Photoinitiated metal-coordinated polyionic liquid catalyst and application thereof

Abstract

The application relates to a method for synthesizing a metal coordination reinforced double-imidazole polyionic liquid driven by ultraviolet light and catalyzing CO2 to synthesize a cyclic carbonate. The structure of the polyionic liquid catalyst is shown in formula I, formula II or formula III: wherein p and m are each independently any natural number, and 4<=p+m; n=1-6; M is selected from any metal ion; R1 and R2 each independently include any one of C1-C6 alkyl or C2-C6 alkenyl; X ‑ Any one of iodine ions, fluorine ions, bromine ions or chlorine ions. The application strengthens the polymerization ability of the double-imidazole ionic liquid under ultraviolet light irradiation by introducing metal ions, and further improves the adsorption and activation ability of CO2 by adding nitrogen-containing substances. The polyionic liquid with high cross-linking synthesized by ultraviolet light initiation at room temperature can efficiently catalyze the reaction of CO2 and an epoxide compound to synthesize a cyclic carbonate without a catalyst and a solvent.

Description

Technical Field

[0001] This invention relates to the field of green catalysis technology for CO2 fixation and conversion, particularly to a method for synthesizing ionic liquid catalysts with multi-center ionic liquids and metal coordination, and nitrogen-containing organic compounds co-polymerized under ultraviolet light catalysis at room temperature, as well as a method for catalyzing the synthesis of cyclic carbonates from CO2 and epoxides. In particular, it relates to a method for synthesizing bisimidazole polyionic liquids with metal coordination driven by ultraviolet light and catalyzing the synthesis of cyclic carbonates from CO2. Background Technology

[0002] With the acceleration of global industrialization, excessive carbon dioxide (CO2) emissions have become a key environmental challenge restricting sustainable development. The chemical fixation and resource utilization of CO2 is an important research direction in the field of green chemistry. Among these, the pathway of CO2 reacting with epoxides to form cyclic carbonates via cycloaddition reactions has attracted much attention due to its 100% atom economy and high added value of the products. However, this reaction faces two major challenges: first, the CO2 molecule itself has extremely high thermodynamic stability and kinetic inertness, requiring highly efficient catalysts for its activation and the ring-opening steps of epoxides; second, existing catalytic systems often suffer from high energy consumption, harsh reaction conditions, and difficulties in separating the product from the catalytic product. Currently, the systems catalyzing this reaction mainly include homogeneous catalysts (such as ionic liquids and metal complexes) and heterogeneous catalysts (such as polymeric ionic liquids and metal-organic frameworks, MOFs). Among these, polymeric ionic liquids, by combining the high activity of ionic liquids with the easy recyclability of polymers, show promising application prospects. Studies have shown that introducing metal sites (such as Zn) into PILs can enhance the effectiveness of this process. 2+ Al 3+ (etc.) to construct Lewis acid sites, which can interact with the halogen anions of PILs themselves (such as Br) - This generates a synergistic catalytic effect, significantly promoting ring-opening of epoxides, thereby achieving efficient catalysis under mild conditions without solvents or co-catalysts. Nevertheless, existing technologies still face significant bottlenecks. First, the synthesis of these multifunctional catalysts typically requires high-temperature heating, consuming substantial energy and potentially leading to side reactions that affect the regularity of the catalyst structure and the uniformity of active sites. Second, the catalysts have insufficient CO2 enrichment capacity, especially under atmospheric or low-pressure conditions, where the limited CO2 concentration at the reaction interface becomes a limiting factor for improving overall reaction efficiency.

[0003] Based on the existing problems, researchers have mainly developed a series of catalysts. For example, the covalent organometallic framework catalyst (CN115960326A) discloses the synthesis of an ionic covalent organometallic framework catalyst by reacting the organic framework material TpBpy with haloalkanes, achieving a conversion rate of 99.9% after 24 hours of reaction at 100℃. This system involves high reaction temperatures and long catalytic times. The preparation conditions of the organic framework material TpBpy remain complex, requiring prolonged high-temperature conditions (three degassing cycles followed by heating at 120℃ for 72 hours).

