Multiphase hindered Lewis acid-base pair synergistic catalyst as well as preparation method and application thereof
By constructing hindered Lewis acid-base pair catalysts by doping heteroatoms into carbon nitride matrix materials, the problem of inefficient depolymerization of polyester materials has been solved, realizing the preparation and application of efficient and environmentally friendly catalysts suitable for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QINGDAO INST OF BIOENERGY & BIOPROCESS TECH CHINESE ACADEMY OF SCI
- Filing Date
- 2025-12-08
- Publication Date
- 2026-04-14
AI Technical Summary
In existing technologies, polyester materials are difficult to depolymerize efficiently under mild conditions, and traditional catalysts have low activity, poor selectivity, and are difficult to recycle, resulting in serious environmental pollution problems.
A hindered Lewis acid-base pair catalyst was constructed using a carbon nitride matrix material doped with heteroatoms. By controlling the calcination temperature and heating rate, a heterophase hindered Lewis acid-base pair synergistic catalyst was prepared, thereby improving catalytic activity and selectivity.
It achieves efficient depolymerization of polyester materials under mild conditions. The catalyst has good water resistance and thermal stability, avoids side reactions, and is suitable for large-scale industrial production, which is economical and environmentally friendly.
Smart Images
Figure CN121847183A_ABST
Abstract
Description
Technical Field
[0001] This application relates to a multiphase hindered Lewis acid-base pair synergistic catalyst, its preparation method, and its application, belonging to the field of nanocatalyst technology. Background Technology
[0002] Polyester materials are widely used in many fields such as packaging, textiles, and electronics due to their excellent properties, such as high strength, chemical resistance, and good processing performance. However, the extensive linear use of polyester materials has also brought serious environmental problems. Polyester is difficult to degrade in the natural environment, resulting in a large accumulation of plastic waste. Therefore, how to degrade and recycle polyester materials is an urgent problem to be solved.
[0003] Currently, polyester depolymerization is one of the important ways to achieve the recycling and reuse of polyester materials. Traditional polyester depolymerization methods usually require high temperature and high pressure conditions, have low depolymerization efficiency, and may also generate a large number of by-products. In addition, the catalysts used have problems such as low activity, poor selectivity, and difficulty in recovery.
[0004] Carbon nitride has been widely reported as a hindered Lewis acid-base pair catalyst matrix material in photocatalysis, electrocatalysis and other fields. However, a search revealed that there are no reports or applications of it in the field of polyester depolymerization.
[0005] Therefore, it is of great significance to develop a highly efficient hindered Lewis acid-base pair catalyst based on carbon nitride matrix materials to achieve efficient chemical cycling of polyester materials under mild conditions. Summary of the Invention
[0006] To address the aforementioned issues, a multiphase hindered Lewis acid-base pair synergistic catalyst, its preparation method, and its application are provided. In this application, heteroatoms with Lewis acidity are doped into an alkaline nitrogen-rich carbon material to construct a hindered Lewis acid-base pair, which greatly improves the catalytic activity and selectivity of the catalyst.
[0007] This application provides a method for preparing a heterogeneous hindered Lewis acid-base pair synergistic catalyst, the method comprising: 1) Add the carbon nitride precursor to the solvent, and then add the heteroatom source and mix and stir. 2) After removing the solvent and drying, a solid mixture is obtained; 3) The resulting solid mixture is calcined and cooled to room temperature to obtain the final product.
[0008] Optionally, the heteroatom source is selected from one or more of zinc nitrate, copper sulfate, tin chloride, ferric chloride, magnesium chloride, aluminum chloride, boric acid, and sodium borohydride.
[0009] Optionally, the carbon nitride precursor is one or more of melamine, dicyandiamide, and urea.
