Titanium-based multimetallic polyester catalysts, methods for their preparation and use

Abstract

The present application relates to the field of catalysis technology, in particular to a titanium-based multimetallic polyester catalyst and a preparation method and application thereof. The present application utilizes an imidazole ligand to synthesize a zeolite-like imidazole ester framework material as a precursor of a catalyst, and introduces titanium into the precursor by using a titanate, thereby preparing a titanium-based multimetallic polyester catalyst with a good stable structure (excellent water stability). The titanium-based multimetallic polyester catalyst provided by the present application will not hydrolyze when used, thereby solving the technical problem that the existing homogeneous titanium-based catalyst has poor water stability, and hydrolysis produces oligomers, thereby causing a substantial reduction in the activity of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and more specifically to a titanium-based multimetallic polyester catalyst, its preparation method, and its application. Background Technology

[0002] Polyethylene terephthalate (PET) production capacity is growing rapidly, and global demand for PET continues to grow at a rate of 8% annually. PET is used in various aspects of daily life, including synthetic fibers, building materials, packaging, and automobiles. In the PET production process, catalysts have a significant impact on PET quality, including indicators such as PET polyester molecular weight, polycondensation reaction rate, thermal stability, and color. Therefore, when selecting a catalyst, its catalytic activity, environmental performance, and thermal stability must be comprehensively considered.

[0003] One type of catalyst used in PET industrial production is the titanium-based catalyst. Titanium-based catalysts are environmentally friendly and are therefore increasingly being used in the polyester industry. Currently, titanium-based catalysts used in PET synthesis are divided into homogeneous titanium-based catalysts and heterogeneous titanium-based catalysts.

[0004] Homogeneous titanium-based catalysts include alkoxytitanium catalysts such as tetrabutyl titanate and isopropyl titanate. During the catalytic synthesis of PET, alkoxytitanium catalysts typically undergo hydrolysis to form dense titanium dioxide oligomers, thus reducing their catalytic activity and potentially clogging reaction lines. Furthermore, alkoxytitanium catalysts exhibit poor selectivity, leading to severe yellowing of the synthesized PET. Therefore, when using alkoxytitanium catalysts in PET synthesis, phosphate ester stabilizers are generally required to suppress side reactions caused by excessive catalyst activity, thereby inhibiting the formation of colored groups.

[0005] Heterogeneous titanium-based catalysts (containing titanium inorganic catalysts) have solved the problem of poor stability in homogeneous organic titanium catalysts. However, heterogeneous titanium-based catalysts still need to overcome the following challenges: ① Dispersion problem: In high-viscosity PET melt, solid heterogeneous catalyst particles are difficult to disperse uniformly, leading to uneven catalytic efficiency and decreased product quality. ② Activity regulation and product color: Excessively high catalytic activity of titanium can easily trigger side reactions, generating chromogenic substances such as quinones, causing the product to turn yellow. ③ Potential thermal stability problem: Catalyst residues may continue to catalyze the chain breakage and degradation of the PET main chain during high-temperature processing, leading to a decrease in viscosity. Summary of the Invention

[0006] To address the technical problem of poor water stability in titanium-based catalysts, this invention provides a titanium-based multimetallic polyester catalyst, its preparation method, and its application.

[0007] This invention prepares a titanium-based multimetallic polyester catalyst with good structural stability (excellent water stability) by reacting a homogeneous titanium-based catalyst, titanate, with imidazole ligands, cobalt salts, and zinc salts. Specifically, it utilizes the zeolite-like imidazole ester framework material synthesized from the imidazole ligands and cobalt and zinc salts as a catalyst precursor, and incorporates titanium into the precursor using titanate. The titanium-based multimetallic polyester catalyst provided by this invention does not hydrolyze during use, solving the technical problem of poor water stability and the formation of oligomers by hydrolysis in existing homogeneous titanium-based catalysts, which leads to a significant reduction in catalyst activity.

[0008] One of the objectives of this invention is to provide a titanium-based multimetallic polyester catalyst.

[0009] The titanium-based multimetallic polyester catalyst comprises a precursor and titanium dioxide supported on the precursor; the precursor is a zeolite-like imidazole ester framework material doped with cobalt and zinc, and the titanium dioxide has a microporous and mesoporous structure.

[0010] The titanium dioxide is bonded to the precursor via N-Ti coordination bonds.

[0011] As a preferred embodiment, the micropore and mesopore structures extend into the precursor.

[0012] As a preferred embodiment, a portion of the cobalt in the precursor is exposed.

[0013] Specifically, the titanium dioxide contains micropores and mesopores that extend from the surface of the titanium dioxide to the interior of the precursor body, thereby exposing the cobalt that was originally located inside the precursor body.

