CN112142872A - Alkaline ionic liquid grafted chitin, and preparation method and application thereof - Google Patents
Alkaline ionic liquid grafted chitin, and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the field of preparation of immobilized ionic liquid, and particularly relates to alkaline ionic liquid grafted chitin as well as a preparation method and application thereof. Using sulfonylation chitin as carrier, reacting with sodium iodide and vinyl imidazole ionic liquid in turn, and finally using inorganic base to carry out anion exchange to obtain the basic ionic liquid grafted chitin. The invention has the advantages that: the chitin carrier has large amount and low price, and the position of the grafted ionic liquid is determined and the amount is large; the prepared chitin material is applied to the reaction of catalytically synthesizing dimethyl carbonate, and has the advantages of high reaction speed, high yield of target products and simple separation and recovery of catalysts. Therefore, the invention provides a green catalyst suitable for transesterification.
Description
Technical Field
The invention relates to the field of preparation of immobilized ionic liquid, in particular to basic ionic liquid grafted chitin and a preparation method thereof, and also relates to application of the catalyst in ester exchange reaction.
Background
Dimethyl carbonate (DMC) is an organic linear carbonate, which has received great attention in recent years, and its annual production rate is now higher than 0.5 megaton, and the production rate still shows a tendency to increase. DMC is a low-toxicity carbonylation and alkylation reagent used in industrial production, is a raw material for producing polycarbonate, and can also be used for producing fuel additives and lithium battery electrolytes. In recent years, due to high atom utilization rate, the toxicity of raw materials is receiving wide attention. However, this reaction generally uses a strong base as a catalyst, and there are problems such as corrosion of equipment and difficulty in separation and recovery of the catalyst.
The ionic liquid has the characteristics of low vapor pressure, good compatibility with a substrate, designable structure and the like, so the ionic liquid is widely applied to organic reactions such as esterification, acetal, ester exchange, alkylation, acylation, Mannich reaction, Beckmann rearrangement, Claisen-Schmidt condensation and the like as a high-efficiency catalyst or solvent. Most of ionic liquids have high viscosity and large dosage, and need rotary evaporation or extraction for recovery after the reaction is finished, so the production cost of the ionic liquids used as catalysts is high, and the industrialization process of the ionic liquids is hindered. The immobilized ionic liquid can effectively solve the problems: the use amount of the ionic liquid can be reduced, the catalyst can be separated through filtration or decantation operation, and the recovered catalyst can be stably recycled for several times, so that the purpose of reducing the use cost of the catalyst is achieved.
The existing inorganic materials for immobilizing ionic liquid, such as silicon dioxide and synthetic molecular sieves, have the main problems that the number of functional groups on the surface of a carrier is uncertain and is not uniformly distributed, and the price of raw materials for immobilizing used silane coupling agents and the like is not high; however, organic carriers such as synthetic resins for immobilizing ionic liquids have poor thermal stability (the maximum operating temperature of basic resins is lower than 60 ℃) and are expensive, so that research on developing silane-free coupling agent immobilization processes and developing novel carriers for overcoming the defects of the existing carriers has been one of the hot topics of research of scientists.
Chitin, as a biological resource, is widely present in crustacean shells, mollusk endoskeletons, algal and fungus cell walls of marine organisms, and has a yield of as high as thousands of tons per year, which is the second most natural resource next to cellulose. The catalyst has a definite molecular structure, contains many functional groups such as hydroxyl, amide and amino groups, and is insoluble in alkali and organic solvents, and thus is expected to be an excellent catalyst or a carrier for organic molecules. The hydroxyl of chitin is utilized to carry out reaction, and domestic reports on the synthesis of sulfonylation chitin and amino chitin exist, for example, Chinese patent CN 107383240A takes chitin as a raw material, p-toluenesulfonyl chloride TsCl is added to prepare sulfonylation chitin, and then amino chitin with antibacterial activity is obtained through azide and reduction reactions in sequence and is used in the fields of biomedicine and the like. However, no literature report is found in the synthesis and catalytic application research of chitin immobilized polymeric alkaline ionic liquid at present.
In conclusion, the application field of the chitin is developed, and a catalyst which is low in raw material cost, high in catalytic activity, easy to separate, stable in structure and friendly to the environment is added to a catalytic family for synthesizing DMC by ester exchange, so that the method has important significance.