[0010] Optionally, the mass ratio of the heteroatom source to the carbon nitride precursor is (0.1~10):100. Within a certain range, the addition of the heteroatom source can increase the heteroatom doping amount, thereby increasing the number of Lewis acid sites and improving catalytic performance. However, when the amount of heteroatom source added increases to a certain extent, excessive heteroatom doping can lead to changes in the catalyst structure, such as a decrease in specific surface area, resulting in a decrease in activity.
[0011] Optionally, step 3) calcination includes: raising the temperature to 300-600°C at a rate of 1-10°C / min and maintaining it for 1-5 hours, then continuing to raise the temperature to 400-700°C at a rate of 1-10°C / min and maintaining it for 1-5 hours.
[0012] Excessively high temperatures can lead to structural collapse and performance degradation, while excessively low temperatures prevent the formation of the target active phase; both significantly impact catalytic performance. The low-temperature stage first removes impurities and low-boiling-point components from the precursor, while the high-temperature stage focuses on constructing a layered structure and pore size distribution, resulting in superior catalytic activity and stability.
[0013] The heating rate of this application allows the moisture and organic components in the precursor to be gradually decomposed and removed without causing damage to the pore structure of the catalyst due to instantaneous gas production. This heating rate balances uniformity and efficiency, shortens the preparation cycle, and does not affect the dispersion of components.
[0014] Optionally, the solvent is one or more of water, acetonitrile, ethanol, and methanol.
[0015] Optionally, step 3) calcination is carried out in air, nitrogen, or argon. Researchers have found that calcination can be performed in an inert gas atmosphere, or in an air atmosphere; an air atmosphere has no negative impact, and the catalyst can be prepared by direct calcination in air.
[0016] This application provides a catalyst prepared by the above-described method for preparing heterogeneous hindered Lewis acid-base pair synergistic catalysts.
[0017] This application provides the application of the above-mentioned catalyst in polyester alcoholysis.
[0018] Optionally, the polyester alcoholysis includes a process of adding polyester and catalyst to an alcohol solution and stirring the reaction under heating conditions; Optionally, the catalyst is used in an amount of 1-10 wt% of the polyester. Optionally, the molar ratio of the polyester to the alcohol is 1:(1~20). Optionally, the reaction temperature for the alcoholysis is 100~200℃; Optionally, the reaction time for the alcoholysis is 30-360 min; Optionally, the alcohol is one or more selected from methanol, ethylene glycol, propylene glycol, and butanediol; Optionally, the polyester is one of BPA-PC (bisphenol A polycarbonate), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PTT (polypropylene terephthalate), and PEN (polyethylene naphthalate).
[0019] The beneficial effects of this application include, but are not limited to: 1. The heterogeneous hindered Lewis acid-base pair synergistic catalyst, its preparation method and application, according to this application, while maintaining excellent activity, has good water resistance and thermal stability. The heteroatom catalyst has a single dispersed active site, avoiding the occurrence of side reactions and the subsequent treatment processes such as purification and treatment that may be caused by by-products, as well as potential environmental problems, making the production process more economical and environmentally friendly, and achieving the goal of "green catalysis".
[0020] 2. According to the heterophase hindered Lewis acid-base pair synergistic catalyst, its preparation method and application, the stability and dispersibility of the heteroatom catalytic material are improved by using a complexation of heteroatom source and carbon nitride precursor to inhibit heteroatom aggregation through the interaction between heteroatom center and ligand.
