Polymeric ionic liquid catalysts, methods of making and using the same

Abstract

This invention relates to a polymeric ionic liquid catalyst, its preparation method, and its application. The structure of the polymeric ionic liquid catalyst is shown in Formula I or Formula II, wherein p and m are each independent natural numbers, and 4 ≤ p + m; R is a hydrogen donor group; X ‑ The ions are fluoride, chloride, bromide, or iodide; R1 includes any one of C1-C6 alkyl or C2-C6 alkenyl groups; n = 1-6. This invention uses imidazole ionic liquids copolymerized with crosslinking agents of different chain lengths and functionalities to form polymeric ionic liquids, which can solve the problem of catalyst separation and recovery while retaining the advantages of ionic liquid monomers.

Description

Technical Field

[0001] This invention relates to the field of green catalysis technology for CO2 fixation and conversion, and particularly to a method for synthesizing a cross-linked methacrylic acid polymeric ionic liquid catalyst under ultraviolet light catalysis at room temperature, as well as a method for catalyzing the synthesis of cyclic carbonates from CO2 and epoxides. It also relates to a polymeric ionic liquid catalyst, its preparation method, and its applications. Background Technology

[0002] With the acceleration of global industrialization, excessive carbon dioxide (CO2) emissions have become a key environmental challenge restricting sustainable development. CO2 capture, utilization, and storage (CCUS) technology has been clearly identified as a core technological pathway. Unlike traditional geological storage, CO2 resource utilization transforms inexpensive and abundant C1 synthons into high-value-added chemicals, offering both environmental and economic benefits, aligning with the principles of circular economy and green chemistry. Among these, the cycloaddition reaction of CO2 with epoxides can synthesize cyclic carbonates under 100% atom economy conditions. The products are widely used in electrolytes, aprotic polar solvents, polycarbonate synthesis intermediates, and biopharmaceuticals, making it one of the most promising industrial routes for CO2 chemical fixation. Although homogeneous catalytic systems (such as Salen-Co and ionic liquids) exhibit excellent catalytic activity, their inherent difficulties in separation and recovery, high product purification costs, and challenges in catalyst recycling severely restrict their industrial application. Heterogeneous catalysts, with their advantages of easy separation, recyclability, and continuous operation, have become the inevitable choice for technological transformation in this field. However, traditional heterogeneous catalysts (such as supported metal oxides and porous organic polymers) generally suffer from drawbacks such as low active site density, poor mass transfer efficiency, easy loss of active components, or insufficient catalytic efficiency, making it difficult to simultaneously achieve high activity, high selectivity, and long-term stability. Furthermore, the preparation of most current heterogeneous catalysts involves complex processes that often require prolonged high-temperature conditions, hindering rapid synthesis and optimization, and leading to further waste of resources.

[0003] To address the existing problems, researchers are primarily developing a series of catalysts, such as bisimidazole ionic liquid catalysts. CN110746357A discloses a bisimidazole ionic liquid catalyst that generates products from imidazole and different anions, achieving a 96% conversion rate at 50°C for 5 hours with a 10 mol% catalyst dosage. However, this system requires a high catalyst dosage and additional separation steps to separate the products, easily leading to resource waste.

[0004] Porous organic polymers: CN118344514A discloses a method for quaternizing vinyl-functionalized pyridine polymer POP-Py to obtain ionic liquid-based porous organic polymers functionalized with different types of polar groups, including carboxyl, hydroxyl, and amino groups, while simultaneously introducing halogen Br. - The reaction was carried out at 90℃ for 24 hours, and the yield of styrene carbonate was 94.2%. The catalyst contained abundant functional groups, but the reaction time was relatively long.

[0005] Mesoporous silica materials: CN116020568A discloses a novel mesoporous catalyst obtained by fully contacting nanocage CS with active centers and co-active centers in a solvent, followed by treatment with a mixture of water and alcohol. The catalyst achieves a conversion rate of 99% at 120℃ for 10 hours. This method requires heat treatment at 400~700℃ under an inert or air atmosphere for 2~6 hours, and the solvent removal temperature must be maintained at 20~40℃. Furthermore, the alcohol and water ratio must be strictly controlled, making the preparation process very complex.

