Composite catalyst for synthesizing polyester as well as preparation method and application of composite catalyst

Abstract

The invention discloses a composite catalyst for synthesizing polyester as well as a preparation method and application thereof, and relates to the technical field of catalysts. According to the technical scheme, the method comprises the following steps: in a nitrogen atmosphere, mixing a first metal catalyst, a slow release agent and an organic solvent, reacting at 130-150 DEG C for 1-3 hours, and distilling to separate by-products to obtain a reaction product; and adding a second metal catalyst and an activity regulator into the reaction product, reacting at 130-150 DEG C for 1-3 hours, and distilling to separate by-products, thereby obtaining the composite catalyst for synthesizing polyester. The composite catalyst for synthesizing polyester has good compatibility with water, ethylene glycol or PET oligomer, and has the characteristic of controllable catalytic activity compared with a traditional titanium catalyst. When the composite catalyst is applied to synthesis of polyester, the composite catalyst has the characteristics of few side reactions and fast ester exchange reaction, and the obtained polyester product has the advantages of high intrinsic viscosity and good product hue.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a composite catalyst for synthesizing polyesters, a preparation method thereof, and an application thereof. Background Art

[0002] Polyethylene terephthalate (PET) is one of the most widely used polymer materials in the world at present and has extensive applications in fields such as synthetic fibers, food packaging, and membrane materials. Currently, the main polyester catalysts are antimony-based, titanium-based, and germanium-based. Among them, the antimony-based catalyst has become the main polyester catalyst variety due to advantages such as low price and stable catalytic performance. However, antimony is a heavy metal element, and its biological toxicity and environmental mobility have caused concerns among researchers. The germanium-based catalyst has high catalytic activity, good color of polyester products, and low catalytic activity of side reactions, but germanium is expensive and difficult to be widely used in industrial production. The titanium-based catalyst is an environmentally friendly catalyst without heavy metals, has no adverse effects on life health and the environment, and has good catalytic effects on the esterification and polycondensation reactions of polyesters, and is a current research hotspot at home and abroad. However, the current titanium-based catalyst still has obvious defects. For example, its catalytic stability is poor, which easily causes the aggravation of side reactions and degradation reactions, and the polyester products produced have problems such as yellowing, which to a certain extent limits the popularization and application of the titanium-based catalyst.

[0003] Chinese Patent CN118581592A discloses a production process of antimony-free metal-catalyzed polyester fibers. Using porous silica as a carrier, its surface is aminated with tetraethylenepentamine, and phytic acid is used to react with the surface of the porous silica. Finally, titanium active centers are loaded on the porous silica carrier with a large specific surface area to obtain a titanium-based catalyst with titanium as the central atom and a phosphorus compound as a ligand. The titanium-based catalyst prepared by this patent gets rid of the problem that the traditional titanium-based catalyst is easy to hydrolyze to form TiO2, but the compatibility between the mesoporous silica carrier and polyester molecules is poor, resulting in low catalytic efficiency, long reaction time, and decline in product performance.

[0004] Chinese Patent CN102234370B discloses an aluminum-based catalyst for polyester synthesis, a preparation method thereof, and a usage method, using aluminum glycolate as a catalyst to synthesize PET polyester. The aluminum-based catalyst for synthesizing polyesters has the characteristics of good transparency and low cost. However, compared with the titanium-based or antimony-based catalyst, the aluminum-based catalyst has problems of relatively low catalytic activity and an increase in gel particles of the product, especially when applied to membrane materials, white spots are likely to appear. The aluminum-based catalyst cannot effectively improve the production capacity of industrial polyester plants, and there are also certain limitations in downstream applications.

