A method for preparing a polyionic liquid / alumina aerogel composite material and its application.

Abstract

This invention relates to the field of catalyst preparation technology, specifically disclosing a method for preparing and applying a polyionic liquid / alumina aerogel composite material. The invention synthesizes Al2O3 aerogel under mild conditions using inexpensive inorganic aluminum salts as precursors, deionized water and ethanol as solvents, and propylene oxide as a coagulant. Further, in the presence of Al2O3 aerogel, using N-vinyl monomers and dibromo derivatives as monomers, a polyionic liquid / Al2O3 aerogel composite catalytic material is obtained through in-situ quaternization and polymerization reactions. The prepared PIL@Al2O3 composite catalytic material exhibits characteristics such as large specific surface area, wide pore size distribution, and rich Lewis acid and nucleophilic (Brˉ) bifunctional sites. As a catalyst, this composite material demonstrates excellent catalytic performance and cycle stability in the cycloaddition reaction of CO2 with epoxides, and is expected to be used in practical industrial production.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a method for preparing a polyionic liquid / alumina aerogel composite material and its application. Background Technology

[0002] In recent years, the excessive use of fossil fuels has led to a sharp rise in atmospheric CO2 concentration, causing environmental problems such as global warming and ocean acidification, which have seriously threatened the ecological balance. How to effectively reduce atmospheric CO2 concentration and realize its resource utilization has become a major challenge in the fields of environment and energy.

[0003] Although CO2 is one of the major greenhouse gases, it is also an abundant, inexpensive, non-toxic, and non-flammable renewable C1 resource. Capturing it and converting it into high-value-added products through chemical conversion technology is of great practical significance and ecological value.

[0004] CO2, as a C1 resource, can be converted into various high-value-added chemical products, such as methanol, urea, formic acid, carbonates, oxazolidinones, and quinazolinones, through the development of advanced catalytic technologies. Among these, the cycloaddition reaction of CO2 with epoxides to synthesize cyclic carbonates has attracted widespread attention. On the one hand, this reaction is 100% atom-economical and can replace the traditional phosgene process to produce high-value-added cyclic carbonates; on the other hand, cyclic carbonates are a very important class of chemical products, widely used in lithium-ion battery solvents, polymer monomers, pharmaceutical intermediates, and other fields.

[0005] Developing efficient catalytic systems is crucial for the efficient synthesis of cyclic carbonates through the cycloaddition reaction of CO2 with epoxides. Polyionic liquids, as heterogeneous catalysts, have shown promising applications in cycloaddition reactions due to their abundant nucleophilic (halogen anion) active sites. However, their application is limited by issues such as single active sites, low specific surface area, complex preparation steps, and relatively low catalytic activity. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the present invention aims to provide a method for preparing polyionic liquid / alumina aerogel composite materials and their applications. This invention leverages the high specific surface area and abundant Lewis acid sites of Al2O3 aerogel as a carrier, employing in-situ quaternization and free radical polymerization reactions between N-vinyl monomers and dibromo derivatives to prepare polyionic liquid / Al2O3 aerogel composite materials. This preparation strategy efficiently integrates polyionic liquids with nucleophilic reagents into low-density, high-porosity, and high-specific-surface-area Al2O3 aerogels, resulting in polyionic liquid / Al2O3 aerogel composite materials rich in both Lewis acid and nucleophilic (Brˉ) bifunctional sites. This improves upon the problems of single active sites, low specific surface area, and low catalytic activity of polyionic liquids, thereby enhancing the catalytic activity of epoxide and CO2 cycloaddition reactions.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a polyionic liquid / alumina aerogel composite material includes the following steps:

[0009] N-vinyl monomer, dibromo derivative, free radical initiator and organic solvent were mixed and stirred to dissolve. Alumina aerogel was then added to the mixture and reacted at 80-130℃ for 12-48 h. After the reaction was completed, the mixture was washed with alcohol and dried to obtain polyionic liquid / alumina aerogel composite material.