[0006] ZIF-8@In2O3 Composite Material: CN119285598A discloses a simplified method for preparing composite catalysts, namely, the ZIF-8@In2O3 composite material is prepared by in-situ composite of ZIF-8 and hollow prismatic In2O3, thus optimizing the preparation method. However, this synthesis method requires maintaining the hollow prismatic precursor at 400~500℃ for 2-3 hours, which requires a large amount of heat. Furthermore, the cycloaddition reaction requires the addition of up to 10 mol% of the co-catalyst TBAB, and the yield of chloroacrylate is only 94% after 24 hours of reaction.

[0007] Based on the above situation, there is an urgent need in this field to develop a heterogeneous ionic liquid green catalyst that not only has mild and simple synthesis conditions, but also high activity, good stability, and is easy to recover. Polymerizable ionic liquids have attracted much attention from researchers due to their characteristics of not requiring a support, simple polymerization methods, and high stability. Therefore, the development of polymerizable ionic liquids has great potential value in industrial application research. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a polymeric ionic liquid catalyst, its preparation method, and its applications. This invention synthesizes a highly crosslinked polymeric ionic liquid by polymerizing an easily crosslinking crosslinking agent with an ionic liquid possessing dual catalytic sites under ultraviolet light initiation at room temperature. This polymeric ionic liquid can efficiently catalyze the reaction of CO2 with epoxides to synthesize cyclic carbonates under catalyst-free and solvent-free conditions. This method achieves regulation of the polymeric ionic liquid structure by altering the crosslinking agent structure, thereby controlling the catalytic activity and stability of the polymeric ionic liquid. Simultaneously, optimizing the ultraviolet light initiation conditions (initiator ratio, irradiation time) enhances the catalytic activity.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a polymeric ionic liquid catalyst, the structure of which is shown in Formula I or Formula II: , Where p and m are each an independent 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.); R is a hydrogen-donating group; X - It is a fluoride ion, chloride ion, bromide ion or iodide ion; R1 includes any one of C1-C6 (e.g., it can be C2, C3, C4 or C5) alkyl or C2-C6 (e.g., it can be C3, C4 or C5) alkenyl; n=1-6 (e.g., it can be 2, 3, 4 or 5).

[0010] Preferably, n is an integer from 1 to 6.

[0011] Secondly, the present invention provides a method for preparing a polymeric ionic liquid catalyst, the method comprising the following steps: (1) Mix propenyl imidazole and compound A and react to obtain an ionic liquid monomer; (2) The ionic liquid monomer, initiator and crosslinking agent are mixed and crosslinking reaction is carried out to obtain the polymeric ionic liquid; The structure of compound A is shown in Formula III: , Where X is a fluorine substituent, a chlorine substituent, a bromine substituent, or an iodine substituent, and R is a hydrogen-donating group.

[0012] In this invention, imidazole ionic liquids have the advantages of strong designability, easy synthesis, and the ability to absorb CO2 to promote activation. By copolymerizing with crosslinking agents of different chain lengths and functionalities to form polymeric ionic liquids, the problem of catalysts being difficult to separate and recover can be solved while retaining the advantages of ionic liquid monomers.

[0013] Preferably, R is a hydroxyl, carboxyl, or amino group.

[0014] Preferably, compound A includes 1,3-dibromopropanol.

[0015] Preferably, the molar ratio of the propenyl imidazole to compound A is (2-2.2):1, for example, it can be 2.05:1, 2.08:1, 2.1:1, 2.12:1 or 2.15:1, etc.

[0016] Preferably, the crosslinking agent comprises compound B and / or compound C. The structure of compound B is shown in Formula IV: Where n = 1-6 (for example, it can be 2, 3, 4 or 5); The structure of compound C is shown in formula V: R1 includes any one of C1-C6 (e.g., C2, C3, C4 or C5) alkyl or C2-C6 (e.g., C3, C4 or C5) alkenyl groups.

[0017] Preferably, compound B comprises propane-1,3-dimethyldiacrylate and / or 1,6-hexanediol diacrylate.

[0018] Preferably, compound C comprises trimethylolpropane triacrylate.

