Quaternary ammonium base ionic liquid, preparation method thereof and method for synthesizing methyl ethyl carbonate

Abstract

The invention belongs to the technical field of catalysts. The invention provides quaternary ammonium base ionic liquid with a structure as shown in a formula (I). The method can be used for synthesis processes of synthesizing methyl ethyl carbonate from dimethyl carbonate and diethyl carbonate and synthesizing methyl ethyl carbonate from dimethyl carbonate and ethanol, and the synthesized methyl ethyl carbonate has excellent purity. Besides, the used quaternary ammonium base ionic liquid has the advantages of being easy to prepare, low in toxicity and renewable, the problems that a traditional sodium alcoholate catalyst is easy to cake and inactivate and difficult to reuse are solved, and the method has important significance for promoting green and efficient production of methyl ethyl carbonate.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to quaternary ammonium ionic liquids, their preparation methods, and methods for synthesizing methyl ethyl carbonate. Background Technology

[0002] Energy is the material foundation for human survival and development, holding a vital strategic position in the national economy. Electrochemical energy storage technology, represented by lithium-ion batteries, is a key technology for the transformation and upgrading of my country's energy industry structure and the achievement of "carbon neutrality" goals in the new era. Lithium-ion batteries mainly consist of a positive electrode, a negative electrode, an electrolyte, and a separator. Ethyl methyl carbonate (EMC) is an environmentally friendly asymmetric carbonate. Due to its structure containing methyl, ethyl, carbonyl, methoxy, and ethoxy groups, it is chemically highly reactive and often used as an intermediate in organic synthesis. Furthermore, its strong solubility in lithium salts and its safety and stability extend battery life, making it the most widely used solvent in lithium-ion battery electrolytes, accounting for approximately 30-35% of the electrolyte composition. Therefore, researching the preparation process of EMC has significant economic and social implications for promoting the large-scale utilization of new energy sources.

[0003] Currently reported methods for synthesizing methyl ethyl carbonate (EMC) mainly fall into three categories: the phosgene method, the oxidative carbonyl method, and the transesterification method. The phosgene method uses carbonyl chloride and alcohols as raw materials to produce EMC under the action of a catalyst. However, this method is gradually being phased out in industry due to its high separation costs, the generation of toxic substances during the reaction, and the corrosive effect of HCl produced. The oxidative carbonyl method uses methanol, ethanol, carbon monoxide, and oxygen as raw materials to catalytically synthesize EMC under high temperature and pressure. This method suffers from harsh reaction conditions, high production costs, complex reaction control, numerous byproducts, and difficult separation, and is also gradually being phased out. The transesterification method for synthesizing EMC has a series of advantages, including mild reaction conditions, environmental friendliness, and high selectivity for target products, making it the main method for industrial EMC preparation. Current reports on the transesterification method for EMC synthesis mainly focus on the alcohol transesterification reaction of dimethyl carbonate and ethanol, and the transesterification reaction of dimethyl carbonate and diethyl carbonate.

[0004] (1) Transesterification reaction of dimethyl carbonate and ethanol

[0005] The transesterification reaction of dimethyl carbonate and ethanol to synthesize EMC has advantages such as low raw material cost, no pollution, and mild reaction conditions. However, this method requires timely separation of the byproduct CH3OH generated during the reaction to propagate the reaction in the forward direction and improve the yield of EMC. Furthermore, when the reactant C2H5OH is in excess, side reactions may occur along this reaction pathway. The specific reaction equations are as follows:

[0006]

[0007] Side reactions:

[0008]

[0009] Shi Lei et al. used sodium ethoxide as a catalyst, with a catalyst dosage of 0.15 w mol When the feed ratio is 1:1, the reaction temperature is 50℃, and the reaction time is 0.5 h, the yield of EMC can reach 45.0%. Zielinska-Nadolska et al. used ion exchange resin as a catalyst and found that the DMC conversion rate was 54% and the EMC yield was 53% under the following conditions: n(DMC):n(EtOH) = 1:2, reaction temperature 75 ℃, reaction time 26.7 h, and catalyst dosage 6.75 wt%.