[0005] In summary, the current polyester catalysts have problems such as difficult regulation of activity, poor compatibility, poor product color difference, and low safety. There is an urgent need to develop a new polyester catalyst to solve these problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a composite catalyst for synthesizing polyester, its preparation method and application. The polyhydroxy structure slow-release agent used is tightly combined with metal ions to form a multi-fork ligand, so that the prepared composite catalyst has good compatibility with water, ethylene glycol or PET oligomers, and at the same time has excellent hydrolysis resistance stability; the activity regulator acts on the second metal catalyst to further adjust the activity of titanium in the second metal catalyst through the electronic effect of the compound. Therefore, compared with the traditional titanium-based catalyst, it has the characteristic of controllable catalytic activity.

[0007] The technical solution of the present invention is as follows: In the first aspect, the present invention provides a preparation method of a composite catalyst for synthesizing polyester, including the following steps: S1: Under a nitrogen atmosphere, the first metal catalyst, the slow-release agent and an organic solvent are mixed and reacted at 130-150 °C for 1-3 h, and the by-products are separated by distillation to obtain a reaction product; wherein, the first metal catalyst is at least one of antimony trioxide, antimony acetate, antimony glycolate, aluminum ethoxide, aluminum isopropoxide, aluminum sec-butoxide and aluminum tert-butoxide; the slow-release agent is sorbitol or mannitol; S2: Add the second metal catalyst and the activity regulator to the reaction product, react at 130-150 °C for 1-3 h, and separate the by-products by distillation to obtain a composite catalyst for synthesizing polyester; wherein, the second metal catalyst is tetraethyl titanate, n-propyl titanate, tetrabutyl titanate, isopropyl titanate or tetra-tert-butyl titanate; the activity regulator is phenol, aniline or benzenethiol; Calculated by metal element, the molar ratio of the first metal catalyst to the second metal catalyst is (20-61):1.

[0008] Preferably, in step S1, the organic solvent is ethylene glycol.

[0009] Preferably, in step S1, the mass ratio of the organic solvent to the first metal catalyst is (0.5-2.5):1.

[0010] Preferably, in step S1, calculated by metal element, the molar ratio of the first metal catalyst to the slow-release agent is 1:(0.6-1).

[0011] Preferably, in step S2, calculated by metal element, the molar ratio of the second metal catalyst to the activity regulator is 1:(1-3).

[0012] In a second aspect, the present invention provides a composite catalyst for synthesizing polyester, which is prepared by the above-mentioned preparation method of the composite catalyst for synthesizing polyester.

[0013] In a third aspect, the present invention provides an application of the above-mentioned composite catalyst for synthesizing polyester, and the composite catalyst for synthesizing polyester is applied to synthesize polyethylene terephthalate (PET).

[0014] Preferably, the application of the composite catalyst for synthesizing polyester to synthesize polyethylene terephthalate includes the following steps: (1) Add terephthalic acid, ethylene glycol and the composite catalyst into a pulping kettle. After pulping, transfer it to an esterification kettle for esterification reaction; (2) Transfer the obtained esterified product to a polycondensation kettle, carry out vacuum polycondensation, extrude the obtained melt, draw it into strips through a die, cool it in a water bath, and then enter a pelletizer to obtain polyethylene terephthalate chips.

[0015] The catalytic activity exhibited by the polyester catalyst is jointly determined by the steric hindrance and electronic effect of metal ions. The present invention uses sorbitol or mannitol with a polyhydroxy structure as a metal ion slow-release agent, which can form a stable tridentate ligand complex structure with metal ions. The spatial steric hindrance of the slow-release agent is small, so it will not hinder the coordination of PET oligomers with metal catalyst cations. The activity regulator used in the present invention is a type of electron-rich group, which has a strong binding force with metal cations and plays a role in regulating the catalytic activity of the metal catalyst in the composite catalyst. In particular, it reduces the catalytic activity of titanium metal and reduces side reactions during the polyester synthesis process, which is beneficial to the preparation of high-performance polyester products.

[0016] Taking sorbitol as an example of the slow-release agent, the reaction principle of sorbitol and the first metal catalyst (taking antimony trioxide as an example) to form a reaction product is as follows: .

[0017] The reaction principle of the reaction product and the second metal catalyst (taking isopropyl titanate as an example) and the activity regulator (taking phenol as an example) to form a composite catalyst is as follows: .

