A high-purity halogen-free ionic liquid and its preparation method
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-26
- Publication Date
- 2026-08-14
AI Technical Summary
但这种离子液体的液体温度范围还是相对比较狭窄的，而且，氯化铝离子液体遇水会放出氯化氢，对皮肤有刺激作用
本发明的N-甲基咪唑与硫酸二乙酯进行烷基化反应，合成的第一步产物硫酸乙酯盐和相应的有机盐进行离子交换合成相应离子液体；再通过萃取、水洗等后处理方式得到高纯无卤离子液体。本发明的制备方法得到的高纯无卤离子液体不仅收率高，纯度高，且制备工艺简单，对外界环境污染小。
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Figure CN122562747A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ionic liquid technology, and in particular to a high-purity halogen-free ionic liquid and its preparation method. Background Technology
[0002] The history of ionic liquids dates back to 1914, when Walden reported (EtNH2) + HNO3. - Synthesis of ionic liquid (melting point 12℃). This substance was prepared by reacting concentrated nitric acid and ethylamine. However, due to its instability in air and tendency to explode, its discovery did not initially attract much interest. This was the earliest ionic liquid. Generally, ionic compounds require very high temperatures to overcome the binding of ionic bonds before dissolving into a liquid; this state is called a "molten salt." The ionic bonds in ionic compounds weaken as the radius of the cation increases, and the melting point decreases accordingly. For most substances, the melting point of a mixture is lower than that of the pure substance. For example, NaCl has a melting point of 803℃, while a mixture of 50% LiCl and 50% AlCl3 (mole fraction) has a melting point of only 144℃. By further increasing the volume and structural asymmetry of the cations or anions, weakening the forces between them, liquid ionic compounds at room temperature can be obtained. Based on this principle, in 1951, FH Hurley and T.P. Wiler first synthesized an ionic liquid that was liquid at ambient temperature. The cation was N-ethylpyridine, and the synthesized ionic liquid was a mixture of n-ethylpyridine bromide and aluminum chloride (the molar ratio of aluminum chloride to ethylpyridine bromide was 1:2). However, the liquid temperature range of this ionic liquid was relatively narrow, and aluminum chloride ionic liquid released hydrogen chloride upon contact with water, which was irritating to the skin. It wasn't until 1976 that Robert of Colorado State University, using AlCl3 / [N-EtPy]Cl as an electrolyte in his organic electrochemical research, discovered that this room-temperature ionic liquid was an excellent electrolyte, miscible with organic matter, proton-free, and with a wide electrochemical window. In 1992, Wilkes synthesized 1-methyl-3-ethylimidazolium chloride using 1-methyl-3-ethylimidazolium as a cation, achieving a melting point of 8°C in the presence of 50% AlCl3. Only after this did the application research of ionic liquids truly begin to be widely carried out.
[0003] Ionic liquids show great promise as antistatic agents in the field of electronic components due to their high melting point, strong conductivity, safety, and environmental friendliness, making them popular across various industries. With current technological advancements, many technology companies prefer to use ionic liquids as high-purity antistatic agents, requiring minimal free halogen content to better meet the requirements of downstream customers. Therefore, there is an urgent need to develop a high-purity, halogen-free ionic liquid. Summary of the Invention
[0004] The purpose of this invention is to provide a high-purity halogen-free ionic liquid and its preparation method, addressing the shortcomings of existing technologies.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing high-purity halogen-free ionic liquids, comprising the following steps: 1) Under nitrogen protection, diethyl sulfate was added dropwise to N-methylimidazolium to obtain a reaction solution; the reaction solution was kept at a constant temperature to obtain 1-ethyl-3-methylimidazolium ethyl sulfate salt; 2) After ion exchange with 1-ethyl-3-methylimidazolium sulfate ethyl ester salt, water, organic salt and dichloromethane, the mixture was extracted and separated. The lower organic layer was then post-treated to obtain a high-purity halogen-free ionic liquid.
[0006] Preferably, the molar ratio of N-methylimidazole to diethyl sulfate is 1.01~1.02:1.