[0019] Preferably, the molar ratio of the ionic liquid monomer to the crosslinking agent 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.

[0020] Preferably, the reaction in step (1) further includes a post-processing step, wherein the post-processing method includes washing the product and drying.

[0021] Preferably, the crosslinking reaction is carried out under the protection of an inert gas.

[0022] Preferably, the initiator is a photoinitiator.

[0023] Preferably, with the total mass percentage of the ionic liquid monomer and crosslinking agent in step (2) being 100%, the mass percentage of the photoinitiator is no more than 8%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6% or 7%, etc.

[0024] Preferably, with the total mass percentage of the ionic liquid monomer and crosslinking agent in step (2) being 100%, the mass percentage of the photoinitiator is 0.5%-8%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6% or 7%, etc.

[0025] Preferably, the crosslinking reaction is carried out under ultraviolet light irradiation.

[0026] Preferably, the wavelength of the ultraviolet light is 365-405 nm, for example, it can be 370 nm, 375 nm, 385 nm, 395 nm or 400 nm, etc.

[0027] Preferably, the reaction time of the crosslinking reaction is 5-100 min, for example, it can be 10 min, 20 min, 40 min, 60 min or 80 min.

[0028] Preferably, the crosslinking reaction further includes a post-processing step, the post-processing method including washing and vacuum drying.

[0029] Preferably, the vacuum drying temperature is 50-100℃, for example, it can be 60℃, 70℃, 75℃, 80℃ or 90℃.

[0030] 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 polymeric ionic liquid catalyst as described in the first aspect to obtain a mixed system; (S2) CO2 is introduced into the mixed system to carry out a cycloaddition reaction to obtain the cyclic carbonate.

[0031] Preferably, the reaction temperature of the cycloaddition reaction is 50-130°C, for example, it can be 70°C, 90°C, 100°C, 110°C or 120°C, and more preferably 50-120°C.

[0032] 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.

[0033] Preferably, after CO2 is introduced in step (S2), the pressure of the mixed system is 0.5-5 MPa, for example, it can be 1 MPa, 2 MPa, 3 MPa, 4 MPa or 4.5 MPa, etc.

[0034] Preferably, the molar ratio of the polymeric ionic liquid catalyst to the epoxy compound is (0.1-5):100, for example, it can be 0.5:100, 1:100, 2:100, 3:100, 4:100 or 4.5:100, and more preferably (0.1-2):100.

[0035] Preferably, the epoxy compound includes any one or a combination of at least two of ethylene oxide, propylene oxide, butane oxide, cyclopentane oxide, epichlorohydrin, styrene oxide, or cyclohexane oxide.

[0036] Preferably, the method for preparing the cyclic carbonate includes the following steps: The epoxy compound and the polymeric ionic liquid catalyst as described in the first aspect are placed in a closed reactor, and CO2 at 0.2 MPa is introduced. The reactor temperature is allowed to reach 60-120°C, and CO2 gas is then introduced into the reactor to maintain the pressure inside the reactor at 1-5 MPa. The cycloaddition reaction is carried out for 2-8 hours to obtain the cyclic carbonate.

[0037] 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.

[0038] (2) The ionic liquid monomer in this invention is a two-site ionic liquid with two active sites. The cross-linked network structure obtained by polymerizing with acrylates of different chain lengths and functionalities can fully disperse the active sites, which is beneficial to the exposure of active sites and mass transfer.

[0039] (3) It has the advantages of simple and efficient separation process 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

[0040] Figure 1 This is the infrared spectrum of the polymeric ionic liquid catalyst of the present invention.

[0041] Figure 2 Thermogravimetric analysis of the polymeric ionic liquid catalyst of the present invention.

[0042] Figure 3 This is the XRD analysis of the polymeric ionic liquid catalyst of the present invention.

[0043] Figure 1-3In this example, PDIm-PDDA is the polymeric ionic liquid catalyst of Example 1; PDIm-HDDA is the polymeric ionic liquid catalyst of Example 2; PDIm-TMPTA is the polymeric ionic liquid catalyst of Example 3; PDIm-TMPTA1 is the polymeric ionic liquid catalyst of Example 4; and PDIm-TMPTA2 is the polymeric ionic liquid catalyst of Example 5. Detailed Implementation

[0044] 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.