Disclosure of Invention
The invention provides a preparation method of a novel environment-friendly catalyst with low cost, high catalytic activity and high reuse stability, aiming at the problems that the cost of raw and auxiliary materials is high in the preparation process of an immobilized ionic liquid catalyst, active components are easy to lose and inactivate in the application process of a catalyst material, the research in the field of catalysis application of chitin is insufficient, and the like.
In order to solve the technical problems, the invention adopts the technical scheme that:
the chitin immobilized basic ionic liquid catalyst has the following structural formula:
in the structure, A is imidazole ionic liquid.
The preparation method of the basic ionic liquid grafted chitin is characterized in that sulfonated chitin Chi-OTs are used as carriers, firstly, iodinated chitin is prepared, then, the iodinated chitin and vinyl ionic liquid are subjected to grafting reaction, and finally, the basic ionic liquid grafted chitin is obtained through inorganic strong base treatment.
Wherein, the synthesis of the sulfonylated chitin Chi-OTs is carried out according to the method of Macromolecules (1992,25, 3786-3790). The synthesis method specifically comprises the following steps: dispersing chitin in 42% sodium hydroxide solution, carrying out reduced pressure operation for 3-5 h, sequentially adding ice and chloroform solution of p-toluenesulfonyl chloride TsCl, reacting at 0 ℃ for 1-3 h, continuing to react at room temperature for 1-3 h, then adding water for precipitation, suction filtering and washing to neutrality to obtain filter cakes, and obtaining the sulfonated chitin Chi-OTs.
Specifically, the chitin grafted by the basic ionic liquid is prepared according to the following steps:
(1) preparing iodinated chitin: Chi-OTs are added into DMSO under the protection of nitrogen, the mixture is stirred until the solution is clear, and then a DMSO solution of sodium iodide is added for reaction. The mixture reacts for 6 to 24 hours at the temperature of 60 to 100 ℃. After the reaction, the solution was poured into acetone to precipitate out a precipitate. Filtered, added with a methanolic solution of potassium hydroxide and stirred at room temperature for 3 h. Then washing to be neutral, and drying for 3h at 80 ℃ to obtain chitin iodide Chi-I.
Wherein the mass ratio of Chi-OTs, NaI and DMSO is 1: 2-6: 20 to 100.
(2) Synthesizing ionic liquid grafted chitin: nitrobenzene is taken as a solvent, and Chi-I obtained in the step (1) and catalyst SnCl are sequentially added4After stirring for 1h, vinyl ionic liquid [ vRIm ] is added]And (4) X. And reacting for 1-5 h at 5-20 ℃ under the protection of nitrogen, and adding methanol to terminate the reaction. Filtering, washing with methanol, drying at 80 deg.C for 3 hr to obtain chitin Chi- [ vRIm grafted with neutral ionic liquid]X。
Wherein Chi-I, SnCl4Nitrobenzene and vinyl ionic liquids [ vRIm]The mass ratio of X is 1: 1-8: 40-100: 8-15.
The vinyl ionic liquid is 1-vinyl-3-alkyl halogenated imidazole ionic liquid, and the structural formula is
or 1-vinyl-3-aminoalkylimidazole hydrobromide, of the formula:
wherein alkyl is ethyl, propyl or butyl, X-Is Cl-Or Br-。
The synthesis method of the 1-vinyl-3-alkyl halogenated imidazole ionic liquid comprises the following steps: dropwise adding halogenated alkane with equal mole number into 1-vinyl imidazole at 80 ℃, continuing to react for 24 hours after dropwise adding, cooling to room temperature, extracting with toluene, performing rotary evaporation, and drying at 80 ℃ for 3 hours to synthesize a product;
wherein the halogenated alkane is 1-chloropropane, 1-chlorobutane, 1-bromopropane and 1-bromobutane.
The synthesis method of the 1-vinyl-3-amino alkyl imidazole hydrobromide comprises the following steps: adding 1-vinylimidazole and 3-bromopropylamine hydrobromide or 2-bromoethylamine hydrobromide with equal molar number into acetonitrile serving as a solvent, stirring and heating to 100 ℃ for reaction for 24 hours, cooling the mixture to room temperature after the reaction is finished, removing the solvent by rotary evaporation, washing the remained solid with ethanol for a plurality of times, and drying at 80 ℃ for 3 hours to obtain the product.