[0021] 3. The heterogeneous hindered Lewis acid-base pair synergistic catalyst, its preparation method, and its application according to this application have simple process conditions, use inexpensive materials, mild reaction conditions, and can produce materials with superior performance at a lower preparation cost. The preparation method has a wide range of applications and is a simple, fast, economical, and environmentally friendly method for preparing heterogeneous hindered Lewis acid-base pair synergistic catalysts. The resulting catalyst has high stability and can be applied to large-scale industrial production. Attached Figure Description
[0022] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 The XRD (X-ray diffraction) patterns of the heterogeneous hindered Lewis acid-base pair synergistic catalysts obtained in Examples 1-3 and Comparative Example 1 are shown. Figure 2 The image shows a TEM (transmission electron microscope) image of the heterogeneous hindered Lewis acid-base pair synergistic catalyst obtained in Example 2 (HAADF is in HAADF-STEM mode). Figure 3 The image shows the energy dispersive spectroscopy (EDS) elemental mapping of the heterogeneous hindered Lewis acid-base pair synergistic catalyst obtained in Example 2 (C for carbon, N for nitrogen, Zn for zinc). Figure 4 The image shows the XPS (X-ray photoelectron spectroscopy) spectrum of the heterogeneous hindered Lewis acid-base pair synergistic catalyst obtained in Example 1 (C represents carbon, N represents nitrogen, and B represents boron). Detailed Implementation
[0023] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the embodiments of the present application are all purchased through commercial channels.
[0024] Example 1 20g of urea was dispersed in 50ml of ethanol and stirred and heated to obtain a urea solution. 1.5g of HBO3 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 70℃ and stirred overnight to remove the solvent, obtaining a solid metal carbon-nitrogen adduct, which was vacuum dried and then ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace and heated under nitrogen protection. It was heated to 500℃ at a rate of 5℃ / min and held for 4 hours. Then, the temperature was increased to 550℃ at a rate of 5℃ / min and held for 1 hour. After natural cooling to room temperature, the obtained solid was reground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material B-CN.
[0025] Example 2 10g of melamine was dispersed in 20ml of deionized water and stirred and heated to obtain a melamine solution. 2g of Zn(NO3)2 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 90℃ and stirred overnight to remove the solvent, yielding a solid metal carbon-nitrogen adduct. This adduct was vacuum dried and then ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace under nitrogen protection for heating. The temperature was increased to 450℃ at a rate of 5℃ / min and held for 2 hours. Then, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 2 hours. The mixture was then naturally cooled to room temperature. The resulting solid was re-ground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material Zn-CN.
[0026] Example 3 20g of dicyandiamide was dispersed in 20ml of acetonitrile and stirred and heated to obtain a dicyandiamide solution. 3g of CuSO4 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 80℃ and stirred overnight to remove the solvent, obtaining a solid metal carbon-nitrogen adduct, which was then vacuum dried and ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace for heating under air. It was heated to 500℃ at a rate of 5℃ / min and held for 3 hours. Then, the temperature was increased to 600℃ at a rate of 5℃ / min and held for 5 hours before naturally cooling to room temperature. The resulting solid was re-ground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material Cu-CN.
[0027] Example 4 20g of dicyandiamide was dispersed in 20ml of acetonitrile and stirred and heated to obtain a melamine solution. 3g of SnCl2 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 80℃ and stirred overnight to remove the solvent, obtaining a solid carbon-nitrogen adduct, which was then vacuum dried and ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace for heating under air. It was heated to 500℃ at a rate of 5℃ / min and held for 3 hours. Then, the temperature was increased to 600℃ at a rate of 5℃ / min and held for 5 hours before naturally cooling to room temperature. The resulting solid was re-ground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material Sn-CN.
[0028] Example 5 20g of dicyandiamide was dispersed in 20ml of acetonitrile and stirred and heated to obtain a melamine solution. 3g of FeCl3 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 80℃ and stirred overnight to remove the solvent, obtaining a solid carbon-nitrogen adduct, which was then vacuum dried and ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace for heating under air. It was heated to 500℃ at a rate of 5℃ / min and held for 3 hours. Then, the temperature was increased to 600℃ at a rate of 5℃ / min and held for 5 hours before naturally cooling to room temperature. The resulting solid was re-ground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material Fe-CN.