[0004] An ionic liquid-metal-organic framework (CN118085312A) discloses an IL-MOF material with ionic liquid-modified metal complexes. The MOF material requires thorough stirring at 60-90℃ for 20-30 h, and the coordination of metal elements necessitates a reaction at 50-80℃ for 20-30 h, resulting in a lengthy and complex preparation time. The obtained catalyst requires a reaction at 120℃ for 24 h to achieve a conversion rate of 96.6%. The drawbacks of this system are the long catalyst preparation time and the low catalyst activity.

[0005] In a SiO2-supported polyionic liquid catalyst (CN116920939A), vinylimidazole-modified silica was obtained in 12–48 h at 60–80 °C. This silica was then subjected to thermally initiated polymerization (reaction at 70–80 °C for 24–48 h) to obtain a polyionic liquid-supported silica catalyst. A conversion rate of 93.5% was achieved after 4 h of reaction at 1.5 MPa and 100 °C. This series of catalysts utilizes traditional thermally initiated polymerization, resulting in a relatively slow synthesis, and the catalyst reaction requires high-temperature conditions.

[0006] A cobalt complex catalyst (CN103381370A) discloses a class of cobalt complex conjugated microporous polymer catalysts. Salen-Co was prepared by reflux at 80–100 °C for 4–6 h under hydrogen protection. After adding alkynylbenzene, reflux was continued for 72–96 h to obtain the polymer. A conversion rate of 91.1% could be achieved at 100 °C and 3 MPa. While this catalyst has a novel structure, the synthesis steps are complex and its activity does not show a significant advantage, indicating considerable room for improvement and enhancement.

[0007] In mesoporous polyionic liquid (CN109939731A), an ionic liquid monomer is obtained by solvothermal reaction of N-vinylimidazolium and dibromomethane (reaction at 80-120℃ for 24-48 h). Further polymerization with a thermal initiator and polyethylene glycol (reaction at 60-100℃ for 6-24 h) yields the mesoporous polyionic liquid. This catalyst, reacting at 120℃ for 12 h, achieves a 94.3% conversion rate of the epoxy substrate. This type of catalyst still maintains the traditional thermally initiated polymerization, requiring a long reaction time and high reaction temperature. While it possesses a large specific surface area, there is still significant room for improvement in its catalytic activity.

[0008] Based on the above situation, there is an urgent need in this field to develop a novel polyionic liquid that not only has a mild and simple synthesis process but also exhibits good CO2 activation, achieves good catalytic activity under mild conditions, and is a green catalyst that is easy to recover. Polymeric ionic liquids have attracted much attention from researchers due to their support-free nature, simple polymerization methods, and high stability. Therefore, the optimization of synthesis methods for polymeric ionic liquids and the development of efficient catalysts have significant potential value in industrial application research. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide a method for the synthesis of bisimidazole polyionic liquids driven by ultraviolet light and enhanced by metal coordination, and for its catalytic synthesis of cyclic carbonates from CO2. By introducing metal ions to enhance the polymerization ability of bisimidazole ionic liquids under ultraviolet light irradiation, and simultaneously adding nitrogen-containing substances to further enhance the adsorption and activation capacity of CO2, a highly cross-linked polymeric ionic liquid is synthesized by ultraviolet light-initiated polymerization at room temperature. This polymer can efficiently catalyze the reaction of CO2 with epoxides to synthesize cyclic carbonates under catalyst-free and solvent-free conditions. This method enhances the room-temperature polymerization of imidazole ionic liquids by adding metal halides, while simultaneously adding nitrogen-containing substances to further regulate the polymer functionality, achieving control over the acid-base properties and catalytic activity of the polymeric ionic liquid. This allows for efficient and rapid polymerization at room temperature, enhancing its application prospects. The polyionic liquid catalyst of the present invention is easy to synthesize, efficiently catalyzes the reaction of CO2 with epoxides to synthesize cyclic carbonates, and is easy to recover.

