CN117447439A - A method for catalytically synthesizing cyclic carbonate with multi-level structure polyionic liquid - Google Patents

Abstract

The invention provides a method for synthesizing cyclic carbonate by multi-stage structure polyion liquid catalysis, which comprises the following steps: preparation of multi-stage structure polyion liquid catalyst and catalytic CO ₂ And synthesizing the cyclic carbonate through cycloaddition reaction with an epoxy compound. The preparation method provided by the invention adjusts the multi-stage structure of the polymerized polyionic liquid through the ionic liquid monomer structure design, so that the catalyst with high activity, high stability and easy separation can be obtained, and various epoxy compounds and CO can be catalyzed ₂ The cycloaddition reaction occurs, so that the method has the advantages of high reaction efficiency, less catalyst consumption, simple preparation process and easy separation, and has higher industrial application value.

Description

A method for catalytically synthesizing cyclic carbonate with multi-level structure polyionic liquid

Technical field

The invention belongs to the technical field of green catalysis and relates to a method for using a polyionic liquid as a high-efficiency catalyst to catalyze the synthesis of cyclic carbonate from _CO2 and epoxy compounds. The method is to copolymerize imidazole ionic liquid and divinylbenzene cross-linking agent through The imidazole ionic liquid anion type, side chain length, substituent group, and the ratio of imidazole ionic liquid and divinylbenzene are adjusted to achieve the purpose of regulating the multi-level structure of the polyionic liquid to enhance the stability and activity of the catalyst. The specific catalytic reaction is the cycloaddition reaction of _CO2 and epoxy compounds. The reaction temperature is 80-150°C, the reaction pressure is 1-5MPa, the reaction time is 1-8h, and the catalyst dosage is 0.1-10wt%. This synthesis method has the advantages of high reaction efficiency, simple catalyst preparation process, small catalyst dosage, and easy separation and reuse.

Background technique

As a greenhouse gas and a rich source of C1 resources, _CO2 's efficient capture and conversion is a global strategic issue. Cyclic carbonate is a very widely used aprotic high-boiling point polar solvent. It can not only serve as an electrolyte in lithium-ion batteries, but also be used in the synthesis of pharmaceutical and fine chemical intermediates. The reaction of _CO2 cycloaddition to synthesize cyclic carbonates is a green and sustainable route with both environmental and economic benefits. The currently reported catalysts for the synthesis of cyclic carbonates mainly include organic catalysts, ionic liquids (CN111362901A), metal organic Skeleton (MOF) (CN111454434A, CN105481821A), porous organic polymer (CN104667974B), transition metal complex (CN107827857A, CN107827858A, CN111215148A), and composite catalyst (CN1139340) 2A, CN107715918B) and other catalysts. Among them, homogeneous catalysts have high catalytic activity, but the separation process is relatively complex and the catalyst stability is poor. Although heterogeneous catalysts simplify the separation process, their catalytic activity is relatively low. Therefore, the development of heterogeneous catalysts that are efficient, stable and easy to separate has attracted more attention.

As a new type of green non-metallic medium, ionic liquids are widely used in the field of catalysis because of their designable structure, good stability and solubility. Ionic liquids can have higher activity than traditional catalysts through anionic and cationic design. CN101130537 discloses a method for preparing cyclic carbonate from hydroxyl ionic liquid. It was found that hydroxyl groups as hydrogen bond donors can promote the activation of epoxides and can efficiently catalyze _CO conversion under mild conditions. Ionic liquid solid support can effectively simplify separation. CN102391241A discloses a method for preparing cyclic carbonate with a chitosan-supported catalyst. The chitosan chemically-supported catalyst is used during the reaction process, which can effectively catalyze the conversion _{of CO2} . The synergistic catalytic effect based on the hydroxyl groups in the carrier enables the catalytic synthesis of cyclic carbonates with high efficiency and selectivity without the need to add other assistants and cocatalysts. However, the existence of the carrier causes a certain amount of interfacial mass transfer steric hindrance, and the interface restraint limits the free movement of ions, resulting in a reduction in effective collisions between reactive molecules and active sites. Therefore, the activity of solid-supported ionic liquids is often lower than the bulk activity of equivalent ionic liquids.