[0014] As a preferred embodiment, the titanium-based multimetallic polyester catalyst has a specific surface area of ​​950~1550 m². 2 / g, for example, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g.

[0015] As a preferred embodiment, the molar content of titanium dioxide in the titanium-based multimetallic polyester catalyst is 0.1~8 mol%, for example 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, or 7 mol%.

[0016] As a preferred embodiment, the molar doping amount of cobalt in the precursor is 0.1~4 mol%, for example 0.5 mol%, 1 mol%, 2 mol%, or 3 mol%.

[0017] As a preferred embodiment, the molar doping amount of zinc in the precursor is 0.01~4 mol%, for example 0.05 mol%, 0.1 mol%, 0.5 mol%, 1 mol%, 2 mol%, or 3 mol%.

[0018] As a preferred embodiment, the average pore size of the microporous structure is 0.5nm~1.3nm, for example 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1.0nm, 1.1nm, or 1.2nm.

[0019] As a preferred embodiment, the average pore size of the mesoporous structure is 4~10nm, for example 5nm, 6nm, 7nm, 8nm, or 9nm.

[0020] The titanium-based multimetallic polyester catalyst can be prepared from raw materials including imidazole ligands, cobalt salts, zinc salts, template agents, and titanates.

[0021] A second objective of this invention is to provide a method for preparing the titanium-based polymetallic polyester catalyst described in one of the objectives of this invention.

[0022] The preparation method of the titanium-based multimetallic polyester catalyst includes: (1) The imidazole ligand solution is reacted with the cobalt-zinc solution, and the solid is collected to obtain the precursor; the cobalt-zinc solution refers to an organic solution of cobalt salt and zinc salt; (2) Add ammonia water dropwise to the suspension containing template agent and precursor, stir, add titanate ester and disperse evenly, carry out reaction, separate the solid, and obtain intermediate product 1; (3) Add intermediate product 1 to an alcohol-water solution to react, separate the solid, and obtain intermediate product 2; (4) Add intermediate product 2 to an alcohol solvent, reflux the reaction, separate the solid, dry it, and obtain the titanium-based polymetallic polyester catalyst.

[0023] In step (1), imidazole ligands, cobalt salts, and zinc salts react to generate a cobalt- and zinc-doped zeolite-like imidazole ester framework material. Therefore, the precursor is a cobalt- and zinc-doped zeolite-like imidazole ester framework material (hereinafter referred to as ZIF material).

[0024] In step (2), the ZIF material, titanate ester and template agent react, and the template agent self-assembles to generate a product containing the template agent - ZIF material loaded with titanium dioxide; the ZIF material loaded with titanium dioxide contains the template agent, and the titanium dioxide therein is in a non-porous state and does not have a microporous or mesoporous structure.

[0025] The purpose of step (3) is to strengthen the connection between titanium dioxide and ZIF material, so that some loosely connected titanium dioxide or a small amount of physically adsorbed titanium dioxide can be stably and firmly connected to the ZIF surface. Therefore, the intermediate product 2 obtained in step (3) is still a titanium dioxide-loaded ZIF material.

[0026] Step (4) is the process of removing the template agent from intermediate product 2 (ZIF material loaded with titanium dioxide), so that micropores and mesopores are formed on the surface and inside of the titanium dioxide loaded on the ZIF material, thereby obtaining the titanium-based polymetallic polyester catalyst described in one of the purposes of the invention.

[0027] The imidazole ligand can be any one or more existing imidazole ligands capable of synthesizing zeolite-like imidazole ester framework materials. As a preferred embodiment, the imidazole ligand is selected from at least one of imidazole, 2-methylimidazolium, benzimidazole, and 2-ethylimidazolium.

[0028] The solvent for the imidazole ligand solution can be any one or more existing solvents capable of dissolving the imidazole ligand. Preferably, the solvent for the imidazole ligand solution is selected from at least one of N,N-dimethylformamide, N,N-diethylformamide, methanol, and ethanol.

[0029] The anion of the cobalt salt can be any one or more existing anions capable of forming cobalt salts. Preferably, the anion of the cobalt salt is selected from at least one of chloride ions, nitrate ions, and acetate ions.

[0030] The anion of the zinc salt can be any one or more existing anions capable of forming zinc salts. Preferably, the anion of the zinc salt is selected from at least one of chloride ions, nitrate ions, and acetate ions.

[0031] The anion of the cobalt salt can be the same as or different from the anion of the zinc salt.

[0032] The solvent for the cobalt-zinc solution can be any one or more existing organic solvents capable of dissolving zinc and cobalt salts. Preferably, the solvent for the cobalt-zinc solution is selected from at least one of methanol, ethanol, and N,N-dimethylformamide (DMF).