[0010] The N-vinyl monomer is one of N-vinylimidazolium, N-vinylpyridine, and N-vinylcarbazole;

[0011] The dibromo derivative is one of 5,5'-bromomethyl-2,2'-bipyridine, 1,2-dibromoethane, 1,2-dibromopropane, 1,4-dibromobutane, and 1,4-(dibromomethyl)benzene;

[0012] The organic solvent is one of anhydrous ethanol, N,N-dimethylformamide, and methanol;

[0013] The free radical initiator is one of benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile;

[0014] Preferably, a method for preparing a polyionic liquid / alumina aerogel composite material includes the following steps: mixing N-vinylimidazole, 5,5'-bromomethyl-2,2'-bipyridine, a free radical initiator, and anhydrous ethanol, stirring to dissolve, adding alumina aerogel to the mixture, and reacting at 90-110℃ for 24-36 h; after the reaction is completed, washing with alcohol and drying to obtain the polyionic liquid / alumina aerogel composite material.

[0015] Furthermore, the molar ratio of the N-vinyl monomer to the dibromo derivative is 2:1;

[0016] The ratio of the sum of the mass of the N-vinyl monomer and the dibromo derivative to the mass of the alumina aerogel is 1:0.5-3, preferably 1:1-2, and most preferably 1:2;

[0017] The free radical initiator accounts for 2%-10% of the mass of the N-vinyl monomer, preferably 5%;

[0018] The mass-to-volume ratio of alumina aerogel to organic solvent is 0.2-0.8 g: 5 mL;

[0019] Drying conditions: Dry at 75-85℃ for 10-12 hours.

[0020] Furthermore, the preparation of the alumina aerogel includes the following steps:

[0021] Aluminum chloride hexahydrate or aluminum nitrate nonahydrate is added to an ethanol-water mixed solvent and stirred until the aluminum salt is completely dissolved. Then, propylene oxide is added to the aluminum salt solution, and the mixture is heated to gel. Next, anhydrous ethanol is added to the gel to immerse it, and the gel is allowed to stand for aging. Then, it is dried to obtain an aerogel precursor. Finally, the aerogel precursor is placed in a muffle furnace and calcined at 500-700℃ for 1-3 hours to obtain the alumina aerogel.

[0022] The molar ratio of H2O to ethanol in the ethanol-water mixed solvent is 1:0.43-0.48; the concentration of the aluminum salt solution is 1.5-2 mmol / L; and the molar ratio of aluminum salt to propylene oxide is 0.18:1.

[0023] The aging temperature is 55-65℃, the aging time is 1-2 days, the drying temperature is 80-120℃, and the drying time is 12-18 hours.

[0024] Preferably, the aerogel precursor is calcined at 600°C for 2 hours to obtain the alumina aerogel.

[0025] The polyionic liquid / alumina aerogel composite material prepared by the above method is used in the catalytic cycloaddition reaction of epoxides with CO2 to synthesize cyclic carbonates. Specific applications include:

[0026] Add epoxide and polyionic liquid / alumina aerogel composite material to a high-pressure reactor, seal the reactor, replace the air in the reactor with CO2, fill with 0.2-3MPa CO2, heat the reactor to 25-150℃, and react for 1-36 hours.

[0027] The epoxide includes at least one of propylene oxide, cyclohexene oxide, and styrene oxide.

[0028] Furthermore, the reaction temperature is 80-150℃, preferably 100-140℃, and most preferably 120℃.

[0029] Furthermore, the reaction pressure is 0.2 MPa.

[0030] Furthermore, the reaction time is 2-6 hours.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) In this invention, alumina aerogel is used as a carrier, and N-vinyl monomer and dibromo derivative undergo quaternization and polymerization reactions in situ in one step to obtain polyionic liquid / Al2O3 aerogel composite catalytic material. The preparation method of this composite catalytic material is simple and efficient.

[0033] (2) The PIL@Al2O3 composite catalytic material prepared by the present invention has the characteristics of large specific surface area, wide pore size distribution, good thermal stability, and rich Lewis acid and nucleophilic reagent (Brˉ) bifunctional sites.

[0034] (3) The composite material, as a catalyst, exhibits excellent catalytic performance and recyclability in the cycloaddition reaction of CO2 and epoxide, and is expected to be used in actual industrial production. Attached Figure Description

[0035] Figure 1 The nitrogen adsorption-desorption isotherm curve of PIL@Al2O3-1 prepared in Example 1 is shown.

[0036] Figure 2 The image shows the XRD pattern of PIL@Al2O3-1 prepared in Example 1.

[0037] Figure 3 This is a TEM image of PIL@Al2O3-1 prepared in Example 1.

[0038] Figure 4 The image shows the FT-IR spectrum of PIL@Al2O3-1 prepared in Example 1.

[0039] Figure 5 This is a SEM image of PIL@Al2O3-1 prepared in Example 1.

