A strong alkaline ionic liquid and its preparation method and application

Abstract

This application discloses a strongly basic ionic liquid comprising a cation and an anion; the cation is an amine salt or phosphate cation containing cyclic or linear chains of varying lengths; and the anion is a hydroxyethoxy anion. The strongly basic ionic liquid of this application has adjustable base strength, high thermal stability, strong basicity, and the ability to efficiently catalyze transesterification reactions. It is simple to prepare, highly basic, and exhibits excellent catalytic activity. Furthermore, it has a low catalyst reaction temperature window for catalyzing transesterification reactions.

Description

Technical Field

[0001] The present application relates to a strongly alkaline ionic liquid and a preparation method and application thereof, belonging to the field of chemistry and chemical engineering, specifically to the technical field of ester exchange reaction catalysts. Background Art

[0002] The excessive consumption of fossil energy and the continuous increase in CO2 emissions have caused environmental problems such as global warming and sea level rise. The transesterification of ethylene carbonate (EC), a product of CO2 cycloaddition, with methanol (MeOH) to synthesize DMC (dimethyl carbonate) is a more environmentally friendly and efficient synthesis route compared to other DMC synthesis routes. It realizes the indirect utilization of CO2 and produces ethylene glycol, a bulk raw material for synthesizing polyester fibers, polyester resins and antifreeze. It is also one of the most important methods for industrial production of DMC in the world. The catalysts reported for the transesterification of EC with MeOH to synthesize DMC include alkoxide catalysts, acid catalysts, ion exchange resin catalysts[8], montmorillonite catalysts, metal oxide catalysts and hydrotalcite catalysts. In recent years, ionic liquids (ILs) have been widely used as green and environmentally friendly solvents, catalysts and additives in gas adsorption, organic synthesis and batteries, and have attracted widespread attention in the transesterification of EC and MeOH to produce DMC and EG.

[0003] Ionic liquids (ILs) have special properties such as good thermal stability, solubility, negligible vapor pressure, controllable polarity, and adjustable structure, which enable them to maintain excellent mass transfer performance during the reaction. The ionic liquid catalysts commonly used in transesterification reactions are mainly divided into two categories: homogeneous catalysts and heterogeneous catalysts. Heterogeneous catalysts include heterogeneous ionic liquid catalysts, specifically polyionic liquid catalysts, ionic liquid-supported or supported catalysts. Heterogeneous ionic liquid catalysts have problems such as high reaction temperature, long reaction time, or high catalyst content. The fundamental reason is the low efficiency of heterogeneous catalytic transesterification. Although the catalytic activity of homogeneous ionic liquids is much higher than that of heterogeneous ionic liquid catalysts, homogeneous ionic liquid catalysts have problems such as difficult separation, high separation energy consumption, initiation of product polymerization, and introduction of impurities. Summary of the Invention

[0004] According to one aspect of the present application, a strongly alkaline ionic liquid is provided, which is a "single-headed, double-headed" quaternary ammonium salt and quaternary phosphonium salt new structure strongly alkaline ionic liquid based on the hydroxyethoxy anion of the reaction product ethylene glycol, and has the ability to efficiently catalyze ester exchange reactions.

[0005] This application adopts the following technical solutions:

[0006] A strongly basic ionic liquid comprising cations and anions;

[0007] The cation is an amine salt or phosphonium salt cation containing a cyclic or linear chain of different chain lengths;

[0008] The anion is a hydroxyethoxy anion.

[0009] Optionally, the cation has a structure shown in any one of Formulas I to V:

[0010]

[0011] Wherein, R1, R2, R3, R4, and R5 are independently selected from C1-C6 alkane groups, C2-C6 olefin groups, C6-C 10 At least one of an aromatic hydrocarbon group and a C3-C6 cycloalkyl group;

[0012] Optionally, R1, R2, R3, R4, and R5 are independently selected from one of -CH3, -CH2CH3, -(CH2)2CH3, and -(CH2)3CH3.

[0013] Optionally, the anion has a structure shown in Formula VI:

[0014]

[0015] Optionally, the pH of the strongly alkaline ionic liquid is 9.8-15.0.