[0010] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a polyionic liquid catalyst, the structure of which is shown in Formula I, Formula II or Formula III: Formula I; Formula II; Formula III; Wherein, p and m are each independently any natural number (p can be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 50, 70, or 100, etc.; m can be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 50, 70, or 100, etc.), and 4≤p+m (for example, it can be 5, 6, 7, 8, or 9, etc.); n=1-6 (for example, it can be 2, 3, 4, or 5, etc.); M is selected from any metal ion; R1 and R2 each independently include any one of C1-C6 (for example, it can be C2, C3, C4, or C5) alkyl or C2-C6 (for example, it can be C3, C4, or C5) alkenyl; X - It includes any one of iodide ions, fluoride ions, bromide ions, or chloride ions.

[0011] In this invention, the ionic liquid monomer has multiple active sites, and the introduction of metal ions introduces more acidic sites for the reaction, which is conducive to the rapid occurrence of cycloaddition reactions. Furthermore, the introduction of nitrogen-containing organic compounds enhances the adsorption and activation capacity for CO2, which can further regulate the functional properties of the catalyst and help to catalyze the conversion of CO2 under relatively harsh conditions.

[0012] In a second aspect, the present invention provides a method for preparing a polyionic liquid catalyst as described in the first aspect, the method comprising the following steps: The 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound was mixed with compound A, and a photoinitiator was added. Under ultraviolet light irradiation, free radical polymerization was carried out to obtain the polyionic liquid catalyst. The compound A includes nitrogen-containing organic compounds of methacrylic acid and / or metal halides.

[0013] Preferably, the wavelength of the ultraviolet light is 365-395 nm, for example, it can be 370 nm, 375 nm, 380 nm, 385 nm or 395 nm.

[0014] Preferably, the preparation method of the polyionic liquid catalyst shown in Formula I includes the following steps: A 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound is mixed with a metal halide and stirred at 30-50°C (e.g., 35°C, 38°C, 40°C, 42°C, or 45°C) for 4-10 h (e.g., 5 h, 6 h, 7 h, 8 h, or 9 h). Then, a nitrogen-containing organic compound of methacrylic acid is added, and stirring is continued for 1-4 h (e.g., 1.5 h, 2 h, 2.5 h, 3 h, or 3.5 h). A photoinitiator is then added, and free radical polymerization is carried out under ultraviolet light irradiation to obtain the polyionic liquid catalyst.

[0015] Preferably, the preparation method of the polyionic liquid catalyst shown in Formula II includes the following steps: The 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound was mixed with a metal halide and stirred at 30-50°C (e.g., 35°C, 38°C, 40°C, 42°C, or 45°C) for 4-10 h (e.g., 5 h, 6 h, 7 h, 8 h, or 9 h). A photoinitiator was then added, and free radical polymerization was carried out under ultraviolet light irradiation to obtain the polyionic liquid catalyst.

[0016] Preferably, the preparation method of the polyionic liquid catalyst shown in Formula III includes the following steps: A 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound is mixed with a nitrogen-containing organic compound of methacrylic acid and stirred at 30-50°C (e.g., 35°C, 38°C, 40°C, 43°C, or 45°C) for 1-8 h (e.g., 2 h, 3 h, 4 h, 5 h, 6 h, or 7 h). A photoinitiator is added, and free radical polymerization is carried out under ultraviolet light irradiation to obtain the polyionic liquid catalyst.

[0017] Preferably, the molar ratio of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound to the nitrogen-containing organic methacrylic acid is (1-4):1, for example, it can be 1.5:1, 2:1, 2.5:1, 3:1 or 3.5:1, and more preferably (1-2):1.

[0018] Preferably, the molar ratio of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound to the metal halide is 1:(1-4), for example, it can be 1:1.5, 1:2, 1:2.5, 1:3 or 1:3.5, and more preferably 1:(1-2).

