A porous nanocatalyst for the synthesis of propylene carbonate, its preparation method and application

Abstract

This invention discloses a porous nanocatalyst for the synthesis of propylene carbonate, its preparation method, and its application. The method includes the following steps: In an inert atmosphere, 1-vinylimidazolium, 4-chloromethylstyrene, and p-divinylbenzene are polymerized to prepare a nanoparticle precursor; the nanoparticle precursor is then subjected to Friedel-Crafts alkylation to prepare highly cross-linked porous nanoparticles; the highly cross-linked porous nanoparticles are then subjected to ion exchange to remove chloride ions, yielding the final product. This porous nanocatalyst is halogen-free, environmentally friendly, has high catalytic efficiency, good structural stability, and can be reused multiple times.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a porous nanocatalyst for the synthesis of propylene carbonate, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Electrolytes, as a crucial component of lithium-ion batteries, bear the core responsibility of transporting lithium ions and are figuratively referred to as the "blood" of lithium-ion batteries. Among numerous electrolyte solvents, propylene carbonate (PC) is highly favored due to its unique properties. Propylene carbonate is not only an excellent polar solvent but also widely used in polymer processing, gas separation processes, and electrochemistry. In the battery industry, it is an ideal solvent for lithium-ion battery electrolytes, effectively conducting ions and ensuring that lithium-ion batteries achieve key characteristics such as high voltage and high specific energy. A significant advantage of propylene carbonate is its low melting point (-48.8℃). This characteristic effectively lowers the eutectic point of the solvent system, thereby suppressing the crystallization of ethylene carbonate (EC) at low temperatures. This characteristic is crucial for improving the low-temperature performance of lithium-ion batteries. To further optimize the application of propylene carbonate in lithium-ion batteries, researchers successfully suppressed the decomposition and co-intercalation of propylene carbonate in artificial graphite anodes by adjusting solvent ratios and adding additives. This improvement makes the application of propylene carbonate in lithium-ion battery electrolytes more widespread and stable.

[0004] In industrial production, propylene carbonate is typically prepared using methods such as phosvaporization and esterification. However, while these traditional methods increase production volume, they also place significant pressure on the environment. They utilize large quantities of toxic and harmful chemical reagents and generate substantial amounts of wastewater, waste gas, and waste residue, increasing the burden of environmental remediation. To find a more environmentally friendly preparation method, researchers have turned their attention to a process for the direct synthesis of propylene carbonate from propylene oxide and carbon dioxide. This new method not only has a simple process flow but also high atom utilization, significantly reducing negative environmental impacts. Therefore, it is considered an important future direction for propylene carbonate synthesis.

[0005] The direct synthesis of propylene carbonate from propylene oxide and carbon dioxide faces significant chemical steric hindrance, often requiring high temperature and pressure conditions in actual production. Researchers have developed numerous catalysts to accelerate this process. However, the inventors discovered that existing propylene carbonate synthesis catalysts generally contain high levels of harmful halogens, which can corrode the reactor during the reaction. While some catalysts are halogen-free, they suffer from low catalytic efficiency, resulting in excessively long reaction times and low conversion rates. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a porous nanocatalyst for the synthesis of propylene carbonate, its preparation method, and its application. This porous nanocatalyst is halogen-free, environmentally friendly, exhibits high catalytic efficiency, and possesses good structural stability, allowing for repeated reuse.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a porous nanocatalyst for the synthesis of propylene carbonate, comprising the following steps:

[0009] Nanoparticle precursors were prepared by polymerization of 1-vinylimidazole, 4-chloromethylstyrene and p-divinylbenzene in an inert atmosphere.

[0010] Ultra-highly cross-linked porous nanoparticles were prepared from nanoparticle precursors via Friedel-Crafts alkylation reaction.

[0011] The ultra-highly cross-linked porous nanoparticles are obtained by removing chloride ions through ion exchange.

[0012] In some embodiments, the molar ratio of 1-vinylimidazole, 4-chloromethylstyrene, and p-divinylbenzene is 1.5-2.5:5.5-6.5:1.