[0033] The template agent can be any one or more existing template agents. As a preferred embodiment, the template agent is selected from hexadecyltrimethylammonium bromide (CTAB).

[0034] The solvent for the suspension can be any one or more existing organic solvents capable of dissolving the template agent. Preferably, the solvent for the suspension is selected from at least one of methanol and ethanol.

[0035] The titanate ester can be any one or more existing titanate esters. As a preferred embodiment, the titanate ester is selected from at least one of tetrabutyl titanate, tetraisobutyl titanate, tetraisopropyl titanate, and tetraethyl titanate.

[0036] The alcohol in the alcohol-water solution can be any one or more existing small molecule alcohols. Preferably, the alcohol in the alcohol-water solution is selected from at least one of methanol and ethanol.

[0037] The alcohol solvent can be any one or more existing alcohol solvents. As a preferred embodiment, the alcohol solvent is selected from at least one of methanol and ethanol.

[0038] The molar ratio of the imidazole ligand, zinc salt, and cobalt salt can be selected within a wide range. As a preferred embodiment, the molar ratio of the imidazole ligand, zinc salt, and cobalt salt is (2~64):1:(0.1~10), for example, 4:1:0.1, 8:1:1, 10:1:0.25, 9:1:0.1, and 20:1:5.

[0039] The mass ratio of the precursor to the template agent can be selected within a wide range. As a preferred embodiment, the mass ratio of the precursor to the template agent is (1~10):1, for example, 2:1, 3:1, 5:1, 7:1, or 9:1.

[0040] The molar ratio of titanium ions in the titanate to zinc ions in the zinc salt can be selected within a wide range. As a preferred embodiment, the molar ratio of titanium ions in the titanate to zinc ions in the zinc salt is (0.1~10):1, for example, 1:1, 2:1, 3:1, 5:1, 7:1, 9:1.

[0041] The volume ratio of methanol to water in the alcohol-water solution can be selected within a wide range. As a preferred embodiment, the volume ratio of methanol to water in the alcohol-water solution is (0.1~60):1, for example, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1.

[0042] The amount of ammonia added relative to the template agent can be selected within a wide range. As a preferred embodiment, the amount of ammonia added relative to the template agent is 0.1 mL to 10 mL / g, for example, 0.5 mL / g, 1 mL / g, 2 mL / g, 3 mL / g, 4 mL / g, 5 mL / g, 6 mL / g, 7 mL / g, 8 mL / g, or 9 mL / g.

[0043] The reaction temperature in step (1) can be selected within a wide range. As a preferred option, the reaction temperature in step (1) is 25~160℃, for example 30℃, 50℃, 80℃, 100℃, 120℃, 140℃.

[0044] The reaction time for step (1) can be selected within a wide range. As a preferred option, the reaction time for step (1) is 12 to 72 hours, for example, 24 hours, 36 hours, 48 ​​hours, or 60 hours.

[0045] The reaction temperature in step (2) can be room temperature, preferably 15~30℃; for example 20℃, 23℃, 25℃, 28℃.

[0046] The reaction time for step (2) is 5 to 60 minutes, for example, 10 minutes, 20 minutes, 30 minutes, 40 minutes, or 50 minutes.

[0047] The reaction temperature in step (3) can be selected within a wide range. As a preferred option, the reaction temperature in step (3) is 40~150℃, for example 60℃, 80℃, 100℃, 120℃, 140℃.

[0048] The reaction time for step (3) can be selected within a wide range. As a preferred option, the reaction time for step (3) is 12 to 24 hours, for example, 16 hours or 18 hours.

[0049] The reaction temperature in step (4) can be selected within a wide range. As a preferred option, the reaction temperature in step (4) is 60~80℃, for example 65℃, 70℃, 75℃.

[0050] The reaction time for step (4) can be selected within a wide range. As a preferred option, the reaction time for step (4) is 0.5 to 8 hours, for example, 1 hour, 2 hours, 4 hours, or 6 hours.