[0007] Preferably, the diethyl sulfate has a purity of ≥99%, and the N-methylimidazole has a purity of ≥99%.
[0008] Preferably, the temperature of the reaction solution remains constant during the addition of diethyl sulfate; the temperature of the reaction solution is 32~40℃, and the addition time is 2~4h.
[0009] Preferably, the temperature of the heat preservation reaction is 32~40℃, and the heat preservation reaction time is 2~6h.
[0010] Preferably, the organic salt comprises one or more of KPF6, LiTFSl, LiFSl, and NaSbF6.
[0011] Preferably, the molar volume ratio of the organic salt to dichloromethane is 1 mol: 150~250 mL; the molar ratio of the organic salt to diethyl sulfate is 0.8~1.2: 0.8~1.2; and the mass ratio of 1-ethyl-3-methylimidazolium sulfate salt to water is 1: 1.5~2.5.
[0012] Preferably, the ion exchange time is 3-5 hours; the post-treatment includes water washing and rotary evaporation, with the number of water washing cycles being 1-5.
[0013] The present invention also provides a high-purity halogen-free ionic liquid prepared by the aforementioned preparation method.
[0014] The beneficial effects of this invention are as follows: The present invention involves the alkylation reaction of N-methylimidazole with diethyl sulfate, followed by ion exchange of the first-step product, ethyl sulfate salt, with a corresponding organic salt to synthesize the corresponding ionic liquid. High-purity halogen-free ionic liquid is then obtained through post-treatment methods such as extraction and washing. The high-purity halogen-free ionic liquid obtained by the preparation method of the present invention not only has high yield and high purity, but also features a simple preparation process and minimal environmental pollution. Attached Figure Description
[0015] Figure 1 The NMR spectrum of the [EMIM][TFSl] ionic liquid synthesized in Example 7; Figure 2 The NMR spectrum of the [EMIM][TFSl] ionic liquid synthesized by conventional methods; Figure 3 The ion chromatogram of the [EMIM][TFSl] ionic liquid synthesized in Example 7 is shown below. Figure 4 The ion chromatogram of the [EMIM][FSl] ionic liquid synthesized in Example 6 is shown below. Figure 5 The ion chromatogram of the [EMIM][PF6] ionic liquid synthesized in Example 8 is shown. Detailed Implementation
[0016] This invention provides a method for preparing high-purity halogen-free ionic liquids, comprising the following steps: 1) Under nitrogen protection, diethyl sulfate was added dropwise to N-methylimidazolium to obtain a reaction solution; the reaction solution was kept at a constant temperature to obtain 1-ethyl-3-methylimidazolium sulfate ethyl salt ([EMIM][EtSO4]). 2) After ion exchange with 1-ethyl-3-methylimidazolium sulfate ethyl ester salt, water, organic salt and dichloromethane, the mixture was extracted and separated. The lower organic layer was then post-treated to obtain a high-purity halogen-free ionic liquid.
[0017] In this invention, the molar ratio of N-methylimidazole to diethyl sulfate is preferably 1.01~1.02:1, and more preferably 1.015~1.016:1.
[0018] In this invention, the purity of the diethyl sulfate is preferably ≥99%, more preferably ≥99.2%, and the purity of the N-methylimidazole is preferably ≥99%, more preferably ≥99.2%.
[0019] In this invention, the temperature of the reaction solution remains constant during the addition of diethyl sulfate; the temperature of the reaction solution is preferably 32~40℃, more preferably 35~36℃, and the addition time is preferably 2~4h, more preferably 2.5~3.5h, and more preferably 3h.
[0020] In this invention, the temperature of the heat preservation reaction is preferably 32~40℃, more preferably 35~36℃, and the heat preservation reaction time is preferably 2~6h, more preferably 3~5h, and even more preferably 4h.
[0021] In this invention, the organic salt preferably comprises one or more of KPF6 (potassium hexafluorophosphate), LiTFSl (lithium bis(trifluoromethanesulfonyl)imide), LiFSl (lithium bis(fluorosulfonyl)imide), and NaSbF6 (sodium hexafluoroantimonate).