[0018] The polycondensation reaction of polyester follows the chelation coordination mechanism. During the reaction of bis(2-hydroxyethyl) terephthalate (BHET), a hydrogen bond is formed between the carbonyl oxygen and the hydroxyethyl ester group hydrogen, and a seven-membered cyclic complex is spontaneously formed. Under the reaction conditions of high-temperature polymerization, the metal ions of the metal catalyst (MX2) displace the hydrogen to form a new seven-membered transition-state cyclic chelate. The coordination of the metal ions with the carbonyl oxygen increases the positive charge of the ester carbonyl carbon, enabling the attracted other hydroxy oxygen to combine. As the reaction progresses, the molecular weight continuously increases to a certain value, and the polycondensation is completed.

[0019] The polycondensation reaction mechanism of polyester is as follows: 。

[0020] Compared with the prior art, the present invention has the following beneficial effects: For the composite catalyst for synthesizing polyester of the present invention, the polyhydroxy structure slow-release agent adopted is tightly combined with metal ions to form a multi-fork ligand, so that the prepared composite catalyst has good compatibility with water, ethylene glycol or PET oligomers, and at the same time has excellent hydrolysis resistance stability. At the same time, the activity regulator acts on the second metal catalyst to further adjust the activity of titanium in the second metal catalyst through the electronic effect of the compound. Therefore, compared with the traditional titanium catalyst, it has the characteristic of controllable catalytic activity. In addition, when the first metal catalyst adopts an antimony-based catalyst, the present invention also adds a second metal catalyst to achieve the effect of replacing part of the antimony-based catalyst with the second metal catalyst, thereby greatly reducing the dosage of the antimony-based catalyst and reducing the problems of biotoxicity and environmental mobility existing in the traditional heavy metal antimony-based catalyst. When the composite catalyst of the present invention is applied to synthesize polyester, it has the characteristics of few side reactions and fast transesterification reaction, and the obtained polyester product has the advantages of high intrinsic viscosity and good product hue. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. is the infrared spectrogram of the composite catalysts prepared in Example 1, Example 3, Comparative Example 1-2 of the present invention, wherein the four infrared spectral curves correspond to the composite catalysts prepared in Example 1, Example 3, Comparative Example 1, and Comparative Example 2 from top to bottom in sequence. DETAILED DESCRIPTION OF THE INVENTION

[0022] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0023] Example 1 The preparation method of the composite catalyst for synthesizing polyester in this example includes the following steps: S1: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide, 218.604 g (1.2 mol) of sorbitol and 145.75 g of ethylene glycol are mixed and reacted at 130 °C for 3 h, and the reaction-generated water is separated by distillation to obtain a reaction product; S2: 7.604 g (0.033 mol) of tetraethyl titanate and 3.137 g (0.033 mol) of phenol are added to the reaction product, and the mixture is reacted at 130 °C for 3 h, and the by-product ethanol is separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-1.

[0024] Example 2 The preparation method of the composite catalyst for synthesizing polyester in this embodiment includes the following steps: S1: Under a nitrogen atmosphere, 298.89 g (1 mol) of antimony acetate, 127.52 g (0.7 mol) of mannitol, and 298.89 g of ethylene glycol are mixed and reacted at 135 °C for 2.5 h. The acetic acid generated by the reaction is separated by distillation to obtain a reaction product. S2: 5.684 g (0.02 mol) of isopropyl titanate and 2.793 g (0.03 mol) of aniline are added to the reaction product, and the mixture is reacted at 135 °C for 2.5 h. The by-product isopropyl alcohol is separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-2.

[0025] Example 3 The preparation method of the composite catalyst for synthesizing polyester in this embodiment includes the following steps: S1: Under a nitrogen atmosphere, 162.16 g (1 mol) of aluminum ethoxide, 145.736 g (0.8 mol) of sorbitol, and 243.24 g of ethylene glycol are mixed and reacted at 140 °C for 2 h. The ethanol generated by the reaction is separated by distillation to obtain a reaction product. S2: 8.508 g (0.025 mol) of tetrabutyl titanate and 4.706 g (0.05 mol) of phenol are added to the reaction product, and the mixture is reacted at 140 °C for 2 h. The by-product n-butanol is separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-3.