[0051] As a specific embodiment, the preparation method of the titanium-based multimetallic polyester catalyst includes the following steps: Imidazole ligands were added to a reaction vessel, followed by the addition of an organic solvent and stirring for 15-20 minutes to form a homogeneous solution. Cobalt and zinc salts were then added to methanol, sonicated for 5-10 minutes, and poured into the reaction vessel. The mixture was then reacted at 25°C-160°C for 12-72 hours. After the reaction was completed, the mixture was washed three times each with ethanol and pure water, centrifuged, and the resulting solid was dried at 80-100°C to obtain the catalyst precursor. The catalyst precursor was added to anhydrous ethanol and sonicated at room temperature for 10-20 minutes to obtain a suspension. Then, hexadecyltrimethylammonium bromide (CTAB) was added to the suspension and stirred rapidly at room temperature until CTAB was completely dissolved. Ammonia water was then added dropwise to the suspension and stirred at room temperature for 10-20 minutes. Titanate ester was then added to the suspension and sonicated at room temperature for 5-30 minutes. The resulting product was washed three times with anhydrous methanol and then added to a mixture of methanol and water. The mixture was incubated overnight at 40-150°C. After centrifugation, the product was added to anhydrous ethanol and refluxed at 60-80°C for 0.5-8 hours. After centrifugation and drying, the titanium-based polymetallic polyester catalyst was obtained.

[0052] A third objective of this invention is to provide an application of the titanium-based polymetallic polyester catalyst described in one objective of the invention or the titanium-based polymetallic polyester catalyst prepared by the preparation method described in the second objective of the invention.

[0053] Specifically, its application in the preparation of polyethylene terephthalate (PET).

[0054] The fourth objective of this invention is to provide a method for preparing polyethylene terephthalate.

[0055] The method for preparing polyethylene terephthalate involves reacting raw materials including terephthalic acid and ethylene glycol. The catalyst used is selected from the titanium-based polymetallic polyester catalyst described in one of the invention objectives or the titanium-based polymetallic polyester catalyst prepared by the preparation method described in the second invention objective. The amount of catalyst used is 0.001 to 0.02 wt% of the total weight of terephthalic acid and ethylene glycol.

[0056] As a preferred embodiment, the catalyst is added to a mixture of terephthalic acid and ethylene glycol, and the mixture undergoes esterification and polycondensation reactions to obtain the polyethylene terephthalate.

[0057] The temperature and time of the esterification and polycondensation reactions can be the same as those used in the preparation of polyethylene terephthalate.

[0058] As a preferred embodiment, the reaction temperature of the esterification reaction is 240~270℃.

[0059] As a preferred embodiment, the esterification reaction time is 120-180 minutes.

[0060] As a preferred embodiment, the reaction temperature of the polycondensation reaction is 260~290℃.

[0061] As a preferred embodiment, the reaction time of the polycondensation reaction is 40 to 240 minutes.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with existing homogeneous titanium-based catalysts, the titanium-based polymetallic polyester catalyst provided by this invention does not hydrolyze during use, thus solving the technical problem that existing homogeneous titanium-based catalysts have poor water stability, produce oligomers through hydrolysis, and thus cause a significant reduction in catalyst activity.

[0063] Compared with existing heterogeneous titanium-based catalysts, the titanium ions in the titanium-based multimetallic polyester catalyst provided by this invention are fixed on organic ligands, which effectively prevents the aggregation of titanium ions and solves the problem of easy agglomeration of heterogeneous titanium-based catalysts during use.

[0064] Compared to titanium-based catalysts, this catalyst effectively reduces the b-value of PET. A possible reason is that the mesoporous and microporous structure of the titanium-based multimetallic polyester catalyst extends into the precursor, exposing Co ions. Co ions can capture free radicals during the hydroxylation process of the benzene ring, inhibiting the formation of quinone structures and thus improving the color of the polyester PET.

[0065] This invention uses a template agent to form mesoporous and microporous structures in the catalyst, thereby increasing the contact area between the active components and reactants in the titanium-based multimetallic polyester catalyst, increasing the reaction sites, and improving the reaction rate.

[0066] The titanium-based multimetallic polyester catalyst provided by this invention is used to catalyze the PET polycondensation reaction, and its main active site is the titanium ion in the catalyst. The immobilization of titanium ions on organic ligands not only effectively prevents the hydrolysis and aggregation of titanium ions, but also effectively regulates the electron density of titanium ions, thereby improving their catalytic performance.

[0067] The titanium-based polymetallic polyester catalyst of the present invention has low cost, is non-toxic, and has good stability and catalytic activity, and has broad prospects for industrial application. Attached Figure Description

[0068] Figure 1 TEM image of the titanium-based multimetallic polyester catalyst prepared in Example 1; Figure 2 EDS characterization diagram of the titanium-based multimetallic polyester catalyst prepared in Example 1; Figure 3 Here is the gas adsorption isotherm diagram of the titanium-based multimetallic polyester catalyst prepared in Example 1; Figure 4 Mesopore size distribution of the titanium-based multimetallic polyester catalyst prepared in Example 1; Figure 5 The micropore size distribution diagram of the titanium-based multimetallic polyester catalyst prepared in Example 1 is shown. Figure 6Thermogravimetric analysis of the titanium-based multimetallic polyester catalyst prepared in Example 1. Detailed Implementation

[0069] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0070] All raw materials used in the examples are commercially available.

