Method for preparing ethylene carbonate under catalysis of ionic liquid

Abstract

The invention provides application of ionic liquid in preparation of ethylene carbonate. The invention also provides a method for preparing ethylene carbonate under the catalysis of the ionic liquid, which comprises the following step of: reacting carbonate as shown in a formula II with ethylene glycol by using the ionic liquid as a catalyst to obtain ethylene carbonate as shown in a formula III. According to the method for preparing ethylene carbonate through catalysis of the ionic liquid, the raw materials are low in price and easy to obtain, the preparation method is simple and convenient, the ionic liquid is low in toxicity and easy to biodegrade and can be recycled as a catalyst, the development requirements of green chemical engineering and clean production are met, and good economic, social and environmental benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis and relates to a method for preparing ethylene carbonate by catalysis of ionic liquid. Background Art

[0002] Ethylene carbonate (EC), as a high-boiling-point organic solvent with excellent performance, is widely used in the production of electrolytes for lithium-ion batteries. It is also a green and environmentally friendly organic synthesis intermediate with the advantages of low toxicity and low corrosiveness. It is widely used in the fields of material synthesis, plastics, textiles and electrochemistry. It has broad market application prospects and is known as the green basic chemical raw material of the 21st century.

[0003] The synthesis methods of ethylene carbonate mainly include phosgene method, transesterification method, halogenated alcohol method, ethylene oxide and CO2 synthesis method, and urea alcoholysis method. Phosgene method is the traditional production method of ethylene carbonate, but it has the disadvantages of complex process, low yield, high cost, etc., and phosgene is highly toxic and polluting, so it is gradually eliminated. Ethylene oxide and CO2 synthesis method is the main production method in industry at present, which has the advantages of fixing greenhouse gas carbon dioxide and short process flow; but the reaction is a volume reduction reaction, and high pressure conditions are conducive to the reaction, so harsh conditions are required and the selection of catalysts and subsequent separation are the difficulties that affect the reaction. Urea alcoholysis method uses urea and ethylene glycol as raw materials. In 1991, Su et al. first proposed the preparation of ethylene carbonate by urea and diols in the presence of tin-containing catalysts. The conversion rate of urea in their method is less than 66%. In recent years, great progress has been made in the research on the synthesis of EC by urea alcoholysis. Bhadauri et al. used ZnO-Cr2O3 as a catalyst and achieved an EC yield of 85.75% under reduced pressure at 150°C. Zhou et al. used Zn-Pb mixed carbonate to catalyze the alcoholysis of urea to synthesize propylene carbonate (PC). They found that the synergistic effect of PbCO3 and Zn5(CO3)2(OH)6 significantly improved the catalyst activity, and the PC yield reached 96.3%. Weak alkalinity is more conducive to the improvement of this synergistic effect, but the raw material urea is easily decomposed by heat. The halogenated alcohol method has high raw material and catalyst costs, harsh reaction conditions, and low yields.

[0004] The reason why the crude ethylene carbonate decomposes during distillation in the reaction is that the crude ethylene carbonate in the distillation kettle contains a trace amount of catalyst, which promotes the decomposition reaction of ethylene carbonate.

[0005] In recent years, the synthesis of ethylene carbonate using dimethyl carbonate and ethylene glycol as raw materials under the action of solid base catalyst is a relatively new synthesis route. This process has the advantages of high product selectivity and low raw material cost. Hu Bin et al. used dibutyltin dilaurate as a catalyst, and obtained the corresponding cyclic carbonate in xylene solvent through toluenesulfonic acid catalytic prepolymerization and tin powder catalytic high-temperature depolymerization, and the EC yield can reach 77%. However, the ester exchange reaction is a reversible reaction, and the reaction is generally not complete. According to the reaction equilibrium principle, in order to increase the conversion rate, the product must be separated in time or a certain reactant must be excessive, thereby promoting the reaction to proceed in the forward direction. This process has the problems of complex catalysts, high reaction temperatures, and numerous reaction processes. Summary of the invention

[0006] In view of the characteristics of the prior art described above, the object of the present invention is to provide a method for preparing ethylene carbonate by catalysis of ionic liquids, wherein the raw materials are cheap and readily available, the preparation method is simple, low in toxicity and easily biodegradable, the ionic liquid catalyst can be recycled, and the development requirements of green chemical industry and clean production are met, and good economic, social and environmental benefits are achieved.