[0019] Preferably, the photoinitiator is 0.5%-8% of the sum of the masses of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound, the nitrogen-containing organic methacrylic acid compound, and the metal halide, for example, it can be 1%, 1.5%, 2%, 3%, 3.5%, or 4%, and more preferably 1%-4%.

[0020] Preferably, the reaction time for the free radical polymerization is 5-100 min, for example, it can be 10 min, 20 min, 40 min, 50 min, 70 min or 90 min.

[0021] Preferably, the free radical polymerization further includes a post-treatment step, the post-treatment method including washing and drying under vacuum conditions of 50-100°C (e.g., 60°C, 70°C, 75°C, 80°C, or 90°C).

[0022] Preferably, the free radical polymerization is carried out under the protection of an inert gas.

[0023] Preferably, the free radical polymerization is carried out in anhydrous acetonitrile solvent.

[0024] Preferably, the nitrogen-containing organic compound of methacrylic acid includes dimethylaminoethyl methacrylate.

[0025] Preferably, the metal halide includes zinc bromide.

[0026] Thirdly, the present invention provides a method for preparing cyclic carbonates, the method comprising the following steps: (S1) The epoxy compound is mixed with the polyionic liquid catalyst as described in claim 1 to obtain a mixed system; (S2) CO2 is introduced into the mixed system to carry out a cycloaddition reaction to obtain the cyclic carbonate.

[0027] Preferably, the reaction temperature of the cycloaddition reaction is 40-120℃, for example, it can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃ or 110℃, and more preferably 50-100℃.

[0028] Preferably, the reaction time of the cycloaddition reaction is 1-24 h, for example, it can be 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h or 20 h, and more preferably 2-10 h.

[0029] Preferably, the reaction pressure of the cycloaddition reaction is 0.5-5 MPa, for example, it can be 1 MPa, 2 MPa, 2.5 MPa, 3 MPa or 4 MPa, and more preferably 1-3 MPa.

[0030] Preferably, the molar amount of the polyionic liquid catalyst is 0.1%-5% of the molar amount of the epoxy compound, for example, it can be 0.5%, 1%, 2%, 2.5%, 3% or 4%, and more preferably 0.1%-2%.

[0031] Preferably, the epoxy compound includes any one or a combination of at least two of ethylene oxide, propylene oxide, butane oxide, epichlorohydrin, styrene oxide, or cyclohexane oxide.

[0032] Preferably, the yield of the cyclic carbonate is 32.5%-99.7%, for example, it can be 40%, 50%, 60%, 70%, 80% or 90%.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention uses ultraviolet light to initiate polymerization, which has a shorter reaction time and can be carried out at room temperature and pressure without heating or pressurization, making it more green and environmentally friendly, energy-saving and low-carbon, which meets the current requirements of low-carbon development.

[0034] (2) The preparation method of epoxy carbonate of the present invention has a simple and efficient separation process, mild catalytic conditions, and outstanding recycling performance, providing an effective solution for solving the bottleneck problems of difficult separation and recovery of homogeneous catalysts and low reuse rate through multiple approaches. Attached Figure Description

[0035] Figure 1 These are the infrared spectra of the polyionic liquid catalysts of Examples 1-3 of this invention.

[0036] Figure 2 Thermogravimetric analysis of the polyionic liquid catalysts in Examples 1-3 of this invention.

[0037] Figure 3 This is the XRD analysis of the polyionic liquid catalysts in Examples 1-3 of this invention.

[0038] Figure 1-3 In the examples, PDImZn-TMPTA2 is the polyionic liquid catalyst of Example 1; PDIm-TMDE is the polyionic liquid catalyst of Example 2; and PDImZn-TMDE is the polyionic liquid catalyst of Example 3. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0040] The sources of some of the raw materials used in the following examples are as follows.