Polyionic liquid is a special polymer with an ionic liquid unit structure. Compared with ionic liquid monomers, it has stronger stability. Compared with solid-supported ionic liquids, it has better structural ductility and adjustable deformation. Its units Structural expansion provides greater flexibility in the active site. CN109134420A discloses a method for using heterogeneous polymeric ionic liquid to efficiently catalyze the synthesis of cyclic carbonates from CO ₂ and epoxides. Quaternary ammonium ionic liquid monomers are synthesized into heterogeneous catalysts through free radical polymerization. This type of catalyst is easy to separate, has good activity, and can effectively catalyze the synthesis of cyclic carbonates from _CO2 and epoxides. CN112341394A discloses a method for preparing a hydrogen bond donor functionalized polyionic liquid catalyst, which is polymerized by imidazole-based ionic liquid monomers and hydrogen bond donor monomers in a certain proportion. The presence of hydrogen bond donors greatly improves the The catalytic efficiency provides ideas for regulating the high activity of polyionic liquids. However, previous studies rarely take into account the control of polyionic liquid molecules and nanostructures, making it difficult to obtain polyionic liquid catalysts with both stability and activity.

The invention uses one or two imidazole-based ionic liquid monomers and a rigid divinylbenzene cross-linking agent to prepare polyionic liquid catalysts with different structures through copolymerization and cross-linking polymerization. By modulating the anions of ionic liquid monomers and introducing hydrogen-donating groups, the intrinsic catalytic activity can be improved from the molecular level; by adjusting the side chain length of ionic liquid monomers and the ratio of cross-linking agents, the spatial structure of polyionic liquids can be controlled from the nano-micro level. Achieve enhanced structural stability of ionic liquids and full dispersion and exposure of active sites.

Contents of the invention

In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a polyionic liquid catalytic synthesis method for cyclic carbonate that has both stability and activity, so as to develop heterogeneous catalysts for the industrial application of cyclic carbonate. potential.

In order to achieve this goal, the first object of the present invention is to provide a multi-stage structure polyionic liquid catalyst, using this type of catalyst to catalyze the synthesis of cyclic carbonate from CO ₂ and epoxy compounds. The preparation method includes the following steps:

The multi-level structure polyionic liquid has a structure as shown in Formula 1, and the preparation process of the multi-level structure of the polyionic liquid is as shown in Formula 2:

Among them, m, n, and l respectively represent the number of different monomers in the unit structure, usually also the ratio of the amounts of the three monomers added during the polymerization reaction, and are each independently selected from any natural number;

R ₁ is selected from a hydrogen atom or any alkane group, such as methyl;

R ₂ is selected from any hydrogen-donating group, such as hydroxyl;

j and k respectively represent the number of carbon atoms in the alkyl chain, and the numbers of carbon atoms in j and k are each independently selected from: 2 to 12.

X ₁ and X ₂ are each independently selected from any one of fluoride ions, chloride ions, bromide ions, and iodide ions.

The present invention takes advantage of the advantages that the polyionic liquid unit structure is rich in active ions and the multi-level structure enhances reaction mass transfer, which is beneficial to improving the efficiency of the catalytic cycloaddition reaction, thereby making the cycloaddition reaction conditions relatively mild.

Preferably, the reaction temperature of the addition reaction is 80-150°C, such as 85°C, 90°C, 95°C, 100°C, 105°C, 115°C, 125°C, 135°C or 145°C, etc.

Preferably, the reaction pressure of the addition reaction is 1 to 5MPa, such as 1.5MPa, 1.8MPa, 2.0MPa, 2.5MPa, 3.2MPa, 3.5MPa, 4.0MPa or 4.5MPa, etc.

Preferably, the reaction time of the addition reaction is 1 to 8h, for example, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h etc.

Preferably, the particle size of the catalyst is 10 to 500nm, such as 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, etc. A suitable catalyst particle size is conducive to the dispersion of active sites. thereby improving catalytic efficiency.