[0010] Because lithium-ion battery electrolytes have stringent requirements regarding the content of methanol and ethanol, the EMC purity of the reactants must be high. The presence of three binary azeotropes in this alcohol-ester reaction system significantly increases the difficulty of subsequent separation. Furthermore, this alcohol-ester reaction system generates a byproduct, DEC, but the current market demand for DEC is relatively low; therefore, how to handle this byproduct is also a problem that needs to be considered in this process.

[0011] (2) Transesterification reaction of dimethyl carbonate and diethyl carbonate

[0012] In recent years, researchers have discovered a promising new method for synthesizing EMC through the transesterification reaction of DMC and DEC. This method offers advantages such as mild reaction conditions and being environmentally friendly and pollution-free. Furthermore, the reactants DMC and DEC can serve as excellent solvents for lithium-ion battery electrolytes. Therefore, the reactants can be used directly without further separation, demonstrating broad application prospects. The specific reaction equation is as follows:

[0013]

[0014] However, the transesterification reaction between DMC and DEC is a reversible reaction with a low equilibrium constant, resulting in a slow reaction rate. Traditional catalysts struggle to achieve high EMC yields, making the development of a highly efficient and environmentally friendly catalyst crucial. Catalysts for the transesterification reaction of DEC and DMC have been reported to fall into two categories: homogeneous and heterogeneous catalysts. Mei et al. studied the transesterification reaction of DMC and ethanol using different nitrate catalysts, achieving a DMC conversion of 86.5% with La(NO3)3 as the catalyst. Zhuo Guanglan et al. used titanates and organotin compounds as catalysts, achieving DEC conversions of 43.1% and 41.7% respectively when n(DMC):n(DEC) = 1:1, catalyst dosage 2.5 wt%, reaction temperature 103 ℃, and reaction time 3 h. While the heterogeneous catalysts reported for the transesterification reaction of DMC and DEC exhibit certain catalytic activity, they suffer from low reaction efficiency, poor stability, and side reactions. Therefore, the development of novel, highly efficient, and stable catalysts is necessary.

[0015] Ionic liquids are a class of substances composed entirely of ions, including organic cations and organic or inorganic anions. Unlike common ionic compounds, ionic liquids are liquid at room temperature, hence they are also known as room-temperature molten salts. Compared to traditional salts and organic solvents, ionic liquids have several significant advantages: 1) a wide liquid temperature range and excellent thermal stability; 2) extremely low vapor pressure and almost non-volatile properties, effectively avoiding material loss and environmental pollution caused by volatilization during use; 3) strong dissolving power, capable of dissolving a variety of organic and inorganic substances; and 4) flexible structural design, allowing for targeted construction according to specific application requirements. Based on these characteristics, ionic liquids have been widely used in separation processes, electrochemical applications, and catalytic reactions, among other fields.

[0016] Currently, various ionic liquids have been developed for the synthesis of methyl ethyl carbonate. Patent (CN 115521204A) discloses the simultaneous synthesis of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate using ethylene carbonate, methanol, and ethanol as raw materials and metal imidazole ionic liquids as catalysts. Patent (CN 114210365A) discloses a method for catalytically synthesizing methyl ethyl carbonate and diethyl carbonate using alkaline ionic liquid catalysts. Although the above ionic liquids have shown good catalytic effects in the synthesis of methyl ethyl carbonate, most of them are metal-based imidazole ionic liquids, which have disadvantages such as poor stability, the need for strict anhydrous and oxygen-free operation, certain corrosiveness, complex synthesis process and high production cost, environmental unfriendliness, and high toxicity.

[0017] Therefore, suitable catalysts need to be developed for the synthesis of methyl ethyl carbonate. Summary of the Invention

[0018] In view of this, the technical problem provided by the present invention is to provide a quaternary ammonium base ionic liquid. The catalyst provided by the present invention has the advantages of being easy to prepare, low in toxicity, and regenerable. It can be used simultaneously in the synthesis processes of dimethyl carbonate and diethyl carbonate to synthesize methyl ethyl carbonate, and dimethyl carbonate and ethanol to synthesize methyl ethyl carbonate, with high yield and high catalytic activity.

