Method for efficiently preparing N-methylimidazole by adopting microchannel reactor

Abstract

The invention belongs to the technical field of compound preparation and purification, and discloses a method for efficiently preparing N-methylimidazole by adopting a microchannel reactor, which comprises the following steps: mixing a methylamine solution with the concentration of 40% with ammonia water to obtain a mixed ammonia solution, and then mixing a formaldehyde solution with a glyoxal solution to obtain a mixed aldehyde solution; feeding the mixed ammonia solution and the mixed aldehyde solution into a micro-channel reactor through a high-precision metering pump, and reacting to obtain a crude product; introducing the crude product into a vacuum distillation condensation system, enabling distilled distillate to enter different collecting tanks through variable-temperature variable-pressure two-step vacuum distillation condensation, and after normal pressure is recovered, enabling a water mixture to flow into a rectification raw material tank; and connecting the rectification raw material tank into a refining system to obtain the N-methylimidazole. The micro-channel reactor is adopted, the synthesis time is greatly shortened, the energy consumption is reduced, and the concentration of the product N-methylimidazole is gt by adopting temperature-variable pressure-variable two-step vacuum distillation condensation and rectification refining combined purification; and 98%.

Description

Technical Field

[0001] The invention belongs to the technical field of compound preparation and purification, and relates to a method for efficiently preparing N-methylimidazole by using a microchannel reactor. Background Art

[0002] N-Methylimidazole, also known as 1-methylimidazole, is a colorless to pale yellow transparent liquid with good solubility in water, alcohols, and ethers, making it widely used in organic synthesis and the chemical industry. N-Methylimidazole is not only commonly used in the synthesis of ionic liquids, but is also widely used in resin curing agents and adhesives, as well as being an important organic synthesis intermediate in pharmaceuticals.

[0003] Ionic liquids are a new class of solvents composed of anions and cations, offering advantages such as low volatility, high design responsiveness, excellent thermal stability, strong solvency, and a wide electrochemical window. In recent years, ionic liquids have become a research hotspot due to their unique physicochemical properties. They have demonstrated tremendous potential for application in a wide range of fields, including catalysis and separation, organic synthesis, material preparation, and resource and environmental utilization. Imidazolium ionic liquids, a common type of ionic liquid, also have extensive and in-depth applications in these areas. However, as a key precursor for the synthesis of imidazole ionic liquids, systematic research and exploration of N-methylimidazole itself remains insufficient.

[0004] The main processes for preparing N-methylimidazole are the imidazole substitution method and the one-step cyclization method. The imidazole substitution method requires the use of expensive and biotoxic methyl iodide as a methylation reagent, which poses safety risks and potential environmental accumulation hazards. In contrast, the one-step cyclization method achieves improved raw material utilization and reduced reaction steps through the precise design of the cyclic skeleton construction pathway, while effectively reducing the formation of by-products. It has now become the mainstream technical route in industrial production. However, the existing one-step cyclization method also has many problems such as complex purification and high energy consumption.

[0005] Chinese patent CN111410634A uses methylamine, glyoxal, formaldehyde and ammonia as raw material reactants and adopts a method combining distillation and rectification to prepare N-methylimidazole. Although it improves the synthesis efficiency and reduces energy consumption to a certain extent, it still faces the problems of long synthesis time and complex purification. Chinese patents CN110343071A and CN103086978A both use imidazole and methanol to synthesize N-methylimidazole. The synthesis of N-methylimidazole is carried out by the participation of a catalyst, which has high energy consumption and is limited by the output of imidazole, which is not conducive to the large-scale preparation of N-methylimidazole. Chinese patent CN105732508A proposes a method for preparing N-methylimidazole using a gas-phase catalytic reaction. Although it speeds up the reaction speed to a certain extent, the reaction risk and safety hazards also increase.

