Imidazole-based polyionic liquid catalyst and its preparation method and application

Abstract

The invention discloses an imidazolyl polyionic liquid catalyst and a preparation method and application thereof, belonging to the technical field of five-membered cyclic carbonate synthesis. The invention polymerizes an imidazolyl polyionic liquid and divinylbenzene to obtain an imidazolyl polyionic liquid catalyst, and uses the catalyst to catalyze carbon dioxide and styrene to prepare styrene cyclic carbonate in one step. The imidazolyl polyionic liquid catalyst can efficiently convert styrene into styrene cyclic carbonate (the yield of styrene cyclic carbonate is greater than 70%), and the catalytic performance of the imidazolyl polyionic liquid catalyst is not significantly reduced after centrifugal separation and drying. The imidazolyl polyionic liquid catalyst provided by the invention has the advantages of high catalytic activity, simple separation, good circulation performance, no need for solvents and co-catalysts, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of five-membered cyclic carbonate synthesis, and in particular relates to an imidazole-based polyionic liquid catalyst and a preparation method and application thereof. Background Art

[0002] In recent decades, carbon dioxide (CO 2 ) has caused a series of environmental problems. In order to reduce the atmospheric CO 2 concentration, the generated CO 2 Capture or convert into other harmless substances. 2 It is a large renewable carbon resource that converts CO 2 Transforming into other high value-added chemicals is an important way to reduce CO 2 An effective means of emission reduction. 2 Among the various high value-added products prepared, five-membered cyclic carbonates such as styrene carbonate (SC) are important high value-added fine chemicals that can be used as aprotic solvents, fuel additives, antifreeze agents, defoaming agents, polymer precursors, and various reaction intermediates. 2 Five-membered cyclic carbonates can be synthesized by cycloaddition reaction with epoxides. 2 One-step synthesis of five-membered cyclic carbonate is a more efficient and green synthetic route. The one-step reaction is olefin epoxidation and CO 2 The series connection of cycloaddition reactions avoids the separation and purification of the intermediate epoxide, simplifies the production process, reduces production costs, and has great application potential. However, there are relatively few studies on the above-mentioned one-step reaction, and most catalyst systems require relatively harsh conditions such as high temperature and high pressure. Therefore, it is of great significance to develop a catalyst system with mild reaction conditions and high activity.

[0003] Ionic liquids have the advantages of low vapor pressure, unique solvation properties, high stability and low volatility. They also have Lewis acid-base sites, which are the bonding agents between olefins and CO. 2 Potential catalysts for one-step reactions. Although ionic liquid homogeneous catalysts have high activity, problems such as separation and recovery are difficult to solve. Therefore, it is necessary to convert homogeneous ionic liquid-based catalysts into heterogeneous ionic liquid-based catalysts. The ionic liquid skeleton in polyionic liquids has similar effects to ionic liquids, where the cations can act as Lewis acid sites to activate epoxides, and the anions can act as Lewis bases to promote the ring opening of epoxides. At present, polyionic liquid catalysts have been widely used in the reaction of olefins with CO. 2There are few applications in one-step reactions. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes an imidazolyl polyionic liquid catalyst and its preparation method and application. The present invention aims to synthesize a series of imidazolyl polyionic liquid catalysts to achieve the reaction of styrene with CO under mild conditions. 2 Efficient transformation to one-step synthesis of styrene cyclocarbonates.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention:

[0007] A method for preparing an imidazole-based polyionic liquid catalyst comprises the following steps:

[0008] Adding the bromide and 1-vinylimidazole into a first organic solvent, heating for a first reaction, cooling, washing, and drying to obtain a viscous liquid;

[0009] The viscous liquid and divinylbenzene are dissolved in a second organic solvent, 2,2'-azobisisobutyronitrile is added, stirred until dissolved, heated for a second reaction, cooled, washed and dried to obtain an imidazole-based polyionic liquid catalyst.

[0010] Preferably, the molar ratio of the bromide to 1-vinylimidazole is 1:1.

[0011] Preferably, the bromide is ethyl bromide, 2-bromoethanol or 2-bromoethylamine.

[0012] Preferably, the first organic solvent is acetonitrile; and the second organic solvent is a mixture of ethanol and water.

[0013] More preferably, the second organic solvent is a mixture of ethanol and water in a volume ratio of 3:1.