[0019] This invention provides a quaternary ammonium ionic liquid with the structure of formula (I):

[0020]

[0021] Wherein, R1, R2, R3 and R4 are independently selected from substituted or unsubstituted C1-C5 alkyl groups; preferably C1-C4 alkyl groups; the substituent of the substituted alkyl group is phenyl;

[0022] R1, R2, R3, and R4 may be the same or different, and the alkyl groups of C1 to C5 may be methyl, ethyl, propyl, butyl, or pentyl.

[0023] In one preferred embodiment of the present invention, the specific structure is as follows:

[0024]

[0025] This invention creatively invented a quaternary ammonium base ionic liquid with the above-mentioned specific structure, and its use as a catalyst for the synthesis of ethyl methyl carbonate has superior technical effects compared with ionic liquids with other structures.

[0026] The core of this invention lies in providing a highly efficient catalyst for the synthesis of ethyl methyl carbonate. In this field and in this application, the yield of the target product is the most direct and comprehensive industrial indicator for evaluating the effectiveness of a catalyst. This application specification has fully disclosed key performance data: under uniform reaction conditions optimized through preliminary experiments, a parallel comparison of five catalysts showed that the [TEA][IM] structure significantly improved the yield of ethyl methyl carbonate.

[0027] The method for preparing the catalyst provided by the present invention includes the following steps:

[0028] The product is obtained by dissolving one of the quaternary ammonium bases or quaternary ammonium salts with imidazole in a solvent and reacting the mixture.

[0029] In a preferred embodiment of the present invention, the method for preparing the catalyst includes:

[0030] The quaternary ammonium base and imidazole are dissolved in methanol, reacted, and the methanol is evaporated before washing with a non-polar solvent to obtain the final product.

[0031] The quaternary ammonium base described in this invention is one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide;

[0032] The reaction temperature is 30~60 ℃, specifically 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃; or any value between the two mentioned above.

[0033] The reaction time is 1 to 24 hours; specifically, it can be 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, 11 hours, 13 hours, 15 hours, 17 hours, 19 hours, 21 hours, 23 hours, or 24 hours.

[0034] The molar ratio of quaternary ammonium base to imidazole is 0.9:1 to 1.5:1; specifically, it can be 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1, or any value within the range of the two mentioned above.

[0035] The molar ratio of methanol to quaternary ammonium base is 10 to 100:1; specifically, it can be 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1; or any value within the range of the above two.

[0036] The present invention does not limit the specific operation of the washing with the non-polar solvent, and any operation well known to those skilled in the art is acceptable. The non-polar solvent mentioned in the present invention is one of n-hexane, benzene, carbon tetrachloride, and dichloroethane.

[0037] The final results are such as [TMA][IM], [TEA][IM], [TPA][IM], and [TBA][IM].

[0038] In a preferred embodiment of the present invention, the method for preparing the catalyst includes:

[0039] The quaternary ammonium salt, imidazole, and sodium hydroxide are dissolved in methanol, reacted, and the methanol is evaporated before washing with a non-polar solvent to obtain the final product.

[0040] The present invention does not limit the specific operation of the washing with the non-polar solvent, and any operation well known to those skilled in the art is acceptable. The non-polar solvent mentioned in the present invention is one of n-hexane, benzene, carbon tetrachloride, and dichloroethane.

[0041] The quaternary ammonium salt of this invention is triethylbenzylammonium chloride;

[0042] The reaction temperature is 30~60 ℃, specifically 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃; or any value between the two mentioned above.

[0043] The reaction time is 1 to 24 hours; specifically, it can be 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, 11 hours, 13 hours, 15 hours, 17 hours, 19 hours, 21 hours, 23 hours, or 24 hours.