[0007] To achieve the above-mentioned object and other related objects, the first aspect of the present invention provides a use of an ionic liquid in the preparation of ethylene carbonate, wherein the cation of the ionic liquid has a structural formula as shown in the following formula I:

[0008]

[0009] In Formula I, R1 and R2 are the same or different and are independently selected from C1-C6 straight or branched chain alkyl;

[0010] The anion of the ionic liquid is selected from Cl - Br - ,I - OH - 、HCO3 - 、BF4 - 、NO3 - CF3SO3 - PF6 - 、HSO4 - 、H2PO4 - At least one of .

[0011] A second aspect of the present invention provides a method for preparing ethylene carbonate using ionic liquid catalysis, comprising:

[0012] The carbonate represented by formula II and ethylene glycol are reacted with the ionic liquid provided by the first aspect of the present invention as a catalyst to obtain ethylene carbonate represented by formula III;

[0013]

[0014] Wherein, R is methyl or ethyl.

[0015] As described above, the method for preparing ethylene carbonate by catalysis of ionic liquid provided by the present invention has the advantages of cheap and easy raw materials, simple preparation method, and the catalyst used: the ionic liquid is biodegradable and has good biocompatibility and non-toxicity, and is easy to separate from the product. The catalyst is crystallized to remove the catalyst, and the uncrystallized material (containing the catalyst) is recycled as a catalyst. At the same time, it avoids the presence of trace catalyst in the crude ethylene carbonate product during refining, and promotes the occurrence of the decomposition reaction of ethylene carbonate. In addition, after the crude ethylene carbonate product is melted, it is subjected to reduced pressure distillation to obtain 99wt% ethylene carbonate. After the catalyst is recycled 1-20 times, preferably 10 times, the activity is not significantly reduced, and the stability is good; the yield can reach more than 95%, the purity is more than 99%, and no catalyst residue is found in the product, which is convenient for subsequent distillation and purification. It meets the development requirements of green chemical industry and clean production, and has good economic, social and environmental benefits. DETAILED DESCRIPTION

[0016] Below, a detailed description specifically discloses an embodiment of the method for preparing ethylene carbonate by ionic liquid catalysis of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0017] "Scope" disclosed in the present application is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The scope defined in this way can include or exclude end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if a scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected.

[0018] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0019] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (1) and (2), which means that the method may include steps (1) and (2) performed sequentially, or may include steps (2) and (1) performed sequentially. For example, the method may further include step (3), which means that step (3) may be added to the method in any order, for example, the method may include steps (1), (2) and (3), or may include steps (1), (3) and (2), or may include steps (3), (2) and (1), etc.

[0020] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0021] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0022] The first aspect of the present invention provides a use of an ionic liquid in the preparation of ethylene carbonate, wherein the cation of the ionic liquid has a structural formula as shown in the following formula I:

[0023]

[0024]

[0025] In Formula I, R1 and R2 are the same or different and are independently selected from C1-C6 straight or branched chain alkyl;

[0026] The anion of the ionic liquid is selected from Cl - Br - ,I - OH - 、HCO3 - 、BF4 - 、NO3 - CF3SO3 - PF6 - 、HSO4 - 、H2PO4 - At least one of .

[0027] The cation of the ionic liquid has the structure type of imidazolium ion. The ionic liquid is synthesized using N-methylimidazole as raw material.

[0028] In the above-mentioned use, the ionic liquid is selected from at least one of 1,3-dimethylimidazole iodide, 1-butyl-3-methylimidazole bromide (CAS is 85100-77-2), 1-butyl-3-methylimidazole hydroxide (CAS is 828818-81-7), 1-butyl-3-methylimidazole bicarbonate (CAS is 366491-15-8), and 1-butyl-3-methylimidazole tetrafluoroborate (CAS is 174501-65-6).