(3) Synthesizing the basic ionic liquid grafted chitin. And (3) preparing a 1mol/LKOH aqueous solution, dripping the aqueous solution into the Chi- [ vRIm ] X obtained in the step (2), stirring at room temperature for 6-24 h, filtering, washing with deionized water and ethanol in sequence until the solution is neutral, and drying at 60 ℃ for 5h in vacuum to obtain the basic ionic liquid grafted chitin Chi- [ vRIm ] OH.
After the technical scheme is adopted, the invention has the beneficial effects that:
the invention grafts the alkaline ionic liquid on the commercial grade chitin for the first time by a covalent bond method. The invention has the advantages that the easily obtained nontoxic biological material chitin is used as a carrier to prepare the catalyst which has stable chemical property, determined grafting position and controllable grafting quantity. The defects of insufficient application and development of the chitin, low catalytic activity of the existing immobilized ionic liquid catalyst and easy loss and inactivation of catalytic activity centers are effectively overcome. Therefore, the invention provides a synthesis scheme for effectively immobilizing the ionic liquid by applying the chitin. When the alkaline ionic liquid grafted chitin prepared by the invention is applied to catalyzing ester exchange reaction of ethylene carbonate and methanol, the highest conversion rate of the ethylene carbonate can reach 94.5%, the DMC selectivity is more than 98%, and a higher catalytic effect is shown in catalyzing other ester exchange reactions.
Detailed Description
The invention will be further described in the following examples, but it is to be understood that these examples are for illustrative purposes only and are not to be construed as limiting the practice of the invention.
Example 1
Synthesis of sulfonylated chitin
1.0g chitin was added to 20mL 42% NaOH aqueous solution and stirred under reduced pressure for 3h, followed by adding 50g crushed ice and stirring until the solution was clear. Dissolving 15g of p-toluenesulfonyl chloride in 40mL of chloroform, pouring the solution into a NaOH solution of chitin at the temperature of 0-5 ℃ in an ice bath, and stirring vigorously for 2 hours. The ice bath was then removed, warmed to room temperature and the reaction continued for 2 h. After the reaction is finished, the product is poured into water to separate out a precipitate, and the precipitate is filtered, washed to be neutral by water. Washing with methanol and ether, and drying at 80 deg.C for 3h to obtain white solid which is sulfonated chitin Chi-OTs.
Example 2
Synthesis of 1-vinyl-3-alkyl halogenated imidazole ionic liquid: under stirring and at 80 ℃, halogenated alkane (such as 1-chloropropane, 1-chlorobutane, 1-bromopropane and 1-bromobutane) with equal mole number is dripped into the toluene solution of 1-vinyl imidazole. After the dripping is finished, the temperature is maintained for further reaction for 24 hours. Then cooling to room temperature, standing for layering, washing the ionic liquid phase with toluene for 3 times, performing rotary evaporation, and performing vacuum drying at 60 ℃ for 5 hours to respectively synthesize 4 ionic liquids: 1-vinyl-3-propyl imidazolium chloride [ vpIm ] Cl, 1-vinyl-3-propyl imidazolium bromide [ vpIm ] Br, 1-vinyl-3-butyl imidazolium chloride [ vbIm ] Cl and 1-vinyl-3-butyl imidazolium bromide [ vbIm ] Br.
Synthesis of 1-vinyl-3-aminoalkylimidazole hydrobromide: acetonitrile is taken as a solvent, 1-vinyl imidazole and 2-bromoethylamine hydrobromide or 3-bromopropylamine hydrobromide with equal mole number are added, and the mixture is stirred and heated to 100 ℃ for reaction for 24 hours. After the reaction is finished, the mixture is cooled to room temperature, the solvent is removed by rotary evaporation, the remained solid is washed for a plurality of times by ethanol, and after vacuum drying is carried out for 5 hours at the temperature of 60 ℃, the corresponding ionic liquids [ vaeIm ] Br & HBr and [ vapIm ] Br & HBr are obtained.
