Preparation method of composite metal catalyst and application of composite metal catalyst in polyester synthesis

Abstract

The invention relates to the technical field of polyester synthesis, and discloses a preparation method of a composite metal catalyst and application of the composite metal catalyst in polyester synthesis, and the preparation method comprises the following steps: (1) weighing zirconium oxychloride to prepare a zirconium solution, weighing copper nitrate to prepare a copper solution, and weighing citric acid to prepare a chelating solution; (2) adding the chelating solution into a zirconium solution, heating and stirring, adding a copper solution, and continuously heating and stirring to obtain a mixed solution; (3) adding ammonia water into the mixed solution to adjust the pH value to 5-6 to obtain sol; (4) standing for gelation, removing impurities, and carrying out solvent replacement by adopting ethanol to obtain gel; and (5) drying and roasting the gel to obtain the composite metal catalyst. The composite metal catalyst with higher catalytic activity and selectivity is obtained by optimizing the preparation steps, the zirconium-copper ratio and other condition parameters, and the food-grade polyester product with high tensile strength, high viscosity and low haze is prepared by applying the composite metal catalyst to the polyester synthesis reaction.

Description

Technical Field

[0001] This invention relates to the technical field of polyester synthesis, and in particular to a method for preparing a composite metal catalyst and its application in polyester synthesis. Background Technology

[0002] Polyester typically refers to polyethylene terephthalate (PET), which is widely used in industry and daily life due to its superior mechanical, physical, and chemical properties. Polyester is generally synthesized using the following methods: First, dimethyl terephthalate (DMT) and ethylene glycol (EG) undergo transesterification in the presence of a catalyst to produce diethyl terephthalate (BHET). Commonly used catalysts are zinc, cobalt, or manganese acetates, or mixtures of these with antimony trioxide, at a concentration of 0.01-0.05% of the DMT mass. Methanol, a byproduct, is continuously discharged during the reaction. The second step involves polycondensation of the generated BHET in a polycondensation reactor at a temperature of 280-290°C. Under the action of a polymerization catalyst, the polycondensation reaction is carried out under high vacuum (below 10 kPa) and high-speed stirring to obtain high molecular weight polyester.

[0003] In the aforementioned polycondensation reaction, it is evident that the quality of polyester is significantly influenced by the type of polymerization catalyst used; different catalysts will result in altered polyester properties. The catalysts most commonly used and researched in production are primarily antimony (Sb), germanium (Ge), and titanium (Ti) compounds. Extensive research indicates that while Ge-based catalysts produce PET with fewer side reactions and higher purity, their reactivity is low, and they are scarce and expensive. Ti-based catalysts exhibit high activity and fast reaction rates, but they also produce numerous catalytic side reactions, leading to poor thermal stability and a yellowish color in the product, generally limiting their use to certain matte finish products. In contrast, Sb-based catalysts not only have higher activity but also produce higher purity products with fewer side reactions and are inexpensive, thus gaining widespread application.

[0004] Antimony-based catalysts, such as antimony glycolate and antimony trioxide, are widely used in industry. For example, patent CN105461906B discloses a polyester and its preparation method, in which terephthalic acid and ethylene glycol are esterified and then polycondensed under the catalysis of a mixture of magnesium glycolate and antimony glycolate to obtain polyester. However, using antimony compounds as polycondensation catalysts presents the following problems: Antimony is a heavy metal with cumulative toxicity, harmful to the human respiratory, digestive, and liver systems, and long-term exposure may be carcinogenic. Furthermore, antimony-based catalysts are difficult to completely remove after polymerization, typically remaining at 10-30 ppm in PET chips, posing a health risk. Secondly, antimony-based catalysts require high temperatures of 270-290℃ to function, leading to increased corrosion of the polycondensation reactor and a higher energy consumption ratio, which does not meet the "dual carbon" target. Finally, if the obtained polyester is used to produce fibers in the spinning and / or stretching processes, the resulting fiber yarns are prone to problems such as fuzzing and breakage, making them unsuitable for high-intensity environments. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a composite metal catalyst and its application in polyester synthesis. By optimizing the preparation steps, zirconium-copper ratio, and other parameters, a composite metal catalyst with higher catalytic activity and selectivity is obtained. When applied to the polyester synthesis reaction, it enables the preparation of food-grade polyester products with high tensile strength, high viscosity, and low haze, while significantly reducing production energy consumption.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a composite metal catalyst, comprising the following steps: (1) Weigh zirconium oxychloride to prepare zirconium solution, weigh copper nitrate to prepare copper solution, and weigh citric acid to prepare chelation solution; (2) Add the chelating solution to the zirconium solution and heat and stir, then add the copper solution and continue to heat and stir to obtain a mixed solution; (3) Add ammonia to the mixed solution to adjust the pH to 5-6 to obtain a sol; (4) Then, allow the mixture to stand and gel, then remove impurities by solvent replacement with ethanol to obtain a gel; (5) The gel is dried and calcined to obtain a composite metal catalyst.