[0016] Optionally, the pH of the strongly alkaline ionic liquid is any value among 9.8, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15.0, or any range therebetween.

[0017] According to another aspect of the present application, a method for preparing the above-mentioned strongly basic ionic liquid is provided, comprising the following steps:

[0018] S1, heating and rotary evaporating the raw materials containing ethylene glycol and alkali under reduced pressure to obtain a metal salt containing an oxygen-containing negative anion;

[0019] S2. subjecting a mixture of a metal salt containing oxygen-containing negative anions obtained in step S1, a solvent, and a cation source to a synthesis reaction to obtain a strongly basic ionic liquid.

[0020] Optionally, in step S1, the molar ratio of ethylene glycol to base is 0.9 to 3:1.

[0021] Optionally, in step S1, the molar ratio of ethylene glycol to base is selected from any value of 0.9:1, 1.1:1, 1.4:1, 1.7:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, or any range therebetween.

[0022] Optionally, in step S1, the molar ratio of ethylene glycol to base is 1.9-2.1:1.

[0023] Optionally, in step S1, the base is selected from at least one of sodium hydroxide, potassium hydroxide, cesium hydroxide, and lithium hydroxide.

[0024] Optionally, in step S1, the process of rotary evaporation with reduced pressure heating includes: heating to 50 to 135° C. and then rotary evaporating for 0.5 to 6 hours under an ambient vacuum degree of -0.1 to -0.08 Pa.

[0025] Optionally, in step S1, the reduced-pressure heating rotary evaporation process includes: heating to 50-60°C, 100-110°C, and 130-135°C in sequence under an ambient vacuum degree of -0.1 to -0.08 Pa, and rotary evaporating for 0.5 to 2 hours respectively.

[0026] In this process, during the reaction between the anion source and the base, the by-product water generated by the reaction is separated from the reaction system at the same time.

[0027] Optionally, step S1 further includes purification, and the purification process includes:

[0028] S11, adding petroleum ether in an amount of 2 to 5 times the weight of the product to the reaction product, heating to 60 to 100° C., and keeping warm until the petroleum ether is completely volatilized;

[0029] S22: Repeat the process of step S11 3 to 5 times.

[0030] Optionally, the step S1 further comprises adding a water-carrying agent during the reduced-pressure heating rotary evaporation process.

[0031] Optionally, the water-carrying agent is selected from at least one of cyclohexane, benzene, toluene and xylene.

[0032] Optionally, in step S1, the prepared metal salt containing oxygen-containing negative anions is an anion K salt.

[0033] Optionally, step S1 further comprises adding a storage solution of 2 to 5 times the weight of the prepared metal salt containing oxygen-containing negative anions to the prepared metal salt containing oxygen-containing negative anions.

[0034] Optionally, the storage solution is selected from at least one of methanol, ethanol, acetonitrile, ethyl acetate, acetone, benzene, toluene, and xylene.

[0035] The purpose of using the above storage solution is to store the product of step S1 at room temperature.

[0036] Optionally, in step S2, the molar ratio of the metal salt containing oxygen-containing negative anions, the solvent, and the cation source is 1:(1-3):(0.8-1.2).

[0037] Optionally, in step S2, the solvent is selected from at least one of methanol, ethanol, acetonitrile, ethyl acetate, acetone, benzene, toluene, and xylene.

[0038] Optionally, in step S2, the cation source is selected from at least one of tetraethylammonium bromide, tetrabutylammonium bromide, tetrabutylphosphonium bromide, 1-butyl-3-methylimidazolium salt, 1-ethyl-3-methylimidazolium salt, N-methylmorpholinium bromide, benzimidazole bromide, two-headed imidazole bromide, and two-headed benzimidazole bromide;

[0039] Optionally, in step S2, the conditions of the synthesis reaction are: reaction temperature of 20 to 30° C., and reaction time of 8 to 24 h.

[0040] Optionally, the step S2 further comprises filtering and rotary evaporating at 50-70° C. for 2.5-3.5 hours after the synthesis reaction is completed to obtain the high-purity strongly alkaline ionic liquid.