[0026] Example 4 The preparation method of the composite catalyst for synthesizing polyester in this embodiment includes the following steps: S1: Under a nitrogen atmosphere, 204.24 g (1 mol) of aluminum isopropoxide, 163.953 g (0.9 mol) of mannitol, and 408.48 g of ethylene glycol are mixed and reacted at 145 °C for 1.5 h. The isopropyl alcohol generated by the reaction is separated by distillation to obtain a reaction product. S2: 9.474 g (0.033 mol) of n-propyl titanate and 7.759 g (0.083 mol) of aniline are added to the reaction product, and the mixture is reacted at 145 °C for 1.5 h. The by-product n-propyl alcohol is separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-4.

[0027] Example 5 The preparation method of the composite catalyst for synthesizing polyester in this embodiment includes the following steps: S1: Under a nitrogen atmosphere, 211.83 g (0.5 mol) of antimony glycolate, 61.58 g (0.25 mol) of aluminum sec-butoxide, 61.58 g (0.25 mol) of aluminum tert-butoxide, 273.255 g (1.5 mol) of sorbitol and 837.475 g of ethylene glycol were mixed and reacted at 150 °C for 1 h. Sec-butyl alcohol and tert-butyl alcohol generated by the reaction were separated by distillation to obtain a reaction product; S2: 25.524 g (0.075 mol) of tetra-tert-butyl titanate and 24.791 g (0.225 mol) of benzenethiol were added to the reaction product, and the mixture was reacted at 150 °C for 1 h. tert-Butyl alcohol as a by-product was separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-5.

[0028] Comparative Example 1 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 1 includes the following steps: S1: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide and 364.354 g of ethylene glycol were mixed and reacted at 130 °C for 3 h. Water generated by the reaction was separated by distillation to obtain a reaction product; S2: 7.604 g (0.033 mol) of tetraethyl titanate was added to the reaction product, and the mixture was reacted at 130 °C for 3 h. Ethanol as a by-product was separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-6.

[0029] Comparative Example 2 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 2 includes the following steps: S1: Under a nitrogen atmosphere, 162.16 g (1 mol) of aluminum ethoxide and 243.24 g of ethylene glycol were mixed and reacted at 140 °C for 2 h. Ethanol generated by the reaction was separated by distillation to obtain a reaction product; S2: 8.508 g (0.025 mol) of tetrabutyl titanate was added to the reaction product, and the mixture was reacted at 140 °C for 2 h. n-Butyl alcohol as a by-product was separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-7.

[0030] The infrared spectra of the composite catalysts prepared in Example 1, Example 3, Comparative Example 1 and Comparative Example 2 are as Figure 1 shown. In the figure, the stretching vibration peak of alcohol -OH is near 3297 cm -1 ; the antisymmetric stretching vibration and symmetric stretching vibration of O-CH2 are near 2940 cm -1 , 2875 cm -1 respectively; the stretching vibration peaks of the benzene ring are near 1595 cm -1 , 1501 cm -1 , 1474 cm -1 ; and near 1233 cm-1 Nearby is the stretching vibration of the C-O bond in phenol. The π electrons of the benzene ring in the phenol molecule are conjugated with the unshared electron pair of the oxygen atom in C-O, making the C-O bond have partial double bond characteristics. Therefore, the stretching vibration frequency of C-O in phenol is higher than that of C-O in alcohol. In ethylene glycol or sorbitol, the C-O and O-H of C-OH share one oxygen atom, and the in-plane bending vibration of O-H couples with the stretching vibration of C-O, splitting into two spectral bands, located at 1082 cm -1 nearby, 1034 cm -1 nearby, and the out-of-plane bending vibration of OH and the stretching vibration peak of C-O are near 880 cm -1 and 860 cm -1 nearby. There is no sharp drop in infrared absorption and strong absorption in the range of 700 - 850 cm -1 , proving that there is no titanium dioxide in this substance; the stretching vibration peak of the characteristic structure Ti-O-C of the multi-fork ligand formed by sorbitol and titanium is near 691 cm -1 ; the stretching vibration peak of the characteristic structure Sb-O-C of the multi-fork ligand formed by sorbitol and antimony is near 753 cm -1 . It can be seen from Figure 1 that the composite catalyst CAT-1 was successfully prepared in Example 1. The composite catalyst CAT-3 prepared in Example 3 has a similar molecular structure to CAT-1. The peak position of the Al-O-C bond should be at 520 - 580 cm -1 , which may overlap with other spectral peaks, so the peak is not obvious. In Comparative Example 1 and Comparative Example 2, no active regulator was added, and no stretching vibration peak of the benzene ring appeared near 1595 cm -1 , 1501 cm -1 , and 1474 cm -1 .

