for 5 hours to allow the epoxy-containing silanes to co-hydrolyze and condense into the SiO2 network, yielding an epoxy-containing nano-silica dispersion (average particle size approximately 20 nm). The solid was collected by centrifugation, washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 12 hours to obtain epoxy-containing nano-silica powder.

[0034] The epoxy-containing nano-silica powder prepared above was dispersed in 50 mL of deionized water, 0.86 g of citric acid (4.5 mmol) was added, and sodium hydroxide was added to adjust the pH of the system to 9-10. The mixture was stirred at 65 °C for 5 hours. After the reaction was completed, the mixture was centrifuged, washed with deionized water until neutral (pH≈7), and dried at 60 °C to obtain carboxyl-grafted nano-silica powder.

[0035] The carboxyl-grafted nano-silica powder prepared above was dispersed in 60 mL of anhydrous ethylene glycol, and 0.72 g of tetrabutyl titanate (2.0 mmol) was slowly added dropwise under a nitrogen atmosphere. The mixture was heated to 80 °C and reacted for 2.5 hours. After cooling, the product was filtered out, washed three times with deionized water, and then vacuum dried, pulverized, and ground at room temperature to obtain the final product.

[0036] Preparation Examples 2-3: Nano-silica supported titanium catalyst, prepared by the following method: Under nitrogen protection, 31.2 g of tetraethyl orthosilicate (150 mmol), 150 mL of anhydrous ethanol, and 27 mL of deionized water were added to a three-necked flask. 7.5 mL of ammonia (25 wt%) was slowly added dropwise as an alkaline catalyst with stirring, and the reaction was carried out at 25 °C for 2 hours to form a primary SiO2 sol. Subsequently, 9.4 g of 3-glycidyl etheroxypropyltrimethoxysilane (42 mmol) was added, and the temperature was raised to 55 °C, and the reaction continued for 3 hours to allow the epoxy-containing silanes to co-hydrolyze and condense into the SiO2 network, yielding an epoxy-containing nano-silica dispersion (average particle size approximately 28 nm). The solid was collected by centrifugation, washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 12 hours to obtain epoxy-containing nano-silica powder.

[0037] The epoxy-containing nano-silica powder prepared above was dispersed in 100 mL of deionized water, 3.86 g of citric acid (20 mmol) was added, and sodium hydroxide was added to adjust the pH of the system to 9-10. The mixture was stirred at 75 °C for 3 hours. After the reaction was completed, the mixture was centrifuged, washed with deionized water until neutral (pH≈7), and dried at 60 °C to obtain carboxyl-grafted nano-silica powder.

[0038] The carboxyl-grafted nano-silica powder prepared above was dispersed in 150 mL of anhydrous ethylene glycol, and 3.22 g of tetrabutyl titanate (9.0 mmol) was slowly added dropwise under a nitrogen atmosphere. The mixture was heated to 85 °C and reacted for 2 hours. After cooling, the product was filtered out, washed three times with deionized water, and then vacuum dried, pulverized, and ground at room temperature to obtain the final product.

[0039] Example Example 1: A method for synthesizing polyester based on a titanium-based catalyst, comprising the following steps: 166.1 g of purified terephthalic acid (1.0 mol) and 74.9 g of ethylene glycol (1.2 mol) were mixed in a slurry preparation tank to form a homogeneous slurry. The slurry was then fed into an esterification reactor and reacted at 260 °C and 0.15 MPa (absolute pressure) for 2.0 hours to produce an oligomer melt with a water content of 0.85 wt% in the discharge.

[0040] Before the melt is transported to the prepolymerization reactor via pipeline, a titanium phosphine catalyst solution (obtained in Preparation Example 1-1, diluted with ethylene glycol to a Ti concentration of 150 ppm) is injected at the first injection point, with an addition amount of 0.012 wt% of purified terephthalic acid. The melt enters the prepolymerization reactor and reacts at 270 °C and 5 kPa for 45 minutes to obtain a prepolymerization melt with an intrinsic viscosity of 0.30 dL / g.