[0029] In the above-mentioned use, when the anions of the ionic liquid are different halogen ions, the catalytic activity of the ionic liquid increases with the increase of the molecular weight of the halogen ion, that is, for example, alkyl imidazole iodide>alkyl imidazole bromide>alkyl imidazole chloride; when the anions of the ionic liquid are the same halogen ion and the cations of the ionic liquid contain different alkyl groups, the catalytic activity of the ionic liquid decreases with the increase of the number of alkyl carbon atoms, that is, for example, methyl imidazole halide>ethyl imidazole halide>butyl imidazole halide.

[0030] A second aspect of the present invention provides a method for preparing ethylene carbonate using ionic liquid catalysis, comprising:

[0031] The carbonate represented by formula II and ethylene glycol are reacted with the ionic liquid provided by the first aspect of the present invention as a catalyst to obtain ethylene carbonate represented by formula III;

[0032]

[0033] Wherein, R is methyl or ethyl.

[0034] In the above method, since R in the carbonate represented by formula II is methyl or ethyl, that is, the carbonate represented by formula II is dimethyl carbonate or diethyl carbonate, preferably dimethyl carbonate (DMC).

[0035] In the above method, the molar ratio of the carbonate represented by formula II to ethylene glycol is 1:1-2, specifically 1:1-1.1, 1:1.1-1.6, 1:1.6-2, preferably 1:1.2-1.5.

[0036] In the above method, the amount of the ionic liquid is 0.3-5% of the mass of ethylene glycol, specifically 0.3-0.8%, 0.8-1.2%, 1.2-5%, preferably 0.9-1.1%, and more preferably 1.0%.

[0037] In the above method, the reaction comprises the steps of:

[0038] 1) heating carbonate and ethylene glycol with an ionic liquid as a catalyst to carry out an ester exchange reaction, cooling and collecting fractions, and crystallizing the reaction solution obtained after the reaction to obtain a crude ethylene carbonate material and an uncrystallized material;

[0039] 2) returning the uncrystallized material to the transesterification reaction;

[0040] 3) Repeat the cycle from step 1) to step 2) at least once;

[0041] 4) Melting the obtained crude ethylene carbonate material, and subjecting the obtained crude ethylene carbonate product to reduced pressure distillation to obtain the desired ethylene carbonate.

[0042] In the above steps 1), 2), 3) or 4), the above reaction is carried out in a reaction tower kettle. Specifically, the transesterification reaction is carried out in a reactor. The crystallization is carried out in a crystallizer.

[0043] In the above step 1), the reaction liquid is the bottom liquid.

[0044] In the above step 1), the reaction temperature is 90-120°C, specifically 90-110°C, 110-120°C, preferably 95-105°C, more preferably 100°C; the reaction time is 2-6h, specifically 2-3h, 3-4h, 4-5h, 5-6h, preferably 3-4h, more preferably 3.5h.

[0045] In the above step 1), the mixing method of the transesterification reaction is magnetic stirring mixing.

[0046] In the above step 1), byproducts: alcohol and carbonate are continuously evaporated in the transesterification reaction, so that the transesterification of carbonate and ethylene carbonate can be achieved. Specifically, the alcohol is methanol or ethanol, and the carbonate is dimethyl carbonate or diethyl carbonate.

[0047] In the above step 1), the transesterification reaction is terminated when no fraction is distilled out. That is, the end point of the transesterification reaction is determined when no fraction is distilled out.

[0048] In the above step 1), the cooling is performed by circulating water cooling.

[0049] In the above step 1), the fraction temperature is 50-90°C, specifically 50-63°C, 63-90°C, preferably 63-90°C.

[0050] In the above step 1), the crystallization conditions are: cooling at a cooling rate of 0.05-0.2°C / min, preferably 0.1°C / min; cooling to 22-24°C, preferably 23°C; maintaining the temperature for ≥30min, preferably 30min; then sweating to 32-34°C, preferably 33.0°C, at a sweating rate of 0.02-0.04°C / min, preferably 0.03°C / min; maintaining the temperature for 25-35min, preferably 30min.