[0031] Comparative Example 3 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 3 includes the following steps: S1: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide and 364.354 g of ethylene glycol were mixed and reacted at 130 °C for 3 h. The reaction-generated water was separated by distillation to obtain a reaction product; S2: 7.604 g (0.033 mol) of tetraethyl titanate and 3.137 g (0.033 mol) of phenol were added to the reaction product, and the mixture was reacted at 130 °C for 3 h. The by-product ethanol was separated by distillation to obtain the composite catalyst for synthesizing polyester, denoted as CAT-8.

[0032] Comparative Example 4 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 4 includes the following steps: S1: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide, 218.604 g (1.2 mol) of sorbitol, and 145.75 g of ethylene glycol were mixed and reacted at 130 °C for 3 h. The water produced by the reaction was separated by distillation to obtain a reaction product; S2: 7.604 g (0.033 mol) of tetraethyl titanate was added to the reaction product, and the mixture was reacted at 130 °C for 3 h. The by-product ethanol was separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-9.

[0033] Comparative Example 5 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 5 includes the following steps: S1: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide, 182.17 g (1 mol) of sorbitol, and 145.75 g of ethylene glycol were mixed and reacted at 130 °C for 3 h. The water produced by the reaction was separated by distillation to obtain a reaction product; S2: 7.604 g (0.033 mol) of tetraethyl titanate and 3.137 g (0.033 mol) of phenol were added to the reaction product, and the mixture was reacted at 130 °C for 3 h. The by-product ethanol was separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-10.

[0034] Comparative Example 6 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 6 includes the following steps: S1: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide, 437.208 g (2.4 mol) of sorbitol, and 145.75 g of ethylene glycol were mixed and reacted at 130 °C for 3 h. The water produced by the reaction was separated by distillation to obtain a reaction product; S2: 7.604 g (0.033 mol) of tetraethyl titanate and 3.137 g (0.033 mol) of phenol were added to the reaction product, and the mixture was reacted at 130 °C for 3 h. The by-product ethanol was separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-11.

[0035] Comparative Example 7 The preparation method of the composite catalyst for synthesizing polyester in Comparative Example 7 includes the following steps: Under a nitrogen atmosphere, 291.5 g (1 mol) of antimony trioxide, 218.604 g (1.2 mol) of sorbitol, 145.75 g of ethylene glycol, 7.604 g (0.033 mol) of tetraethyl titanate, and 3.137 g (0.033 mol) of phenol were mixed and reacted at 130 °C for 3 h. The ethanol and water produced by the reaction were separated by distillation to obtain a composite catalyst for synthesizing polyester, denoted as CAT-12.