[0041] The preparation method of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound includes the following steps: Propylene imidazole and 1,3-dibromopropanol were added to a 250 mL three-necked flask at a molar ratio of 2.1:1, along with 50 mL of acetonitrile as a solvent. The mixture was thoroughly mixed at room temperature. The three-necked flask was kept under an inert atmosphere and reacted in an oil bath at 80 °C for 48 h. After the reaction was complete, most of the reaction solvent was removed to obtain the crude product. This crude product was then washed repeatedly with ethyl acetate 5-8 times to obtain a white solid. The solid was dried at 50-100 °C for 24 h to obtain the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound.

[0042] Example 1 A polyionic liquid catalyst and its preparation method are disclosed. The preparation method includes the following steps: 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound and ZnBr2 were added to anhydrous acetonitrile at a molar ratio of ILs:ZnBr2 = 1:2. The mixture was stirred continuously at 50°C for 8 h under an inert gas atmosphere. After cooling to room temperature, ethyl 2,4,6-trimethylbenzoylphenylphosphonate (2% by mass of the photoinitiator, equal to 2% of the combined mass of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound and ZnBr2) was added. Nitrogen gas was continuously bubbled through the flask as a protective gas. The three-necked flask was placed on a magnetic stirrer and irradiated with a 365-395 nm UV lamp for 30 min. After the reaction was complete, the reaction solvent and unreacted ionic liquid monomers were repeatedly washed with anhydrous ethanol and anhydrous methanol. The thoroughly washed polyionic liquid was placed in a vacuum drying oven at 60°C for 24 hours to remove excess solvent and moisture. The structure of the polyionic liquid catalyst is as follows. Example 2 A polyionic liquid catalyst and its preparation method are disclosed. The preparation method includes the following steps: 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound and dimethylaminoethyl methacrylate were added to anhydrous acetonitrile at a molar ratio of ILs:dimethylaminoethyl methacrylate = 1:2. The mixture was stirred continuously at 50°C for 8 h under an inert gas atmosphere. After cooling to room temperature, a UV photoinitiator (ethyl 2,4,6-trimethylbenzoylphenylphosphonate) was added, with the mass of the photoinitiator being 2% of the sum of the masses of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound and dimethylaminoethyl methacrylate. Nitrogen gas was continuously bubbled through the flask as a protective gas. The three-necked flask was placed on a magnetic stirrer and irradiated with a 365-395 nm UV lamp for 30 min. After the reaction was complete, the reaction solvent and unreacted ionic liquid monomers were repeatedly washed with anhydrous ethanol and anhydrous methanol. The thoroughly washed polyionic liquid was placed in a vacuum drying oven at 60°C for 24 hours to remove excess solvent and moisture. The structure of the polyionic liquid catalyst is as follows. Example 3 A polyionic liquid catalyst and its preparation method are disclosed. The preparation method includes the following steps: 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound and ZnBr2 were added to anhydrous acetonitrile at a molar ratio of ILs:ZnBr2 = 1:2. The mixture was stirred continuously at 50°C for 8 h under an inert gas atmosphere. Then, dimethylaminoethyl methacrylate was added at a molar ratio of ILs:dimethylaminoethyl methacrylate = 1:2. After cooling to room temperature, a UV photoinitiator (2,4,6-trimethylbenzoylphenylphosphonate ethyl ester) was added. The mass of the UV photoinitiator was 2% of the sum of the masses of 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound, ZnBr2, and dimethylaminoethyl methacrylate. Nitrogen gas was continuously purged into the flask as a protective gas. The three-necked flask was placed on a magnetic stirrer and irradiated with a 365-395 nm UV lamp for 30 min. After the reaction was complete, the reaction solvent and unreacted ionic liquid monomers were repeatedly washed with anhydrous ethanol and anhydrous methanol. The thoroughly washed polyionic liquid was then placed in a vacuum drying oven at 60°C for 24 hours to remove excess solvent and moisture. The structure of the polyionic liquid catalyst is as follows. Application Example 1 A method for preparing a cyclic carbonate. The preparation method includes the following steps: In a 15 mL sealed reactor, 1 mL (14.3 mmol) of propylene oxide and 0.0715 mmol of polyionic liquid catalyst (from Example 1) were added. The vent of the reactor was quickly closed, and CO2 at 2 MPa was introduced into the system. The instrument was then heated to 120 °C. After reaching the target temperature, the instrument parameters were adjusted to 500 r / min, pressure 2 MPa, and maintained at 120 °C for 2 h to obtain propylene carbonate. The equipment was allowed to automatically cool to room temperature. Gas chromatography evaluation showed that the yield of propylene carbonate from the catalyst was 95.2%, and the selectivity was 99.9%.