[0051] In the above step 2), the uncrystallized material contains the ionic liquid as a catalyst, so it can be returned to the transesterification reaction for recycling.

[0052] In the above step 3), the number of repeated cycles is 1-20 times, preferably 10 times.

[0053] In the above step 4), the melting temperature is 35-60°C, preferably 50°C.

[0054] In the above step 4), the melting is carried out until all the crystal layers formed by crystallization in the crude ethylene carbonate material are melted.

[0055] In the above step 4), the melting temperature rise rate is 1-10°C / min, preferably 2°C / min.

[0056] In the above step 4), the reaction pressure of the reduced pressure distillation is -0.10 to -0.090 MPa, preferably -0.095 MPa.

[0057] In the above step 4), the reaction temperature of the reduced pressure distillation is 70-95°C, specifically 70-74°C, 74-91°C, 91-95°C, preferably 75-90°C, more preferably 85°C.

[0058] In the above step 4), the reduced pressure distillation is continued until no fraction is distilled out.

[0059] In the above step 4), the concentration of ethylene carbonate is ≥ 99 wt%, preferably 99 wt%.

[0060] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0061] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0062] Example 1

[0063] N-methylimidazole and iodoethane were added into a 250mL three-necked flask in a molar ratio of 1:1, reacted at 70°C for 24 hours under N2 protection, cooled to room temperature, and a light yellow oily liquid was obtained. After washing with ethyl acetate three times, the washed product was vacuum dried at 80°C for 24 hours to obtain a light yellow ionic liquid: 1,3-dimethylimidazole iodide.

[0064] Ethylene glycol (186.0 g, 3.0 mol), dimethyl carbonate (180.0 g, 2.0 mol) and 1,3-dimethylimidazole iodide (1.86 g) were added into a three-necked flask, heated with magnetic stirring in an oil bath, the reaction temperature was 100°C, methanol and dimethyl carbonate were continuously evaporated during the reaction, the 80°C fraction was collected by cooling; the reaction was continued for 4 hours.

[0065] The reaction solution was then crystallized, cooled to 23°C at a cooling rate of 0.1°C / min, kept at this temperature for 30 minutes, and then sweated to 33.0°C at a sweating rate of 0.03°C / min, kept at this temperature for 30 minutes, to obtain ethylene carbonate crude material and uncrystallized material. The uncrystallized material was collected and returned to the transesterification reaction for 10 catalyst cycles.

[0066] The crude ethylene carbonate obtained from each repeated reaction was melted at 50°C to melt all the crystal layers formed by the crystals to obtain a crude ethylene carbonate product. The crude ethylene carbonate product was then subjected to reduced pressure distillation at a pressure of -0.095 MPa and a heating temperature of 85°C to obtain the desired ethylene carbonate.

[0067] The catalyst was recycled 10 times, and the yield and purity of the obtained ethylene carbonate are shown in Table 1. As shown in Table 1, the activity of the catalyst did not decrease significantly after 10 times of recycling, the yield of ethylene carbonate was not less than 95%, and the purity of ethylene carbonate was not less than 99%.

[0068] Table 1

[0069] Serial number 1 2 3 4 5 6 7 8 9 10 Yield % 95.0 95.1 95.4 95.3 95.2 95.0 95.4 95.2 95.0 95.1 purity% 99.1 99.2 99.4 99.0 99.2 99.5 99.4 99.3 99.1 99.0

[0070] Example 2

[0071] N-methylimidazole and n-butyl bromide were added into a 250 mL three-necked flask in a molar ratio of 1:1, reacted at 70 °C for 24 h under N2 protection, cooled to room temperature, and a light yellow oily liquid was obtained. After washing with ethyl acetate three times, the washed product was vacuum dried at 80 °C for 24 h to obtain a light yellow ionic liquid: 1-butyl-3-methylimidazole bromide.