[0041] According to another aspect of the present application, there is provided a use of the above-mentioned strongly basic ionic liquid, or the strongly basic ionic liquid prepared by the above-mentioned preparation method, as a homogeneous catalyst for transesterification reaction.

[0042] Optionally, the catalyst reaction temperature window is 20-110°C.

[0043] Optionally, in the application, the strong alkaline ionic liquid is a hydroxyethoxy strong alkaline ionic liquid.

[0044] Optionally, in the application, the transesterification reaction is to catalyze the transesterification of ethylene carbonate and alcohol to synthesize DMC.

[0045] Optionally, the application is the use of the strongly basic ionic liquid [TBAB]OCH2CH2OH as a homogeneous catalyst for catalyzing the transesterification reaction of ethylene carbonate and alcohol to synthesize DMC.

[0046] In this application, C1 to C6 refers to the number of carbon atoms contained. For example, "C1 to C6 alkane group" refers to an alkane group containing 1 to 6 carbon atoms.

[0047] In this application, "alkane group" is a group formed by losing any hydrogen atom from an alkane compound molecule. The alkane compound includes straight-chain alkanes, branched-chain alkanes, cycloalkanes, and branched cycloalkanes.

[0048] In the present application, an "alkene group" is a group formed by losing any hydrogen atom from an alkene compound molecule.

[0049] In the present application, an "aromatic hydrocarbon group" is a group formed by losing a hydrogen atom from the aromatic ring of an aromatic compound.

[0050] In the present application, "cycloalkyl" refers to a group formed by losing a hydrogen atom from a cycloalkane molecule.

[0051] The beneficial effects of this application include:

[0052] The strong alkaline ionic liquid provided in the present application has an active center of an ethanol oxygen anion with affinity, and an oxygen anion of alcohols with different chain lengths; the cation is a cyclic or linear amine or phosphonium salt with different chain lengths containing nitrogen and phosphorus atoms. The strong alkaline ionic liquid of the present application has adjustable base strength, high thermal stability, strong alkalinity, and the ability to efficiently catalyze transesterification reactions. It is simple to prepare, has strong alkalinity, and has excellent catalytic activity. It also has a low catalyst reaction temperature window range in the catalytic transesterification reaction. In particular, in the catalytic transesterification reaction of ethylene carbonate and methanol, it has excellent catalytic performance. Using a tetrabutylethylene glycol ammonium oxyhydroxide catalyst with a molar content of ethylene carbonate of 0.18%, the DMC yield is 42.8%, and the TOF value is as high as 2853.6h. -1 The strong alkaline ionic liquid of the present application has a strong ability to open the ring of ethylene carbonate and transesterify with methanol as a catalyst, and therefore has important industrial application value in the field of carbonate chemical synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the synthesis process of potassium dialkoxide (EGK) in Example 1 of the present application;

[0054] Figure 2 Schematic diagram of the synthesis process of [TBAB]OCH2CH2OH in Example 1 of the present application;

[0055] Figure 3 H of [TBAB]OCH2CH2O prepared in Example 1 of the present application 1 H NMR spectrum;

[0056] Figure 4 [TBAB]OCH2CH2OH prepared in Example 1 of the present application 13 C NMR spectrum;

[0057] Figure 5 FT-IR spectra of EGK, TBAB, and [TBAB]OCH2CH2OH during the preparation process of Example 1 of the present application;

[0058] Figure 6FT-IR spectra of the strongly alkaline ionic liquids prepared in Examples 2 to 9 of the present application, wherein (a) [TEAB] OCH2CH2OH, (b) [P 4444 ]OCH2CH2OH,(c)[Emim]OCH2CH2OH,(d)[Bmim]OCH2CH2OH,(e)[Nbmm]OCH2CH2OH,(f)[C4Ben Im]OCH2CH2OH,(g)HOCH2CH2O[C4(Mim)2]OCH2CH2OH,(h)HOCH2CH2O[C4(BenIM)2]OCH2CH2O;

[0059] Figure 7 A comparison chart showing the effects of different reaction temperatures on the DMC synthesis reaction by carbonate transfusion when [TBAB]OCH2CH2OH prepared in Example 1 of the present application is used as a catalyst;

[0060] Figure 8 This is a comparison chart of the effects of different structural alcohols on the transesterification reaction when [TBAB]OCH2CH2OH prepared in Example 1 of the present application is used as a catalyst.