[0040] Figure 6 This is a SEM image of the Al2O3 aerogel prepared in this invention.

[0041] Figure 7 The image shown is a TGA image of the Al2O3 aerogel prepared in this invention. Detailed Implementation

[0042] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, so as to further illustrate the technical content of the present invention.

[0043] The alumina aerogels used in each embodiment are prepared by the following methods:

[0044] First, AlCl3·6H2O (4.35 g, 18 mmol) was dissolved in a mixture of distilled water (4 ml) and anhydrous ethanol (5.4 ml) (H2O / ethanol molar ratio 1:0.43), and stirred until completely dissolved. Then, propylene oxide (7 ml, 0.1 mol) was added to the mixture, and stirring was continued for 20 s. The resulting homogeneous solution was sealed with plastic wrap and gelled at 60 °C. After gelation, anhydrous ethanol was added to the gel to immerse it, and the gel was aged at 60 °C for 2 days. Subsequently, the gel was dried under normal pressure: at 80 °C for 4 h, at 100 °C for 6 h, and at 120 °C for 6 h to obtain an aerogel precursor. The precursor was ground and placed in a muffle furnace, and calcined at 600 °C for 2 h to obtain Al2O3 aerogel.

[0045] Example 1: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-1)

[0046] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.56 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-1.

[0047] Elemental analysis showed that Br in PIL@Al2O3-1 - The content was 9.46 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-1 showed that the specific surface area of ​​PIL@Al2O3-1 was 550 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 19nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-1 was in the state of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-1 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0048] Example 2: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-2)

[0049] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.14 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-2.

[0050] Elemental analysis showed that Br in PIL@Al2O3-2 - The content was 18.8 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-2 showed that the specific surface area of ​​PIL@Al2O3-2 was 310 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 11.3nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-2 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-2 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0051] Example 3: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-3)

[0052] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.28 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-3.

[0053] Elemental analysis showed that Br in PIL@Al2O3-3 - The content was 14.1 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-3 showed that the specific surface area of ​​PIL@Al2O3-3 was 420 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 13.4nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-3 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-3 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0054] Example 4: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-4)

[0055] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.11 g (1 mmol) of 4-vinylpyridine, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.58 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-4.

[0056] Elemental analysis showed that Br in PIL@Al2O3-4 -The content was 9.14 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-4 showed that the specific surface area of ​​PIL@Al2O3-4 was 520 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 12.2nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-4 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-4 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0057] Example 5: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-5)

[0058] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.19 g (1 mmol) of N-vinylcarbazole, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.74 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-5.

[0059] Elemental analysis showed that Br in PIL@Al2O3-5 - The content was 7.17 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-5 showed that the specific surface area of ​​PIL@Al2O3-5 was 305 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 9.7nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-5 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-5 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0060] Example 6: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-6)

[0061] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.11 g (0.5 mmol) of 1,2-dibromobutane, and 0.005 g of azobisisobutyronitrile. After complete dissolution, 0.42 g of Al2O3 aerogel was added to the mixture, and stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al2O3 aerogel composite catalyst, denoted as PIL@Al2O3-6.

[0062] Elemental analysis showed that Br in PIL@Al2O3-6 - The content was 11.76 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-6 showed that the specific surface area of ​​PIL@Al2O3-6 was 510 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 15.5nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-6 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-6 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0063] Example 7: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-7)

[0064] 5 ml of anhydrous ethanol was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.14 g (0.5 mmol) of 1,4-di(bromomethyl)benzene, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.48 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-7.

[0065] Elemental analysis showed that Br in PIL@Al2O3-7 -The content was 10.9 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-7 showed that the specific surface area of ​​PIL@Al2O3-7 was 472 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 14.5nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-7 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-7 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0066] Example 8: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-8)

[0067] 5 ml of N,N-dimethylformamide was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.56 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-8.

[0068] Elemental analysis showed that Br in PIL@Al2O3-8 - The content was 9.3 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-8 showed that the specific surface area of ​​PIL@Al2O3-8 was 542 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 18.5nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-8 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-8 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0069] Example 9: Polyionic liquid / Al2O3 aerogel composite catalytic material (PIL@Al2O3-9)

[0070] 5 ml of tetrahydrofuran was added to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. The mixture was stirred until completely dissolved, and then 0.56 g of Al₂O₃ aerogel was added. Stirring continued for 30 min. The reactor was then sealed and transferred to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed 3-5 times with anhydrous ethanol and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the polyionic liquid / Al₂O₃ aerogel composite catalyst, denoted as PIL@Al₂O₃-9.