[0013] Preferably, the solvent used in the polymerization reaction is a mixture of ethanol and water. The volume ratio of ethanol to water is 2-4:1. For example, it can be 2:1, 3:1, or 4:1.

[0014] Further preferably, 5-8 ml of mixed solvent is added to each gram of monomer. The monomer here refers to the mixed monomer obtained by mixing 1-vinylimidazole, 4-chloromethylstyrene, and p-divinylbenzene in a predetermined ratio.

[0015] Preferably, the initiator for the polymerization reaction is azobisisobutyronitrile (AIBN), and the mass ratio of the total mass of the three monomers to the mass of the initiator is 1:0.08-0.12. For example, it can be 1:0.08, 1:0.09, 1:0.1, 1:0.11, or 1:0.12.

[0016] In some embodiments, during the polymerization reaction, 1-vinylimidazolium, 4-chloromethylstyrene and p-divinylbenzene are preheated in a solvent at 35-45°C for 1-2 hours. Preheating is used to ensure uniform contact between the substrate and the catalyst, preventing uneven polymerization and burst polymerization in the subsequent reaction. Then, the polymerization reaction is carried out at 70-80°C for 18-24 hours.

[0017] In some embodiments, the catalyst for the Friedel-Crafts alkylation reaction is ferric chloride.

[0018] Preferably, the mass ratio of the nanoparticle precursor to the catalyst is 3.5-4.5:1. For example, it can be 3.5:1, 4:1 or 4.5:1.

[0019] Preferably, each gram of nanoparticle precursor is mixed with 12-15 ml of solvent.

[0020] More preferably, the solvent can be dichloroethane, trichloromethane, or nitrobenzene.

[0021] Preferably, the Friedel-Crafts alkylation reaction method is as follows: first, the nanoparticle precursor is dispersed in a solvent, preheated at 35-45℃ for 1-2 hours, and after adding a catalyst, the temperature is raised to 60-80℃ to carry out the Friedel-Crafts alkylation reaction for 6-10 hours.

[0022] In some embodiments, the solution for ion exchange is a sodium bicarbonate solution, a sodium hydroxide solution, or a sodium bisulfate solution.

[0023] Preferably, the concentration of the solution for ion exchange is 0.7-1.3 mol / L, such as 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L or 1.3 mol / L.

[0024] Preferably, the temperature for the ion exchange reaction is 35-55℃ and the reaction time is 5-8h.

[0025] Secondly, the present invention provides a porous nanocatalyst for the synthesis of propylene carbonate, which is prepared by the aforementioned preparation method.

[0026] Thirdly, the present invention provides the application of the porous nanocatalyst in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate.

[0027] Fourthly, the present invention provides a method for synthesizing propylene carbonate using the aforementioned porous nanocatalyst, comprising the following steps:

[0028] Propylene carbonate was prepared by placing propylene oxide and the porous nanoparticle catalyst in a carbon dioxide atmosphere and heating them to carry out a cyclic esterification reaction.

[0029] In some embodiments, the mass of porous nanoparticle catalyst added to each mole of propylene oxide is 3-5 g.

[0030] In some embodiments, the cyclization reaction is carried out at a temperature of 60-80°C for 10-15 hours.

[0031] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0032] The catalyst provided by this invention has a high loading of catalytic active centers and abundant pores, which makes the catalyst highly active and can efficiently catalyze the direct reaction of propylene oxide and carbon dioxide to produce the electrolyte propylene carbonate under mild conditions. The catalyst is prepared by crosslinking and polymerization of 1-vinylimidazolium, 4-chloromethylstyrene and stilbene, which makes the catalyst structure stable and reusable. After the catalyst is recycled 10 times, the yield reaches 95.3% and the selectivity is greater than 99%.

[0033] This porous nanocatalyst was prepared by polymerization, Friedel-Crafts alkylation, and ion exchange of three monomers, achieving a specific surface area of ​​654.3 m². 2 / g, with abundant meso / micropores, the catalyst's abundant pores can enrich CO2, increasing the contact between the substrate and the catalytic active site.