[0006] Therefore, the development of new methods for the synthesis and purification of N-methylimidazole through equipment innovation, which has high synthesis efficiency, good product purity, and is easy to prepare on an industrial scale, has extremely important value and broad application potential for addressing the practical challenges currently faced. Summary of the Invention

[0007] The present invention addresses the technical problems of complex purification and high energy consumption in a one-step cyclization process for preparing N-methylimidazole. The present invention provides a method for efficiently preparing N-methylimidazole by using a microchannel reactor. The microchannel reactor is used to synthesize N-methylimidazole, thereby greatly shortening the synthesis time of N-methylimidazole and reducing energy consumption. The method also combines temperature and pressure variable two-step vacuum distillation and condensation with rectification and refining for purification, thereby ensuring that the concentration of the product N-methylimidazole is greater than 98%.

[0008] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for efficiently preparing N-methylimidazole using a microchannel reactor, comprising the following steps: 1) mixing a 40% methylamine solution and aqueous ammonia to obtain a mixed ammonia solution, and then mixing a formaldehyde solution and a glyoxal solution to obtain a mixed aldehyde solution; 2) the mixed ammonia solution and the mixed aldehyde solution obtained in step 1) are introduced into a microchannel reactor through a high-precision metering pump to react to obtain a crude product containing N-methylimidazole; 3) The crude product obtained in step 2) is connected to a vacuum distillation and condensation system. The distillate is distilled into different collection tanks through a two-step vacuum distillation and condensation process with variable temperature and pressure. After returning to normal pressure, the water mixture containing a large amount of N-methylimidazole is flowed into a distillation feed tank. 4) Connecting the distillation raw material tank in step 3) to the refining system to distill off excess water to obtain N-methylimidazole with a concentration greater than 98%.

[0009] Preferably, in step 1), the molar ratio of 40% methylamine, aqueous ammonia, formaldehyde and glyoxal is 1:(1-3):(1-2):(1-3).

[0010] Preferably, in step 2), the reaction temperature is 50-80° C., the reaction time is 3-10 min, the mixed ammonia flow rate is controlled at 30-80 mL / min, and the mixed aldehyde flow rate is controlled at 30-80 mL / min.

[0011] Preferably, step 3) specifically comprises the following steps: 1) raising the temperature of the circulating oil bath of the reaction unit to 60-70°C, maintaining the vacuum degree at 80-90 kPa, and collecting the condensate at a circulating condensing water temperature of 10°C into a water collection tank until no fraction is evaporated; 2) switching the condensate collection tank, raising the temperature of the circulating oil bath of the reaction unit to 130-150°C, maintaining the vacuum degree at 90-99 kPa, and collecting the condensate at a circulating condensing water temperature of 10°C into a crude product collection tank until no fraction is evaporated, restoring the pressure of the reaction unit to normal pressure, and sending the water mixture containing a large amount of N-methylimidazole in the crude product collection tank into the raw material tank of the distillation system.

[0012] More preferably, after the crude product in step 3) is connected to the vacuum distillation and condensation system, the distillation parameters are dynamically adjusted step by step according to the desired distilled condensate.

[0013] Preferably, in step 4), the temperature of the refining system is 50-80° C., and the vacuum degree is 90-97 kPa.

[0014] More preferably, after the distillation feedstock tank in step 4) is connected to the refining system, distillation parameters, such as the bottom, middle, and top temperatures of the distillation unit, as well as the distillation pressure, are dynamically adjusted in real time based on the feedstock concentration and the concentration of the product N-methylimidazole, to achieve an optimal purification process. An online optical electronic detector is installed at the bottom of the distillation unit to monitor the concentration of the distilled product in real time. Once the product concentration reaches the required level, it is discharged through a pipeline for packaging.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a microchannel reactor to synthesize N-methylimidazole, which greatly shortens the synthesis time of N-methylimidazole, reduces energy consumption, realizes continuous production, and is suitable for large-scale industrial production.

[0016] (2) The present invention adopts a two-step vacuum distillation and condensation method with variable temperature and pressure to purify N-methylimidazole, thereby achieving rapid separation of the reaction product from waste residue and wastewater, and then refining the product by distillation to make the concentration of the product N-methylimidazole >98%. DETAILED DESCRIPTION

[0017] The following examples are used to illustrate the present invention but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples are all conventional methods unless otherwise specified.