[0007] The composite metal catalyst in this invention is a CuO-ZrO2 composite catalyst, in which CuO is dispersed on a ZrO2 support to form a structure. Due to the abundant oxygen vacancies and specific hydroxyl groups on the ZrO2 surface, CuO becomes a suitable catalyst for ZrO2. 2+Ions provide anchoring sites, and there is a strong interaction between CuO and ZrO2. Furthermore, by optimizing the preparation steps, zirconium-copper ratio, and other conditional parameters, the dispersion of CuO is improved, and the synergistic effect between CuO and ZrO2 is enhanced, resulting in higher catalytic activity and selectivity.

[0008] Specifically, by adding chelating agents and selecting gelation preparation methods, not only can the Cu... 2+ The dispersion of ions is improved, and a more stable Cu-O-Zr interface structure is formed. This interface is an active region for electron transfer and mass transport, requiring higher energy to break. Further drying and calcination yield CuO and ZrO2. The introduction of CuO affects the crystal phase structure of ZrO2. 2+ CuO can stabilize the highly active metastable tetragonal phase (t-ZrO2) of ZrO2, preventing its transformation into the thermodynamically stable monoclinic phase (m-ZrO2). The tetragonal phase (t-ZrO2) exhibits higher catalytic activity in polyester polycondensation reactions. Moreover, ZrO2 itself has certain acidity and basicity; the introduction of CuO increases the Lewis acidity of the ZrO2 surface, enhancing its adsorption capacity for reactants (such as the carbonyl oxygen in hydroxyethyl ester groups).

[0009] Preferably, in step (1), the molar concentration of zirconium ions in the zirconium solution is 0.3-1 mol / L; the molar concentration of copper ions in the copper solution is 0.4-0.6 mol / L; and the molar concentration of citric acid in the chelation solution is 1.2-1.5 mol / L.

[0010] Preferably, in step (2), the molar ratio of citric acid to the total molar ratio of zirconium ions and copper ions in the mixed solution is 1:1, and the molar ratio of zirconium ions to copper ions is 3-10:1; more preferably, the molar ratio of zirconium ions to copper ions is 5-8:1.

[0011] If the zirconium-copper ratio is too high (molar ratio of zirconium ions to copper ions > 10:1), insufficient CuO content leads to a decrease in the density of active sites and a reduction in catalytic activity. If the zirconium-copper ratio is too low (molar ratio of zirconium ions to copper ions < 3:1), the CuO particles lack a carrier for dispersion, resulting in an increased particle size and a decreased specific surface area.

[0012] Preferably, in step (2), the heating and stirring is carried out at 80-90°C for 1-2 hours.

[0013] Preferably, in step (2), the continued heating and stirring is performed at 50-60°C for 30-60 minutes.

[0014] Preferably, in step (5), the calcination is as follows: first, the temperature is increased to 200-250℃ at a rate of 1-5℃ / min and held for 30-60min; then, the temperature is increased to 300-350℃ at a rate of 1-5℃ / min and held for 1-2h; finally, the temperature is increased to 450-500℃ at a rate of 1-5℃ / min and held for 2-3h.

[0015] First, calcination is carried out at 200-250℃ to remove citric acid, then calcination is carried out at 300-350℃ to decompose nitrates, and finally calcination is carried out at 450-500℃ to promote the formation of highly active tetragonal phase (t-ZrO2) of ZrO2. By adopting staged calcination, the Cu-O-Zr structure in the catalyst can be made more stable, and a higher proportion of tetragonal phase ZrO2 can be obtained, thus achieving better catalytic performance.

[0016] Secondly, the present invention also provides an application of a composite metal catalyst in polyester synthesis, comprising: performing an ester exchange reaction on DMT, EG and an ester exchange catalyst; after the reaction is completed, adding an ethylene glycol solution containing the composite metal catalyst to perform a polycondensation reaction to obtain polyester.

[0017] Polyester polycondensation is a chain-extending reaction, and its catalytic mechanism is chelation coordination. The most common polycondensation catalysts are antimony-based catalysts, but due to Cu... 2+ The smaller radius and transition metal d orbital electronic properties result in stronger electron attraction, providing a stronger coordination effect and thus a stronger catalytic effect.