[0034] The catalyst prepared by this invention does not contain toxic or harmful substances such as halogens, and the process for synthesizing propylene carbonate electrolyte has high atom utilization and does not require excessive amounts of toxic or harmful organic solvents. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0036] Figure 1 This is a flowchart illustrating the preparation and application of the porous nanoparticle catalyst in Example 1 of the present invention.

[0037] Figure 2 This is a TEM image of the porous nanoparticle catalyst prepared in Example 1 of the present invention;

[0038] Figure 3 The image shows an FT-IR image of the porous nanoparticle catalyst prepared in Example 1 of this invention. Detailed Implementation

[0039] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] The present invention will be further described below with reference to the embodiments.

[0041] Example 1

[0042] A porous nanocatalyst for the synthesis of propylene carbonate comprises the following steps:

[0043] 1) In a nitrogen atmosphere, 1-vinylimidazole, 4-chloromethylstyrene and p-divinylbenzene were added to a 500 mL reaction flask in a molar ratio of 2:6:1. A mixed solvent of ethanol and water (volume ratio of ethanol to water of 3:1) was added at a total mass ratio of 1 g to 6 mL. After preheating and stirring at 40 °C for 1.5 h, the initiator azobisisobutyronitrile (mass ratio of the three monomers to azobisisobutyronitrile of 1:0.1) was added dropwise. The temperature was raised to 78 °C and the reaction was stopped after 20 h. The resulting solid-liquid mixture was centrifuged, washed and dried to obtain the nanoparticle precursor.

[0044] 2) Under a nitrogen atmosphere, the nanoparticle precursor obtained in step 1) and dichloroethane solvent were added to a 500 mL reaction flask at a ratio of 1 g: 15 mL. After preheating and stirring at 40 °C for 1.5 h, ferric chloride catalyst was added (the mass ratio of nanoparticle precursor to ferric chloride catalyst was 4:1). The temperature was raised to 70 °C, and the reaction was stopped after Friedel-Crafts alkylation reaction for 8 h. The resulting solid-liquid mixture was centrifuged, washed and dried to obtain the porous nanoparticle precursor.

[0045] 3) The porous nanoparticle precursor obtained in step 2) was dissolved in a 1 mol / L sodium bicarbonate solution, and heated and stirred at 40°C for 6 h to carry out an ion exchange reaction. After the reaction, the resulting solid-liquid mixture was centrifuged, washed, and dried to obtain the porous nanoparticle catalyst. The catalyst was characterized and analyzed by TEM, FT-IR, and BET. Figure 2 It is known that the diameter of the porous nanoparticle catalyst is about 10-20 nm. Due to the strong adsorption force generated by the high specific surface area of ​​the nanoparticles, they aggregate into a cluster of solid particles.

[0046] FT-IR images of the prepared porous nanoparticle catalyst, as shown below. Figure 3 As shown in the figure, the values ​​are 2913, 2851, 1675, and 1501 cm. -1 The characteristic peak of CH indicates that the catalyst possesses a carbon skeleton structure, 1261 cm⁻¹. -1 The characteristic peak of CN indicates that the active center of the catalyst has been successfully loaded.

[0047] The method for synthesizing propylene carbonate using the porous nanoparticle catalyst includes the following steps:

[0048] 1) In a carbon dioxide atmosphere, propylene oxide and porous nanoparticle catalyst were added to a reaction flask and heated and stirred. The molar ratio of propylene oxide to porous nanoparticle catalyst was 1 mol: 4 g. The heating temperature was 70 °C and the reaction time was 12 h.

[0049] 2) After the reaction is complete, the solid-liquid mixture is centrifuged. The liquid part is analyzed by GC, and the solid part is washed and dried. Then, step 1) is repeated 10 times to evaluate the stability of the catalyst.

[0050] Example 2

[0051] The difference between Example 2 and Example 1 is that in step 3), the sodium bicarbonate solution is replaced with sodium hydroxide solution, while the other steps, parameters and raw materials remain unchanged.

[0052] Example 3

[0053] The difference between Example 3 and Example 1 is that in step 3), the sodium bicarbonate solution is replaced with sodium bisulfate solution, while the other steps, parameters and raw materials remain unchanged.