[0072] Ethylene glycol (186.0 g, 3.0 mol), dimethyl carbonate (135.0 g, 1.5 mol) and 1-butyl-3-methylimidazolium bromide (3.72 g) were added into a three-necked flask, heated with magnetic stirring in an oil bath, the reaction temperature was 95°C, methanol and dimethyl carbonate were continuously evaporated during the reaction, the 75°C fraction was cooled and collected; the reaction was continued for 2 hours.

[0073] The reaction solution was then crystallized, cooled to 22°C at a cooling rate of 0.2°C / min, kept at this temperature for 35 minutes, and then sweated to 34.0°C at a sweating rate of 0.04°C / min, kept at this temperature for 35 minutes, to obtain ethylene carbonate crude material and uncrystallized material. The uncrystallized material was collected and returned to the transesterification reaction for 10 catalyst cycles.

[0074] The crude ethylene carbonate obtained from each repeated reaction is melted at 45°C to melt all the crystal layers formed by the crystals to obtain a crude ethylene carbonate product. The crude ethylene carbonate product is then subjected to reduced pressure distillation at a pressure of -0.095 MPa and a heating temperature of 87°C to obtain the desired ethylene carbonate.

[0075] The catalyst was recycled 10 times, and the yield and purity of the obtained ethylene carbonate are shown in Table 2. As shown in Table 2, the activity of the catalyst was not significantly reduced after 10 times of recycling, the yield of ethylene carbonate was not less than 93.5%, and the purity of ethylene carbonate was not less than 99%.

[0076] Table 2

[0077] Serial number 1 2 3 4 5 6 7 8 9 10 Yield % 93.5 94.2 93.8 94.1 93.9 94.0 93.8 93.7 94.5 93.8 purity% 99.0 99.1 99.5 99.2 99.4 99.3 99.7 99.2 99.4 99.1

[0078] Example 3

[0079] Prepare 1-butyl-3-methylimidazolium bromide according to Example 2. Add 40 g of KOH and 300 mL of CH2Cl2 to 130 g of 1-butyl-3-methylimidazolium bromide and stir thoroughly for 10 h. Filter to remove KBr to obtain a filtrate, rotary evaporate and vacuum dry to obtain a reddish-brown viscous liquid as an ionic liquid: 1-butyl-3-methylimidazolium hydroxide.

[0080] Ethylene glycol (198.4 g, 2.4 mol), dimethyl carbonate (180.0 g, 2.0 mol) and 1-butyl-3-methylimidazole hydroxide (1.79 g) were added into a three-necked flask, heated with magnetic stirring in an oil bath, the reaction temperature was 105°C, methanol and dimethyl carbonate were continuously evaporated during the reaction, the 70°C fraction was collected after cooling; the reaction was continued for 3.5 hours.

[0081] The reaction solution was then crystallized, cooled to 24°C at a cooling rate of 0.05°C / min, kept at this temperature for 50 minutes, and then sweated to 34.0°C at a sweating rate of 0.02°C / min, kept at this temperature for 25 minutes, to obtain ethylene carbonate crude material and uncrystallized material. The uncrystallized material was collected and returned to the transesterification reaction for 10 catalyst cycles.

[0082] The crude ethylene carbonate obtained from each repeated reaction is melted at 40°C to melt all the crystal layers formed by the crystals to obtain a crude ethylene carbonate product. The crude ethylene carbonate product is then subjected to reduced pressure distillation at a pressure of -0.095 MPa and a heating temperature of 85°C to obtain the desired ethylene carbonate.

[0083] The catalyst was recycled 10 times, and the yield and purity of the obtained ethylene carbonate are shown in Table 3. As shown in Table 3, the activity of the catalyst was not significantly reduced after 10 times of recycling, the yield of ethylene carbonate was not less than 93.8%, and the purity of ethylene carbonate was not less than 99%.