[0018] In composite metal catalysts, the strong interaction between ZrO2 and CuO is utilized to fully leverage the bifunctional catalysis of the Cu-O-Zr bond structure. Through the arc-pair electron coordination between CuO and the carbonyl oxygen in the hydroxyethyl ester group, the positive charge on the carbon atom of the hydroxyethyl ester group is significantly enhanced, lowering the nucleophilic substitution barrier and making it more susceptible to nucleophilic attack. Simultaneously, the oxygen vacancy on the adjacent ZrO2 group activates the hydroxyl group in the other hydroxyethyl ester group, increasing the nucleophilicity of the hydroxyl group and enabling it to attack the adjacent carbon atom of the hydroxyethyl ester group, thereby promoting intermolecular condensation polymerization of BHET.

[0019] Preferably, the mass ratio of DMT, EG, transesterification catalyst, and ethylene glycol solution containing composite metal catalyst is 2:1:0.02-0.03:0.04-0.08; the mass concentration of composite metal catalyst in ethylene glycol solution containing composite metal catalyst is 15-20%; the transesterification catalyst is manganese acetate and / or zinc nitrate, more preferably manganese nitrate.

[0020] Preferably, the transesterification reaction is carried out at a temperature of 190-230°C for 2.5-3.5 hours.

[0021] Preferably, the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction. The temperature of the pre-polycondensation reaction is 235-240℃, the pressure is 1-10kPa, and the time is 30-60min. The temperature of the final polycondensation reaction is 250℃, the pressure is <100Pa, and the time is 1-2h.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The high specific surface area of ​​the composite metal catalyst provides more active sites, which greatly improves the rate of polycondensation reaction; there is no antimony residue, which effectively overcomes the pollution problem of traditional Sb catalysts.

[0023] (2) The new polyester has high strength and easy stretching properties, with acetaldehyde content ≤5ppm and haze ≤1.5%, and can be widely used in medical fiber, food packaging bottle and other scenarios.

[0024] (3) Compared with the traditional antimony-based process (which requires 280-290℃), the production process significantly reduces energy consumption and equipment corrosion. At the same time, no other waste liquid is generated, making it a green production process. Attached Figure Description

[0025] Figure 1 This is a SEM image of the composite metal catalyst in this invention. Detailed Implementation

[0026] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] The preparation of the composite metal catalyst in this invention includes the following steps: (1) Weigh zirconium oxychloride and add it to water to prepare a zirconium solution. The molar concentration of zirconium ions in the zirconium solution is 0.3-1 mol / L. Weigh copper nitrate and add it to ethanol to prepare a copper solution. The molar concentration of copper ions in the copper solution is 0.4-0.6 mol / L. Weigh citric acid and add it to water to prepare a chelation solution. The molar concentration of citric acid in the chelation solution is 1.2-1.5 mol / L. (2) Add the chelation solution to the zirconium solution and stir at 80-90℃ for 1-2 hours, then add the copper solution and stir at 50-60℃ for 30-60 minutes to obtain a mixed solution. In the mixed solution, the molar ratio of citric acid to the total molar ratio of zirconium ions and copper ions is 1:1, and the molar ratio of zirconium ions to copper ions is 3-10:1. (3) Add ammonia to the mixed solution to adjust the pH to 5-6 to obtain a sol; (4) Then, allow the mixture to stand and gel, then remove impurities by solvent replacement with ethanol to obtain a gel; (5) Dry the gel and then calcine it. First, raise the temperature to 200-250℃ at a rate of 1-5℃ / min and hold for 30-60min; then raise the temperature to 300-350℃ at a rate of 1-5℃ / min and hold for 1-2h; finally, raise the temperature to 450-500℃ at a rate of 1-5℃ / min and hold for 2-3h to obtain the composite metal catalyst.

[0028] The preparation of polyester in this invention includes the following steps: S1. Add DMT, EG, and the transesterification catalyst to the transesterification reactor, slowly increase the reactor temperature to 190-210℃ to carry out the transesterification reaction to generate BHET, maintain the reaction for 2-3 hours, and continuously distill off methanol byproducts during the reaction; then add an ethylene glycol solution containing a composite metal catalyst at a mass concentration of 15-20%, a stabilizer, and a matting agent. The mass ratio of DMT, EG, transesterification catalyst, ethylene glycol solution containing composite metal catalyst, stabilizer, and matting agent is 2:1:0.02-0.03:0.04-0.08:0.05-0.1:1-1.5; continue to increase the reactor temperature to 210-230℃, maintain the reaction for 0.5-1 hours, distill off excess ethylene glycol in the reactor, take a sample to test the BHET conversion rate, confirm that the BHET purity is ≥98%, and send the product through a filter into a polycondensation reactor.