[0044] The molar ratio of triethylbenzylammonium chloride to imidazole and sodium hydroxide is 0.9:1 to 1.5:1; specifically, it can be 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1, or any value within the range of any two of the above.

[0045] The molar ratio of methanol to quaternary ammonium salt is 10 to 100:1; specifically, it can be 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1; or any value within the range of the above two.

[0046] This invention provides the application of the quaternary ammonium ionic liquid described above as a catalyst in the synthesis of ethyl methyl carbonate.

[0047] This invention selects an easily prepared, low-toxicity, and regenerable quaternary ammonium ionic liquid to replace metal-based imidazole ionic liquids as the catalyst for the preparation of ethyl methyl carbonate. This helps overcome the problems of traditional sodium alkoxide catalysts, such as easy agglomeration and deactivation, difficulty in reuse, and the poor stability of metal-based imidazole ionic liquids, which require strict anhydrous and oxygen-free operation, have certain corrosiveness, complex synthesis processes, high production costs, are environmentally unfriendly, and have high toxicity. In addition, the synthesized quaternary ammonium ionic liquid has the advantages of high activity and strong solubility, and can be used in the synthesis processes of ethyl methyl carbonate from dimethyl carbonate and diethyl carbonate, as well as the synthesis of ethyl methyl carbonate from dimethyl carbonate and ethanol.

[0048] This invention provides a method for synthesizing methyl ethyl carbonate, comprising the following steps:

[0049] A) Activate the mixed carbonate or mixed alcohol ester to obtain a clear solution;

[0050] B) Mix the clarified liquid with the quaternary ammonium ionic liquid according to claim 1 or 2, react, and cool to obtain the product.

[0051] The present invention provides a method for synthesizing methyl ethyl carbonate by first activating it with a mixed carbonate or a mixed alcohol ester to obtain a clear liquid.

[0052] In a preferred embodiment of the present invention, the mixed carbonate or mixed alcohol ester is activated at a temperature of 20-50 °C and a stirring speed of 5-20 r / min for 10-30 min to obtain a uniform clear liquid.

[0053] Specifically, the temperature can be 20℃, 30℃, 40℃ or 50℃, the stirring speed can be 5 r / min, 10 r / min, 15 r / min or 20 r / min, and the constant temperature activation time is 10~30 min; specifically, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes.

[0054] According to the present invention, the mixed carbonate is dimethyl carbonate and diethyl carbonate, wherein the molar ratio of dimethyl carbonate to diethyl carbonate is 0.5:1 to 3:1; specifically, it can be 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, or 3.0:1.

[0055] The mixed alcohol ester is dimethyl carbonate and ethanol; specifically, the molar ratio of dimethyl carbonate to ethanol is 0.5:1 to 3:1; specifically, it can be 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, or 3.0:1.

[0056] The clarified liquid is mixed with the quaternary ammonium ionic liquid described in the above technical solution, reacted, and cooled to obtain the final product.

[0057] According to the present invention, the reaction is carried out at 70~130℃ for 0.5~10 h; specifically, it can be 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, or 130℃; the reaction time can be 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6.0h, 6.5h, 7.0h, 7.5h, 8.0h, 8.5h, 9.0h, 9.5h, or 10.0h.

[0058] The amount of the quaternary ammonium base ionic liquid catalyst used is 1% to 12% of the total mass of the clarified liquid; specifically, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, or 12%.

[0059] This invention provides a quaternary ammonium ionic liquid with the structure of formula (I). It can be used in the synthesis processes of dimethyl carbonate and diethyl carbonate to synthesize methyl ethyl carbonate, and dimethyl carbonate and ethanol to synthesize methyl ethyl carbonate, producing methyl ethyl carbonate with excellent purity. Furthermore, the quaternary ammonium ionic liquids used are easy to prepare, low in toxicity, and regenerable, overcoming the problems of easy agglomeration and deactivation of traditional sodium alkoxide catalysts and their difficulty in reuse. This is of great significance for promoting the green and efficient production of methyl ethyl carbonate.