Example 3
Preparing basic ionic liquid grafted chitin Chi- [ vpIm ] OH:
(1) under the protection of nitrogen, mixing the sulfonylated Chi-OTs, NaI and DMSO in a ratio of 1: 2: 20. the reaction was carried out at 60 ℃ for 6 h. After the reaction is finished, pouring the solution into acetone, precipitating, carrying out suction filtration, washing by using acetone and ether, adding 20ml of 0.05 mol/L potassium hydroxide methanol solution, and stirring for 3h at room temperature. And (3) carrying out suction filtration, washing with methanol, and drying at 80 ℃ for 3h to obtain chitin iodide Chi-I.
(2) Sequentially adding chitin Chi-I iodide and catalyst SnCl into a flask in an ice bath at 5 DEG C4And solvent nitrobenzene in a ratio of 1:1: 40. Stirring for 1h, adding 1-vinyl-3-propyl imidazolium chloride [ vpIm [ ]]And Cl, wherein the mass ratio of the ionic liquid to Chi-I is 8: 1. Under the protection of nitrogen, after reacting for 1h at 5 ℃, adding methanol to end the reaction. Filtering, washing with ether, drying at 80 deg.C for 3h to obtain Chi- [ vpIm]Cl。
(3) 1.0g of Chi- [ vpIm ] Cl and 10mL of water are added with stirring at room temperature, 10mL of 1mol/L aqueous potassium hydroxide solution are added dropwise, and stirring is continued for 6h after the dropwise addition. And (3) carrying out suction filtration, fully washing by using deionized water and ethanol in sequence, and then carrying out vacuum drying for 5h at the temperature of 60 ℃ to obtain the chitin Chi- [ vpIM ] OH-1 grafted by the alkaline ionic liquid.
The reaction process can be represented as follows:
example 4
(1) Under the protection of nitrogen, mixing the sulfonylated Chi-OTs, NaI and DMSO in a ratio of 1: 6: 100, and reacting for 18 hours at 100 ℃. After the reaction is finished, pouring the solution into acetone, precipitating, carrying out suction filtration, washing by using acetone and ether, adding 20ml of 0.05 mol/L potassium hydroxide methanol solution, and stirring for 3h at room temperature. And (3) carrying out suction filtration, washing with methanol, and drying at 80 ℃ for 3h to obtain chitin iodide Chi-I.
(2) Sequentially adding chitin Chi-I iodide and catalyst SnCl into a flask in a cold water bath at 10 DEG C4And solvent nitrobenzene in a ratio of 1:4: 60. Stirring for 1h, adding 1-vinyl-3-propyl imidazole bromide ionic liquid [ vpIm [ ]]Br，[vpIm]The mass ratio of Br to Chi-I is 10: 1. Under the protection of nitrogen, after reacting for 2h at 10 ℃, adding methanol to end the reaction. Filtering, washing with ether, drying at 80 deg.C for 3h to obtain Chi- [ vpIm]Br。
(3) 1.0g of Chi- [ vpIm ] Br and 10mL of water are added in turn at room temperature with stirring, 10mL of 1mol/L potassium hydroxide aqueous solution is added dropwise, and stirring is continued for 10h after the dropwise addition. Filtering, washing with deionized water and ethanol, vacuum drying at 60 deg.C for 5 hr to obtain basic ionic liquid grafted chitin Chi- [ vpIM ] OH-2
Example 5
(1) Under the protection of nitrogen, mixing the sulfonylated Chi-OTs, NaI and DMSO, and reacting at 85 ℃ for 24 hours, wherein the proportion of the sulfonylated Chi-OTs to the NaI to the DMSO is 1:4: 40. after the reaction is finished, pouring the solution into acetone, precipitating, carrying out suction filtration, washing by using acetone and ether, adding 20ml of 0.05 mol/L potassium hydroxide methanol solution, and stirring for 3h at room temperature. And (3) carrying out suction filtration, washing with methanol, and drying at 80 ℃ for 3h to obtain chitin iodide Chi-I.