[0045] Example 1 A method for preparing a cyclic carbonate, the method comprising the following steps: (1) Preparation of polymeric ionic liquid catalysts: (1.1) Propylene imidazole and 1,3-dibromopropanol were added to a 250 mL three-necked flask at a molar ratio of 2.1:1, and 50 mL of acetonitrile was added as a solvent. The mixture was stirred thoroughly 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 completed, most of the reaction solvent was removed to obtain the crude product. The crude product was then washed repeatedly with ethyl acetate 5-8 times to obtain a white solid substance. The solid was dried at 50-100 °C for 24 h to obtain the ionic liquid monomer.

[0046] (1.2) The ionic liquid monomer and propane-1,3-dimethyldiacrylate were added to a 100 mL beaker at a molar ratio of 4:1 and stirred. A mixed solution of anhydrous methanol and anhydrous acetonitrile was used as the solvent (volume ratio: anhydrous methanol: anhydrous acetonitrile = 1:3). Based on a total mass percentage of 100% for the ionic liquid monomer and propane-1,3-dimethyldiacrylate, 8% by mass of UV photoinitiator TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) was added. An inert gas was continuously introduced into the flask as a protective gas. The three-necked flask was placed on a magnetic stirrer and irradiated with a 365 nm UV lamp for 60 min. After the reaction was complete, the reaction solvent and unreacted ionic liquid monomer were repeatedly washed with anhydrous ethanol and anhydrous methanol. The thoroughly washed product was placed in a vacuum drying oven at 60 °C for 24 h to remove excess solvent and moisture, yielding the polymerized ionic liquid catalyst.

[0047] (2) Preparation of cyclic carbonates: In a 15 mL sealed reactor, 1 mL (14.3 mmol) of propylene oxide and 0.0715 mmol of polymeric ionic liquid catalyst 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 and maintained at 120 °C for 2 h to obtain the cyclic carbonate. The equipment was allowed to automatically cool to room temperature. The performance of the catalyst was evaluated by gas chromatography. The yield of the cyclic carbonate was 46%, and the selectivity was 99%.

[0048] Example 2 A method for preparing a cyclic carbonate differs from Example 1 only in that propane-1,3-dimethyldiacrylate is replaced with the same amount of 1,6-hexanediol diacrylate.

[0049] The yield of cyclic carbonates was 19%, with a selectivity of 99%.

[0050] Example 3 A method for preparing a cyclic carbonate differs from Example 1 only in that propane-1,3-dimethyldiacrylate is replaced with the same amount of trimethylolpropane triacrylate.

[0051] The yield of cyclic carbonates was 48%, with a selectivity of 99%.

[0052] Example 4 A method for preparing cyclic carbonate differs from Example 3 only in that the ultraviolet light wavelength in step (1.2) is 395 nm, the irradiation time is 20 min, and the mass percentage of ultraviolet photoinitiator is 2%.

[0053] The yield of cyclic carbonates was 53%, with a selectivity of 99%.

[0054] Example 5 A method for preparing cyclic carbonates differs from Example 4 only in that the ultraviolet light wavelength in step (1.2) is 365 nm.

[0055] The yield of cyclic carbonates was 54%, with a selectivity of 99%.

[0056] Example 6 A method for preparing cyclic carbonates differs from Example 5 only in that the phrase “holding at a constant temperature of 120°C for 2 h” in step (2) is changed to “holding at a constant temperature of 120°C for 12 h”.

[0057] The yield of cyclic carbonates was 82%, with a selectivity of 99%.

[0058] Example 7 A method for preparing cyclic carbonates differs from Example 6 only in that "120°C" in step (2) is changed to "80°C".

[0059] The yield of cyclic carbonates was 38%, with a selectivity of 99%.

[0060] Example 8 A method for preparing cyclic carbonates differs from Example 5 only in that the number of moles of the polymeric ionic liquid catalyst in step (2) is 0.143 mmol.

[0061] The yield of cyclic carbonates was 92%, with a selectivity of 99%.