[0061] Figure 9 [TBAB]OCH2CH2OH, [TEAB]OCH2CH2OH, [P 4444 ]OCH2CH2OH, [Emim]OCH2CH2OH, [Bmim]OCH2CH2OH, [Nbmm]OCH2CH2OH, [C4BenIm]OCH2CH2OH, HOCH2CH2O[C4(Mim)2]OCH2CH2OH, and HOCH2CH2O[C4(BenIM)2]OCH2CH2OH as catalysts, showing a comparison of their effects on the transesterification reaction of EC and MeOH to synthesize DMC. DETAILED DESCRIPTION

[0062] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0063] Unless otherwise specified, the raw materials and catalysts in the examples of this application were purchased from commercial sources.

[0064] In the examples of the present application, the base strength analysis, base amount calculation, nuclear magnetic resonance (H) spectrum analysis, nuclear magnetic resonance (C) spectrum analysis (Ascend III 500 MHz liquid-solid dual-purpose nuclear magnetic resonance instrument, Bruker, Switzerland) and infrared spectrum analysis (IRTracer-100 Fourier transform infrared spectrometer, Shimadzu, Japan) characterization analysis are all routine operations, and those skilled in the art can operate according to the instrument instructions.

[0065] In this application, "EGK" refers to ethylene glycol potassium.

[0066] In this application, "[TBAB]OCH2CH2OH" refers to tetrabutylammonium glycolate.

[0067] As used herein, "EC" refers to ethylene carbonate.

[0068] In this application, "MeOH" refers to methanol.

[0069] As used herein, "DMC" refers to dimethyl carbonate.

[0070] In this application, "EG" refers to diol.

[0071] The conversion rate, selectivity and yield in the examples of this application are calculated as follows:

[0072] The calculation methods of EC conversion, product selectivity and DEC yield are as follows:

[0073]

[0074]

[0075]

[0076]

[0077] Y / %=100×X×S a

[0078]

[0079]

[0080] Where: X is the conversion rate of ethylene carbonate; S a is the selectivity for dimethyl carbonate; S b Selectivity for hydroxyethyl methyl carbonate; S c is the selectivity of dihydroxyethyl carbonate; Y is the yield of dimethyl carbonate; n a is the amount of dimethyl carbonate; n b For hydroxyethyl methyl carbonate substances; n c is the amount of dihydroxyethyl carbonate; n d is the amount of unreacted ethylene carbonate. t is the reaction time, h; n EC is the molar amount of DMC; n cat is the molar amount of catalyst active sites, mol.

[0081] Example 1 Preparation of strongly basic ionic liquid

[0082] (1) As attached Figure 1 As shown in the steps, the synthesis of potassium ethylene glycol (EGK): add ethylene glycol (EG) solution (2 mol, 124.14 g) to a 500 mL beaker, add crushed potassium hydroxide (KOH) powder (1 mol, 56.11 g) to the ethylene glycol solution, and use a glass rod to stir the KOH powder until it is completely dissolved. Then perform rotary evaporation, maintain for 30 minutes under the conditions of an initial temperature of 50°C, a rotation speed of 50r / min, and a vacuum degree of -0.1Mpa; then raise the temperature to 110°C and maintain for 60 minutes; then maintain at 135°C for 2 hours; finally, add a MeOH solution with a mass twice that of the obtained sample, mix evenly, and store at room temperature. This process is to separate the by-product water generated by the reaction of potassium hydroxide and ethylene glycol from the reaction system to obtain EG and EGK catalysts with a molar ratio of about 1:1. The synthesis process is as follows Figure 1 shown.

[0083] (2) As attached Figure 2 As shown in the steps, according to the principle of acid-base titration, the base amount of EGK is calculated to be 5.34 mmol / g, 32.24 g of tetrabutylammonium bromide (0.1 mol) is weighed and dissolved in 50 g of methanol solution, and then an equal molar amount of EGK (18.73 g) is added thereto; stirred at room temperature for 24 hours, filtered; the filtrate is rotary evaporated at 60 ° C for 3 hours to obtain the desired ionic liquid. The synthesis process is as follows Figure 2 shown.