[0029] S2. Heat the polycondensation reactor to 235-240℃ and start stirring (50-100 rpm), controlling the heating time to 5 minutes. After reaching the temperature, turn on the vacuum pump and maintain a low vacuum (1-10 kPa) for 30-60 minutes to initially increase the molecular weight. Then, heat the reactor to the set temperature of 250℃ and turn off the heat transfer system. Because the polymer material polymerizes at a certain temperature and vacuum, the heat generated by the polymer friction itself will cause the polymer temperature to rise as the viscosity increases. To ensure product quality, it is necessary to control the final discharge temperature of the polymer. Maintain a high vacuum of less than 100 Pa for 1-2 hours. Under high vacuum, the viscosity of the material will continuously increase. Use a viscometer to measure the melt viscosity in segments. When the viscosity growth rate drops to a certain value (<0.001 dL / g / min), the reaction is considered complete. Pressurize and drop the material through an electric valve, then pelletize it through an underwater pelletizer to finally obtain polyester.

[0030] Example 1 1. Composite metal catalysts The preparation of composite metal catalysts includes the following steps: (1) Weigh 16.10g of zirconium oxychloride (ZrOCl2•8H2O, 0.05mol) and dissolve it in 100mL of deionized water to prepare a zirconium solution (pH≈1-2 at this time); weigh 2.42g of copper nitrate (Cu(NO3)2•3H2O, 0.01mol) and dissolve it in 20mL of ethanol to prepare a copper solution; weigh 11.52g of citric acid (0.06mol, CA:(Zr+Cu)=1:1) and dissolve it in 45mL of deionized water to prepare a chelation solution.

[0031] (2) First, add the chelation solution to the zirconium solution, control the water bath temperature at 80℃, and stir continuously for 1 hour to form a transparent Zr-CA complex; then slowly add copper solution, control the water bath temperature at 60℃, and stir continuously for 30 minutes to turn the system into a blue-green solution. Next, slowly add ammonia water, and the viscosity of the system will increase accordingly. Adjust the pH to 5 to form a dark blue sol.

[0032] (3) Then, control the water bath temperature to 70℃, and stir continuously for 3 hours with the container open. After the solvent evaporates to 50% of its original volume, transfer the remaining sol to a petri dish and place it at room temperature (25℃) for 24 hours. After a semi-solid wet gel is formed, cover the gel with 20% ethanol solution and seal the petri dish to enhance network crosslinking. After standing for 72 hours, remove the gel and break it up. Soak and wash it three times (2 hours each time) with a 1:1 ammonia / ethanol mixture until the leachate shows no Cl- when tested with AgNO3. - To reduce drying stress, the solution was replaced three times with anhydrous ethanol to obtain a gel.

[0033] (3) Then, maintaining a vacuum of 0.09 MPa, vacuum drying at 60°C for 24 h was performed to obtain a porous blue dry gel. The dry gel was transferred to a crucible and placed in a muffle furnace. The temperature was increased to 200°C at 2°C / min and calcined for 0.5 h, then increased to 300°C at 2°C / min and calcined for 1 h, and then increased to 450°C at 1°C / min and calcined for 2 h. Finally, the calcined product was ground in a grinder for 30 min and passed through a 200-mesh sieve to obtain a composite metal catalyst, such as... Figure 1 The image shows the surface morphology of the composite metal catalyst, indicating that CuO has a good dispersion state on the ZrO2 surface.

[0034] 2. Polyester The preparation of polyester includes the following steps: S1. DMT, ethylene glycol, and transesterification catalyst (manganese acetate) were added to the transesterification reactor. The reactor temperature was slowly increased to 210°C to initiate the transesterification reaction and generate BHET. The reaction was maintained for 3 hours, during which methanol byproducts were continuously distilled off. Subsequently, an ethylene glycol solution containing a 20% mass concentration of the composite metal catalyst, a stabilizer (trimethyl phosphate), and a matting agent (titanium dioxide) were added to the transesterification reactor. The mass ratio of DMT, EG, transesterification catalyst, ethylene glycol solution containing the composite metal catalyst, stabilizer, and matting agent was 2:1:0.025:0.04:0.09:1.2. The reactor temperature was further increased to 220°C, and the reaction was maintained for 0.5 hours. After distilling off excess ethylene glycol from the reactor, a sample was taken to test the BHET conversion rate, confirming that the BHET purity was ≥98%.