[0054] Example 4

[0055] The difference between Example 4 and Example 1 is that in step 1), the molar ratio of the three monomers 1-vinylimidazolium, 4-chloromethylstyrene and p-divinylbenzene is adjusted to 2.5:6:1, while other steps, parameters and raw materials remain unchanged.

[0056] Comparative Example 1

[0057] The difference between Comparative Example 1 and Example 1 is that step 2) of Example 1 is omitted, and step 3) of ion exchange reaction is carried out directly to obtain nanoparticle catalyst, while other steps, parameters and raw materials remain unchanged.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 1 is that in step 2), the mass ratio of nanoparticle precursor to ferric chloride catalyst is adjusted to 2:1, the Friedel-Crafts alkylation reaction temperature is adjusted to 50°C, and other steps, parameters and raw materials remain unchanged.

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 1 is that in step 1), the molar ratio of the three monomers 1-vinylimidazolium, 4-chloromethylstyrene and p-divinylbenzene is adjusted to 0.5:6:1, while other steps, parameters and raw materials remain unchanged.

[0062] Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 1 is that in step 1), the molar ratio of the three monomers 1-vinylimidazolium, 4-chloromethylstyrene and p-divinylbenzene is adjusted to 3.5:6:1, while other steps, parameters and raw materials remain unchanged.

[0064] Comparative Example 5

[0065] The difference between Comparative Example 5 and Example 1 is that in step 1), p-divinylbenzene is omitted from the three monomers, and only 1-vinylimidazolium and 4-chloromethylstyrene are added in a molar ratio of 1:3. Other steps, parameters and raw materials remain unchanged.

[0066] Table 1 shows the catalyst properties and catalytic performance data for Examples 1-4 and Comparative Examples 1-4.

[0067]

[0068] In Table 1, the yield = (molar amount of propylene oxide before reaction - molar amount of propylene oxide after reaction) / molar amount of propylene oxide before reaction × 100%;

[0069] Selectivity = Molar amount of propylene carbonate / (Molar amount of propylene oxide before reaction - Molar amount of propylene oxide after reaction) × 100%.

[0070] As shown in Table 1, the catalysts prepared in Examples 1-4 have a high loading of catalytic active centers, a nitrogen content of 5-7%, and a porous structure with a specific surface area of ​​600 m². 2 The yields were approximately 90% / g, with single-cycle yields all exceeding 90%. Example 1 exhibited the highest catalytic efficiency, achieving a propylene carbonate yield of 96.7%. Even after 10 cycles, the yield remained stable above 95%, demonstrating the excellent catalytic performance and stability of the catalyst provided by this invention. Comparative Example 1 omitted the Friedel-Crafts alkylation reaction in its catalyst synthesis, resulting in a catalyst with a specific surface area of ​​only 56.3 m². 2 / g, which is much lower than the levels in Examples 1-4, and correspondingly, its yield also decreased to 36.5%. The synthesis steps in Comparative Example 2 significantly reduced the amount of ferric chloride catalyst used, significantly lowered the Friedel-Crafts alkylation reaction temperature, and the specific surface area of ​​the synthesized catalyst decreased to 235.7 m². 2 / g, and correspondingly its yield also decreased to 61.3%.

[0071] In summary, comparing Examples 1-4, Comparative Examples 1 and 2, it is evident that Friedel-Crafts alkylation is crucial for the formation of mesoporous / microporous channels. A well-executed Friedel-Crafts alkylation reaction can promote the formation of abundant channels in the catalyst, thereby increasing the specific surface area. This increased specific surface area further enhances the contact between the catalytic active centers and propylene oxide, and allows for the containment of more carbon dioxide, thus reducing mass transfer resistance and increasing the synthesis yield. Comparative Example 3 significantly reduced the amount of 1-vinylimidazole used in the polymerization reaction, resulting in a decrease in the nitrogen content of the synthesized catalyst to 1.53%, leading to a decrease in the yield to 27.8%. This demonstrates that excessively low catalytic active center loading leads to a decrease in the reaction rate. Comparative Example 4 significantly increased the amount of 1-vinylimidazole used in the polymerization reaction, increasing the nitrogen content of the synthesized catalyst to 9.26%. However, the yield was lower than in Example 1. This is because the proportion of 4-chloromethylstyrene decreased compared to Example 1, resulting in a decrease in the bound chlorine content of the Friedel-Crafts alkylation reaction, leading to a decrease in the specific surface area of ​​the synthesized material and consequently, a decrease in catalytic activity.