[0071] Example 1 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 15 minutes to form a homogeneous solution. Cobalt nitrate and zinc nitrate were then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole, cobalt nitrate, and zinc nitrate was 4:1:0.1.

[0072] Upon testing, the precursor prepared in this embodiment was found to contain 1 mol% cobalt and 0.1 mol% zinc.

[0073] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.2 g of hexadecyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 1 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.15 g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature to separate the solid, yielding intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0074] The TEM image of the titanium-based multimetallic polyester catalyst prepared in this embodiment is shown below. Figure 1 As shown.

[0075] The EDS characterization diagram of the titanium-based multimetallic polyester catalyst prepared in this embodiment is shown below. Figure 2 As shown. Figure 2This indicates that the titanium-based multimetallic polyester catalyst contains a cobalt- and zinc-doped zeolite-like imidazole ester framework material and titanium dioxide.

[0076] The gas adsorption isotherm diagram of the titanium-based multimetallic polyester catalyst prepared in this embodiment is shown below. Figure 3 As shown. From Figure 3 The hysteresis loop diagram can be seen, indicating that the titanium dioxide loaded on the precursor has a microporous and mesoporous structure.

[0077] The mesopore size distribution diagram of the titanium-based multimetallic polyester catalyst prepared in this embodiment is shown in the figure below. Figure 4 As shown. Figure 4 The results show that the mesopore size is mainly distributed at 5nm, 6nm and 8nm.

[0078] The micropore size distribution diagram of the titanium-based multimetallic polyester catalyst prepared in this embodiment is shown in the figure below. Figure 5 As shown. Figure 5 The results show that the micropore size is mainly distributed at 1.6 nm.

[0079] The specific surface area of ​​the titanium-based multimetallic polyester catalyst prepared in this embodiment was measured to be 1520 m². 2 / g, with a titanium dioxide content of 1mol%, its microporous structure has an average pore size of 1.1nm; its mesoporous structure has an average pore size of 8.2nm.

[0080] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0081] Example 2 Catalyst preparation: Add benzylimidazole to a reaction vessel, then add N,N-dimethylformamide and stir for 20 minutes to form a homogeneous solution. Next, add cobalt nitrate and zinc nitrate to methanol, sonicate for 10 minutes, and pour the mixture into the reaction vessel. Then, react at 120°C for 72 hours. After the reaction is complete, separate the solid; wash the separated solid three times each with ethanol and pure water, and then dry it at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of benzylimidazole, cobalt nitrate, and zinc nitrate is 4:0.5:0.5.

[0082] Testing revealed that the precursor prepared in this embodiment contained 0.5 mol% cobalt and 0.5 mol% zinc.

[0083] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.3 g of hexadecyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 1.2 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.3 g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 10 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 70°C for 4 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0084] The specific surface area of ​​the titanium-based polymetallic polyester catalyst prepared in this embodiment was measured to be 1103 m². 2 / g, with a titanium dioxide content of 2mol%, its microporous structure has an average pore size of 0.6nm, and its mesoporous structure has an average pore size of 6.7nm.

[0085] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.04g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0086] Example 3 Catalyst preparation: 2-Ethylimidazole was added to a reaction vessel, followed by N,N-dimethylacetamide, and stirred for 20 minutes to form a homogeneous solution. Cobalt nitrate and zinc acetate were then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 120°C for 36 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-ethylimidazole, cobalt nitrate, and zinc acetate was 4:0.4:0.1.

[0087] Testing revealed that the precursor prepared in this embodiment contained 0.4 mol% cobalt and 0.1 mol% zinc.

[0088] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.25 g of cetyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 0.5 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.05 g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 10 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 4 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0089] The specific surface area of ​​the titanium-based polymetallic polyester catalyst prepared in this embodiment was measured to be 1329 m². 2 / g, the titanium dioxide content is 0.3mol%, the average pore size of its microporous structure is 0.9nm, and the average pore size of its mesoporous structure is 7.1nm.

[0090] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.1g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0091] Example 4 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 10 minutes to form a homogeneous solution. Cobalt nitrate and zinc nitrate were then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 36 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole, cobalt nitrate, and zinc nitrate was 4:0.45:0.05.

[0092] Upon testing, the precursor prepared in this embodiment contained 0.45 mol% cobalt and 0.05 mol% zinc.

[0093] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.5 g of cetyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 3 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.1 g of tetrabutyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 70°C for 3 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0094] The specific surface area of ​​the titanium-based polymetallic polyester catalyst prepared in this embodiment was measured to be 1471 m². 2 / g, the titanium dioxide content is 0.6mol%, the average pore size of its microporous structure is 0.93nm, and the average pore size of its mesoporous structure is 8.6nm.