[0022] In this invention, the preferred molar volume ratio of the organic salt to dichloromethane is 1 mol: 150-250 mL, more preferably 1 mol: 170-230 mL, and even more preferably 1 mol: 190-200 mL; the preferred molar ratio of the organic salt to diethyl sulfate is 0.8-1.2: 0.8-1.2, more preferably 0.9-1.1: 0.9-1.1, and even more preferably 1:1; the preferred mass ratio of 1-ethyl-3-methylimidazolium sulfate ethyl ester salt to water is 1:1.5-2.5, more preferably 1:1.8-2.2, and even more preferably 1:2.
[0023] In this invention, the ion exchange time is preferably 3-5 h, more preferably 3.5-4.5 h, and even more preferably 4 h; the post-treatment preferably includes water washing and rotary evaporation, and the number of water washings is preferably 1-5 times, more preferably 2-4 times, and even more preferably 3 times.
[0024] In this invention, the purpose of rotary evaporation is to remove dichloromethane.
[0025] The present invention also provides a high-purity halogen-free ionic liquid prepared by the aforementioned preparation method.
[0026] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0027] In the examples and comparative examples, the purity of N-methylimidazole, diethyl sulfate, lithium bis(fluorosulfonyl)imide (LiFSl), lithium bis(trifluoromethanesulfonyl)imide (LiTFSl), potassium hexafluorophosphate (KPF6), and sodium hexafluoroantimonate (NaSbF6) was 99%.
[0028] Example 1
[0029] 1.01 mol of N-methylimidazole was placed in a single-mouth double-layered glass reactor. 1 mol of diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C. The addition was stopped after 3 hours. The reaction was then kept at this temperature for 6 hours to obtain [EMIM][EtSO4].
[0030] Example 2
[0031] 1.01 mol of N-methylimidazole was placed in a single-mouth double-layered glass reactor. 1 mol of diethyl sulfate was added to the dropping funnel. The mixture was heated to 40°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 40°C and the addition was stopped after 3 hours. The reaction was then kept at this temperature for 6 hours to obtain [EMIM][EtSO4].
[0032] Example 3
[0033] 1.01 mol of N-methylimidazole was placed in a single-mouth double-layered glass reactor. 1 mol of diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C. The addition was stopped after 3 hours. The reaction was then kept at this temperature for 5 hours to obtain [EMIM][EtSO4].
[0034] Example 4
[0035] 1.01 mol of N-methylimidazole was placed in a single-mouth double-layered glass reactor. 1 mol of diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C. The addition was stopped after 3 hours. The reaction was then kept at this temperature for 4 hours to obtain [EMIM][EtSO4].
[0036] Example 5
[0037] 1.01 mol of N-methylimidazole was placed in a single-mouth double-layered glass reactor. 1 mol of diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C and the addition was stopped after 3 hours. The reaction was then kept at this temperature for 3 hours to obtain [EMIM][EtSO4].
[0038] Comparative Example 1
[0039] 1.05 mol N-methylimidazole was placed in a single-mouth double-layered glass reactor, and 1 mol diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C and the addition was stopped after 3 hours. The reaction was then kept at this temperature for 6 hours to obtain [EMIM][EtSO4].
[0040] Comparative Example 2
[0041] 1.03 mol N-methylimidazole was placed in a single-mouth double-layered glass reactor, and 1 mol diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C and the addition was stopped after 3 hours. The reaction was then kept at this temperature for 6 hours to obtain [EMIM][EtSO4].
[0042] Comparative Example 3
[0043] 1.0 mol N-methylimidazole was placed in a single-mouth double-layered glass reactor, and 1 mol diethyl sulfate was added to the dropping funnel. The mixture was heated to 35°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 35°C and the addition was stopped after 3 hours. The reaction was then kept at this temperature for 6 hours to obtain [EMIM][EtSO4].