[0036] Application evaluation of the composite catalysts of Examples 1-5 and Comparative Examples 1-7: The PET polycondensation activity and the color of the final product of the composite catalysts of Examples 1-5 and Comparative Examples 1-7 were evaluated. The specific experimental steps are as follows: (1) 43.75 kg of terephthalic acid, 22.89 kg of ethylene glycol and 3 ppm of the composite catalyst (calculated based on titanium element, the addition amount of the composite catalyst is 3 ppm of the theoretical output of PET) were added to the pulping kettle. After pulping, it was transported to the esterification kettle. (2) The temperature was raised to 265 °C, the kettle pressure was maintained at 0.15 - 0.25 MPa, and the stirring speed was 100 rpm until no more distillate came out from the top of the esterification fractionation column, that is, the esterification end point was reached. (3) The esterified product was transferred to the polycondensation kettle for vacuum polycondensation. The vacuum pumping process was divided into two stages: low vacuum and high vacuum. In the low vacuum stage, the temperature in the kettle was controlled at 270 °C, the stirring speed was 80 rpm, and the vacuum degree in the polycondensation kettle was controlled at 1000 Pa for a duration of 60 min. Then it entered the high vacuum stage. The temperature in the kettle was controlled at 280 °C, the stirring speed was 20 rpm, and the vacuum degree in the polycondensation kettle was controlled below 130 Pa. When the current of the stirring motor in the polycondensation kettle reached 800 W, the stirring was stopped, and the melt was pressed out with nitrogen, pulled into strips through a die, cooled in a water bath, and then entered the pelletizer to obtain polyester chips.

[0037] The obtained polyester chips were dried and then tested. The testing methods are as follows: 1) Titanium content of the composite catalyst - spectrophotometry The test was carried out according to "GB / T14190-2017 Test Methods for Fiber Grade Polyester (PET) Chips": The sample was dissolved with concentrated sulfuric acid and hydrogen peroxide under heating; after cooling, hydrogen peroxide was added again to form a yellow complex, and its absorbance value was measured at 410 nm on a spectrophotometer; the titanium content of the composite catalyst was calculated based on the titanium dioxide content in the calculation results.

[0038] 2) Intrinsic viscosity - capillary viscometer method The test was carried out according to "GB / T14190-2017 Test Methods for Fiber Grade Polyester (PET) Chips": Using the capillary viscometry method, the outflow time of the solvent at 25 °C and the polyester solution with a concentration of 0.5 g / dL was measured, and its intrinsic viscosity was calculated; the solvent used was phenol and 1,1,2,2-tetrachloroethane with a mass ratio of 60:40, and the Ubbelohde viscometer was used for the test.

[0039] 3) Chromaticity - dry pulverization method The test was conducted according to GB / T14190-2017 Test Method for Fiber-Grade Polyester (PET) Chips: After the samples were dried and crushed, the colorimetry of the samples was tested using an automatic colorimeter, and the results were expressed in the HunterLab color system; the equipment model was X-RiteCi7600.

[0040] The test results are shown in Table 1-2: Table 1 Application evaluation results of the composite catalysts of Examples 1-5

[0041] Table 2 Application evaluation results of the composite catalysts of Comparative Examples 1-7

[0042] It can be seen from Table 1-2 that the composite catalyst prepared by the present invention has excellent performance in catalytic activity and product color after being used to synthesize polyester. When the same characteristic viscosity is reached, the vacuum polycondensation time of the composite catalysts of Examples 1 and 3 is slightly longer than that of Comparative Examples 1-2, respectively, which proves that the activity regulator and the slow-release agent have an inhibitory effect on the activity of the composite catalyst, so that the composite catalyst has a moderate catalytic activity, thereby causing the polyester to produce less side reactions during the high-temperature polycondensation process. Correspondingly, the color b value of the polyester products obtained in Examples 1 and 3 is significantly better than that of the polyester products obtained in Comparative Examples 1-2. At the same time, it can also be seen from Table 1 that compared with the titanium / antimony composite catalyst of Examples 1-2, the L value of the polyester product prepared by the titanium / aluminum composite catalyst of Example 3 is significantly improved, because a small amount of trivalent antimony is reduced to metallic antimony in the polymerization reaction of Examples 1-2, resulting in a decrease in the L value of the product.