[0014] Preferably, the temperature of the first heating reaction is 75°C and the time is 24h;

[0015] The temperature of the second heating reaction is 70° C. and the time is 24 h.

[0016] Preferably, the drying method is vacuum drying.

[0017] Preferably, both heating reactions are carried out under nitrogen protection.

[0018] More preferably, the preparation method of the imidazole-based polyionic liquid catalyst is:

[0019] (1) 10.6 mmol of the bromide and 10.6 mmol of 1-vinylimidazole were added to 5 mL of acetonitrile, heated to 75° C. under nitrogen protection for 24 h, cooled to room temperature, washed with ethyl acetate, and the solvent was removed in vacuo, and dried in vacuo at 50° C. to obtain a viscous liquid, wherein the bromide is ethyl bromide, 2-bromoethanol or 2-bromoethylamine;

[0020] (2) 400 mg of the viscous liquid and 240 μL of divinylbenzene were dissolved in ethanol / water (volume ratio (V:V) = 3:1) solvent, 10 mg of 2,2′-azobisisobutyronitrile was added, and the mixture was stirred at room temperature until all the sample was dissolved. The stirring was continued for 30 min, and then the mixture was heated to 70° C. under nitrogen protection for 24 h. The mixture was cooled to room temperature, centrifuged, washed several times with ethanol / water (V:V = 3:1) solvent, and dried in vacuo at 60° C. to obtain an imidazole-based polyionic liquid catalyst.

[0021] The second technical solution of the present invention:

[0022] The present invention also provides an imidazole-based polyionic liquid catalyst prepared according to the above method, the chemical formula of which is [C 10 H 10 C 7 H 10 N 2 -R] n , R is methyl, n is the degree of polymerization, ranging from 100 to 200, and the structural formula is Wherein R is methyl, hydroxyl or amino; * represents the terminal group.

[0023] The third technical solution of the present invention:

[0024] The present invention also provides the use of the imidazole-based polyionic liquid catalyst in synthesizing five-membered cyclic carbonate.

[0025] The fourth technical solution of the present invention:

[0026] The present invention also provides the use of the imidazole-based polyionic liquid catalyst in catalyzing the one-step synthesis of styrene cyclic carbonate from styrene.

[0027] The fifth technical solution of the present invention:

[0028] The present invention also provides a method for catalyzing styrene to synthesize styrene cyclic carbonate in one step, wherein the catalyst is the above-mentioned imidazolyl-based polyionic liquid catalyst, comprising the following steps: mixing styrene and tert-butyl hydroperoxide, adding the imidazolyl-based polyionic liquid catalyst, introducing carbon dioxide (CO 2 ), styrene cyclic carbonate was synthesized by a one-step reaction.

[0029] Reaction principle: During the styrene epoxidation stage, the oxidant tert-butyl hydroperoxide undergoes homolysis to produce tert-butyl oxygen radical (·O-tBu), which is then adsorbed to the epoxidation active site. Afterwards, free TBHP reacts with the adsorbed ·O-tBu to generate tert-butyl peroxy radical (·OO-tBu). ·OO-tBu reacts with the olefin group of styrene to generate styrene oxide, which desorbs from the epoxidation active site to complete the catalytic cycle. 2 In the cycloaddition stage, the epoxidation reaction generates styrene oxide, which is adsorbed onto the active sites of the catalyst to activate styrene oxide. Afterwards, the bromide ions in the catalyst attack the activated styrene oxide with less steric hindrance, completing the ring opening to generate oxygen anion intermediates. At the same time, the mesoporous structure of the catalyst adsorbs and activates CO 2 The oxygen anion of the oxygen anion intermediate attacks CO 2 A bromocarbonate intermediate is generated, and the oxygen anion in the bromocarbonate intermediate attacks the methylene carbon connected to the bromine to generate styrene cyclic carbonate.

[0030] Preferably, in the method for catalyzing styrene to synthesize styrene cyclic carbonate in one step, the molar ratio of styrene to tert-butyl hydroperoxide is 1:1.5.

[0031] Preferably, in the method for catalyzing styrene to synthesize styrene cyclic carbonate in one step, the reaction pressure is 0.5-2 MPa, the reaction temperature is 80-100° C., and the reaction time is 12-28 h.