[0084] Examples 2-9 Series of Hydroxyethoxy Strongly Alkaline Ionic Liquids

[0085] The preparation method is the same as that in Example 1, except that the cationic structure is different. The strong alkaline ionic liquids prepared in Examples 2 to 9 are [TEAB]OCH2CH2OH, [P4444]OCH2CH2OH, [Emim]OCH2CH2OH, [Bmim]OCH2CH2OH, [Nbmm]OCH2CH2OH, [C4BenIm]OCH2CH2OH, HOCH2CH2O[C4(Mim)2]OCH2CH2OH, and HOCH2CH2O[C4(BenIM)2]OCH2CH2OH, respectively.

[0086] The structural formulas, chemical formulas and raw materials of the ionic liquids prepared in Examples 1 to 9 are shown in Table 1.

[0087] Table 1 Ionic liquids prepared in Examples 1 to 9

[0088]

[0089]

[0090] Test Example 1

[0091] The base strength and base weight of the strongly basic ionic liquids prepared in Examples 1 to 9 were determined using Hammett indicator and acid-base titration, respectively. The base strength of the catalysts ranged from 9.8 to 15.0, which is comparable to that of sodium methoxide. This indicates that the base strength of the synthesized ionic liquids is affected by the anion and has little to do with the cationic structure. The base weight results were 2.09, 2.27, 1.82, 2.43, 2.38, 1.78, 1.32, 2.27, and 1.29 mmol / g, respectively. It was found that as the catalyst side chain length (molecular weight) increased, the molar weight of base per unit mass decreased. Ionic liquids containing imidazole rings had higher base weights than linear ionic liquids, while catalysts with imidazole-linked benzene rings had lower base weights than linear catalysts. Catalysts containing two imidazole rings had lower base weights than catalysts with a single imidazole ring or imidazole-linked benzene rings. Under the same structural conditions, quaternary ammonium salt catalysts had higher base weights than quaternary phosphonium catalysts.

[0092] Test Example 2

[0093] [TBAB]OCH2CH2OH prepared in Example 1 was subjected to 1 H NMR nuclear magnetic detection, the results are as attached Figure 3 As shown, 1 The HNMR spectrum shows that [TBAB]OCH2CH2OH has obvious resonance peaks at 2.4, 1.7, 0.8, 0.6 and 0.2 ppm, among which the peak at 2.4 ppm ( Figure 3 The peak appearing at positions 4 and 7 is attributed to the stretching vibration peak of the hydrogen connected to the carbon atom closest to the nitrogen atom and the hydrogen on the hydroxyl group in the ethylene glycol oxygen anion; the peak appearing at 1.7 ppm (shown in positions 5 and 6) is attributed to the stretching vibration peak of the hydrogen connected to the two carbon atoms in the ethylene glycol oxygen anion; 0.6 and 0.2 ppm (shown in positions 2 and 3) are attributed to the peak positions of the hydrogen atoms on the remaining two methylene groups in the quaternary ammonium cation chain; 0.8 ppm (position 1) is attributed to the peak position of the hydrogen connected to the terminal carbon atom in the quaternary ammonium cation chain.

[0094] Test Example 3

[0095] [TBAB]OCH2CH2OH prepared in Example 1 was subjected to 13 C NMR nuclear magnetic test, the results are as attached Figure 4 As shown, 13 In the CNMR spectrum, six obvious resonance peaks of [TBAB]OCH2CH2OH were observed at 77.3, 63.9, 58.9, 24.1, 19.7 and 13.7 ppm, of which 77.3 ppm and 63.9 ppm were attributed to the peak positions of the two carbon atoms C5 and C6 in the ethylene glycol oxygen anion liquid; 58.9 ppm was attributed to the peak position of the carbon atom (C4) closest to the nitrogen atom ( Figure 44); 24.1ppm and 19.7ppm are attributed to the peak positions of the two carbon atoms C2 and C3 in the quaternary ammonium cation chain; 13.7ppm is attributed to the peak position of the terminal carbon atom (C1) in the quaternary ammonium cation chain ( Figure 4 Position 1).