[0043] Application Example 2 A method for preparing cyclic carbonates differs from Application Example 1 only in that the polyionic liquid catalyst is derived from Example 2. The catalyst yields 74.5% acrylate carbonate with a selectivity of 99.9%.

[0044] Application Example 3 A method for preparing cyclic carbonates differs from Application Example 1 only in that the polyionic liquid catalyst is derived from Example 3. The catalyst yields 96.1% acrylate carbonate and has a selectivity of 99%.

[0045] Application Example 4 A method for preparing cyclic carbonates differs from Application Example 1 only in that the reaction temperature is 80°C, the yield of propylene carbonate is 69.1%, and the selectivity is 99.9%.

[0046] Application Example 5 A method for preparing cyclic carbonates differs from Application Example 2 only in that the reaction temperature is 80°C, the yield of propylene carbonate is 79.6%, and the selectivity is 99.9%.

[0047] Application Example 6: A method for preparing cyclic carbonates differs from Application Example 4 only in that the reaction time is 6 h, the yield of propylene carbonate is 83.7%, and the selectivity is 99.9%.

[0048] Application Example 7: A method for preparing cyclic carbonates differs from Application Example 6 only in that the reaction time is 8 h, the yield of propylene carbonate is 92.3%, and the selectivity is 99.9%.

[0049] Application Example 8: A method for preparing cyclic carbonates differs from Application Example 5 only in that the reaction time is 6 h, the yield of propylene carbonate is 95.3%, and the selectivity is 99.9%.

[0050] Application Example 9: A method for preparing cyclic carbonates differs from Application Example 7 only in that the molar amount of catalyst is 0.7% of the molar amount of propylene oxide, and the yield of propylene carbonate is 96.7% with a selectivity of 99.9%.

[0051] Application Example 10: A method for preparing cyclic carbonates differs from Application Example 8 only in that the molar amount of catalyst is 0.7% of the molar amount of propylene oxide, and the yield of propylene carbonate is 99.7% with a selectivity of 99.9%.

[0052] Application Example 11: A method for preparing cyclic carbonates differs from Application Example 10 only in that the epoxy substrate is changed to epichlorohydrin, and the yield of the product chloroacrylate is 98.7% with a selectivity of 99.9%.

[0053] The test results show that: (1) As can be seen from Application Examples 1-11, the present invention enhances the polymerization ability of bisimidazole ionic liquid under ultraviolet light by introducing metal ions, and at the same time adds nitrogen-containing substances to further enhance the adsorption and activation ability of CO2. The polymer ionic liquid with high crosslinking is polymerized by ultraviolet light under room temperature conditions, which can efficiently catalyze the reaction of CO2 and epoxy compounds to synthesize cyclic carbonates under conditions without catalysts or solvents.

[0054] In summary, this invention provides a simple and feasible synthesis strategy for polyionic liquid catalysts under room temperature conditions. It is environmentally friendly and introduces multiple active sites. The addition of nitrogen-containing substances enables the catalyst to absorb CO2 and promote ring opening. It can achieve high product yields with low catalyst dosage and has good catalytic activity for the cycloaddition reaction of CO2 and epoxides. The catalyst is easy to separate after the reaction and has the advantages of low catalyst dosage, which have potential application value.