[0029] Example 6 20g of dicyandiamide was dispersed in 20ml of acetonitrile and stirred and heated to obtain a melamine solution. 3g of MeCl2 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 80℃ and stirred overnight to remove the solvent, obtaining a solid carbon-nitrogen adduct, which was then vacuum dried and ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace for heating under air. It was heated to 500℃ at a rate of 5℃ / min and held for 3 hours. Then, the temperature was increased to 600℃ at a rate of 5℃ / min and held for 5 hours before naturally cooling to room temperature. The resulting solid was re-ground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material Me-CN.
[0030] Example 7 20g of dicyandiamide was dispersed in 20ml of acetonitrile and stirred and heated to obtain a melamine solution. 3g of AlCl3 was added to the above solution and stirred for 6 hours. The mixed solution was heated to 80℃ and stirred overnight to remove the solvent, obtaining a solid carbon-nitrogen adduct, which was then vacuum dried and ground. The solid powder was placed in a ceramic crucible and placed in a tube furnace for heating under air. It was heated to 500℃ at a rate of 5℃ / min and held for 3 hours. Then, the temperature was increased to 600℃ at a rate of 5℃ / min and held for 5 hours before naturally cooling to room temperature. The resulting solid was re-ground to obtain the heterogeneous hindered Lewis acid-base pair synergistic catalytic material Al-CN.
[0031] Comparative Example 1 Based on Example 1, the main difference is that the method in Example 1 is followed, but the heteroatom doping step is not performed, and HBO3 is not added to prepare the nitrogen-rich carbon material g-C3N4.
[0032] Comparative Example 2 Based on Example 1, the main difference is that the method in Example 1 is followed, but the calcination step is as follows: heat to 200°C at a rate of 5°C / min and hold for 5 hours. Then continue to heat to 250°C at a rate of 5°C / min and hold for 5 hours.
[0033] Comparative Example 3 Based on Example 1, the main difference is that the method in Example 1 is followed, but the calcination step is as follows: heat to 650°C at a rate of 5°C / min and hold for 1 hour. Then continue to heat to 750°C at a rate of 5°C / min and hold for 1 hour.
[0034] Figure 1 The XRD (X-ray diffraction) patterns of the heterogeneous hindered Lewis acid-base pair synergistic catalysts obtained in Examples 1-3 and Comparative Example 1 are shown. Figure 2 and Figure 3 The images show the TEM (transmission electron microscopy) image and EDS-mapping image of the heterogeneous hindered Lewis acid-base pair synergistic catalyst obtained in Example 2, where HAADF is in HAADF-STEM mode, C is carbon, N is nitrogen, and Zn is zinc. Figure 4 The image shows the XPS (X-ray photoelectron spectroscopy) spectrum of the heterogeneous hindered Lewis acid-base pair synergistic catalyst obtained in Example 1, where C represents carbon, N represents nitrogen, and B represents boron.
[0035] In the following applications, the conversion rate of polyester and the yield of depolymerization products are calculated using the following formulas: Conversion rate % = (initial mass of polyester added - remaining mass after depolymerization) ÷ initial mass of polyester added, Yield % = actual mass of product ÷ theoretical mass of product.
[0036] Test Example 1 The catalysts from the different embodiments and comparative examples described above were applied to the depolymerization of PET: 0.02 g of the catalysts from the embodiments and comparative examples and 0.5 g of PET were added to a reactor, along with 10 molar equivalents of ethylene glycol. The reaction was carried out at 190 °C for 4 h. After the reaction was completed, the reaction solution was added to 100 mL of boiling water, and the undepolymerized PET and catalyst were separated by filtration. The solution was then vacuum dried at 80 °C for 2 h and weighed. The filtrate was recrystallized at 0 °C, and the depolymerized product BHET (ethylene terephthalate) was obtained by filtration. The depolymerized product was then vacuum dried at 80 °C for 2 h and weighed.
[0037] The performance evaluation results are shown in Table 1 below.