Preferably, the catalyst mass fraction is 0.1 to 10%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% %wait.

Preferably, the epoxy-containing compound is any one or at least one of ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, styrene oxide, cyclohexane oxide or cyclopentane oxide. A mixture of both.

Preferably, in the structure shown in Formula 1, m+n≤136, excessive polymerization can easily lead to a decrease in catalytic efficiency.

Preferably, in the structure shown in Formula 1, R ₁ is selected from a hydrogen atom or any alkane group with a carbon number of ≤ 16 such as methyl, ethyl, propyl, butyl, etc.

Preferably, in the structure shown in Formula 1, R ₂ is selected from any one of hydroxyl, amino, amine group, carboxyl and thiol group.

Preferably, in the structure shown in Formula 1, X ₁ and X ₂ are each independently selected from any one of fluoride ions, chloride ions, bromide ions, and iodide ions.

Preferably, in the structure shown in formula 1, the number ratio of carbon atoms in m, n, l is 2:3:0, 1:1:0, 0:3:2, 0:1:1, 1:3: 1, 1:3:2, 2:3:1.

Preferably, in the structure shown in Formula 1, the numbers of carbon atoms in j and k are each independently selected from: 2 to 12.

Preferably, the preparation method includes the following steps:

Place the catalyst powder containing the epoxy compound and the particle size of 10 to 500 nm into a closed reactor and mix evenly. Maintain the temperature of the reactor in the range of 80 to 150°C. Continue to pass CO ₂ gas into the reactor to maintain the temperature in the reactor. The pressure of the reaction system is in the range of 1 to 5 MPa, and the addition reaction is carried out for 1 to 8 hours to obtain cyclic carbonate.

The numerical range described in the present invention not only includes the above-mentioned point values, but also includes any point value between the above-mentioned numerical ranges that are not exemplified. Due to space limitations and for the sake of simplicity, the present invention will not exhaustively list all the above-mentioned numerical ranges. The specific point values included in the stated range.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The present invention provides a multi-stage structure polyionic liquid catalyst, which is used to catalyze the cycloaddition of CO ₂ and epoxy compounds to synthesize cyclic carbonate, with high selectivity and conversion rate, and the obtained The yield of cyclic carbonate can reach 99m%.

(2) Compared with the traditional method of synthesizing cyclic carbonates, the polyionic liquid catalyst used in the present invention has high active site utilization, low dosage, high catalytic efficiency, stability and difficulty in decomposition, simple preparation process, and easy product Separation and many other advantages, it has high industrial application value.

Detailed ways

The technical solution of the present invention will be further described below through specific implementations.

The polyionic liquid used in the following examples and comparative examples can be obtained by self-synthesis.

Illustratively, the polyionic liquid can be synthesized through the following steps:

Step (1), add a certain amount of vinylimidazole monomer and ethyl bromide into a 250mL flask, condense and reflux at 70°C for 24 hours to react. After the reaction is completed, pour out the unreacted liquid in the upper layer, add acetonitrile and heat at 80°C. Condensate and reflux for 4 hours, and freeze the reaction solution for 24 hours. The crude product was obtained by distillation under reduced pressure, washed three times with ethyl acetate, and finally dried in a vacuum drying oven at 50°C for 48 h to obtain the ionic liquid monomer.

Step (2): Add a certain amount of the ionic liquid monomer synthesized in step (1), a certain proportion of divinylbenzene (DVB), and 50 mL of acetonitrile into a 100 mL three-necked flask. After stirring for 1 hour, add a certain proportion of divinyl benzene (DVB). Nitrogen-diisobutylnitrile (AIBN). The air was replaced with _N2 through the Schlenk technique, and then the temperature was raised to the specified temperature and reacted for 24h to obtain the crude product. Repeatedly wash with water and ethanol three times, and vacuum dry at 50°C for 24 hours to obtain a white powder polyionic liquid.