[0062] Example 9 A method for preparing a cyclic carbonate differs from Example 8 only in that propylene oxide is replaced with the same amount of epichlorohydrin.

[0063] The yield of cyclic carbonates was 97%, with a selectivity of 99%.

[0064] The test results show that: (1) As can be seen from Examples 1-9, the present invention provides a simple and feasible synthesis strategy for heterogeneous catalysts, which is more environmentally friendly. At the same time, the catalyst has a certain absorption effect on CO2 and can promote ring opening. It can achieve a high product yield with a low catalyst dosage. It has good catalytic activity for the cycloaddition reaction of CO2 and epoxides. The catalyst has the advantages of easy separation after the reaction and low catalyst dosage, and has potential application value.

[0065] 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 polymeric ionic liquid catalyst, characterized in that, The structure of the polymeric ionic liquid catalyst is shown in Formula I or Formula II: ， Where p and m are each independent natural numbers, and 4 ≤ p + m; R is a hydrogen donor group; X - It can be a fluoride ion, chloride ion, bromide ion, or iodide ion; R1 includes any one of C1-C6 alkyl or C2-C6 alkenyl groups; n=1-6.

2. A method for preparing the polymeric ionic liquid catalyst as described in claim 1, characterized in that, The preparation method includes the following steps: (1) Mix propenyl imidazole and compound A and react to obtain an ionic liquid monomer; (2) The ionic liquid monomer, initiator and crosslinking agent are mixed and crosslinking reaction is carried out to obtain the polymeric ionic liquid; The structure of compound A is shown in Formula III: ， Where X is a fluorine substituent, a chlorine substituent, a bromine substituent, or an iodine substituent, and R is a hydrogen-donating group.

3. The preparation method according to claim 2, characterized in that, R is a hydroxyl, carboxyl, or amino group; Preferably, compound A comprises 1,3-dibromopropanol; Preferably, the molar ratio of the propenyl imidazole to compound A is (2-2.2):

1.

4. The preparation method according to claim 2 or 3, characterized in that, The crosslinking agent includes compound B and / or compound C. The structure of compound B is shown in Formula IV: Where n = 1 - 6; The structure of compound C is shown in formula V: R1 includes any one of C1-C6 alkyl or C2-C6 alkenyl groups; Preferably, compound B comprises propane-1,3-dimethyldiacrylate and / or 1,6-hexanediol diacrylate; Preferably, compound C comprises trimethylolpropane triacrylate; Preferably, the molar ratio of the ionic liquid monomer to the crosslinking agent is (1-4):1, and more preferably (1-2):

1.

5. The preparation method according to any one of claims 2-4, characterized in that, The reaction in step (1) is followed by a post-processing step, which includes washing the product and drying it. Preferably, the crosslinking reaction is carried out under the protection of an inert gas; Preferably, the initiator is a photoinitiator; Preferably, based on the total mass percentage of the ionic liquid monomer and crosslinking agent described in step (2) being 100%, the mass percentage of the photoinitiator is no more than 8%; Preferably, the crosslinking reaction is carried out under ultraviolet light irradiation; Preferably, the reaction time of the crosslinking reaction is 5-100 min; Preferably, the crosslinking reaction further includes a post-processing step, the post-processing method including washing and vacuum drying; Preferably, the vacuum drying temperature is 50-100℃.

6. 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 polymeric ionic 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.

7. The cyclic carbonate according to claim 6, characterized in that, The reaction temperature for the cycloaddition reaction is 50-130℃; Preferably, the reaction time of the cycloaddition reaction is 1-24 h.

8. The preparation method according to claim 6 or 7, characterized in that, After CO2 is introduced in step (S2), the pressure of the mixed system is 0.5-5 MPa.

9. The preparation method according to any one of claims 6-8, characterized in that, The molar ratio of the polymeric ionic liquid catalyst to the epoxy compound is (0.1-5):

100.

10. The preparation method according to any one of claims 6-9, characterized in that, The epoxy compound includes any one or a combination of at least two of ethylene oxide, propylene oxide, butane oxide, cyclopentane oxide, epichlorohydrin, styrene oxide, or cyclohexane oxide.

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