[0038] Table 1 Comparison of Catalytic Performance of Catalysts
[0039] As shown in Table 1, the comparative catalyst exhibits weak catalytic performance in the PET glycololysis process, while the catalyst provided in this application demonstrates significantly enhanced catalytic performance through heteroatom doping, resulting in a substantial increase in PET conversion activity in the examples. The researchers also found that, similar to Examples 1 and Comparative Example 1, if the heteroatom doping step is not performed in Examples 2-7, the resulting nitrogen-rich carbon material C3N4 exhibits the same weak catalytic performance as Comparative Example 1.
[0040] Furthermore, the researchers found through experiments that raising the temperature to 300-600℃ in the first stage and 400-700℃ in the second stage, while maintaining the final temperature of the second stage higher than that of the first stage, ensured good catalytic performance of the catalyst. In contrast, in Comparative Examples 2 and 3, excessively low or high temperatures resulted in poor catalyst performance.
[0041] Test Example 2 The catalytic chemical recovery performance of PET polyester obtained in Example 1 was investigated. The operation steps of Example 1 were repeated, except that the catalyst after the above test was separated, dried under vacuum at 80°C for 4 hours, and put back into the PET depolymerization reactor. After the system was heated to 190°C, the reaction was carried out for 4 hours. The catalytic activity of the sample was evaluated again according to the above method.
[0042] Table 2 Evaluation of Catalytic Performance in Catalyst Cyclic Reaction in Example 1
[0043] According to the results in Table 2, under these conditions, the PET conversion rate was 95% and the monomer BHET yield was 90%. The results show that after 9 cycles of testing, the catalyst performance remained good and the monomer BHET yield was still over 80%.
[0044] Experiments revealed that the catalysts in Examples 2-7 exhibited the same good recyclability as those in Example 1. However, the comparative catalysts showed a decline in performance during cycling. This was due to excessively high or low calcination temperatures leading to unstable catalyst structures; for example, the catalysts in Comparative Examples 2 and 3 lost their catalytic effect after five and three cycles, respectively.
[0045] Example 4 Compared with the catalytic conditions in Test Example 1, only the reaction temperature of the catalytic reaction was adjusted, while everything else remained the same. The performance evaluation results of the catalyst are shown in Table 3 below.
[0046] Table 3 Evaluation of B-CN catalytic performance in Example 1 at different reaction temperatures
[0047] As shown in Table 3, the efficiency of polyester degradation is highly dependent on temperature, with 190°C being optimal. Lower temperatures of 180°C and 170°C lead to a significant decrease in conversion rate and yield. Therefore, considering the reaction efficiency, the reaction temperature should be higher than 185°C, preferably 190°C.
[0048] Example 5 Compared with the catalytic conditions in Test Example 1, only the reaction time of the catalytic reaction was adjusted, while everything else remained the same. The performance evaluation results of the catalyst are shown in Table 4 below.
[0049] Table 4 Evaluation of B-CN catalytic performance in Example 1 at different reaction times
[0050] As shown in Table 4, reaction time is also a key factor. Shortening the reaction time from the optimal 4 hours to 3 hours leads to a significant decrease in conversion and yield, and further shortening it to 1-2 hours results in an even more pronounced decrease. Therefore, a reaction time of at least 4 hours is crucial for achieving high efficiency, as it brings the reaction closer to complete depolymerization.
[0051] Example 6 Compared with the catalytic conditions in Test Example 1, only the amount of catalyst was adjusted, while everything else remained the same. The performance evaluation results are shown in Table 5 below.
[0052] Table 5. Catalytic performance evaluation of B-CN with different PET feedstock mass ratios in Example 1
[0053] As shown in Table 5, the proposed method achieves high depolymerization efficiency with extremely low catalyst loading. Reducing the catalyst loading to 4-6 wt% significantly affects the conversion or yield. However, as the catalyst loading is further reduced to 2 wt%, a significant decrease in catalytic activity is observed, with a PET conversion of 72% and a BHET yield of 65%. While those skilled in the art can improve the conversion and yield by increasing the reaction time, this would lead to an increase in the production cycle.