[0032] More preferably, in the method for catalyzing styrene to synthesize styrene cyclic carbonate in one step, the reaction pressure is 0.5-2 MPa, the reaction temperature is 80-100° C., and the reaction time is 16-28 h.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] Ionic liquid homogeneous catalysts have high activity, but problems such as separation and recovery are difficult to solve. The present invention converts homogeneous ionic liquid-based catalysts into heterogeneous ionic liquid-based catalysts, successfully solving the above problems. In the present invention, imidazolyl-based polyionic liquid catalysts with different substituents are synthesized. The ionic liquid skeleton in the imidazolyl-based polyionic liquid catalyst has a similar effect to that of ionic liquids, wherein the cation can act as a Lewis acid site to activate epoxides, and the anion can act as a Lewis base to promote the ring opening of epoxides. The present invention has a great effect on the ionic liquid-based catalyst in the reaction of olefins with CO 2The application of one-step cascade reaction provides a high reference value. Among them, PIL has the largest specific surface area and pore size and the highest ionic liquid content, so PIL shows the best catalytic activity. 2 , 24h conditions, the yield of styrene cyclic carbonate was 71%, and the selectivity was 71%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 XRD (A) and FT-IR (B) images of imidazole-based polyionic liquid catalysts;

[0037] Figure 2 The SEM image of the imidazole-based polyionic liquid catalyst, where A is PIL, B is PIL-OH, and C is PIL-NH 2 ;

[0038] Figure 3 is the BET diagram of the imidazolyl polyionic liquid catalyst, where A is N 2 B is the adsorption-desorption isotherm curve, and C is the pore size distribution diagram. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] Unless otherwise specified, the room temperature in the present invention is 25±2°C.

[0045] All raw materials used in the examples of the present invention are commercially available.

[0046] The technical solution of the present invention is further illustrated by the following embodiments.

[0047] 1. Preparation of imidazolyl-based polyionic liquid catalysts

[0048] Example 1

[0049] (1) 10.6 mmol of ethyl bromide and 10.6 mmol of 1-vinylimidazole were added to 5 mL of acetonitrile, heated to 75°C under nitrogen protection for 24 h, cooled to room temperature, washed with ethyl acetate, the solvent was removed in vacuo, and dried in vacuo at 50°C to obtain a viscous liquid;

[0050] (2) 400 mg of the viscous liquid and 240 μL of divinylbenzene were dissolved in an ethanol / water (V:V=3:1) solvent, 10 mg of 2,2′-azobisisobutyronitrile was added, and the mixture was stirred at room temperature until all the sample was dissolved. The mixture was stirred for 30 min, and then heated to 70° C. under nitrogen protection for 24 h. The mixture was cooled to room temperature, centrifuged, washed three times with an ethanol / water (V:V=3:1) solvent, and dried under vacuum at 60° C. to obtain an imidazole-based polyionic liquid catalyst, labeled as PIL, with a chemical formula of [C 10 H 10 C 7 H 10 N 2 -R] n , R is methyl, n is the degree of polymerization, ranging from 100 to 200, and the structural formula is

[0051]

[0052] Example 2

[0053] The same as Example 1, except that ethyl bromide is replaced by 2-bromoethanol, and the obtained imidazole-based polyionic liquid catalyst is labeled as PIL-OH, and its chemical formula is [C 10 H 10 -C 7 H 10 N 2 -R] n , R is hydroxyl group, n is degree of polymerization, ranging from 100 to 185, and the structural formula is

[0054] Example 3

[0055] Same as Example 1, except that ethyl bromide was replaced by 2-bromoethylamine, and the obtained imidazole-based polyionic liquid catalyst was labeled as PIL-NH 2 , whose chemical formula is [C 10 H 10 -C 7 H 10 N 2 -R] n , R is amino group, n is degree of polymerization, ranging from 100 to 193, and the structural formula is