(2) Sequentially adding chitin Chi-I iodide and catalyst SnCl into a flask in a cold water bath at 15 DEG C4Mixing with solvent nitrobenzene according to the ratio of 1:4:80And (6) mixing. Stirring for 1h, and adding 1-vinyl-3-butyl imidazole chloride ionic liquid [ vbIm]Cl，[vbIm]The mass ratio of Cl to Chi-I is 8.5: 1. Reacting for 3 hours at 15 ℃ under the protection of nitrogen, and adding methanol to finish the reaction. Filtering, washing with ether, drying at 80 deg.C for 3h to obtain Chi- [ vbIm]Cl。
(3) 1.0g of Chi- [ vbIm ] Cl and 10mL of water are added in sequence at room temperature under stirring, 10mL of 1mol/L potassium hydroxide aqueous solution is added dropwise, and stirring is continued for 12 hours after the dropwise addition. And (3) carrying out suction filtration, fully washing by using deionized water and ethanol in sequence, and then carrying out vacuum drying for 5h at the temperature of 60 ℃ to obtain the basic ionic liquid grafted chitin Chi- [ vbIm ] OH-1.
Example 6
(1) Chitin iodide Chi-I was synthesized as in example 5.
(2) Sequentially adding chitin iodide Chi-I and catalyst SnCl into a flask at the temperature of 20 DEG C4And solvent nitrobenzene in a ratio of 1:8: 100. Stirring for 1h, and adding 1-vinyl-3-butyl imidazole bromide ionic liquid [ vbIm]Br，[vbIm]The mass ratio of Br to Chi-I is 12: 1. Reacting for 4 hours at 20 ℃ under the protection of nitrogen, and adding methanol to finish the reaction. Filtering, washing with ether, drying at 80 deg.C for 3h to obtain Chi- [ vbIm]Br。
(3) 1.0g of Chi- [ vbIm ] Br and 10mL of water were added successively at room temperature with stirring, 10mL of 1mol/L aqueous potassium hydroxide solution was added dropwise, and stirring was continued for 18 hours after completion of the dropwise addition. And (3) carrying out suction filtration, fully washing by using deionized water and ethanol in sequence, and then carrying out vacuum drying for 5h at the temperature of 60 ℃ to obtain the basic ionic liquid grafted chitin Chi- [ vbIm ] OH-2.
Example 7
(1) Chitin iodide Chi-I was synthesized as in example 5.
(2) Sequentially adding chitin iodide Chi-I and catalyst SnCl into a flask at 10 DEG C4And solvent nitrobenzene in a ratio of 1:4: 40. Stirring for 1h, and adding 1-vinyl-3-aminoethylimidazole hydrobromide ionic liquid [ vaeIm [ ]]Br·HBr，[vaeIm]The mass ratio of Br & HBr to Chi-I is 13: 1. Reacting for 5 hours at 10 ℃ under the protection of nitrogen, and adding methanol to finish the reaction. Filtering, washing with ether, drying at 80 deg.C for 3h to obtain Chi- [ vaeIm]Br·HBr。
(3) 1.0g of the above Chi- [ vaeIm ] Br · HBr and 10mL of water are added successively at room temperature with stirring, 15mL of 1mol/L aqueous potassium hydroxide solution are added dropwise, and stirring is continued for 24h after the dropwise addition. And (3) carrying out suction filtration, fully washing by using deionized water and ethanol in sequence, and then carrying out vacuum drying for 5h at the temperature of 60 ℃ to obtain the chitin Chi- [ vaeIm ] OH grafted by the alkaline ionic liquid.
Example 8
(1) Chitin iodide Chi-I was synthesized as in example 5.
(2) Sequentially adding chitin iodide Chi-I and catalyst SnCl into a flask at 10 DEG C4And solvent nitrobenzene in a ratio of 1:4: 50. Stirring for 1h, adding 1-vinyl-3-aminopropylimidazole hydrobromide ionic liquid [ vapIm [ ]]Br·HBr，[vapIm]The mass ratio of Br & HBr to Chi-I is 15: 1. Reacting for 5 hours at 10 ℃ under the protection of nitrogen, and adding methanol to finish the reaction. Filtering, washing with ether, drying at 80 deg.C for 3h to obtain Chi- [ vapIm]Br·HBr。
(3) 1.0g of Chi- [ vapIm ] Br & HBr and 10mL of water are added in sequence at room temperature under stirring, 15mL of 1mol/L potassium hydroxide aqueous solution is added dropwise, and stirring is continued for 12 hours after dropwise addition. And (3) carrying out suction filtration, fully washing by using deionized water and ethanol in sequence, and then carrying out vacuum drying for 5h at the temperature of 60 ℃ to obtain the chitin Chi- [ vapIm ] OH grafted by the alkaline ionic liquid.