[0095] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.05g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0096] Example 5 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 15 minutes to form a homogeneous solution. Cobalt nitrate and zinc nitrate were then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole, cobalt nitrate, and zinc nitrate was 4:1:0.1.

[0097] Upon testing, the precursor prepared in this embodiment was found to contain 1 mol% cobalt and 0.1 mol% zinc.

[0098] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.2 g of hexadecyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 1 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.1 g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0099] The specific surface area of ​​the titanium-based polymetallic polyester catalyst prepared in this embodiment was measured to be 1509 m². 2 / g, the titanium dioxide content is 0.6mol%, the average pore size of its microporous structure is 1.1nm, and the average pore size of its mesoporous structure is 8.1nm.

[0100] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0101] Example 6 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 15 minutes to form a homogeneous solution. Cobalt nitrate and zinc nitrate were then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole, cobalt nitrate, and zinc nitrate was 4:1:0.1.

[0102] Upon testing, the precursor prepared in this embodiment was found to contain 1 mol% cobalt and 0.1 mol% zinc.

[0103] 2g of the catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.2g of hexadecyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 1mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.2g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0104] The specific surface area of ​​the titanium-based polymetallic polyester catalyst prepared in this embodiment was measured to be 1497 m². 2 / g, the titanium dioxide content is 1.3mol%, the average pore size of its microporous structure is 1.1nm, and the average pore size of its mesoporous structure is 8.2nm.

[0105] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0106] Comparative Example 1 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 15 minutes to form a homogeneous solution. Zinc nitrate was then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole to zinc nitrate was 4:1.

[0107] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.2 g of hexadecyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 1 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.15 g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based metal polyester catalyst.

[0108] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0109] Comparative Example 2 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 15 minutes to form a homogeneous solution. Cobalt nitrate was then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole to cobalt nitrate was 4:1.

[0110] 2 g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.2 g of hexadecyltrimethylammonium bromide (CTAB) was added to the suspension, and the mixture was rapidly stirred at room temperature until the CTAB was completely dissolved. Subsequently, 1 mL of ammonia water was added dropwise to the suspension, and the mixture was stirred for 20 minutes at room temperature. Next, 0.15 g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature. The solid was separated to obtain intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based metal polyester catalyst.

[0111] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0112] Comparative Example 3 Catalyst preparation: 2-Methylimidazole was added to a reaction vessel, followed by methanol and stirring for 15 minutes to form a homogeneous solution. Cobalt nitrate and zinc nitrate were then added to methanol, sonicated for 10 minutes, and poured into the reaction vessel. The mixture was then reacted at 30°C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80°C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole, cobalt nitrate, and zinc nitrate was 4:1:0.1.

[0113] 2g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. Then, 0.15g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature to separate the solid, yielding intermediate product 1. Intermediate product 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate product 2. Intermediate product 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. After centrifugation, the solid was collected and dried to obtain the titanium-based multimetallic polyester catalyst.

[0114] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0115] Comparative Example 4 Catalyst preparation: 2-Methylimidazole and 0.2 g of hexadecyltrimethylammonium bromide (CTAB) were added to a reaction vessel, followed by the addition of methanol and stirring for 15 minutes to form a homogeneous solution. Then, 1 mL of ammonia water was added dropwise to the solution, and the mixture was stirred at room temperature for 20 minutes. Next, cobalt nitrate and zinc nitrate were added to methanol, sonicated for 10 minutes, and then poured into the reaction vessel. The mixture was then reacted at 30 °C for 72 hours. After the reaction was complete, the solid was separated. The separated solid was washed three times each with ethanol and pure water, and then dried at 80 °C for 8 hours to obtain the catalyst precursor. In this step, the molar ratio of 2-methylimidazole, cobalt nitrate, and zinc nitrate was 4:1:0.1.

[0116] 2g of catalyst precursor was added to anhydrous ethanol and sonicated for 10 minutes at room temperature to obtain a suspension. 0.15g of isopropyl titanate was added to the suspension, and the suspension was sonicated for 5 minutes at room temperature to separate the solid, yielding intermediate 1. Intermediate 1 was washed three times with anhydrous methanol and then added to a mixed solution of methanol and water (methanol to water volume ratio 1:1). The mixture was incubated overnight at 80°C and centrifuged to obtain solid intermediate 2. Intermediate 2 was added to anhydrous ethanol and reacted under total reflux at 60°C for 5 hours. The mixture was centrifuged, the solid was collected, and dried to obtain the titanium-based multimetallic polyester catalyst.