[0056] Figure 1 Figure 1 is the XRD (A) and FT-IR (B) graphs of the imidazolyl polyionic liquid catalyst. In the XRD graph, only one peak appears on the imidazolyl polyionic liquid catalyst, indicating that the imidazolyl polyionic liquid catalyst is an amorphous structure. In the FT-IR graph, PIL and PIL-OH are located at 3423 cm -1 and 3416cm -1 The broad characteristic peak at is attributed to the OH stretching vibration peak. 2 Located at 3422cm -1 The broad characteristic peak at is attributed to NH 2 In addition, at 3000cm -1 -3100cm -1 The characteristic peaks in the range are attributed to the stretching vibration peaks of CH on the benzene ring structure. These characteristic peaks indicate that there is a benzene ring structure on the skeleton of the imidazolyl polyionic liquid catalyst. In addition, -1 、2925cm -1 and 2926cm -1 The characteristic peak is attributed to the stretching vibration peak of CH. -1 and 1567cm -1The two characteristic peaks belong to the stretching vibration peaks of C=N and C=C on the imidazole ring, indicating that there is an imidazole structure on the skeleton of the imidazole-based polyionic liquid catalyst. The above results show that there are both benzene ring structures and imidazole structures, indicating that divinylbenzene and ionic liquids are successfully polymerized to form an imidazole-based polyionic liquid catalyst.

[0057] Figure 2 The SEM image of the imidazole-based polyionic liquid catalyst, where A is PIL, B is PIL-OH, and C is PIL-NH 2 , it can be seen that the imidazolyl-based polyionic liquid catalyst exhibits an irregular morphology.

[0058] Figure 3 is the BET diagram of the imidazolyl polyionic liquid catalyst, where A is N 2 Adsorption-desorption isotherm curve, B is the pore size distribution diagram, in N 2 In the adsorption-desorption isotherm curve, the imidazolyl polyionic liquid catalyst showed a typical type IV adsorption isotherm, indicating that the imidazolyl polyionic liquid catalyst was a typical mesoporous material (porous material with a pore size of 2-50 nm). 2 The specific surface areas are 19.4m 2 ·g -1 、9.0m 2 ·g -1 and 10.1m 2 ·g -1 The average pore sizes are 18.9nm, 11.1nm and 10.5nm respectively.

[0059] 2. One-step synthesis of styrene cyclic carbonate from styrene and carbon dioxide

[0060] Example 4

[0061] Add 3mmol styrene and 4.5mmol tert-butyl hydroperoxide to the reactor, add 30mg catalyst PIL; fill with carbon dioxide 1MPa at room temperature, heat the autoclave to 90℃ for 24h, exhaust carbon dioxide after cooling, add m-xylene as internal standard, centrifuge to separate the catalyst, take the supernatant for gas chromatography analysis, and determine the conversion rate and selectivity of the reaction. The yield of the product styrene cyclocarbonate was 71% and the selectivity was 71%.

[0062] Example 5 (for comparison)

[0063] The same as Example 4, except that the reaction temperature is 70°C, the yield of the product styrene cyclic carbonate is 18%, and the selectivity is 19%. The results of this example show that low temperature is not conducive to the conversion of the reaction, and there are still a lot of by-products in the reaction, so the yield and selectivity in this example are relatively low.

[0064] Example 6

[0065] The same as Example 4, except that the reaction temperature was 80°C, the yield of the product styrene cyclic carbonate was 45%, and the selectivity was 47%. The results of this example show that increasing the temperature is helpful to convert styrene oxide into styrene cyclic carbonate, and it is speculated that higher temperature may be beneficial to convert CO 2 activation, thereby promoting CO 2 The cycloaddition reaction with styrene oxide improves the selectivity of styrene cyclocarbonate.

[0066] Example 7

[0067] The same as Example 4, except that the reaction temperature was 100°C, the yield of the product styrene cyclic carbonate was 70%, and the selectivity was 72%. The results of this example show that further increasing the temperature has little effect on the catalytic activity.

[0068] Example 8 (for comparison)

[0069] The same as Example 4, except that the reaction pressure is 0.1 MPa, the yield of the product styrene cyclic carbonate is 19%, and the selectivity is 20%. The results of this example show that low pressure is not conducive to the conversion of the reaction, and there are still a large number of by-products in the reaction, so the yield and selectivity in this example are both low.

[0070] Example 9

[0071] The same as Example 4, except that the reaction pressure was 0.5 MPa, the yield of the product styrene cyclic carbonate was 64%, and the selectivity was 64%. 2 The increase in pressure increases the CO 2 concentration, thus promoting CO 2 The cycloaddition reaction with styrene oxide, thus a large amount of styrene oxide further generates styrene cyclocarbonate.