By changing the ratio of ionic liquid monomers to DVB cross-linking agents, the chain length and substituent groups of ionic liquid monomers, replacing bromoethanol with other types of compounds or changing the amount of initiator added, those skilled in the art can obtain a A series of polyionic liquids with different multi-level structures. By controlling the ratio of ionic liquid monomers to DVB cross-linking agents, a polyionic liquid catalyst with a higher micropore ratio and smaller particle sizes can be obtained, thereby utilizing the dispersion of active sites to improve catalytic activity; ionic liquid monomer chain length Control can obtain polyionic liquid catalysts with smaller particle sizes that are easy to swell, thereby utilizing the exposure of active sites to improve catalytic activity; the introduction of hydrogen-donating groups in ionic liquid monomers is conducive to enhancing the intrinsic activity of the polyionic liquid unit structure, and thus Improve catalytic performance.

In each embodiment of the present invention, the yield of the product was quantitatively measured using an Agilent 7890B gas chromatograph produced by Agilent.

Example 1

Place 0.034 mol propylene oxide and ionic liquid content of 2 mol% propylene oxide content (prepared by the ratio of ethylvinylimidazole ionic liquid and DVB (n:m) = 0.4) polyionic liquid 1 powder into a 250 mL closed reaction kettle Mix evenly in the medium, maintain the temperature of the reaction kettle at 120°C, continuously introduce carbon dioxide gas into the reaction kettle, maintain the pressure of the reaction system in the kettle at 2.5MPa, and perform the addition reaction for 2 hours to obtain the product propylene carbonate. The yield of propylene carbonate is 95mol%.

The polyionic liquid 1 has a structure as shown in compound 1: a specific surface area of 157.8 m ² /g, a micropore area of 49.8 m ² /g, and a particle size of 15 nm.

Example 2

The only difference from Example 1 is that n:m is replaced with 0.5, and the obtained polyionic liquid 2 is 130.1 m ² /g, 30.9 ^{m 2} /g, and has a particle size of 50 to 270 nm. The product propylene carbonate was obtained in Example 2, and the yield of propylene carbonate was 86 mol%.

Example 3

The only difference from Example 1 is that the propylene oxide is replaced by ethylene oxide. The product ethylene carbonate is obtained in Example 3, and the yield of ethylene carbonate is 94 mol%.

Example 4

The only difference from Example 1 is that polyionic liquid 1 is replaced by polyionic liquid 3 (ethylvinylimidazole ionic liquid is replaced by butylvinylimidazole ionic liquid, that is, j=3), and the ionic liquid content in the polyionic liquid is 1 mol% propylene oxide.

Example 4 obtained the product propylene carbonate, and the yield of propylene carbonate was 96 mol%.

The ionic liquid polymer 3 has a structure as shown in compound 3: a particle size of 50 nm and a swelling degree of 4.1.

Example 5

The only difference from Example 4 is that j is replaced by 7, and the resulting polyionic liquid 4 is obtained. The particle size is 50nm and the swelling degree is 2.7. The product propylene carbonate was obtained in Example 5, and the yield of propylene carbonate was 95 mol%.

Example 6

The only difference from Example 4 is that the propylene oxide is replaced by ethylene oxide. The product ethylene carbonate is obtained in Example 6, and the yield of ethylene carbonate is 93 mol%.

Example 7

The only difference from Example 1 is that the polyionic liquid 1 is replaced by polyionic liquid 5 (j=11 and the hydroxyethylimidazole ionic liquid monomer is introduced, that is, _R2 is -OH), and the reaction time is replaced from 2h to 1h. .

The product propylene carbonate was obtained in Example 7, and the yield of propylene carbonate was 96 mol%.

The polyionic liquid 5 has a structure as shown in compound 5: a particle size of 200 to 400 nm.

Example 8

The only difference from Example 7 is that the polyionic liquid 5 is replaced by polyionic liquid 6 (R ₂ is -COOH), and the particle size is 200 to 400 nm. The product propylene carbonate was obtained in Example 8, and the yield of propylene carbonate was 96 mol%.

Example 9

The only difference from Example 7 is that the polyionic liquid 6 is replaced by polyionic liquid 7 (R ₂ is -NH ₂ ), and the particle size is 200 to 400 nm. The product propylene carbonate was obtained in Example 9, and the yield of propylene carbonate was 95 mol%.