[0071] Elemental analysis showed that Br in PIL@Al2O3-9 - The content was 7.6 wt%; nitrogen adsorption-desorption isotherm analysis of PIL@Al2O3-9 showed that the specific surface area of ​​PIL@Al2O3-9 was 380 m². 2 / g, the material is rich in micropores, mesopores and macropores, with an average pore size of 13.6nm; TEM and SEM analysis showed that the prepared PIL@Al2O3-9 was in the form of stacked microspheres; XRD results showed that characteristic diffraction peaks of Al2O3 appeared at 2θ of 37.72°, 46.7° and 66.94°, corresponding to the (311), (400) and (440) crystal planes, respectively, indicating that Al in PIL@Al2O3-9 exists in the form of Al2O3; FT-IR spectrum showed that the polyionic liquid was successfully loaded on Al2O3 aerogel.

[0072] Example 10: PIL-catalyzed cycloaddition reaction of propylene oxide with CO2

[0073] 29.04 g (0.5 mol) of propylene oxide and 2.65 mg of PILs catalyst (n(Br)) were added to a high-pressure reactor. - (0.01 mmol) was used to seal the reaction vessel, and the air inside the vessel was replaced with CO2. This process was repeated three times, followed by priming with 0.2 MPa of CO2. The reaction vessel was then heated to 120 °C and reacted for 2 hours. After the reaction was complete, the product was qualitatively and quantitatively analyzed by gas chromatography. The yield of propylene carbonate was 25%, the selectivity was 99.8%, and the TOF frequency was 6250 (mol / L). PC mol Br -1 h -1 ).

[0074] The preparation method of the PILs catalyst includes the following steps:

[0075] Add 5 ml of ethanol solution to a hydrothermal reactor, followed by 0.1 g (1 mmol) of N-vinylimidazolium, 0.18 g (0.5 mmol) of 5,5'-bromomethyl-2,2'-bipyridine, and 0.005 g of azobisisobutyronitrile. Stir until completely dissolved, then seal the reactor and transfer it to a forced-air drying oven for free radical polymerization at 100 °C for 24 h. After the reaction, allow it to cool naturally to room temperature. Wash the resulting solid 3-5 times with anhydrous ethanol, then dry it in a vacuum drying oven at 80 °C for 12 h to obtain polyionic liquids, denoted as PILs.

[0076] Example 11: Cycloaddition reaction of propylene oxide with CO2 catalyzed by PIL@Al2O3-1

[0077] 29.04 g (0.5 mol) of propylene oxide and 7.9 mg of PIL@Al2O3-1 catalyst (n(Br) were added to a high-pressure reactor. - (0.0093 mmol) was used to seal the reaction vessel. The air inside the vessel was replaced with CO2, and the mixture was purged and vented three times. Then, 0.2 MPa of CO2 was introduced, and the reaction vessel was heated to 120 °C and reacted for 2 hours. After the reaction was completed, the product was qualitatively and quantitatively analyzed by gas chromatography. The yield of propylene carbonate was 93%, the selectivity was 99.6%, and the TOF frequency was 25000 (mol / L). PC mol Br -1 h -1 ).

[0078] Example 12: Cycloaddition reaction of propylene oxide with CO2 catalyzed by PIL@Al2O3-1

[0079] The reaction temperature was changed from 120°C to room temperature, while all other conditions and parameters remained the same as in Example 11. The yield of propylene carbonate was 0.2%, the selectivity was 99.9%, and the TOF was 53.76 (mol). PC mol Br -1 h -1 ).

[0080] The reaction temperature was changed from 120°C to 80°C, while the other conditions and parameters remained the same as in Example 11. The yield of propylene carbonate was 77%, the selectivity was 99.6%, and the TOF was 20699 (mol). PC mol Br -1 h -1 ).

[0081] The reaction temperature was changed from 120°C to 100°C, while the other conditions and parameters remained the same as in Example 11. The yield of propylene carbonate was 86%, the selectivity was 99.5%, and the TOF was 23118 (mol). PC mol Br -1 h -1 ).

[0082] The reaction temperature was changed from 120°C to 140°C, while the other conditions and parameters remained the same as in Example 11. The yield of propylene carbonate was 95%, the selectivity was 99.2%, and the TOF was 25537 (mol). PC mol Br -1 h -1 ).