[0035] S2. The product is fed into the polycondensation reactor through a filter. The reactor is heated to 240°C and stirred (100 rpm) for 5 minutes. After reaching the set temperature, the vacuum pump is turned on to maintain a low vacuum (5 kPa) for 0.5 hours. The temperature is then raised to the set temperature of 250°C, and the heat transfer system of the polycondensation reactor is turned off. The reaction is carried out under a high vacuum of less than 50 Pa for 2 hours. The melt viscosity is measured in segments using a viscometer. When the viscosity growth rate drops to a certain value (<0.001 dL / g / min), the reaction is considered complete. The material is then pressurized and dropped through an electric valve and pelletized by an underwater pelletizer to obtain polyester.

[0036] Example 2 This embodiment uses the same composite metal catalyst as in Example 1, but the amount added during the polyester preparation process is different.

[0037] The preparation of polyester includes the following steps: S1. DMT, ethylene glycol, and transesterification catalyst (manganese acetate) were added to the transesterification reactor. The reactor temperature was slowly increased to 210°C to initiate the transesterification reaction and generate BHET. The reaction was maintained for 3 hours, during which methanol byproducts were continuously distilled off. Subsequently, an ethylene glycol solution containing a 20% mass concentration of the composite metal catalyst, a stabilizer (trimethyl phosphate), and a matting agent (titanium dioxide) were added to the transesterification reactor. The mass ratio of DMT, EG, transesterification catalyst, ethylene glycol solution containing the composite metal catalyst, stabilizer, and matting agent was 2:1:0.025:0.06:0.09:1.2. The reactor temperature was further increased to 220°C, and the reaction was maintained for 0.5 hours. After distilling off excess ethylene glycol from the reactor, a sample was taken to test the BHET conversion rate, confirming that the BHET purity was ≥98%.

[0038] S2. The product is fed into the polycondensation reactor through a filter. The reactor is heated to 240°C and stirred (100 rpm) for 5 minutes. After reaching the set temperature, the vacuum pump is turned on to maintain a low vacuum (5 kPa) for 0.5 hours. The temperature is then raised to the set temperature of 250°C, and the heat transfer system of the polycondensation reactor is turned off. The reaction is carried out under a high vacuum of less than 50 Pa for 2 hours. The melt viscosity is measured in segments using a viscometer. When the viscosity growth rate drops to a certain value (<0.001 dL / g / min), the reaction is considered complete. The material is then pressurized and dropped through an electric valve and pelletized by an underwater pelletizer to obtain polyester.

[0039] Example 3 This embodiment uses the same composite metal catalyst as in Example 1, but the amount added during the polyester preparation process is different.

[0040] The preparation of polyester includes the following steps: S1. DMT, ethylene glycol, and transesterification catalyst (manganese acetate) were added to the transesterification reactor. The reactor temperature was slowly increased to 210°C to initiate the transesterification reaction and generate BHET. The reaction was maintained for 3 hours, during which methanol byproducts were continuously distilled off. Subsequently, an ethylene glycol solution containing a 20% mass concentration of the composite metal catalyst, a stabilizer (trimethyl phosphate), and a matting agent (titanium dioxide) were added to the transesterification reactor. The mass ratio of DMT, EG, transesterification catalyst, ethylene glycol solution containing the composite metal catalyst, stabilizer, and matting agent was 2:1:0.025:0.08:0.09:1.2. The reactor temperature was further increased to 220°C, and the reaction was maintained for 0.5 hours. After distilling off excess ethylene glycol from the reactor, a sample was taken to test the BHET conversion rate, confirming that the BHET purity was ≥98%.

[0041] S2. The product is fed into the polycondensation reactor through a filter. The reactor is heated to 240°C and stirred (100 rpm) for 5 minutes. After reaching the set temperature, the vacuum pump is turned on to maintain a low vacuum (5 kPa) for 0.5 hours. The temperature is then raised to the set temperature of 250°C, and the heat transfer system of the polycondensation reactor is turned off. The reaction is carried out under a high vacuum of less than 50 Pa for 2 hours. The melt viscosity is measured in segments using a viscometer. When the viscosity growth rate drops to a certain value (<0.001 dL / g / min), the reaction is considered complete. The material is then pressurized and dropped through an electric valve and pelletized by an underwater pelletizer to obtain polyester.

[0042] Example 4 This embodiment uses the same polyester preparation process as in Example 1, but employs a high zirconium-copper ratio composite metal catalyst.

[0043] 1. Composite metal catalysts The preparation of composite metal catalysts includes the following steps: (1) Weigh 32.20g of zirconium oxychloride (ZrOCl2•8H2O, 0.1mol) and dissolve it in 200mL of deionized water to prepare a zirconium solution (pH≈1-2 at this time); weigh 2.42g of copper nitrate (Cu(NO3)2•3H2O, 0.01mol) and dissolve it in 20mL of ethanol to prepare a copper solution; weigh 21.12g of citric acid (0.11mol, CA:(Zr+Cu)=1:1) and dissolve it in 45mL of deionized water to prepare a chelation solution.