[0060] The reaction conditions (temperature, pressure, time, molar ratio of materials, etc.) selected in this invention are not arbitrarily set, but rather are "optimal reaction conditions" with good universality, screened based on preliminary experiments and existing technical knowledge for the specific reaction system of "synthesis of ethyl methyl carbonate from dimethyl carbonate and diethyl carbonate". These conditions aim to provide a fair, neutral, and efficient competitive platform for catalysts with different structures. On this platform, the influence of common external factors such as mass transfer and thermodynamic equilibrium on the reaction has been optimized to a relatively ideal state. Therefore, when parallel comparisons are performed under these unified and optimized conditions, the observed significant differences in yield can be more confidently attributed to the intrinsic properties of the catalysts—namely, the intrinsic activity differences resulting from the different cation structures. This further eliminates the possibility of accidentally amplifying or reducing the performance of a particular catalyst due to incompatible reaction conditions, making the comparative conclusions between examples more reliable and targeted. Attached Figure Description

[0061] Figure 1 The structural diagrams are of the quaternary ammonium base ionic liquids [TMA][IM], [TEA][IM], [TPA][IM], [TBA][IM], and [TEB][IM].

[0062] Figure 2 Quaternary ammonium base ionic liquid [TMA][IM] 1 H NMR spectrum;

[0063] Figure 3 Quaternary ammonium base ionic liquid [TEA][IM] 1 H NMR spectrum;

[0064] Figure 4 Quaternary ammonium base ionic liquid [TPA][IM] 1 H NMR spectrum;

[0065] Figure 5 Quaternary ammonium base ionic liquid [TBA][IM] 1 H NMR spectrum;

[0066] Figure 6 Quaternary ammonium base ionic liquid [TEB][IM] 1 H NMR spectrum. Detailed Implementation

[0067] This invention provides quaternary ammonium ionic liquids, their preparation methods, and methods for synthesizing methyl ethyl carbonate. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of protection of this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0068] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0069] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0070] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0071] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0072] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0073] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0074] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately". Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0075] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0076] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0077] To further illustrate the present invention, the following examples demonstrate the quaternary ammonium ionic liquid, its preparation method, and the method for synthesizing methyl ethyl carbonate provided by the present invention.

[0078] Example 1

[0079] Tetramethylammonium hydroxide was dissolved in methanol at a molar ratio of 30:1. Then, imidazole was added to the solution at a molar ratio of 1:1 to tetramethylammonium hydroxide. The reaction was carried out at room temperature for 24 h. After the reaction was completed, excess solvent methanol was removed by rotary evaporation. Then, n-hexane was added for washing, with the amount of n-hexane being 5 times the mass of tetramethylammonium hydroxide. After washing three times, the n-hexane was removed to obtain tetramethylimidazolium ammonium ionic liquid [TMA][IM].

[0080] 1 H NMR (600 MHz, D2O) δ 7.68 (s, 1H), 7.06 (s, 2H), 3.11 (s, 12H).

[0081] Dimethyl carbonate and diethyl carbonate were added to a pressure-resistant bottle at a molar ratio of 2:1. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous, clear solution. 5% by mass of [TMA][IM] quaternary ammonium ionic liquid catalyst was added to the homogeneous, clear solution, and the reaction was carried out at 110 °C for 3 h. After the reaction was complete, the solution was cooled to room temperature, and the yield of methyl ethyl carbonate was 20.72%.

[0082] Example 2

[0083] Tetraethylammonium hydroxide was dissolved in methanol at a molar ratio of 30:1. Then, imidazole was added to the solution at a molar ratio of 1:1 to tetraethylammonium hydroxide. The reaction was carried out at room temperature for 24 h. After the reaction was completed, excess solvent methanol was removed by rotary evaporation. Then, n-hexane was added for washing. The amount of n-hexane added was 5 times the mass of tetraethylammonium hydroxide. After washing three times, the n-hexane was removed to obtain tetraethylimidazolium ammonium ionic liquid [TEA][IM].