Comparative example 1
Synthesizing non-immobilized alkaline ionic liquid 1-vinyl-3-aminopropyl imidazole hydroxide salt [ vapIm ] OH:
mixing the 1-vinyl-3-aminopropylimidazole hydrobromide ionic liquid [ vapIm ] Br & HBr synthesized in the example 2 with 2 times of equivalent of 1mol/L KOH aqueous solution, stirring and reacting for 24h at room temperature, performing rotary evaporation, and performing vacuum drying for 5h at 60 ℃ to synthesize [ vapIm ] OH.
Comparative example 2
The chitin impregnation method is used for loading alkaline ionic liquid [ vapIm ] OH:
commercial chitin, [ vapIm ] OH and deionized water were added to the flask in sequence at room temperature. The solvent used in the dipping method is deionized water, the proportion of the deionized water to the deionized water is 1:15:50, and the mixture is stirred for 24 hours. And (3) performing suction filtration, fully washing with ethanol, and performing vacuum drying at 60 ℃ for 5h to obtain the chitin solid Chi- [ vapIm ] OH-impreg.
Comparative example 3
Changing the ionic liquid monomer to be grafted into 1-vinyl-3-butylimidazole bicarbonate ionic liquid [ vbIm]HCO3The synthesized catalyst is Chi- [ vbIm]HCO3. The rest is the same as example 8.
The catalyst is used for the reaction of ethylene carbonate and methanol, the reaction condition is 10mL of methanol, 2.2g of ethylene carbonate and 0.1g of catalyst, and the reaction is carried out for 4h at 90 ℃. Analyzing the reaction result by adopting gas chromatography, wherein the chromatographic conditions are as follows: the temperatures of the SE-54 capillary column, the FID detector, the vaporizing chamber and the detection chamber are 250 ℃, the temperature is programmed to be 80-140 ℃, the temperature is raised by 10 ℃/min, and the analysis results are shown in the table 1:
TABLE 1 evaluation results of Activity for catalyzing transesterification of ethylene carbonate and methanol
| Serial number | Catalyst and process for preparing same | Conversion of ethylene carbonate (%) | DMC selectivity (%) |
| 1 | Chi-[vpIm]OH-1 | 84.2 | 98 |
| 2 | Chi-[vpIm]OH-2 | 91.4 | 98 |
| 3 | Chi-[vbIm]OH-1 | 89.0 | 100 |
| 4 | Chi-[vbIm]OH-2 | 85.6 | 100 |
| 5 | Chi-[vaeIm]OH | 93.0 | 100 |
| 6 | Chi-[vapIm]OH | 94.5 | 100 |
| 7 | [vapIm]OH | 96.4 | 100 |
| 8 | Chi-[vbIm]Br | 0 | 0 |
| 9 | Chi-[vbIm]HCO3 | 61.5 | 31.2 |
| 10 | Chi-[vapIm]OH-impreg. | 94.8(31％) | 100(6％) |
As can be seen from Table 1, the alkaline ionic liquid grafted chitin prepared by the invention (examples 3-8, No. 1-6) is applied to catalyzing the ester exchange reaction of ethylene carbonate and methanol, the conversion rate is 84.2-94.5%, the selectivity is more than 98%, and a good catalytic effect is achieved.
Ionic liquid [ vapIm ] of comparative example 1]OH is catalyst Chi- [ vapIm ] of example 8]The OH in the unsupported form is always a homogeneous reaction in the transesterification. The catalyst has good catalytic performance, but after the reaction is finished, the recovery of the catalyst needs reduced pressure distillation, so the operation is complicated, and the recovery rate of the catalyst is low (less than 80%). When the anion of the chitin immobilized alkaline ionic liquid is Br-、HCO3 -When other ions are used, i.e., Chi- [ vbIm synthesized in comparative example 3]HCO3And Chi- [ vbIm ] catalyst precursor form of example 6]Br, the catalytic activity and DMC selectivity of which are reduced significantly when the catalyst is used in transesterification. Comparative example 2 Synthesis of catalyst Chi- [ vapIm ] by impregnation]And OH-impreg, when the ionic liquid is repeatedly used for the 2 nd time, the ionic liquid is almost completely dissolved and removed, and the catalytic activity data is not ideal (the conversion rate is 31 percent, and the selectivity is 6 percent). In conclusion, the basic ionic liquid grafted chitin has obvious advantages in catalytic performance.