[0054] Test Example 3 The difference from the catalytic conditions in Test Example 1 is that the polyester type and corresponding alcohol were adjusted. When using methanol, the reaction conditions were 180°C for 6 hours. The undepolymerized portion was separated from the catalyst by filtration, and the filtrate was passed through... 1The products were quantitatively analyzed by ¹H NMR, and all other parameters were the same. The performance evaluation results are shown in Table 6 below. Among them, BPA is bisphenol A, DMT is dimethyl terephthalate, BHBT is butylene terephthalate, BHPT is propylene glycol terephthalate, and BHEN is ethylene glycol 2,6-naphthalenedicarboxylate.
[0055] Table 6. Chemical recovery performance of different polyesters catalyzed by B-CN.
[0056] As shown in Table 6, this catalytic system is compatible with various polyesters. By regulating the active sites to address the structural differences among different polyesters, targeted conversion is achieved, solving the problem of limited adaptability of traditional catalysts to polyester substrates. Furthermore, experiments revealed that the catalysts in Examples 2-7 exhibited the same degradation effects on various polyesters as in Example 1.
[0057] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.
Claims
1. A method for preparing a heterogeneous hindered Lewis acid-base pair synergistic catalyst, characterized in that, The preparation method includes: 1) Add the carbon nitride precursor to the solvent, and then add the heteroatom source and mix and stir. 2) After removing the solvent and drying, a solid mixture is obtained; 3) The resulting solid mixture is calcined and cooled to room temperature to obtain the final product.
2. The method for preparing the heterogeneous hindered Lewis acid-base pair synergistic catalyst according to claim 1, characterized in that, The heteroatom source is selected from one or more of zinc nitrate, copper sulfate, tin chloride, ferric chloride, magnesium chloride, aluminum chloride, boric acid, and sodium borohydride.
3. The method for preparing the heterogeneous hindered Lewis acid-base pair synergistic catalyst according to claim 1, characterized in that, The carbon nitride precursor is one or more of melamine, dicyandiamide, and urea.
4. The method for preparing the heterogeneous hindered Lewis acid-base pair synergistic catalyst according to claim 1, characterized in that, The mass ratio of the heteroatom source to the carbon nitride precursor is (0.1~10):
100.
5. The method for preparing a heterogeneous hindered Lewis acid-base pair synergistic catalyst according to claim 1, characterized in that, Step 3) calcination includes: heating to 300-600℃ at a rate of 1-10℃ / min and maintaining for 1-5 hours, then continuing to heat to 400-700℃ at a rate of 1-10℃ / min and maintaining for 1-5 hours.
6. The method for preparing the heterogeneous hindered Lewis acid-base pair synergistic catalyst according to claim 1, characterized in that, The solvent is one or more of water, acetonitrile, ethanol, and methanol.
7. The method for preparing a heterogeneous hindered Lewis acid-base pair synergistic catalyst according to claim 1, characterized in that, Step 3) calcination is carried out under air, nitrogen or argon.
8. The catalyst prepared by the method for preparing a heterogeneous hindered Lewis acid-base pair synergistic catalyst according to any one of claims 1 to 7.
9. The application of the catalyst as described in claim 8 in polyester alcoholysis.
10. The application according to claim 9, characterized in that, The polyester alcoholysis includes the process of adding polyester and catalyst to an alcohol solution and stirring the reaction under heating conditions; Optionally, the catalyst is used in an amount of 1-10 wt% of the polyester. Optionally, the molar ratio of the polyester to the alcohol is 1:(1~20). Optionally, the reaction temperature for the alcoholysis is 100~200℃; Optionally, the reaction time for the alcoholysis is 30-360 min; Optionally, the alcohol is one or more selected from methanol, ethylene glycol, propylene glycol, and butanediol; Optionally, the polyester is one of BPA-PC, PET, PBT, PTT, and PEN.