[0072] Example 10

[0073] The same as Example 4, except that the reaction pressure was 1.5 MPa, the yield of the product styrene cyclic carbonate was 70%, and the selectivity was 70%. The results of this example show that when the pressure continues to increase, the selectivity does not change significantly, which may be because the concentration of styrene oxide in the reaction system is too low and cannot react further.

[0074] Embodiment 11

[0075] The same as Example 4, except that the reaction pressure was 2.0 MPa, the yield of the product styrene cyclic carbonate was 71%, and the selectivity was 72%. The results of this example show that when the pressure continues to increase, the selectivity does not increase significantly, which may be because the concentration of styrene oxide in the reaction system is too low and cannot react further.

[0076] Example 12

[0077] The same as Example 4, except that the reaction time was 16 h, the yield of the product styrene cyclic carbonate was 39%, and the selectivity was 42%.

[0078] Embodiment 13

[0079] The same as Example 4, except that the reaction time was 20 h, the yield of the product styrene cyclic carbonate was 54%, and the selectivity was 54%.

[0080] Embodiment 14

[0081] The same as Example 4, except that the reaction time was 28 h, the yield of the product styrene cyclic carbonate was 71%, and the selectivity was 72%, indicating that the further increase of the reaction time had no significant effect on the styrene conversion rate and selectivity.

[0082] Embodiment 15

[0083] The same as Example 6, except that the catalyst is PIL-OH, the yield of the product styrene cyclic carbonate is 53%, and the selectivity is 56%.

[0084] Example 16

[0085] Same as Example 6, except that the catalyst is PIL-NH 2 The yield of the product styrene cyclic carbonate was 45% and the selectivity was 47%.

[0086] PIL has the largest specific surface area and pore size and the highest ionic liquid content, so PIL exhibits the best catalytic activity. 2 , 24h conditions, the yield of styrene cyclic carbonate was 71%, and the selectivity of styrene cyclic carbonate was 71%.

[0087] In summary, the present invention prepares an imidazolyl-based polyionic liquid catalyst and studies the catalytic performance of the imidazolyl-based polyionic liquid catalyst in catalyzing the one-step reaction of styrene and carbon dioxide to synthesize styrene cyclocarbonate under relatively mild conditions. The results of this work provide a high reference value for the application of ionic liquid-based catalysts in the one-step reaction of olefins and carbon dioxide.

[0088] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An application of an imidazole-based polyionic liquid catalyst in catalyzing the one-step synthesis of styrene cyclic carbonate from styrene, characterized in that: The method comprises the following steps: mixing styrene and tert-butyl hydroperoxide, adding an imidazole-based polyionic liquid catalyst, introducing carbon dioxide, and synthesizing styrene cyclic carbonate through a one-step reaction, wherein the reaction pressure is 0.5-2 MPa, the reaction temperature is 80-100°C, and the reaction time is 12-28 h; The preparation method based on imidazole-based polyionic liquid catalyst comprises the following steps: Adding the bromide and 1-vinylimidazole into a first organic solvent, heating for a first reaction, cooling, washing, and drying to obtain a viscous liquid; The viscous liquid and divinylbenzene are dissolved in a second organic solvent, 2,2′-azobisisobutyronitrile is added, stirred until dissolved, and then heated for a second reaction, cooled, washed, and dried to obtain an imidazole-based polyionic liquid catalyst; The molar ratio of the bromide to 1-vinyl imidazole is 1:1; The bromide is ethyl bromide, 2-bromoethanol or 2-bromoethylamine.

2. The use according to claim 1, characterized in that: The first organic solvent is acetonitrile; the second organic solvent is a mixture of ethanol and water.

3. The use according to claim 1, characterized in that: The temperature of the first heating reaction is 75°C and the time is 24 h; The second heating reaction was carried out at a temperature of 70°C and for 24 hours.

4. A method for catalyzing styrene to synthesize styrene cyclic carbonate in one step, characterized in that: The catalyst is the imidazolyl polyionic liquid catalyst according to claim 1, and comprises the following steps: mixing styrene and tert-butyl hydroperoxide, adding the imidazolyl polyionic liquid catalyst, introducing carbon dioxide, and synthesizing styrene cyclic carbonate through a one-step reaction.

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