[0041] Subsequently, before entering the final polycondensation reactor, a nano-silica-supported titanium catalyst suspension (obtained in Preparation Example 2-1, diluted with ethylene glycol to a Ti concentration of 180 ppm) was added at the second injection point to the melt at an amount of 0.003 wt% of the PTA mass. The melt entered the final polycondensation reactor and was subjected to polymerization at 280 °C and 40 Pa for 90 minutes to obtain the final polymer melt with an intrinsic viscosity of 0.65 dL / g and approximately 20 mol / t of terminal carboxyl groups. The moisture content of the entire polycondensation system was controlled to ≤25 ppm, and the process was carried out under nitrogen protection.

[0042] Example 2, a method for synthesizing polyester based on a titanium-based catalyst, includes the following steps: 166.1 g of purified terephthalic acid (1.0 mol) and 74.9 g of ethylene glycol (1.2 mol) were mixed in a slurry preparation tank to form a homogeneous slurry. The slurry was then fed into an esterification reactor and reacted at 252 °C and 0.18 MPa (absolute pressure) for 1.6 hours to produce an oligomer melt with a discharge water content of 0.9 wt%.

[0043] Before the melt is transported to the prepolymerization reactor via pipeline, a titanium phosphine catalyst solution (obtained in Preparation Examples 1-2, diluted with ethylene glycol to a Ti concentration of 100 ppm) is injected at the first injection point, with an addition amount of 0.006 wt% of purified terephthalic acid. The melt enters the prepolymerization reactor and reacts at 266 °C and 8 kPa for 35 minutes to obtain a prepolymerization melt with an intrinsic viscosity of 0.26 dL / g.

[0044] Subsequently, before entering the final polycondensation reactor, a nano-silica-supported titanium catalyst suspension (obtained in Preparation Example 2-2, diluted with ethylene glycol to a Ti concentration of 150 ppm) was added at the second injection point to the melt at an amount of 0.0012 wt% of the PTA mass. The melt entered the final polycondensation reactor and was subjected to polymerization at 276 °C and 48 Pa for 65 minutes to obtain the final polymer melt with an intrinsic viscosity of 0.63 dL / g and approximately 21 mol / t of terminal carboxyl groups. The moisture content of the entire polycondensation system was controlled to ≤25 ppm, and the process was carried out under nitrogen protection.

[0045] Example 3, a method for synthesizing polyester based on a titanium-based catalyst, comprising the following steps: 166.1 g of purified terephthalic acid (1.0 mol) and 74.9 g of ethylene glycol (1.2 mol) were mixed in a slurry preparation tank to form a homogeneous slurry. The slurry was then fed into an esterification reactor and reacted at 264 °C and 0.35 MPa (absolute pressure) for 2.8 hours to produce an oligomer melt with a discharge water content of 0.75 wt%.

[0046] Before the melt is transported to the prepolymerization reactor via pipeline, a titanium phosphine catalyst solution (obtained in Preparation Examples 1-3, diluted with ethylene glycol to a Ti concentration of 200 ppm) is injected at the first injection point, with an addition amount of 0.018 wt% of purified terephthalic acid. The melt enters the prepolymerization reactor and reacts at 274 °C and 5 kPa for 55 minutes to obtain a prepolymerization melt with an intrinsic viscosity of 0.38 dL / g.

[0047] Subsequently, before entering the final polycondensation reactor, a nano-silica-supported titanium catalyst suspension (obtained in Preparation Examples 2-3, diluted with ethylene glycol to a Ti concentration of 240 ppm) was added at the second injection point to the melt at an amount of 0.0045 wt% of the PTA mass. The melt entered the final polycondensation reactor and was subjected to polymerization at 284 °C and 30 Pa for 110 minutes to obtain the final polymer melt with an intrinsic viscosity of 0.67 dL / g and approximately 18 mol / t of terminal carboxyl groups. The moisture content of the entire polycondensation system was controlled to ≤25 ppm, and the process was carried out under nitrogen protection.