[0084] 1 H NMR (600 MHz, DMSO-d6) δ 7.54 (s, 1H), 6.95 (s, 2H), 3.18 (q, J =7.3 Hz, 8H), 1.17 – 1.11 (m, 12H).

[0085] Dimethyl carbonate and diethyl carbonate were added to a pressure-resistant bottle at a molar ratio of 2:1. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear solution. 5% by mass of [TEA][IM] quaternary ammonium ionic liquid catalyst was added to the homogeneous clear solution, and the reaction was carried out at 110 °C for 3 h. After the reaction was complete, the temperature was lowered to room temperature, and the yield of methyl ethyl carbonate was 48.43%.

[0086] Example 3

[0087] Tetrapropylammonium hydroxide was dissolved in methanol at a molar ratio of 30:1. Then, imidazole was added to the solution at a molar ratio of 1:1 to tetrapropylammonium hydroxide. The reaction was carried out at room temperature for 24 h. After the reaction was completed, excess solvent methanol was removed by rotary evaporation. Then, n-hexane was added for washing. The amount of n-hexane added was 5 times the mass of tetrapropylammonium hydroxide. After washing three times, the n-hexane was removed to obtain tetrapropylimidazolium ammonium ionic liquid [TPA][IM].

[0088] 1 H NMR (600 MHz, DMSO-d6) δ 7.51 (s, 1H), 6.94 (s, 2H), 3.16 – 3.08 (m, 8H), 1.65 – 1.57 (m, 8H), 0.90 (t, J = 7.3 Hz, 12H).

[0089] Dimethyl carbonate and diethyl carbonate were added to a pressure-resistant bottle at a molar ratio of 2:1. The mixture was stirred at 15 r / min for 10 min under constant temperature (30 °C) to obtain a homogeneous, clear solution. 5% (by mass) of [TPA][IM] quaternary ammonium ionic liquid catalyst was added to the homogeneous, clear solution, and the reaction was carried out at 110 °C for 3 h. After the reaction was complete, the solution was cooled to room temperature, yielding 31.65% methyl ethyl carbonate.

[0090] Example 4

[0091] Tetrabutylammonium hydroxide was dissolved in methanol at a molar ratio of 30:1. Then, imidazole was added to the solution at a molar ratio of 1:1 to tetrabutylammonium hydroxide. The reaction was carried out at room temperature for 24 h. After the reaction was completed, excess solvent methanol was removed by rotary evaporation. Then, n-hexane was added for washing. The amount of n-hexane added was 5 times the mass of tetrabutylammonium hydroxide. After washing three times, n-hexane was removed to obtain tetrabutylimidazolium ionic liquid [TPA][IM].

[0092] 1 H NMR (600 MHz, D2O) δ 7.70 (s, 1H), 7.08 (s, 2H), 3.18 – 3.10 (m,8H), 1.64 – 1.56 (m, 8H), 1.32 (h, J = 7.4 Hz, 8H), 0.91 (t, J = 7.4 Hz,12H).

[0093] Dimethyl carbonate and diethyl carbonate were added to a pressure-resistant bottle at a molar ratio of 2:1. The mixture was stirred at 15 r / min for 10 min under constant temperature (30 °C) to obtain a homogeneous, clear solution. 5% (by mass) of the [TBA][IM] quaternary ammonium ionic liquid catalyst was added to the homogeneous, clear solution, and the reaction was carried out at 110 °C for 3 h. After the reaction was complete, the solution was cooled to room temperature, yielding 28.04% methyl ethyl carbonate.

[0094] Example 5

[0095] Triethylbenzylammonium chloride was dissolved in methanol at a molar ratio of 30:1. Then, imidazole was added to the solution at a molar ratio of 1:1 to triethylbenzylammonium chloride. The mixture was reacted at 60 °C for 1 h, followed by the addition of sodium hydroxide at a molar ratio of 1.1:1 to triethylbenzylammonium chloride. The reaction was then continued for another 24 h. After the reaction was completed, the solution was filtered under reduced pressure to obtain a clear solution. Excess methanol was removed by rotary evaporation. The solution was then washed with n-hexane, with the amount of n-hexane added being 5 times the mass of tetrabutylammonium hydroxide. After washing three times, the n-hexane was removed to obtain the triethylbenzylimidazolium ammonium ionic liquid [TEB][IM].