[0044] (2) First, add the chelation solution to the zirconium solution, control the water bath temperature at 80℃, and stir continuously for 1 hour to form a transparent Zr-CA complex; then slowly add copper solution, control the water bath temperature at 60℃, and stir continuously for 30 minutes to turn the system into a blue-green solution. Next, slowly add ammonia water, and the viscosity of the system will increase accordingly. Adjust the pH to 5 to form a dark blue sol.

[0045] (3) Then, control the water bath temperature to 70℃, and stir continuously for 3 hours with the container open. After the solvent evaporates to 50% of its original volume, transfer the remaining sol to a petri dish and place it at room temperature (25℃) for 24 hours. After a semi-solid wet gel is formed, cover the gel with 20% ethanol solution and seal the petri dish to enhance network crosslinking. After standing for 72 hours, remove the gel and break it up. Soak and wash it three times (2 hours each time) with a 1:1 ammonia / ethanol mixture until the leachate shows no Cl- when tested with AgNO3. - To reduce drying stress, the solution was replaced three times with anhydrous ethanol to obtain a gel.

[0046] (3) Then, maintaining a vacuum of 0.09 MPa, vacuum drying at 60°C for 24 h was performed to obtain a porous blue dry gel. The dry gel was transferred to a crucible and placed in a muffle furnace. The temperature was increased to 200°C at 2°C / min and calcined for 0.5 h, then increased to 300°C at 2°C / min and calcined for 1 h, and then increased to 450°C at 1°C / min and calcined for 2 h. Finally, the calcined product was placed in a grinder and ground for 30 min, and then passed through a 200-mesh sieve to obtain the composite metal catalyst.

[0047] 2. Polyester The preparation steps for the polyester are the same as in Example 1.

[0048] Comparative Example 1 This comparative example uses the same composite metal catalyst as Example 1, but the polycondensation temperature during polyester preparation is different.

[0049] The preparation of polyester includes the following steps: S1. DMT, ethylene glycol, and transesterification catalyst (manganese acetate) were added to the transesterification reactor. The reactor temperature was slowly increased to 210°C to initiate the transesterification reaction and generate BHET. The reaction was maintained for 3 hours, during which methanol byproducts were continuously distilled off. Subsequently, an ethylene glycol solution containing a 20% mass concentration of the composite metal catalyst, a stabilizer (trimethyl phosphate), and a matting agent (titanium dioxide) were added to the transesterification reactor. The mass ratio of DMT, EG, transesterification catalyst, ethylene glycol solution containing the composite metal catalyst, stabilizer, and matting agent was 2:1:0.025:0.04:0.09:1.2. The reactor temperature was further increased to 220°C, and the reaction was maintained for 0.5 hours. After distilling off excess ethylene glycol from the reactor, a sample was taken to test the BHET conversion rate, confirming that the BHET purity was ≥98%.

[0050] S2. The product is fed into the polycondensation reactor through a filter. The reactor is heated to 265°C and stirred (100 rpm) for 5 minutes. After reaching the set temperature, the vacuum pump is turned on to maintain a low vacuum (5 kPa) for 0.5 hours. The temperature is then raised to the set temperature of 285°C, and the heat transfer system of the polycondensation reactor is turned off. The reaction is carried out under a high vacuum of less than 50 Pa for 2 hours. The melt viscosity is measured in segments using a viscometer. When the viscosity growth rate drops to a certain value (<0.001 dL / g / min), the reaction is considered complete. The material is then pressurized and dropped through an electric valve and pelletized by an underwater pelletizer to obtain polyester.

[0051] Comparative Example 2 This comparative example uses the same polyester preparation process as Comparative Example 1, but uses antimony glycol as the polycondensation catalyst.

[0052] The preparation of polyester includes the following steps: S1. DMT, ethylene glycol, and transesterification catalyst (manganese acetate) were added to the transesterification reactor. The reactor temperature was slowly increased to 210°C to initiate the transesterification reaction and generate BHET. The reaction was maintained for 3 hours, during which methanol byproducts were continuously distilled off. Subsequently, an ethylene glycol solution containing 20% ​​antimony glycol, a stabilizer (trimethyl phosphate), and a matting agent (titanium dioxide) were added to the transesterification reactor. The mass ratio of DMT, EG, transesterification catalyst, ethylene glycol solution containing antimony glycol, stabilizer, and matting agent was 2:1:0.025:0.04:0.09:1.2. The reactor temperature was further increased to 220°C, and the reaction was maintained for 0.5 hours. After distilling off excess ethylene glycol from the reactor, a sample was taken to test the BHET conversion rate, confirming that the BHET purity was ≥98%.