[0048] Example 4: A polyester synthesis method based on a titanium-based catalyst, differing from Example 1 in that an equal amount of the titanium phosphine catalyst prepared in Examples 1-4 is used instead of the titanium phosphine catalyst prepared in Example 1-1. The resulting final polymer melt.

[0049] Example 5: A polyester synthesis method based on a titanium-based catalyst, differing from Example 1 in that an equal amount of the titanium phosphine catalyst prepared in Examples 1-5 is used instead of the titanium phosphine catalyst prepared in Example 1-1. The resulting final polymer melt.

[0050] Comparative Example Comparative Example 1, a polyester synthesis method based on a titanium-based catalyst, differs from Example 1 in that, at the first injection point, an equal amount of the nano-silica-supported titanium catalyst obtained in Preparation Example 2-1 (diluted with ethylene glycol to a Ti concentration of 150 ppm) is used instead of the titanium phosphine catalyst obtained in Preparation Example 1-1. The resulting final polymer melt.

[0051] Comparative Example 2, a polyester synthesis method based on a titanium-based catalyst, differs from Example 1 in that, at the second injection point, an equal amount of the titanium phosphine catalyst obtained in Preparation Example 1-1 (diluted with ethylene glycol to a Ti concentration of 180 ppm) is used instead of the nano-silica-supported titanium catalyst obtained in Preparation Example 2-1. The resulting final polymer melt.

[0052] Comparative Example 3: A method for synthesizing polyester based on a titanium-based catalyst, comprising the following steps: 166.1 g of purified terephthalic acid (1.0 mol) and 74.9 g of ethylene glycol (1.2 mol) were mixed in a slurry preparation tank to form a homogeneous slurry. The slurry was then fed into an esterification reactor and reacted at 260 °C and 0.15 MPa (absolute pressure) for 2.0 hours to produce an oligomer melt with a water content of 0.85 wt% in the discharge.

[0053] Before the melt is transported to the prepolymerization reactor via pipeline, a titanium phosphine catalyst solution (obtained in Preparation Example 1-1, diluted with ethylene glycol to a Ti concentration of 150 ppm) is injected at the first injection point at an amount of 0.012 wt% of purified terephthalic acid. Then, a nano-silica-supported titanium catalyst suspension (obtained in Preparation Example 2-1, diluted with ethylene glycol to a Ti concentration of 180 ppm) is added at an amount of 0.003 wt% of PTA. The melt enters the prepolymerization reactor and reacts at 270 °C and 5 kPa for 45 minutes to obtain a prepolymerization melt with an intrinsic viscosity of 0.30 dL / g.

[0054] The melt enters the final polycondensation reactor and is carried out at 280°C and 40 Pa for 90 minutes to obtain the final polymer melt. The moisture content of the entire polycondensation system is controlled to ≤25ppm, and the process is carried out under nitrogen protection.

[0055] Performance testing Test 1: The intrinsic viscosity, terminal carboxyl group content, crystallization temperature, and color (b value) were tested according to the provisions of GB / T 14189-2015 "Fiber Grade Polyester Chips (PET)".

[0056] Sample preparation: The final polymer melts obtained in the examples and comparative examples were granulated underwater and dried (160°C, 4h) to obtain fiber-grade PET chips; the chips were sealed and stored, and the tests were completed within 24h.

[0057] 1. Determination of intrinsic viscosity: Weigh 0.1250g of slices, dissolve in 25mL of phenol / 1,1,2,2-tetrachloroethane (1:1, v / v) mixed solvent, keep at 25±0.05℃, measure with Ubbelohde viscometer, and calculate IV (dL / g) according to the formula.

[0058] 2. Determination of terminal carboxyl groups: Weigh 2.0 g of slices, dissolve them in 20 mL of phenol / chloroform (1:1) mixture, use bromophenol blue as an indicator, and titrate with 0.01 mol / L KOH-ethanol standard solution to a blue-green endpoint. Calculate the terminal carboxyl group content (mol / t).