[0083] The reaction pressure was changed from 0.2 MPa to 3 MPa, while the other conditions and parameters remained the same as in Example 11. The yield of propylene carbonate was 94%, the selectivity was 99.6%, and the TOF was 25268 (mol). PC mol Br -1 h -1 ).

[0084] Example 13: Cycloaddition reaction of propylene oxide with CO2 catalyzed by other catalysts

[0085] Replace 7.9 mg of PIL@Al2O3-1 catalyst with 7.9 mg of PIL@Al2O3-2 catalyst (n(Br) - With a concentration of 0.019 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 61.8%, the selectivity was 99.7%, and the time-to-flight (TOF) frequency was 8131 mol / L. PC mol Br -1 h -1 ).

[0086] Replace 7.9 mg of PIL@Al2O3-1 catalyst with 7.9 mg of PIL@Al2O3-3 catalyst (n(Br) - With a concentration of 0.014 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 81%, the selectivity was 99.4%, and the time-to-flight (TOF) frequency was 14464 mol / L. PC mol Br -1 h -1 ).

[0087] Replace 7.9 mg of PIL@Al2O3-1 catalyst with 8.8 mg of PIL@Al2O3-4 catalyst (n(Br)- With a concentration of 0.01 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 68%, the selectivity was 99.5%, and the time-to-flight (TOF) frequency was 17000 (mol / L). PC mol Br -1 h -1 ).

[0088] The 7.9 mg PIL@Al2O3-1 catalyst was replaced with 11.4 mg PIL@Al2O3-5 catalyst (n(Br) - With a concentration of 0.01 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 50.5%, the selectivity was 99.8%, and the time-to-flight (TOF) frequency was 12625 (mol / L). PC mol Br -1 h -1 ).

[0089] Replace 7.9 mg of PIL@Al2O3-1 catalyst with 6.9 mg of PIL@Al2O3-6 catalyst (n(Br) - With a concentration of 0.01 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 85%, the selectivity was 99.7%, and the time-to-flight (TOF) frequency was 21250 (mol). PC mol Br -1 h -1 ).

[0090] The 7.9 mg PIL@Al2O3-1 catalyst was replaced with 7.4 mg PIL@Al2O3-7 catalyst (n(Br) - With a concentration of 0.01 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 79%, the selectivity was 99.9%, and the time-to-flight (TOF) frequency was 19750 (mol). PC mol Br -1 h -1 ).

[0091] Replace 7.9 mg of PIL@Al2O3-1 catalyst with 7.9 mg of PIL@Al2O3-8 catalyst (n(Br) - With a concentration of 0.0092 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 92.8%, the selectivity was 99.6%, and the time-to-flight (TOF) frequency was 25217 mol / L. PC mol Br -1 h -1 ).

[0092] Replace 7.9 mg of PIL@Al2O3-1 catalyst with 7.9 mg of PIL@Al2O3-9 catalyst (n(Br) - With a concentration of 0.0075 mmol, and all other conditions and parameters remaining unchanged, the yield of propylene carbonate was 42.6%, the selectivity was 99.7%, and the time-to-flight (TOF) frequency was 14200 (mol). PC mol Br -1 h -1 ).

[0093] Example 14: Cycloaddition reaction of cyclohexene oxide with CO2 catalyzed by PIL@Al2O3-1

[0094] Referring to Example 11, 29.04 g of propylene oxide was replaced with 49.07 g (0.5 mol) of cyclohexene oxide, and the reaction time was changed from 2 hours to 6 hours, while all other conditions and parameters remained unchanged. The yield of cyclohexene carbonate was 34.86%, the selectivity was 94%, and the TOF was 3123 (mol). PC mol Br -1 h -1 ).

[0095] Example 15: Cycloaddition reaction of styrene with CO2 catalyzed by PIL@Al2O3-1

[0096] Referring to Example 11, 29.04 g of propylene oxide was replaced with 60.1 g (0.5 mol) of styrene oxide, and the reaction time was changed from 2 hours to 4 hours, with all other conditions and parameters remaining unchanged. The yield of styrene carbonate was 56.86%, the selectivity was 98%, and the TOF was 7642 (mol). PC mol Br -1 h -1 ).