[0096] Test Example 4

[0097] The FT-IR spectra of EGK, TBAB and [TBAB]OCH2CH2OH prepared in Example 1 were tested. The results are shown in the attached figure. Figure 5 As shown, the characteristic functional group spectra of potassium ethylene glycolate (EGK), tetrabutylammonium bromide (TBAB), and tetrabutylammonium glycolate ([TBAB]OCH2CH2OH) are compared. Figure 5 As shown in a, EGK has the peaks at 3358, 1653, 1380, 1296, 1091, 1043 and 885 cm -1 There are obvious characteristic peaks at 3358 and 1296 cm -1 1653 cm-1 is the stretching vibration and in-plane bending vibration peak of the OH bond in EGK; -1 The absorption peak at 1380cm is the bending vibration peak of the HOH bond of water, which can be confirmed by the TG-DTA diagram; -1 The absorption peaks at 1091 and 1043 cm are attributed to the symmetrical bending vibration peaks of the CH bond in the methylene group; -1 The absorption peak at 885cm is attributed to the two CO bond stretching vibration peaks in EGK; -1 The absorption peak at is attributed to the CC bond skeleton vibration peak. Figure 5 b is the FT-IR spectrum of TBAB, with the wavelengths at 2958, 2874, and 1473 cm -1 There are obvious functional group characteristic peaks at 2958 and 2874 cm -1 The wavenumbers at 1473 cm are attributed to the symmetric and asymmetric stretching vibrations of the CH bond; -1 The peak at 37° is attributed to the asymmetric bending vibration of the CH bond of the methyl group in TBAB. Figure 5 c also observed Figure 5 a and Figure 5 b shows the characteristic functional group peak, which proves that the glycoloxy anion has successfully replaced the bromide anion and combined with the quaternary ammonium salt in the form of an ionic bond.

[0098] Test Example 5

[0099] The FT-IR spectra of the strong alkaline ionic liquids prepared in Examples 1 to 9 were compared and the results are shown in the attached figure. Figure 6There are obvious characteristic peaks at 3483, 2949, 2854, 1653, 1456, 1296, 1097, 1033, 885 and 754 cm-1, among which the wavenumbers are located at 3358 and 1296 cm-1. -1 The stretching vibration and in-plane bending vibration peaks of the OH bond; 2949 and 2854 cm -1 The wavenumbers at 1653 cm are attributed to the symmetric and asymmetric stretching vibrations of the CH bond; -1 The absorption peak at 1456 cm is the bending vibration peak of the HOH bond of water; -1 The peaks at 1097 and 1033 cm are attributed to the asymmetric bending vibration of the CH bond; -1 The absorption peak at 885cm is attributed to the CO bond stretching vibration peak; -1 The absorption peak at 754cm is attributed to the vibration peak of CC bond skeleton; -1 The absorption peak at is the CH out-of-plane bending vibration.

[0100] Test Example 6

[0101] As attached Figure 7 As shown, using [TBAB]OCH2CH2OH prepared in Example 1 as the catalyst, the effects of different reaction temperatures on the DMC synthesis reaction by carbonate transesterification were investigated. The reaction conditions were an EC / MeOH molar ratio of 1 / 10, a reaction time of 5 to 240 minutes, and a catalyst loading of 0.18% of the EC molar weight. At 20°C, the DMC yield reached 35.35% after 30 minutes of reaction, with a TON value of 196.4. This indicates that the [TBAB]OCH2CH2OH catalyst exhibits high activity at lower temperatures, promoting EC ring opening and transesterification with MeOH. When the reaction temperature was raised to 30°C, the DMC yield reached 45.89%, and the TON value increased to 254.9. Further increases in temperature to 40 and 50°C resulted in a continued increase in DMC yield, with TON values ​​increasing to 359.8 and 408.4, respectively. However, at the azeotropic temperature (68°C), the DMC yield and TON value did not change significantly. The results showed that the synthesized catalyst had excellent catalytic EC ring-opening and ester exchange ability with MeOH. As the reaction temperature increased, the catalytic efficiency increased significantly.