[0059] 3. Colorimetric (b* value) test: Take a dried slice and lay it flat on a standard white board. Use a colorimeter, D65 light source, and 10° field of view to measure b* (yellow-blue color, the larger the positive value, the more yellow); measure 5 points for each sample and take the average value.

[0060] Experiment 2: Performance Testing of Polyester Filament Sample preparation: Polyester filament was prepared by melt spinning according to the following spinning process parameters: The moisture content of the dried slices is ≤30ppm; Screw extruder temperature: 285℃ (feed section) → 290℃ (compression section) → 295℃ (metering section); Component pressure: 8-10 MPa; Spinning speed: 4500 m / min; Cooling air temperature: 20±1℃, air humidity: 65±3%; Oiling rate: 0.6 wt% Winding tension: 0.08 cN / dtex.

[0061] 1. Spinning stability test Each sample group was spun continuously for 8 hours; the number of yarn breaks was recorded (unit: times).

[0062] 2. Mechanical property testing The breaking strength and tensile breaking length of chemical fiber filaments were determined according to GB / T 14344-2008 "Test Method for Tensile Properties of Chemical Fiber Filaments". The wound filaments were equilibrated for 24 hours under standard atmospheric conditions (20±2℃, 65±3% RH) using an electronic single-fiber tensile strength tester. The test conditions were: clamping distance 20mm, tensile speed 20mm / min; 50 filaments were tested, outliers were discarded, and the breaking strength (cN / dtex) and elongation at break (%) were calculated.

[0063] Table 1 Performance Test Results Analysis of Experimental Results Compared to Example 1, Example 4 showed poorer performance in intrinsic viscosity and terminal carboxyl group content, indicating that amino acids, as auxiliary ligands, play a crucial role in catalytic activity. This may be because, compared to 4-aminophenylphosphonic acid, smaller molecule amino acids have less steric hindrance, facilitating the proximity of BHET to the titanium center and compensating for catalytic activity. The absence of amino acids leads to a decreased probability of substrate-active site contact, incomplete polymerization, resulting in a lower intrinsic viscosity and increased terminal carboxyl group content in the final polymer.

[0064] Example 5 showed poor performance in terms of terminal carboxyl groups and b* value, indicating the crucial role of aminophenylphosphonic acid ligands in inhibiting hydrolysis and yellowing. This may be because the hydrophobicity of aminophenylphosphonic acid reduces water molecule attack; the absence of phosphonic acid leads to hydrolysis of the melt catalyzed by active titanium during polycondensation, resulting in a wider molecular weight distribution, increased side reactions, and the generation of colored groups such as acetaldehyde, thus increasing b*.

[0065] Compared to Example 1, Comparative Example 1 performed worse in all aspects, indicating that the first injection point setting and the titanium phosphine catalyst have a synergistic effect, significantly impacting catalytic performance, polyester quality, and spinning quality. This may be because the nano-silica-supported titanium catalyst is heterogeneous, resulting in slow diffusion and low contact efficiency at the first injection point (low-viscosity prepolymer melt), hindering the rapid establishment of polymerization kinetics and causing a decrease in intrinsic viscosity. Furthermore, the absence of a titanium phosphine catalyst prevents the grafting of long chain segments onto the surface of the nano-silica-supported titanium catalyst, thus hindering the formation of an interpenetrating structure. Consequently, the toughening effect cannot be effectively exerted, leading to a decrease in elongation at break.

[0066] Comparative Example 2 showed poor performance in color, mechanical strength, and breakage rate, indicating the necessity of setting a second injection point to supplement catalytic activity in the high-viscosity stage. This may be because the titanium phosphine catalyst has poor stability in the high-viscosity final polycondensation melt, and the ligands are prone to dissociation, leading to thermal degradation and side reactions, exacerbating yellowing. Simultaneously, the lack of nano-silica-supported titanium catalyst prevents it from playing a nucleation role in subsequent processes, resulting in decreased spinning breaking strength; it also fails to form an interpenetrating toughening structure, reducing elongation at break.