[0084] Table 3

[0085] Serial number 1 2 3 4 5 6 7 8 9 10 Yield % 93.8 94.2 93.8 93.9 94.0 95.2 95.6 94.1 93.9 94.0 purity% 99.0 99.1 99.5 99.2 99.3 99.7 99.5 99.1 99.3 99.0

[0086] Example 4

[0087] Prepare 1-butyl-3-methylimidazolium bromide according to Example 2, weigh 110 g of 1-butyl-3-methylimidazolium bromide and dissolve it in 200 mL of methanol, add 42 g of NaHCO3, stir at 40°C for 24 h, and distill the filtered clear liquid to remove methanol to obtain a colorless viscous liquid as an ionic liquid: 1-butyl-3-methylimidazolium bicarbonate.

[0088] Ethylene glycol (248.0 g, 3.0 mol), diethyl carbonate (321.82 g, 2.73 mol) and 1-butyl-3-methylimidazole hydroxide (1.86 g) were added into a three-necked flask, heated with magnetic stirring in an oil bath, the reaction temperature was 120°C, methanol and dimethyl carbonate were continuously evaporated during the reaction, the 90°C fraction was cooled and collected; the reaction was continued for 5 hours.

[0089] The reaction solution was then crystallized, cooled to 22°C at a cooling rate of 0.2°C / min, kept at this temperature for 40 minutes, and then sweated to 33.0°C at a sweating rate of 0.02°C / min, kept at this temperature for 25 minutes, to obtain ethylene carbonate crude material and uncrystallized material. The uncrystallized material was collected and returned to the transesterification reaction for 10 catalyst cycles.

[0090] The crude ethylene carbonate obtained from each repeated reaction was melted at 35°C to melt all the crystal layers formed by the crystals to obtain a crude ethylene carbonate product. The crude ethylene carbonate product was then subjected to reduced pressure distillation at a pressure of -0.095 MPa and a heating temperature of 85°C to obtain the desired ethylene carbonate.

[0091] The catalyst was recycled 10 times, and the yield and purity of the obtained ethylene carbonate are shown in Table 4. As shown in Table 4, the activity of the catalyst was not significantly reduced after 10 times of recycling, the yield of ethylene carbonate was not less than 92.8%, and the purity of ethylene carbonate was not less than 99%.

[0092] Table 4

[0093] Serial number 1 2 3 4 5 6 7 8 9 10 Yield % 92.8 93.1 93.1 93.0 93.5 93.8 93.2 93.5 93.1 93.2 purity% 99.1 99.0 99.4 99.1 99.2 99.1 99.0 99.4 99.0 99.1

[0094] Example 5

[0095] Prepare 1-butyl-3-methylimidazolium bromide according to Example 2, weigh 130 g of 1-butyl-3-methylimidazolium bromide, 62 g of 6.5% NH4BF4 and 300 mL of methanol, add them into a flask in sequence, stir at a constant temperature of 40°C for 3 h, and distill the filtered clear liquid to remove methanol to obtain a light yellow viscous liquid as an ionic liquid: 1-butyl-3-methylimidazolium tetrafluoroborate.

[0096] Ethylene glycol (248.0 g, 3.0 mol), dimethyl carbonate (180.0 g, 2.0 mol) and 1-butyl-3-methylimidazolium tetrafluoroborate (24.96 g) were added into a three-necked flask, heated with magnetic stirring in an oil bath, the reaction temperature was 105°C, methanol and dimethyl carbonate were continuously evaporated during the reaction, the 85°C fraction was collected after cooling; the reaction was continued for 4 hours.

[0097] The reaction solution was then crystallized, cooled to 23°C at a cooling rate of 0.1°C / min, kept at this temperature for 30 minutes, and then sweated to 33.0°C at a sweating rate of 0.03°C / min, kept at this temperature for 30 minutes, to obtain ethylene carbonate crude material and uncrystallized material. The uncrystallized material was collected and returned to the transesterification reaction for 10 catalyst cycles.

[0098] The crude ethylene carbonate obtained from each repeated reaction is melted at 45°C to melt all the crystal layers formed by the crystals to obtain a crude ethylene carbonate product. The crude ethylene carbonate product is then subjected to reduced pressure distillation at a pressure of -0.095 MPa and a heating temperature of 85°C to obtain the desired ethylene carbonate.