[0097] Example 15: Catalyst Recycling

[0098] 29.04 g of propylene oxide and 7.9 mg of PIL@Al2O3-1 catalyst were added to a high-pressure reactor. The reactor was sealed, and the air inside was replaced with CO2. This process was repeated three times, followed by charging with 0.2 MPa of CO2. The reactor was then heated to 120 °C and reacted for 2 hours. After the reaction, the product was qualitatively and quantitatively analyzed by gas chromatography. The yield of propylene carbonate was 93%, and the selectivity was 99.6%. After the reaction, the centrifuged catalyst was washed 3-5 times, dried under vacuum at 80 °C for 12 hours, and the catalytic reaction was repeated. The catalyst was reused 20 times to examine its recycling performance. The catalytic activity results are shown in Table 1 below.

[0099] Table 1

[0100]

Claims

1. The application of polyionic liquid / alumina aerogel composite material in the catalytic cycloaddition reaction of epoxides with CO2 to synthesize cyclic carbonates, characterized in that, The epoxide includes at least one of propylene oxide, cyclohexene oxide, and styrene oxide; The preparation method of the polyionic liquid / alumina aerogel composite material includes the following steps: N-vinylimidazole, dibromo derivative, free radical initiator and organic solvent are mixed, stirred and dissolved, alumina aerogel is added to the mixture, and reacted at 95-110 ℃ for 12-48 h; after the reaction is completed, the mixture is washed with alcohol and dried to obtain the polyionic liquid / alumina aerogel composite material. The molar ratio of N-vinylimidazole to the dibromo derivative is 2:1; the ratio of the sum of the masses of N-vinylimidazole and the dibromo derivative to the mass of the alumina aerogel is 1:1-2. The dibromo derivative is one of 5,5'-bromomethyl-2,2'-bipyridine, 1,2-dibromoethane, 1,2-dibromopropane, 1,4-dibromobutane, and 1,4-(dibromomethyl)benzene; The organic solvent is one of anhydrous ethanol, N,N-dimethylformamide, and methanol; and / or The free radical initiator is one of benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile.

2. The application according to claim 1, characterized in that, The ratio of the total mass of the N-vinylimidazole and the dibromo derivative to the mass of the alumina aerogel is 1:

2.

3. The application according to claim 1, characterized in that, N-vinylimidazole, 5,5'-bromomethyl-2,2'-bipyridine, a free radical initiator, and anhydrous ethanol were mixed and stirred to dissolve. Alumina aerogel was then added to the mixture and reacted at 95-110℃ for 12-48 h. After the reaction was completed, the mixture was washed with alcohol and dried to obtain a polyionic liquid / alumina aerogel composite material.

4. The application according to claim 1, characterized in that, include: Add epoxide and polyionic liquid / alumina aerogel composite material to a high-pressure reactor, seal the reactor, replace the air in the reactor with CO2, fill with 0.2-3 MPa CO2, heat the reactor to 80-150 ℃, and react for 1-36 h.

5. The application according to claim 4, characterized in that, The reaction temperature is 100-140 ℃; and / or the reaction time is 2-6 h.

6. The application according to claim 5, characterized in that, The reaction temperature is 120 ℃.

7. The application according to claim 1, characterized in that, The free radical initiator accounts for 2%-10% of the mass of N-vinylimidazole; and / or The mass-to-volume ratio of alumina aerogel to organic solvent is 0.2-0.8 g: 5 mL.

8. The application according to claim 1, characterized in that, The free radical initiator accounts for 5% of the mass of N-vinylimidazole.

9. The application according to claim 1, characterized in that, The preparation of the alumina aerogel includes the following steps: aluminum chloride hexahydrate or aluminum nitrate nonahydrate is added to an ethanol-water mixed solvent and stirred until the aluminum salt is completely dissolved. Then, propylene oxide is added to the aluminum salt solution, and the mixture is heated to gel. Next, anhydrous ethanol is added to the gel to immerse it, and the gel is allowed to stand for aging. Then, it is dried to obtain the aerogel precursor. Finally, the aerogel precursor is placed in a muffle furnace and calcined at 500-700 °C for 1-3 h to obtain the alumina aerogel.

10. The application according to claim 9, characterized in that, The molar ratio of H2O to ethanol in the ethanol-water mixed solvent is 1:0.43-0.48; the concentration of the aluminum salt solution is 1.5-2 mmol / L; and the molar ratio of aluminum salt to propylene oxide is 0.18:

1. The aging temperature is 55-65 ℃, the aging time is 1-2 days, the drying temperature is 80-120 ℃, and the drying time is 12-18 h.

11. The application according to claim 9, characterized in that, The alumina aerogel was obtained by calcining the aerogel precursor at 600 °C for 2 h.

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