After the reaction is finished, the catalyst is separated by adopting a filtering method, washed by using ethanol and dried, and then the catalyst can be put into reactants for the next round of reaction. Table 2 shows the results of the experiments of the catalyst Chi- [ vapIm ] OH for catalyzing the transesterification of ethylene carbonate and methanol for recycling:
TABLE 2 recycle experiment of catalyst Chi- [ vapIm ] OH
| Number of times of use | Conversion of ethylene carbonate (%) | DMC selectivity (%) |
| 1 | 94.5 | 100 |
| 2 | 93 | 99 |
| 3 | 92.2 | 98 |
| 4 | 90 | 98 |
| 5 | 90 | 98 |
As can be seen from Table 2, after 5 times of recycling of the catalyst Chi- [ vapIm ] OH, the catalytic activity is only reduced by 4.5%, and the selectivity of DMC is not lower than 98%, which indicates that the prepared catalyst has the advantage of being capable of recycling for several times.
TABLE 3 catalyst Chi- [ vapIm ] OH for other transesterification reactions
| Esters | Alcohol(s) | Conversion of ester (%) | Product selectivity (%) |
| Ethylene carbonate | Ethanol | 83.0 | 95.0 |
| Ethylene carbonate | Butanol | 92.9 | 100 |
| Acetoacetic acid ethyl ester | Butanol | 86.7 | 100 |
| Propylene carbonate | Methanol | 79.0 | 99.0 |
As can be seen from Table 3, the catalyst Chi- [ vapIm ] OH has better catalytic performance on the transesterification of different substrates, the conversion rate is 79.0-92.9%, and the selectivity is higher than 95.0%.
From the above, it can be seen that: the chitin grafted basic ionic liquid catalyst prepared by the method of the invention shows excellent catalytic activity and high DMC selectivity, and hardly has corrosivity to a reaction vessel; after the reaction is finished, the catalyst can be separated from the reaction mixture through simple filtering operation; when the catalyst is recycled for multiple times, the catalyst can resist the erosion action of reaction media such as solvents and the like, and shows excellent dissolution and desorption resistance; the chitin carrier is rich in resources in China, is low in price and is easy to biodegrade in the environment. The research results show that the prepared alkaline ionic liquid grafted chitin is a high-efficiency stable environment-friendly catalyst suitable for catalyzing dimethyl carbonate.
In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (10)
1. The basic ionic liquid grafted chitin is characterized in that the structural formula of the basic ionic liquid grafted chitin is as follows:
wherein A represents imidazole ionic liquid.
2. A preparation method of basic ionic liquid grafted chitin is characterized by comprising the following steps: using sulfonylated chitin as carrier, firstly carrying out iodination reaction with sodium iodide while eliminating sulfonyl ester group-OTs, then carrying out polymerization grafting reaction with vinyl-containing imidazole ionic liquid to prepare neutral ionic liquid grafted chitin, and finally exchanging anion with inorganic strong base to obtain anion of OH-The basic ionic liquid grafted chitin.
3. The method for preparing the basic ionic liquid grafted chitin according to claim 2, wherein the method comprises the following steps:
(1) preparing iodinated chitin: under the protection of nitrogen, mixing the sulfonated chitin Chi-OTs and dimethyl sulfoxide (DMSO), and stirring until the solution is clear; adding a DMSO solution of sodium iodide for reaction, reacting the mixture at 60-100 ℃ for 6-24 h, pouring the solution into acetone after the reaction is finished, separating out a precipitate, filtering, adding a methanol solution of potassium hydroxide, stirring at room temperature for 3h, then washing to neutrality, and drying at 80 ℃ for 3h to obtain chitin iodide Chi-I;
(2) synthesizing ionic liquid grafted chitin: nitrobenzene is taken as a solvent, and the chitin Chi-I iodide obtained in the step (1) and the catalyst SnCl are added in turn under stirring4After stirring for 1h, vinyl ionic liquid [ vRIm ] is added]X, reacting for 1-5 h at 5-20 ℃ under the protection of nitrogen, adding methanol to stop the reaction, filtering, washing, and drying for 3h at 80 ℃ to obtain the neutral ionic liquid grafted chitin Chi- [ vRIm]X and R are functional groups on the vinyl ionic liquid monomer, and X is halogen negative ion;
(3) synthesizing alkaline ionic liquid grafted chitin: and (3) preparing a 1mol/LKOH aqueous solution, dripping the aqueous solution into the Chi- [ vRIm ] X obtained in the step (2), stirring for 6-24 h at room temperature, filtering, washing with deionized water and ethanol in sequence to be neutral, and then drying for 5h in vacuum at 60 ℃ to obtain the alkaline ionic liquid grafted chitin Chi- [ vRIm ] OH.