[0102] Test Example 7

[0103] The results of the synthesized catalyst [TBAB]OCH2CH2OH used in the transesterification reaction between EC and different alcohols are shown in the attached figure. Figure 8As shown, the selected alcohols included linear methanol, ethanol, n-propanol, and n-butanol, as well as branched isopropanol, isobutanol, and tert-butanol. The molar ratio of EC to these different alcohols was 1 / 10, the catalyst content was 0.18% of the molar weight of EC, the reaction time was 60 min, and the reaction temperature was 68°C. When transesterifying with methanol, the EC conversion and DMC yield were 84.4% and 83.4%, respectively; with ethanol, the EC conversion and DMC yield were 21.4% and 18.2%, respectively; with n-propanol, the EC conversion and DMC yield were 17.9% and 10.9%, respectively; and with n-butanol, the EC conversion and DMC yield were 12.2% and 7.8%, respectively. These results demonstrate that [TBAB]OCH2CH2OH catalyzes the transesterification of EC with C1-C4 normal alcohols to a certain extent, but the EC conversion and the yield of the target carbonate decrease with increasing carbon chain length. The effects of C3 and C4 isomeric alcohols were also investigated. The yield of diisopropyl carbonate was only 1.0%, while the yields of diisobutyl carbonate and di-tert-butyl carbonate were 1.1% and 0.4%, respectively. These results indicate that the catalytic activity decreases significantly with increasing the number of branches in alcohols with the same carbon number. Based on our understanding of the mechanism of the transcarbonate reaction, the primary reason for this phenomenon is that the isomeric alcohol oxyanion, after strong base activation, has a weaker electronegativity and affinity than the normal alcohol oxyanion, making it more difficult for the isomeric alcohols to be activated by the glycol oxyanion than the normal alcohol. Furthermore, the generated isomeric alcohol oxyanion is less likely to abstract hydrogen from ethylene glycol to form the corresponding isomeric alcohol. A secondary reason is the steric hindrance of the isomeric alcohol oxyanion, which makes it relatively difficult for the nucleophilic attack on EC to form the corresponding isomeric alcohol. In summary, the activity of [TBAB]OCH2CH2OH in the transesterification of C1-C4 normal alcohols and the specificity of EC in the transesterification reaction with different alcohol structures are demonstrated.

[0104] Test Example 8

[0105] As attached Figure 9As shown, the effects of [TBAB]OCH2CH2OH, [TEAB]OCH2CH2OH, [P4444]OCH2CH2OH, [Emim]OCH2CH2OH, [Bmim]OCH2CH2OH, [Nbmm]OCH2CH2OH, [C4BenIm]OCH2CH2OH, HOCH2CH2O[C4(Mim)2]OCH2CH2OH, and HOCH2CH2O[C4(BenIM)2]OCH2CH2OH prepared in Examples 1 to 9 as catalysts on the transesterification reaction of EC and MeOH to synthesize DMC were investigated. The reaction conditions were an EC / MeOH molar ratio of 1 / 10, a reaction temperature of 50°C, a reaction time of 30 min, and a catalyst addition amount of 0.18% of the EC molar amount. When [TBAB]OCH2CH2OH was used as the ionic liquid catalyst, the EC conversion rate was 75.3%, the DMC yield was 73.5%, and the TOF was 816.7 h. -1 . When the anion of the ionic liquid catalyst remains unchanged, the EC conversion rate, DMC yield and TOF value do not change significantly when the chain length of the cation becomes shorter; there is no significant difference in the catalytic effect between the ionic liquid catalyst with a straight chain cation and the cation with an imidazole ring; there is no significant difference in the catalytic effect between the ionic liquid catalyst containing an imidazole ring and a benzene ring in the cation and the ionic liquid catalyst containing only an imidazole ring; the catalytic effect of the ionic liquid catalyst with a quaternary phosphonium catalyst is not significantly different from that of the quaternary ammonium salt catalyst. The experimental results show that the ionic liquid with an ethylene glycol anion has a comparable ability to catalyze the conversion of EC to DMC, indicating that the structure of the cation in the catalyst has a weak effect on the conversion of EC to DMC.