[0053] S2. The product is fed into the polycondensation reactor through a filter. The reactor is heated to 265°C and stirred (100 rpm) for 5 minutes. After reaching the set temperature, the vacuum pump is turned on to maintain a low vacuum (5 kPa) for 0.5 hours. The temperature is then raised to the set temperature of 285°C, and the heat transfer system of the polycondensation reactor is turned off. The reaction is carried out under a high vacuum of less than 50 Pa for 2 hours. The melt viscosity is measured in segments using a viscometer. When the viscosity growth rate drops to a certain value (<0.001 dL / g / min), the reaction is considered complete. The material is then pressurized and dropped through an electric valve and pelletized by an underwater pelletizer to obtain polyester.

[0054] Comparative Example 3 This comparative example uses the same polyester preparation process as Example 1, but uses a composite metal catalyst prepared by a different method.

[0055] 1. Composite metal catalysts The preparation of composite metal catalysts includes the following steps: A suitable amount of zirconium dioxide (ZrO2) support was weighed and placed in a muffle furnace, heated to 550℃ at a heating rate of 5℃ / min, and calcined for 4 hours to remove surface adsorbed impurities and moisture. Copper nitrate powder, weighed at 15% of the support mass, was dissolved in deionized water to prepare a 0.5 mol / L copper nitrate solution. The cooled zirconium dioxide support was placed in the copper nitrate solution, with a liquid-to-solid ratio controlled at 5:1. The solution was magnetically stirred at 200 rpm for 3 hours at a constant temperature of 60℃. The copper-adsorbed support was then separated by centrifugation, and the solid was placed in a vacuum drying oven and dried at 120℃ for 6 hours. The dried sample was transferred to a crucible, placed in a muffle furnace, and calcined at 250℃ at a heating rate of 3℃ / min for 3 hours to convert copper ions into the active component, copper oxide. Finally, the calcined product was ground in a grinder for 30 minutes and passed through a 200-mesh sieve to obtain the composite metal catalyst.

[0056] 2. Polyester The preparation steps for the polyester are the same as in Example 1.

[0057] Performance testing 1. Metal ion content: detected by atomic absorption spectroscopy.

[0058] 2. Tensile strength and elongation at break: According to "Tension properties of plastics" (ISO 527-2:2012), the equipment uses an electronic universal testing machine and an extensometer. I-type samples are prepared by injection molding or hot pressing. The sample is fixed in the fixture, ensuring that the axis is consistent with the direction of the tensile force. It is stretched at a constant speed until the sample breaks. At least 5 samples are tested in each group, and the average value is taken.

[0059] 3. Heat distortion temperature: According to "Determination of the load deformation temperature of plastics" (ISO 75-2:2013), the equipment uses a heat distortion Vicat softening point temperature tester. The sample is placed in the instrument and heated at a rate of 60±10℃ / h. The temperature at which the sample bends and deforms to 0.32 mm is recorded. At least 5 samples are tested in each group, and the average value is taken.

[0060] Table 1 Table 2 As shown in Table 1, the comparison of Examples 1-3 indicates that with the increase of the amount of composite metal catalyst added, the intrinsic viscosity, melting point, and terminal carboxyl group content of polyester chips all increase to a certain extent. However, excessive addition of composite metal catalyst is not meaningful for production. A comparison between Comparative Example 1 and Example 1 shows that using a higher polycondensation reaction temperature, due to the possibility of other side reactions occurring in ethylene glycol at high temperatures, leads to an increase in the diethylene glycol content in Example 4.

[0061] Comparing the traditional antimony-based processes in Comparative Example 1 and Comparative Example 2, the latter exhibits significantly higher intrinsic viscosity due to its longer molecular chains, resulting in a substantial improvement in mechanical properties. In Comparative Example 1, the lower content of terminal carboxyl groups indicates a more uniform degree of polymerization and improved hydrolysis resistance. The polyester chips have an L-value (brightness) ≥90 and a b-value (yellowness) ≤1.5, requiring no additional decolorization treatment. The lower diethylene glycol content is attributed to fewer side reactions in the polymerization reaction under the action of the composite metal catalyst compared to traditional antimony-based catalysts.

[0062] A comparison between Example 4 and Example 1 shows that the intrinsic viscosity and diethylene glycol content of polyester chips produced using the high zirconium-copper ratio composite metal catalyst are significantly different from those of Example 1. This is because the insufficient CuO content in the high zirconium-copper ratio powdered composite metal catalyst leads to a decrease in the density of active sites and a decrease in catalytic activity, resulting in an excessively long polyester production time, which in turn leads to a decrease in intrinsic viscosity and an increase in diethylene glycol content.