[0096] 1 H NMR (600 MHz, D2O) δ 7.70 (s, 1H), 7.58 – 7.42 (m, 5H), 7.39 – 7.05(m, 2H), 4.35 (s, 2H), 3.17 (q, J = 7.3 Hz, 6H), 1.35 (t, J = 7.2 Hz, 9H).

[0097] Dimethyl carbonate and diethyl carbonate were added to a pressure-resistant bottle at a molar ratio of 2:1. The mixture was stirred at 15 r / min for 10 min under constant temperature (30 °C) to obtain a homogeneous, clear solution. 5% (by mass) of the [TEB][IM] quaternary ammonium ionic liquid catalyst was added to the homogeneous, clear solution, and the reaction was carried out at 110 °C for 3 h. After the reaction was complete, the solution was cooled to room temperature, yielding 26.64% methyl ethyl carbonate.

[0098] Example 6

[0099] The reusability of the five quaternary ammonium ionic liquids recovered in Examples 1-5 was tested. Specifically, dimethyl carbonate and diethyl carbonate were added to a pressure-resistant bottle at a molar ratio of 2:1, and stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear liquid. 5% by weight of the recovered [TMA][IM], [TEA][IM], [TPA][IM], [TBA][IM], and [TEB][IM] quaternary ammonium ionic liquid catalysts were added to the homogeneous clear liquid, respectively, and reacted at a constant temperature of 110 °C for 3 h. After the reaction was complete, the mixture was cooled to room temperature, and the quaternary ammonium ionic liquids were recovered. The above process was repeated twice, and the results are shown in Table 1. The reused quaternary ammonium ionic liquids exhibited catalytic effects similar to those of the fresh ionic liquids, indicating that the five quaternary ammonium ionic liquids used have good stability in the catalytic preparation of methyl ethyl carbonate.

[0100] Table 1. Reusability of Quaternary Ammonium Ionic Liquids in the Catalytic Reaction of Cellulose to Cellulose Acetate

[0101]

[0102] Example 7

[0103] Dimethyl carbonate and ethanol were added to a pressure-resistant bottle at a 1:1 molar ratio. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear solution. 2% [TMA][IM] quaternary ammonium ionic liquid catalyst (based on the total molar amount of ethanol) was added to the homogeneous clear solution, and the reaction was carried out at 70 °C for 0.5 h. After the reaction was complete, the mixture was cooled to room temperature, and the yield of ethyl methyl carbonate was 25.88%.

[0104] Example 8

[0105] Dimethyl carbonate and ethanol were added to a pressure-resistant bottle at a 1:1 molar ratio. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear solution. 2% (by total molar amount) of [TEA][IM] quaternary ammonium ionic liquid catalyst was added to the homogeneous clear solution, and the reaction was carried out at 70 °C for 0.5 h. After the reaction was complete, the temperature was lowered to room temperature, and the yield of ethyl methyl carbonate was 25.97%.

[0106] Example 9

[0107] Dimethyl carbonate and ethanol were added to a pressure-resistant bottle at a 1:1 molar ratio. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear solution. 2% of the total molar amount of ethanol in the homogeneous clear solution was added to the [TPA][IM] quaternary ammonium ionic liquid catalyst, and the reaction was carried out at 70 °C for 0.5 h. After the reaction was complete, the mixture was cooled to room temperature, and the yield of ethyl methyl carbonate was 26.95%.

[0108] Example 10

[0109] Dimethyl carbonate and ethanol were added to a pressure-resistant bottle at a molar ratio of 1:1. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear solution. 2% of the total molar amount of ethanol in the homogeneous clear solution was added to the [TBA][IM] quaternary ammonium ionic liquid catalyst, and the reaction was carried out at 70 °C for 0.5 h. After the reaction was complete, the mixture was cooled to room temperature, and the yield of ethyl methyl carbonate was 26.12%.