[0117] Synthesis of polyethylene terephthalate: 1000g of terephthalic acid, 485g of ethylene glycol, and 0.02g of the prepared titanium-based multimetallic polyester catalyst were added to a 5L reactor. Esterification was then carried out at 250℃ and 0.2MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced to below 100Pa, followed by a polycondensation reaction at 278℃. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0118] Comparative Example 5 1000g of terephthalic acid, 485g of ethylene glycol, and 0.2g of tetrabutyl titanate were added to a 5L reactor. Esterification was then carried out at 265℃ and 0.12MPa. The esterification reaction was considered complete when the amount of water produced reached 95% of the theoretical amount. Subsequently, the reaction system was gradually heated and the pressure reduced, and then a polycondensation reaction was carried out at 280℃ and below 100Pa. The polymerization reaction was terminated when the required intrinsic viscosity of 0.6dL / g was reached. The product was then removed and pelletized to obtain PET.

[0119] Performance testing Thermogravimetric analysis was performed on the titanium-based multimetallic polyester catalyst prepared in Example 1, and the results were obtained. Figure 6 .from Figure 6 It can be seen that the titanium-based polymetallic polyester catalyst can maintain structural stability below 300℃.

[0120] The intrinsic viscosity (IV) and b-value of the PET prepared in Comparative Examples 1-6 and Comparative Examples 1-5 were tested. The test standard was GB / T17931-2018.

[0121] The test results are shown in Table 1.

[0122] In Table 1, the lower the b value, the lower the degree of yellowing of PET.

[0123] Table 1

[0124] Compared to Comparative Examples 1 and 2, the b-value of Example 1 was significantly reduced. The only difference between Example 1 and Comparative Examples 1 and 2 was the catalyst precursor used; the precursor for Example 1 was a zeolite-like imidazolium ester framework material simultaneously doped with cobalt and zinc, the precursor for Comparative Example 1 was a zinc-doped zeolite-like imidazolium ester framework material, and the precursor for Comparative Example 2 was a cobalt-doped zeolite-like imidazolium ester framework material. This indicates that using a zeolite-like imidazolium ester framework material simultaneously doped with cobalt and zinc as a precursor can further reduce the b-value of PET compared to zeolite-like imidazolium ester framework materials doped only with zinc or only doped with cobalt.

[0125] Compared to Comparative Example 3, the b-value of Example 1 was significantly reduced. The only difference between Example 1 and Comparative Example 3 was whether CTAB was added during catalyst preparation; Example 1 added CTAB, while Comparative Example 3 did not. This indicates that adding CTAB during catalyst preparation (after precursor synthesis) can further reduce the b-value of PET. A possible reason is that in this invention, CTAB is introduced simultaneously with the titanium source after precursor synthesis. CTAB can create pores in TiO2 while forming TiO2, and the resulting pore structure extends from the TiO2 surface to the precursor, exposing Co in the precursor. Co ions can inhibit PET yellowing to some extent. In Comparative Example 3, no CTAB was added, and therefore no pore structure was formed in TiO2.

[0126] Compared to Comparative Example 4, the b-value of Example 1 was significantly reduced. The only difference between Example 1 and Comparative Example 4 was the timing of CTAB addition; in Example 1, CTAB was introduced simultaneously with the titanium source after precursor synthesis, while in Comparative Example 4, CTAB was introduced simultaneously with precursor synthesis. This indicates that introducing CTAB simultaneously with the titanium source after precursor synthesis, compared to introducing it simultaneously with precursor synthesis, further reduces the b-value of PET. A possible reason is that introducing CTAB simultaneously with precursor synthesis allows CTAB to open pores in the precursor during its formation, improving the pore size of the precursor material; subsequently, TiO2 is loaded. 2， TiO2 can enter or cover the porous structure of the precursor material without exposing Co in the precursor (Co ions can inhibit PET yellowing to some extent). However, after synthesizing the precursor, CTAB is introduced along with the titanium source. CTAB can create pores in TiO2 while forming TiO2. The resulting pore structure extends from the TiO2 surface to the precursor, exposing Co in the precursor. Co ions can inhibit PET yellowing to some extent.