[0072] Comparative Example 5 did not use divinylbenzene as a monomer, which resulted in a decrease in the structural stability of the synthesized catalyst. The yield after 10 cycles was only 73.4%, which was significantly lower than the yield of 91.5% in the first reaction.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a porous nanocatalyst in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The preparation method of porous nanocatalysts for the synthesis of propylene carbonate includes the following steps: Nanoparticle precursors were prepared by polymerization of 1-vinylimidazole, 4-chloromethylstyrene, and p-divinylbenzene in an inert atmosphere; the molar ratio of 1-vinylimidazole, 4-chloromethylstyrene, and p-divinylbenzene was 1.5-2.5:5.5-6.5:

1. Highly cross-linked porous nanoparticles were prepared from nanoparticle precursors via Friedel-Crafts alkylation reaction at a temperature of 60-80℃; the mass ratio of nanoparticle precursors to the catalyst for Friedel-Crafts alkylation reaction was 3.5-4.5:

1. The ultra-highly cross-linked porous nanoparticles are obtained by removing chloride ions through ion exchange.

2. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The solvent used in the polymerization process is a mixture of ethanol and water, with a volume ratio of ethanol to water of 2-4:

1.

3. The application of the porous nanocatalyst according to claim 2 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: Add 5-8 ml of mixed solvent to each gram of monomer. The monomer here refers to the mixed monomer obtained by mixing 1-vinylimidazole, 4-chloromethylstyrene and p-divinylbenzene in a preset ratio.

4. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The initiator for the polymerization reaction is azobisisobutyronitrile (AIBN), and the total mass ratio of the three monomers to the initiator is 1:0.08-0.

12.

5. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: During the polymerization reaction, 1-vinylimidazolium, 4-chloromethylstyrene and p-divinylbenzene are preheated in a solvent at 35-45℃ for 1-2 hours, and then polymerized at 70-80℃ for 18-24 hours.

6. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The catalyst for the Friedel-Crafts alkylation reaction is ferric chloride.

7. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: In the Friedel-Crafts alkylation reaction, each gram of nanoparticle precursor is mixed with 12-15 ml of solvent.

8. The application of the porous nanocatalyst according to claim 7 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The solvent is dichloroethane, trichloromethane, or nitrobenzene.

9. The application of the porous nanocatalyst according to claim 8 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The method of Friedel-Crafts alkylation reaction is as follows: first, the nanoparticle precursor is dispersed in a solvent, preheated at 35-45℃ for 1-2 hours, and after adding the catalyst, the temperature is raised to 60-80℃ to carry out the Friedel-Crafts alkylation reaction for 6-10 hours.

10. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The solution used for ion exchange is sodium bicarbonate solution, sodium hydroxide solution, or sodium bisulfate solution.

11. The application of the porous nanocatalyst according to claim 10 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The concentration of the solution used for ion exchange is 0.7-1.3 mol / L.

12. The application of the porous nanocatalyst according to claim 10 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The temperature for the ion exchange reaction is 35-55℃, and the reaction time is 5-8h.

13. The application of the porous nanocatalyst according to claim 1 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: Includes the following steps: Propylene carbonate was prepared by placing propylene oxide and the porous nanocatalyst in a carbon dioxide atmosphere and heating them to carry out a cyclic esterification reaction.

14. The application of the porous nanocatalyst according to claim 13 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The mass of porous nanoparticle catalyst added per mole of propylene oxide is 3-5g.

15. The application of the porous nanocatalyst according to claim 13 in the catalytic reaction of propylene oxide and carbon dioxide to prepare propylene carbonate, characterized in that: The cyclization reaction is carried out at a temperature of 60-80℃ for 10-15 hours.

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