Example 10

The only difference from Example 9 is that the propylene oxide is replaced by ethylene oxide. The product ethylene carbonate is obtained in Example 10, and the yield of ethylene carbonate is 99 mol%.

In summary, the present invention provides a method for catalytically synthesizing cyclic carbonate using multi-level structure polyionic liquid. The prepared multi-stage structure polyionic liquid catalyst is used to catalyze the cycloaddition of CO ₂ and epoxy compounds to synthesize cyclic carbonate. It has high selectivity and conversion rate, and the yield of cyclic carbonate can reach 99m %. Compared with the traditional method of synthesizing cyclic carbonates, the polyionic liquid catalyst used in the present invention has the advantages of high active site utilization and low dosage, high catalytic efficiency, stability and difficulty in decomposition, simple preparation process, easy product separation, etc. Advantages: It has high industrial application value.

The above-mentioned specific embodiments further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (11)

1. A method for polyionic liquid catalysis to synthesize cyclic carbonate, characterized in that the synthesis method is: _CO2 and epoxy-containing compounds undergo a cycloaddition reaction under the catalysis of a catalyst to obtain cyclic carbonate; The catalyst is a polyionic liquid; the polyionic liquid has a structure shown in Formula 1: Among them, m, n, and l respectively represent the number of different monomers in the unit structure, and are each independently selected from any natural number; R ₁ is selected from a hydrogen atom or any alkane group, such as methyl; R ₂ is selected from any hydrogen-donating group, such as hydroxyl; Among them, j and k respectively represent the number of carbon atoms in the alkyl chain, and each of them independently selects any natural number. 2. The preparation method according to claim 1, characterized in that the temperature of the cycloaddition reaction is 80~150°C; the reaction pressure is 1~5MPa; the reaction time is 1~8h; the catalyst mass fraction is 0.1~ 10%. 3. The preparation method according to claim 1, characterized in that the particle size of the catalyst is 10-500 nm. 4. The preparation method according to claim 1, wherein the epoxy compound is ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, styrene oxide, or cyclohexane oxide. Or any one or a mixture of at least two of the oxidized cyclopentanes. 5. The preparation method according to claim 1, characterized in that, in the structure represented by Formula 1, m+n≤136. 6. The preparation method according to claim 1, characterized in that, in the structure shown in Formula 1, R ₁ is independently selected from a hydrogen atom or any alkane group, such as methyl; Preferably, R ₁ is independently selected from a hydrogen atom or any alkane group with a carbon number of ≤ 16 such as methyl, ethyl, propyl, butyl, etc. 7. The preparation method according to claim 1, characterized in that, in the structure shown in Formula 1, R ₂ is independently selected from any hydrogen-donating group, such as hydroxyl; Preferably, R ₂ is independently selected from any one of hydroxyl group, amino group, amine group, carboxyl group and thiol group. 8. The preparation method according to claim 7, characterized in that, in the structure shown in Formula 1, X ₁ and X ₂ are each independently selected from any of fluoride ions, chloride ions, bromide ions, and iodide ions. A sort of. 9. The preparation method according to claim 8, characterized in that, in the structure shown in Formula 1, the number of carbon atoms in m, n, and l is any natural number; Preferably, the number ratio of carbon atoms in m, n, l is 2:3:0, 1:1:0, 0:3:2, 0:1:1, 1:3:1, 1:3:2, 2:3:1. 10. The preparation method according to claim 9, characterized in that, in the structure shown in formula 1, the number of carbon atoms in j and k is any natural number; Preferably, the number of carbon atoms in j and k is each independently selected from: 2 to 12. 11. The preparation method according to claim 9, characterized in that the preparation method includes the following steps: Place the catalyst powder containing the epoxy compound and the particle size of 10 to 500 nm into a closed reactor and mix evenly. Maintain the temperature of the reactor in the range of 80 to 150°C. Continue to pass CO ₂ gas into the reactor to maintain the temperature in the reactor. The pressure of the reaction system is in the range of 1 to 5 MPa, and the addition reaction is carried out for 1 to 8 hours to obtain cyclic carbonate.