[0044] Comparative Example 4
[0045] 1.01 mol of N-methylimidazole was placed in a single-mouth double-layered glass reactor. 1 mol of diethyl sulfate was added to the dropping funnel. The mixture was heated to 45°C in a water bath and the diethyl sulfate was added dropwise. As the addition proceeded, the reaction began to exothermic. The water temperature was maintained at 45°C. The addition was stopped after 3 hours. The reaction was then kept at this temperature for 6 hours to obtain [EMIM][EtSO4].
[0046] The [EMIM][EtSO4] of Examples 1-5 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1.
[0047] Table 1. Test results of [EMIM][EtSO4] in the examples and comparative examples.
[0048] As can be seen from Example 1 and Comparative Examples 1-3 in Table 1, as the proportion of N-methylimidazole decreases, the pH value of the product becomes closer to neutral. However, when the molar ratio of N-methylimidazole to diethyl sulfate is less than 1.01:1, the pH value of the product drops rapidly, resulting in unsatisfactory product purity and color.
[0049] As can be seen from Examples 1-5 and Comparative Example 4, when other variables are kept constant, the product quality is relatively stable when the reaction temperature is 35-40℃. However, when the temperature reaches 45℃, the product pH value decreases and the color turns yellow. The heat preservation time of 2-6h has no effect on the product.
[0050] Example 6
[0051] The [EMIM][EtSO4] from Example 5 was placed in a beaker, and twice the mass of deionized water was added and mixed thoroughly. Then, 1 mol of lithium bis(fluorosulfonyl)imide and 200 mL of dichloromethane were added, and the mixture was stirred at room temperature for 4 hours. After standing, the mixture was extracted and separated to obtain the lower organic layer. The organic layer was washed three times with 30 mL of deionized water. Then, the dichloromethane was removed using a rotary evaporator to obtain the [EMIM][FSl] ionic liquid.
[0052] Example 7
[0053] The lithium bisfluorosulfonylimide in Example 6 was replaced with lithium bistrifluoromethanesulfonylimide, and other process conditions were the same as in Example 6, to obtain the [EMIM][TFSl] ionic liquid.
[0054] Example 8
[0055] The lithium difluorosulfonylimide in Example 6 was replaced with potassium hexafluorophosphate, and other process conditions were the same as in Example 6, to obtain the [EMIM][PF6] ionic liquid.
[0056] Example 9
[0057] The lithium difluorosulfonylimide in Example 6 was replaced with sodium hexafluoroantimonate, and other process conditions were the same as in Example 6, to obtain the [EMIM][SbF6] ionic liquid.
[0058] The performance of the ionic liquids in Examples 6-9 was tested. Purity was determined by ion chromatography. In ion chromatography, 1.0 g of sample was dissolved and injected onto an anion exchange column. After separation of the components by the anion exchange column, the sample purity was calculated using the peak area normalization method. The arithmetic mean of two parallel tests (with an absolute difference of no more than 0.3%) was taken as the result. Anion exchange chromatography conditions: KOH eluent concentration 15 mmol / L, flow rate 0.7 mL / min, column temperature 35℃, detector temperature 35℃, injection volume 25 μL. The results are shown in Table 2.