4. The method for preparing the basic ionic liquid grafted chitin according to claim 2 or 3, wherein the chitin is sulfonated chitin, and the synthesis method comprises the following steps: dispersing chitin in 42% sodium hydroxide solution, carrying out reduced pressure operation for 3-5 h, sequentially adding ice and chloroform solution of p-toluenesulfonyl chloride TsCl, reacting at 0 ℃ for 1-3 h, continuing to react at room temperature for 1-3 h, then adding water for precipitation, suction filtering and washing to neutrality to obtain filter cakes, and obtaining the sulfonated chitin Chi-OTs.
5. The method for preparing basic ionic liquid grafted chitin according to claim 3, wherein the mass ratio of Chi-OTs, NaI and DMSO in step (1) is 1: 2-6: 20 to 100.
6. The method of claim 3, wherein Chi-I, SnCl is added in step (2)4And the mass ratio of the nitrobenzene to the ionic liquid monomer is 1: 1-8: 40-100: 8-15.
7. The method of claim 3, wherein the vinyl ionic liquid in step (2) is selected from the group consisting of
1-vinyl-3-alkyl halogenated imidazole ionic liquid with the structural formula
Or 1-vinyl-3-aminoalkylimidazole hydrobromide, of the formula:
wherein alkyl is ethyl, propyl or butyl, X-Is Cl-Or Br-。
8. The method for preparing the basic ionic liquid grafted chitin according to claim 7, wherein the method for synthesizing the 1-vinyl-3-alkyl halogenated imidazole ionic liquid comprises the following steps: dropwise adding halogenated alkane with equal mole number into 1-vinyl imidazole at 80 ℃, continuing to react for 24 hours after dropwise adding, cooling to room temperature, extracting with toluene, performing rotary evaporation, and drying at 80 ℃ for 3 hours to obtain a product; wherein the halogenated alkane is 1-chloropropane, 1-chlorobutane, 1-bromopropane and 1-bromobutane.
9. The method for preparing the basic ionic liquid grafted chitin according to claim 7, wherein the method for synthesizing the 1-vinyl-3-aminoalkyl imidazole hydrobromide comprises: adding 1-vinylimidazole and 3-bromopropylamine hydrobromide or 2-bromoethylamine hydrobromide with equal molar number into acetonitrile serving as a solvent, stirring and heating to 100 ℃ for reaction for 24 hours, cooling the mixture to room temperature after the reaction is finished, removing the solvent by rotary evaporation, washing the remained solid with ethanol for a plurality of times, and drying at 80 ℃ for 3 hours to obtain the product.
10. The use of the basic ionic liquid grafted chitin according to claim 1, wherein the ionic liquid grafted chitin is used in ester exchange reaction.
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| CN102060657A (en) * | 2009-11-13 | 2011-05-18 | 中国科学院兰州化学物理研究所 | Method for preparing dibasic alcohol |
| US20110236295A1 (en) * | 2008-08-08 | 2011-09-29 | University Of Toledo | Polymeric Ionic Liquids, Methods of Making and Methods of Use Thereof |
| CN102391241A (en) * | 2011-10-21 | 2012-03-28 | 中国科学院过程工程研究所 | Method for preparing cyclic carbonate with chitosan loading type catalyst |
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| CN101695673A (en) * | 2009-10-26 | 2010-04-21 | 南昌航空大学 | Method for preparing chitosan immobilized Lewis acidic ionic liquid and DCPP synthesized by using chitosan immobilized Lewis acidic ionic liquid in presence of high-efficient catalyst |
| CN102060657A (en) * | 2009-11-13 | 2011-05-18 | 中国科学院兰州化学物理研究所 | Method for preparing dibasic alcohol |
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