[0099] The catalyst was recycled 10 times, and the yield and purity of the obtained ethylene carbonate are shown in Table 5. As shown in Table 5, the activity of the catalyst was not significantly reduced after 10 times of recycling, the yield of ethylene carbonate was not less than 94.1%, and the purity of ethylene carbonate was not less than 99%.

[0100] Table 5

[0101] Serial number 1 2 3 4 5 6 7 8 9 10 Yield % 94.1 95.0 94.8 94.5 95.2 95.6 94.9 95.1 94.7 95.0 purity% 99.0 99.5 99.8 99.4 99.2 99.5 99.3 99.1 99.0 99.5

[0102] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. Use of an ionic liquid in the preparation of ethylene carbonate, wherein the cation of the ionic liquid has a structural formula as shown in Formula I below: In Formula I, R1 and R2 are the same or different and are independently selected from C1-C6 straight or branched chain alkyl; The anion of the ionic liquid is selected from Cl - Br - ,I - OH - 、HCO3 - 、BF4 - 、NO3 - CF3SO3 - PF6 - 、HSO4 - 、H2PO4 - At least one of .

2. Use of the ionic liquid according to claim 1 in the preparation of ethylene carbonate, characterized in that: The ionic liquid is selected from at least one of 1,3-dimethylimidazolium iodide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium hydroxide, 1-butyl-3-methylimidazolium bicarbonate, and 1-butyl-3-methylimidazolium tetrafluoroborate.

3. A method for preparing ethylene carbonate by ionic liquid catalysis, comprising: The carbonate ester shown in formula II and ethylene glycol, Using the ionic liquid according to any one of claims 1 or 2 as a catalyst to react to obtain ethylene carbonate represented by formula III; Wherein, R is methyl or ethyl.

4. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 3, characterized in that: The molar ratio of the carbonate represented by formula II to ethylene glycol is 1:1-2.

5. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 3, characterized in that: The amount of the ionic liquid used is 0.3-5% of the mass of ethylene glycol.

6. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 3, characterized in that: The reaction comprises the following steps: 1) heating carbonate and ethylene glycol with an ionic liquid as a catalyst to carry out an ester exchange reaction, cooling and collecting fractions, and crystallizing the reaction solution obtained after the reaction to obtain a crude ethylene carbonate material and an uncrystallized material; 2) returning the uncrystallized material to the transesterification reaction; 3) Repeat the cycle from step 1) to step 2) at least once; 4) Melting the obtained crude ethylene carbonate material, and subjecting the obtained crude ethylene carbonate product to reduced pressure distillation to obtain the desired ethylene carbonate.

7. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 6, characterized in that: In step 1), the transesterification reaction includes any one or more of the following conditions: A1) the reaction temperature is 90-120°C; A2) reaction time is 2-6h; A3) The transesterification reaction is continued until no fraction is distilled out.

8. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 6, characterized in that: In step 1), any one or more of the following conditions are also included: B1) the fraction temperature is 50-90°C; B2) The crystallization conditions are: cooling to 22-24°C at a cooling rate of 0.05-0.2°C / min; Maintain constant temperature for ≥30 minutes; then sweat to 32-34℃ at a sweating rate of 0.02-0.04℃ / min; maintain constant temperature for 25-35 minutes.

9. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 6, characterized in that: In step 3), the number of repeated cycles is 1-20 times.

10. The method for preparing ethylene carbonate by ionic liquid catalysis according to claim 6, characterized in that: In step 4), any one or more of the following conditions are included: C1) the melting temperature is 35-60°C; C2) melting until all the crystal layers formed by crystallization in the crude ethylene carbonate material are melted; C3) the heating rate of the melting is 1-10°C / min; C4) the reaction pressure of the reduced pressure distillation is -0.10 to -0.090 MPa; C5) the reaction temperature of the reduced pressure distillation is 70-95°C; C6) the reduced pressure distillation is continued until no fraction is distilled out.

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