[0043] In Comparative Example 3, no additional sustained-release agent was added, and an excess of ethylene glycol was used as a sustained-release agent. Under the same reaction conditions, the polycondensation took the shortest time, but the product color was yellow and accompanied by light gray. This is because the complex ligand structure formed by ethylene glycol and metal ions is unstable, and part of the catalyst active center is reduced during the polymerization reaction, and precipitated in the form of metal elements, resulting in a decrease in product quality. In Comparative Example 4, no active regulator was added, resulting in the titanium catalyst still maintaining high activity, increasing thermal degradation reactions, and the product color being significantly yellow. The amount of sustained-release agent added in Comparative Example 5 is too small, and some metal ions combine with ethylene glycol to form ethylene glycol titanium or ethylene glycol antimony, resulting in a decrease in product quality. The amount of sustained-release agent added in Comparative Example 6 is too much, and some titanium metal ions and sorbitol can form a double trident ligand structure, which further hinders the active regulator from combining with titanium metal ions, resulting in a decrease in product quality. Comparative Example 7 adopts a one-step feeding reaction. The second metal catalyst has high reaction activity and preferentially reacts with high concentration sorbitol to form a double trident ligand structure, which hinders the binding of the activity regulator with titanium metal ions, resulting in a decrease in product quality.

Claims

1. Preparation method of composite catalyst for synthesizing polyester, characterized in that, It includes the following steps: S1: Under a nitrogen atmosphere, mix a first metal catalyst, a slow-release agent and an organic solvent, react at 130 - 150 °C for 1 - 3 h, and distill and separate by-products to obtain a reaction product; wherein, the first metal catalyst is at least one of antimony trioxide, antimony acetate, antimony glycolate, aluminum ethoxide, aluminum isopropoxide, aluminum sec-butoxide and aluminum tert-butoxide; the slow-release agent is sorbitol or mannitol; S2: Add a second metal catalyst and an activity regulator to the reaction product, react at 130 - 150 °C for 1 - 3 h, and distill and separate by-products to obtain a composite catalyst for synthesizing polyester; wherein, the second metal catalyst is tetraethyl titanate, n-propyl titanate, tetrabutyl titanate, isopropyl titanate or tetra-tert-butyl titanate; the activity regulator is phenol, aniline or benzenethiol; Calculated by metal element, the molar ratio of the first metal catalyst to the second metal catalyst is (20 - 61):

1.

2. The preparation method of the composite catalyst for synthesizing polyester according to claim 1, characterized in that, In step S1, the organic solvent is ethylene glycol.

3. The preparation method of the composite catalyst for synthesizing polyester according to claim 1, characterized in that, In step S1, the mass ratio of the organic solvent to the first metal catalyst is (0.5 - 2.5):

1.

4. The preparation method of the composite catalyst for synthesizing polyester according to claim 1, characterized in that, In step S1, calculated by metal element, the molar ratio of the first metal catalyst to the slow-release agent is 1:(0.6 - 1).

5. The preparation method of the composite catalyst for synthesizing polyester according to claim 1, characterized in that, In step S2, calculated by metal element, the molar ratio of the second metal catalyst to the activity regulator is 1:(1 - 3).

6. Composite catalyst for synthesizing polyester, characterized in that, It is prepared by the preparation method of the composite catalyst for synthesizing polyester according to any one of claims 1 - 5.

7. Use of the composite catalyst for synthesizing polyester according to claim 6, characterized in that, The composite catalyst for synthesizing polyester is applied to synthesize polyethylene terephthalate.

8. Use of the composite catalyst for synthesizing polyester according to claim 7, characterized in that, It includes the following steps: (1) Add terephthalic acid, ethylene glycol and the composite catalyst into a pulping kettle, after pulping, transfer it to an esterification kettle for esterification reaction; (2) Transfer the obtained esterified product to a polycondensation kettle, carry out vacuum polycondensation, extrude the obtained melt, draw it into strips through a die, cool it in a water bath, and then enter a pelletizer to obtain polyethylene terephthalate chips.

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