[0067] Compared to Example 1, Comparative Example 3 performed worse in all aspects, indicating that the two injection point settings and the two types of catalysts have a synergistic effect and must be matched one-to-one. This has a significant impact on catalytic performance, polyester quality, and spinning quality. The reason may be that if the nano-silica-supported titanium catalyst is added to the first injection point too early, it is prone to agglomeration with the titanium phosphine catalyst, which reduces the catalytic efficiency, increases the end carboxyl group content, and leads to a wider molecular weight distribution or the formation of oligomers. At the same time, the agglomerated catalyst prevents its nucleation and toughening effects from being effectively exerted, resulting in a decrease in spinning mechanical strength (breaking strength and elongation at break) and processing stability (breakage rate).

[0068] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for synthesizing polyester based on a titanium-based catalyst, characterized in that, Includes the following steps: Purified terephthalic acid and ethylene glycol are esterified in an esterification reactor to generate an oligomer melt. The oligomer melt is fed into a prepolymerization reactor for prepolymerization reaction to obtain prepolymerized melt; The prepolymer melt is fed into the final polymerization reactor for final polymerization reaction to obtain the final polymer melt. A first injection point is set between the discharge pipeline of the esterification reactor and the prepolymerization reactor, and a titanium phosphine catalyst accounting for 0.005 to 0.02 wt% of the PTA mass is injected in solution form. A second injection point is set between the outlet of the prepolymerization reactor and the inlet of the final polymerization reactor, and a co-catalyst of 0.001 to 0.005 wt% of the PTA mass is added in solution form. The co-catalyst is a titanium catalyst supported on nano-silica.

2. The polyester synthesis method according to claim 1, characterized in that, The esterification reaction is carried out at a temperature of 250–265°C and a pressure of 0.05–0.3 MPa.

3. The polyester synthesis method according to claim 1, characterized in that, The reaction temperature of the pre-condensation reaction is 265–275°C, and the pressure is 1–10 kPa.

4. The polyester synthesis method according to claim 1, characterized in that, The final polycondensation reaction is carried out at a temperature of 275–285°C and a pressure of ≤50 Pa.

5. The polyester synthesis method according to claim 1, characterized in that, The intrinsic viscosity of the prepolymer melt is 0.20–0.40 dL / g; the intrinsic viscosity of the final polymer melt is 0.62–0.68 dL / g, and the end carboxyl group content is ≤25 mol / t.

6. The polyester synthesis method according to claim 1, characterized in that, The titanium phosphine catalyst is diluted with ethylene glycol to a solution of 50–200 ppm and injected into the first injection point in a pulsed or continuous manner using a metering pump.

7. The polyester synthesis method according to claim 1, characterized in that, The titanium phosphine catalyst is a complex formed by titanate, aminophenylphosphonic acid ligand, and amino acid; the molar ratio of titanate to aminophenylphosphonic acid ligand and amino acid is 1:(1.0-1.5):(0.2-0.5).

8. The polyester synthesis method according to claim 1, characterized in that, The aminophenylphosphonic acid ligand is 4-aminophenylphosphonic acid.

9. The polyester synthesis method according to claim 1, characterized in that, The titanium catalyst supported on nano-silica was prepared by the following method: Using silicate compounds and epoxy-based silane coupling agents in a molar ratio of 1:(0.1–0.3) as raw materials, epoxy-based nano-silica was prepared by sol-gel method. Carboxyl-grafted nano-silica was prepared by ring-opening reaction of epoxy-containing nano-silica and carboxylic acid-containing ligands under an alkaline catalyst. The carboxyl-grafted nano-silica is obtained by coordinating it with titanate; The molar ratio of the carboxylic acid ligand to the epoxy group is (0.8-1.2):1, and the molar ratio of the titanate to the carboxylic acid ligand is 1:(1.0-1.3).

10. A spinning process, characterized in that, Using the final polymer melt described in any one of claims 1 to 9 as raw material, melt spinning is performed.

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