[0110] Example 11

[0111] Dimethyl carbonate and ethanol were added to a pressure-resistant bottle at a 1:1 molar ratio. The mixture was stirred at 15 r / min for 10 min under constant temperature of 30 °C to obtain a homogeneous clear solution. 2% [TEB][IM] quaternary ammonium ionic liquid catalyst (based on the total molar amount of ethanol) was added to the homogeneous clear solution, and the reaction was carried out at 70 °C for 0.5 h. After the reaction was complete, the mixture was cooled to room temperature, and the yield of ethyl methyl carbonate was 27.33%.

[0112] 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 quaternary ammonium base ionic liquid of the structure of formula (I): ###0001### wherein R1, R2, R3 and R4 are independently selected from substituted or unsubstituted C1-C4 alkyl groups; and the substituents of the substituted alkyl groups are phenyl groups. Formula (I); wherein Specific structures are as follows:

2. The quaternary ammonium base ionic liquid according to claim 1, characterized in that, The method comprises the following steps: 。 3. Process for the preparation of a quaternary ammonium base ionic liquid according to claim 1 or 2, characterized in that, One of the quaternary ammonium base or quaternary ammonium salt is dissolved in a solvent with imidazole to obtain a product. The quaternary ammonium base is one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; and the quaternary ammonium salt is triethylbenzylammonium chloride.

4. The production method according to claim 3, characterized by, The reaction temperature is 30-60 ℃, and the reaction time is 1-24 h. The solvent is one of n-hexane, benzene, carbon tetrachloride and dichloroethane. The preparation method of the catalyst comprises:

5. The preparation method according to claim 3, characterized in that, The quaternary ammonium base is dissolved in methanol with imidazole to obtain a product; the reaction temperature is 30-60 ℃, and the reaction time is 1-24 h. The molar ratio of the quaternary ammonium base to imidazole is 0.9:1-1.5:

1. The molar ratio of methanol to the quaternary ammonium base is 10-100. The non-polar solvent is one of n-hexane, benzene, carbon tetrachloride and dichloroethane. The preparation method of the catalyst comprises:

6. The preparation method according to claim 3, characterized in that, The quaternary ammonium salt, imidazole and sodium hydroxide are dissolved in methanol to obtain a product. The reaction temperature is 30-60 ℃, and the reaction time is 1-24 h. The molar ratio of triethylbenzylammonium chloride to imidazole and sodium hydroxide is 0.9:1-1.5:

1. The molar ratio of methanol to the quaternary ammonium salt is 10-100. The non-polar solvent is one of n-hexane, benzene, carbon tetrachloride and dichloroethane.

7. The quaternary ammonium base ionic liquid of claim 1 or 2 as a catalyst for synthesizing methyl ethyl carbonate. The method comprises the following steps:

8. A method of synthesizing methyl ethyl carbonate, characterized by, A) mixing a carbonic ester or mixed alcohol ester to obtain a clear solution; B) mixing the clear solution with the quaternary ammonium base ionic liquid of claim 1 or 2 to obtain a product. The parameters of the activation in step A) are as follows: the activation is carried out at a temperature of 20-50 ℃ and a stirring speed of 5-20 r / min for 10-30 min.

9. The method of claim 8, wherein, The mixed carbonic ester is dimethyl carbonate and diethyl carbonate, and the molar ratio of dimethyl carbonate to diethyl carbonate is 0.5:1-3:1; and the mixed alcohol ester is dimethyl carbonate and ethanol, and the molar ratio of dimethyl carbonate to ethanol is 0.5:1-3:

1. The reaction in step B) is carried out at 70-130 ℃ for 0.5-10 h.

10. The method of claim 8, wherein, The amount of the quaternary ammonium base ionic liquid is 1%-12% of the total mass of the clear solution. ​

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