[0059] Table 2 Performance test results of ionic liquids in Examples 6-9
[0060] The conventional methods for synthesizing ionic liquids of ethyl-3-methylimidazolium difluorosulfonylimide ([EMIM][FSl]), 1-ethyl-3-methylimidazolium ditrifluoromethylsulfonylimide ([EMIM][TFSl]), 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]), and 1-ethyl-3-methylimidazolium hexafluoroantimonate ([EMIM][SbF6]) are as follows: 82.1 g of N-methylimidazole was placed in a 500 mL reaction flask at 50 °C, and 130 g of bromoethane was added dropwise over a period of 5 h while maintaining the temperature at 50 °C. After the addition was complete, the mixture was kept at this temperature for 20 h. After the reaction was completed, the pressure was reduced and the excess bromoethane was recovered at 50 °C. The mixture was then transferred to a packaging bag and allowed to crystallize naturally to obtain white crystalline 1-ethyl-3-methylimidazole bromide. 1-Ethyl-3-methylimidazolium bromide was dissolved in twice its mass of deionized water, then 1 mol of lithium difluorosulfonylimide and 200 mL of ethyl acetate were added. The mixture was stirred at room temperature for 4 h, then allowed to stand, extracted, and separated to obtain the upper organic layer. The organic layer was washed three times with 30 mL of deionized water, and then the ethyl acetate was removed using a rotary evaporator to obtain the [EMIM][FSl] ionic liquid. Replacing 1 mol of lithium difluorosulfonylimide with 1 mol of lithium bis(trifluoromethylsulfonylimide) while keeping other process conditions unchanged yielded the [EMIM][TFSl] ionic liquid; replacing 1 mol of lithium difluorosulfonylimide with 1 mol of potassium hexafluorophosphate while keeping other process conditions unchanged yielded the [EMIM][PF6] ionic liquid; and replacing 1 mol of lithium difluorosulfonylimide with 1 mol of sodium hexafluoroantimonate while keeping other process conditions unchanged yielded the [EMIM][SbF6] ionic liquid.
[0061] The yields of [EMIM][FSl] ionic liquids synthesized by conventional methods were 97.5%, [EMIM][TFSl] ionic liquids synthesized by conventional methods were 98%, [EMIM][PF6] ionic liquids synthesized by conventional methods were 97.8%, and [EMIM][SbF6] ionic liquids synthesized by conventional methods were 94.5%. All the liquids synthesized by the above conventional methods contained 50-100 ppm of halogen.
[0062] Figure 3 The ion chromatogram of the [EMIM][TFSl] ionic liquid synthesized in Example 7 is shown below. Figure 4 The ion chromatogram of the [EMIM][FSl] ionic liquid synthesized in Example 6 is shown below. Figure 5 This is the ion chromatogram of the [EMIM][PF6] ionic liquid synthesized in Example 8. Figures 3-5 Ion chromatography showed that no halogens were detected.
[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing a high-purity halogen-free ionic liquid, characterized in that, It includes the following steps: 1) Under nitrogen protection, diethyl sulfate was added dropwise to N-methylimidazolium to obtain a reaction solution; the reaction solution was kept at a constant temperature to obtain 1-ethyl-3-methylimidazolium ethyl sulfate salt; 2) After ion exchange with 1-ethyl-3-methylimidazolium sulfate ethyl ester salt, water, organic salt and dichloromethane, the mixture was extracted and separated. The lower organic layer was then post-treated to obtain a high-purity halogen-free ionic liquid.
2. The preparation method according to claim 1, characterized in that, The molar ratio of N-methylimidazole to diethyl sulfate is 1.01~1.02:
1.
3. The preparation method according to claim 1 or 2, characterized in that, The purity of the diethyl sulfate is ≥99%, and the purity of the N-methylimidazole is ≥99%.
4. The preparation method according to claim 3, characterized in that, During the addition of diethyl sulfate, the temperature of the reaction solution remains constant; the temperature of the reaction solution is 32~40℃, and the addition time is 2~4h.
5. The preparation method according to claim 3, characterized in that, The temperature for the heat preservation reaction is 32~40℃, and the heat preservation reaction time is 2~6h.
6. The preparation method according to claim 4 or 5, characterized in that, The organic salt comprises one or more of KPF6, LiTFSl, LiFSl, and NaSbF6.
7. The preparation method according to claim 6, characterized in that, The molar volume ratio of organic salt to dichloromethane is 1 mol: 150~250 mL; the molar ratio of organic salt to diethyl sulfate is 0.8~1.2: 0.8~1.2; the mass ratio of 1-ethyl-3-methylimidazolium sulfate salt to water is 1:1.5~2.
5.
8. The preparation method according to claim 7, characterized in that, The ion exchange time is 3-5 hours; the post-treatment includes water washing and rotary evaporation, with the number of water washing cycles being 1-5.
9. The high-purity halogen-free ionic liquid prepared by the preparation method according to any one of claims 1 to 8.