[0106] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for using a strongly basic ionic liquid as a homogeneous catalyst for transesterification, characterized in that: The transesterification reaction is to catalyze the transesterification of ethylene carbonate and alcohol to synthesize DMC; The strong alkaline ionic liquid includes cations and anions The cation has a structure shown in any one of Formulas I to V: Wherein, R1, R2, R3, R4, and R5 are independently selected from C1-C6 alkane groups, C2-C6 olefin groups, C6-C 10 At least one of an aromatic hydrocarbon group and a C3-C6 cycloalkyl group; The anion is a hydroxyethoxy anion.

2. The use according to claim 1, characterized in that In the structure of the cation, R1, R2, R3, R4, and R5 are independently selected from one of -CH3, -CH2CH3, -(CH2)2CH3, and -(CH2)3CH3.

3. The use according to claim 1, characterized in that The anion has the structure shown in Formula VI:

4. The use according to claim 1, characterized in that The pH of the strongly alkaline ionic liquid is 9.8-15.

0.

5. The use according to claim 1, characterized in that, The preparation method of the strongly basic ionic liquid comprises the following steps: S1, heating and rotary evaporating the raw materials containing ethylene glycol and alkali under reduced pressure to obtain a metal salt containing an oxygen-containing negative anion; S2. subjecting a mixture of a metal salt containing oxygen-containing negative anions obtained in step S1, a solvent, and a cation source to a synthesis reaction to obtain a strongly basic ionic liquid.

6. The use according to claim 5, characterized in that In the step S1, the molar ratio of ethylene glycol to base is 0.9 to 3:

1.

7. The use according to claim 5, characterized in that In step S1, the base is selected from at least one of sodium hydroxide, potassium hydroxide, cesium hydroxide, and lithium hydroxide.

8. The use according to claim 5, characterized in that In the step S1, the reduced pressure heating rotary evaporation process includes: heating to 50 to 135° C. under an ambient vacuum degree of -0.1 to -0.08 Pa and then rotary evaporating for 0.5 to 6 hours.

9. The use according to claim 5, characterized in that In step S1, the reduced-pressure heating rotary evaporation process includes: heating to 50-60° C., 100-110° C., and 130-135° C. in sequence under an ambient vacuum degree of -0.1 to -0.08 Pa, and rotary evaporating for 0.5 to 2 hours respectively.

10. The use according to claim 5, characterized in that The step S1 also includes purification, and the purification process includes: S11, adding petroleum ether in an amount of 2 to 5 times the weight of the product to the reaction product, heating to 60 to 100° C., and keeping warm until the petroleum ether is completely volatilized; S22: Repeat the process of step S11 3 to 5 times.

11. The use according to claim 5, characterized in that The step S1 further includes adding a water-carrying agent during the reduced-pressure heating rotary evaporation process.

12. The use according to claim 11, characterized in that The water-carrying agent is selected from at least one of cyclohexane, benzene, toluene and xylene.

13. The use according to claim 5, characterized in that In step S2, the molar ratio of the metal salt containing oxygen-containing negative anions, the solvent, and the cation source is 1:(1-3):(0.8-1.2).

14. The use according to claim 5, characterized in that In step S2, the solvent is selected from at least one of methanol, ethanol, acetonitrile, ethyl acetate, acetone, benzene, toluene, and xylene.

15. The use according to claim 5, characterized in that In step S2, the cation source is selected from at least one of tetraethylammonium bromide, tetrabutylammonium bromide, tetrabutylphosphonium bromide, 1-butyl-3-methylimidazolium salt, 1-ethyl-3-methylimidazolium salt, N-methylmorpholinium bromide, benzimidazole bromide, double-headed imidazole bromide, and double-headed benzimidazole bromide.

16. The use according to claim 5, characterized in that In step S2, the conditions of the synthesis reaction are: reaction temperature of 20 to 30° C., and reaction time of 8 to 24 hours.

17. The use according to claim 1, characterized in that The catalyst reaction temperature window is 20-110°C.

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