Claims

1. A titanium-based multimetallic polyester catalyst comprising a precursor and titanium dioxide supported on the precursor; wherein the precursor is a cobalt- and zinc-doped zeolite-like imidazole ester framework material, and the titanium dioxide has a microporous and mesoporous structure. Its preparation methods include: (1) The imidazole ligand solution was reacted with the cobalt-zinc solution, and the solid was collected to obtain the precursor; The cobalt-zinc solution refers to an organic solution of cobalt and zinc salts; (2) Add ammonia water dropwise to the suspension containing template agent and precursor, stir, add titanate ester and disperse evenly, carry out reaction, separate the solid, and obtain intermediate product 1; (3) Add intermediate product 1 to an alcohol-water solution to react, separate the solid, and obtain intermediate product 2; (4) Add intermediate product 2 to an alcohol solvent, reflux the reaction, separate the solid, dry it, and obtain the titanium-based polymetallic polyester catalyst. The molar ratio of the imidazole ligand, zinc salt, and cobalt salt is (2~64):1:(0.1~10). The mass ratio of the precursor to the template agent is (1~10):1; The molar ratio of titanium ions in the titanate to zinc ions in the zinc salt is (0.1~10):1; The template agent is selected from hexadecyltrimethylammonium bromide.

2. The titanium-based multimetallic polyester catalyst as described in claim 1, characterized in that, The specific surface area of ​​the titanium-based multimetallic polyester catalyst is 950~1550 m². 2 / g; or / and, The average pore size of the microporous structure is 0.5 nm to 1.3 nm; or / and, The average pore size of the mesoporous structure is 4~10 nm.

3. A method for preparing the titanium-based polymetallic polyester catalyst as described in any one of claims 1-2, comprising: (1) The imidazole ligand solution is reacted with the cobalt-zinc solution, and the solid is collected to obtain the precursor; the cobalt-zinc solution refers to an organic solution of cobalt salt and zinc salt; (2) Add ammonia water dropwise to the suspension containing template agent and precursor, stir, add titanate ester and disperse evenly, carry out reaction, separate the solid, and obtain intermediate product 1; (3) Add intermediate product 1 to an alcohol-water solution to react, separate the solid, and obtain intermediate product 2; (4) Add intermediate product 2 to an alcohol solvent, reflux the reaction, separate the solid, dry it, and obtain the titanium-based polymetallic polyester catalyst. The molar ratio of the imidazole ligand, zinc salt, and cobalt salt is (2~64):1:(0.1~10). The molar ratio of titanium ions in the titanate to zinc ions in the zinc salt is (0.1~10):1; The template agent is selected from hexadecyltrimethylammonium bromide; The mass ratio of the precursor to the template agent is (1~10):

1.

4. The preparation method according to claim 3, characterized in that, The imidazole ligand is selected from at least one of imidazole, 2-methylimidazolium, benzimidazole, and 2-ethylimidazolium; or / and, The solvent for the imidazole ligand solution is selected from at least one of N,N-dimethylformamide, N,N-diethylformamide, methanol, and ethanol; or / and, The anion of the cobalt salt is selected from at least one of chloride ions, nitrate ions, and acetate ions; or / and, The anion of the zinc salt is selected from at least one of chloride ions, nitrate ions, and acetate ions; or / and, The solvent for the cobalt-zinc solution is selected from at least one of methanol, ethanol, and N,N-dimethylformamide; or / and, The solvent for the suspension is selected from at least one of methanol and ethanol; or / and, The titanate is selected from at least one of tetrabutyl titanate, tetraisobutyl titanate, tetraisopropyl titanate, and tetraethyl titanate; or / and, The alcohol in the alcohol-water solution is selected from at least one of methanol and ethanol; or / and, The alcohol solvent is selected from at least one of methanol and ethanol.

5. The preparation method according to claim 3, characterized in that, The volume ratio of methanol to water in the alcohol-water solution is (0.1~60):1; or / and, The amount of ammonia added relative to the template agent is 0.1 mL to 10 mL / g.

6. The preparation method according to claim 3, characterized in that, The reaction temperature in step (1) is 25~160℃; or / and, The reaction time for step (1) is 12 to 72 hours; or / and, The reaction temperature in step (2) is room temperature; or / and, The reaction time for step (2) is 5-60 minutes; or / and, The reaction time for step (3) is 12-24 hours; or / and, The reaction temperature in step (4) is 60~80℃; or / and, The reaction time for step (4) is 0.5 to 8 hours.

7. The application of a titanium-based multimetallic polyester catalyst as described in any one of claims 1-2 or a titanium-based multimetallic polyester catalyst prepared by the preparation method as described in any one of claims 3-6 in the field of preparing polyethylene terephthalate.

8. A method for preparing polyethylene terephthalate, comprising reacting raw materials including terephthalic acid and ethylene glycol; The catalyst used is selected from the titanium-based polymetallic polyester catalyst as described in any one of claims 1-2 or the titanium-based polymetallic polyester catalyst prepared by the preparation method as described in any one of claims 3-6; The amount of catalyst used is 0.001 to 0.02 wt% of the total weight of terephthalic acid and ethylene glycol.

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