[0063] A comparison between Comparative Example 3 and Example 1 shows that the properties of polyester chips produced using composite metal catalysts prepared by different methods are similar to those of Example 1, both exhibiting excellent catalytic characteristics. However, as shown in Table 2, the polyester chips produced in Comparative Example 3 have significantly higher metal ion content and haze. This is because copper oxide in Comparative Example 3 cannot be uniformly dispersed on the zirconium dioxide support. Although the loading is high, it easily clogs the support pores or accumulates on the surface, resulting in a high metal ion content in the product. Furthermore, the agglomerated particles easily form luminescent clusters, scattering light and increasing haze and color, thus affecting the product's color and leading to poor performance in actual product applications.

[0064] As shown in Table 2, Examples 1-4 are compared with Comparative Examples 1-2, and the Sb content of polyester chips produced by conventional antimony-based processes is... + The residual amount and haze are significantly higher, while the tensile strength, elongation at break and heat distortion temperature are significantly lower. The polyester obtained by this invention has higher transparency, tensile strength and heat resistance, and can be used in high-strength scenarios. It is not easy to crack during processing.

[0065] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a composite metal catalyst, characterized by, It comprises the following steps: (1) Zirconium oxychloride is weighed to prepare a zirconium solution, copper nitrate is weighed to prepare a copper solution, and citric acid is weighed to prepare a chelating solution; (2) The chelating solution is added to the zirconium solution and heated and stirred, then the copper solution is added and heated and stirred, to obtain a mixed solution; (3) Ammonia water is added to the mixed solution to adjust the pH to 5-6, to obtain a sol; (4) Then the sol is left to gel, impurities are removed, and solvent replacement is performed with ethanol, to obtain a gel; (5) The gel is dried and calcined, to obtain a composite metal catalyst.

2. The method of claim 1, wherein the composite metal catalyst is prepared by the steps of: In step (1), the molar concentration of zirconium ions in the zirconium solution is 0.3-1 mol / L; the molar concentration of copper ions in the copper solution is 0.4-0.6 mol / L; and the molar concentration of citric acid in the chelating solution is 1.2-1.5 mol / L.

3. The method of claim 1 or 2, wherein the composite metal catalyst is prepared by the steps of: In step (2), in the mixed solution, the molar ratio of citric acid to the total molar amount of zirconium ions and copper ions is 1:1, and the molar ratio of zirconium ions to copper ions is 3-10:

1.

4. The method of claim 1, wherein the composite metal catalyst is prepared by the steps of: In step (2), the heating and stirring is performed at 80-90℃ for 1-2h.

5. The method for preparing the composite metal catalyst according to claim 1 or 4, characterized in that, In step (2), the continued heating and stirring is performed at 50-60℃ for 30-60min.

6. The method of claim 1 or 4, wherein the composite metal catalyst is prepared by the steps of: In step (5), the calcination is performed as follows: first, the temperature is raised to 200-250℃ at a rate of 1-5℃ / min, and the temperature is maintained for 30-60min; then, the temperature is raised to 300-350℃ at a rate of 1-5℃ / min, and the temperature is maintained for 1-2h; finally, the temperature is raised to 450-500℃ at a rate of 1-5℃ / min, and the temperature is maintained for 2-3h.

7. Use of a composite metal catalyst prepared by the process of claim 1 in the synthesis of polyesters. It comprises: DMT, EG and transesterification catalysts are subjected to a transesterification reaction; After the reaction is completed, an ethylene glycol solution containing a composite metal catalyst is added, and a polycondensation reaction is performed, to obtain a polyester.

8. Use according to claim 7, characterized in that, The mass ratio of the DMT, EG, transesterification catalysts and ethylene glycol solution containing a composite metal catalyst is 2:1:0.02-0.03:0.04-0.08; and the mass concentration of the composite metal catalyst in the ethylene glycol solution containing a composite metal catalyst is 15-20%.

9. Use according to claim 7 or 8, characterized in that, The temperature of the transesterification reaction is 190-230℃, and the time is 2.5-3.5h; and the transesterification catalyst is manganese acetate and / or zinc nitrate.

10. Use according to claim 7 or 8, characterized in that, The polycondensation reaction comprises a pre-polycondensation reaction and a final polycondensation reaction; the temperature of the pre-polycondensation reaction is 235-240℃, the pressure is 1-10kPa, and the time is 30-60min; the temperature of the final polycondensation reaction is 250℃, the pressure is <100Pa, and the time is 1-2h.

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