[0055] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A polyionic liquid catalyst, characterized in that, The structure of the polyionic liquid catalyst is shown in Formula I, Formula II, or Formula III: Formula I; Formula II; Formula III; Where p and m are each an arbitrary natural number, and 4 ≤ p + m; n = 1-6; M is selected from any metal ion; R1 and R2 each independently include any one of C1-C6 alkyl or C2-C6 alkenyl groups; X - It includes any one of iodide ions, fluoride ions, bromide ions, or chloride ions.

2. A method for preparing the polyionic liquid catalyst as described in claim 1, characterized in that, The preparation method includes the following steps: The 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound was mixed with compound A, and a photoinitiator was added. Under ultraviolet light irradiation, free radical polymerization was carried out to obtain the polyionic liquid catalyst. Compound A includes nitrogen-containing organic compounds of the methacrylic acid class and / or metal halides.

3. The preparation method according to claim 2, characterized in that, The preparation method of the polyionic liquid catalyst shown in Formula I includes the following steps: The 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound was mixed with a metal halide and stirred at 30-50°C for 4-10 h. Then, a nitrogen-containing organic compound of methacrylic acid was added and stirred for another 1-4 h. Finally, a photoinitiator was added and free radical polymerization was carried out under ultraviolet light irradiation to obtain the polyionic liquid catalyst.

4. The preparation method according to claim 2, characterized in that, The preparation method of the polyionic liquid catalyst shown in Formula II includes the following steps: The 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound was mixed with a metal halide and stirred at 30-50°C for 4-10 h. A photoinitiator was then added and free radical polymerization was carried out under ultraviolet light irradiation to obtain the polyionic liquid catalyst.

5. The preparation method according to claim 2, characterized in that, The preparation method of the polyionic liquid catalyst shown in Formula III includes the following steps: The 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound was mixed with a nitrogen-containing organic compound of methacrylic acid, stirred at 30-50°C for 1-8 h, a photoinitiator was added, and free radical polymerization was carried out under ultraviolet light irradiation to obtain the polyionic liquid catalyst.

6. The preparation method according to any one of claims 2-5, characterized in that, The molar ratio of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound to the nitrogen-containing organic methacrylic acid is (1-4):1, and more preferably (1-2):1; Preferably, the molar ratio of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound to the metal halide is 1:(1-4), more preferably 1:(1-2); Preferably, the photoinitiator is 0.5%-8% of the sum of the masses of the 3,3'-(2-hydroxy-1,3-propadiyl)-bis(1-propylimidazolium)dibromo compound, the nitrogen-containing organic methacrylic acid compound, and the metal halide. Preferably, the reaction time for the free radical polymerization is 5-100 min; Preferably, the free radical polymerization further includes a post-treatment step, the post-treatment method including washing and drying under vacuum conditions at 50-100°C; Preferably, the free radical polymerization is carried out under the protection of an inert gas; Preferably, the free radical polymerization is carried out in anhydrous acetonitrile solvent; Preferably, the nitrogen-containing organic compound of methacrylic acid includes dimethylaminoethyl methacrylate; Preferably, the metal halide includes zinc bromide.

7. A method for preparing a cyclic carbonate, characterized in that, The preparation method includes the following steps: (S1) The epoxy compound is mixed with the polyionic liquid catalyst as described in claim 1 to obtain a mixed system; (S2) CO2 is introduced into the mixed system to carry out a cycloaddition reaction to obtain the cyclic carbonate.

8. The preparation method according to claim 7, characterized in that, The reaction temperature for the cycloaddition reaction is 40-120℃; Preferably, the reaction time of the cycloaddition reaction is 1-24 h; Preferably, the reaction pressure of the cycloaddition reaction is 0.5-5 MPa.

9. The preparation method according to claim 7 or 8, characterized in that, The molar number of the polyionic liquid catalyst is 0.1%-5% of the molar number of the epoxy compound.

10. The preparation method according to any one of claims 7-9, characterized in that, The epoxy compound includes any one or a combination of at least two of ethylene oxide, propylene oxide, butane oxide, epichlorohydrin, styrene oxide, or cyclohexane oxide.

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