[0018] The microchannel reactor model used in the following examples is C0-10, purchased from Shandong Jinde New Materials Co., Ltd.; the metering pump model is Sanotac-MPF2002C, purchased from Shanghai Sanwei Technology Instrument Co., Ltd.

[0019] Example 1 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:2) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1:1.5) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 50°C. A high-precision metering pump was turned on to control the flow rates of the mixed ammonia and mixed aldehyde at 50 mL / min and 50 mL / min, respectively. The reaction was carried out at this temperature for 3 min. The concentration of N-methylimidazole was determined to be 11.5%.

[0020] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 60°C, the vacuum is maintained at 85 kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 130°C, the vacuum is maintained at 95 kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 93.5% after testing.

[0021] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 50°C, the distillation vacuum is controlled to 96 kPa, and the reflux ratio is adjusted to 1.6. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 98.6%.

[0022] Example 2 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:1.5) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1:1) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 60°C. A high-precision metering pump was turned on to control the flow rates of the mixed ammonia and mixed aldehyde at 50 mL / min and 50 mL / min, respectively. The reaction was carried out at this temperature for 4 min. The concentration of N-methylimidazole was determined to be 12.1%.

[0023] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 65 °C, the vacuum degree is maintained at 88 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 140 °C, the vacuum degree is maintained at 96 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 94.8% after detection.

[0024] (3) The crude product in the distillation system's raw material tank was flowed into the distillation unit. The bottom temperature of the distillation unit was adjusted to 55°C, the distillation vacuum was controlled to 97 kPa, and the reflux ratio was adjusted to 1.7. The distillation operation was carried out. The N-methylimidazole remained at the bottom of the unit after distillation, with a concentration of 98.9%.

[0025] Example 3 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:1.5) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1:2) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 70°C. A high-precision metering pump was turned on to control the flow rates of the mixed ammonia and mixed aldehyde at 60 mL / min and 60 mL / min, respectively. The reaction was carried out at this temperature for 3 min. The concentration of N-methylimidazole was determined to be 12.7%.

[0026] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 65 °C, the vacuum degree is maintained at 89 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 150 °C, the vacuum degree is maintained at 95 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 95.3% after detection.

[0027] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 60°C, the distillation vacuum is controlled to 96 kPa, and the reflux ratio is adjusted to 1.8. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 99.1%.

[0028] Example 4 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:1.3) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1:1.5) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 80°C. A high-precision metering pump was turned on to control the flow rate of the mixed ammonia at 50 mL / min and the flow rate of the mixed aldehyde at 60 mL / min. The reaction was carried out at this temperature for 5 minutes. The concentration of N-methylimidazole was detected to be 13.2%.

[0029] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 70 °C, the vacuum degree is maintained at 80 kPa, and the temperature of the circulating condensing water is kept at 10 °C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 150 °C, the vacuum degree is maintained at 96 kPa, and the temperature of the circulating condensing water is kept at 10 °C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 95.9% after detection.

[0030] (3) The crude product in the distillation system raw material tank was flowed into the distillation unit. The bottom temperature of the distillation unit was adjusted to 60°C, the distillation vacuum was controlled to 97 kPa, and the reflux ratio was adjusted to 2.0. The distillation operation was carried out. The N-methylimidazole remained at the bottom of the unit after distillation, with a concentration of 99.4%.

[0031] Example 5 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:1) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1.2:1.5) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 75°C. A high-precision metering pump was turned on to control the mixed ammonia flow rate to 60 mL / min and the mixed aldehyde flow rate to 55 mL / min. The reaction was carried out at this temperature for 6 minutes. The concentration of N-methylimidazole was detected to be 12.9%.

[0032] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 60°C, the vacuum degree is maintained at 85kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 140°C, the vacuum degree is maintained at 93kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 94.8% after testing.

[0033] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 65°C, the distillation vacuum is controlled to 95 kPa, and the reflux ratio is adjusted to 1.5. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 98.3%.

[0034] Example 6 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:2.5) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1.5:2.5) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 70°C. A high-precision metering pump was turned on to control the flow rate of the mixed ammonia at 50 mL / min and the flow rate of the mixed aldehyde at 50 mL / min. The reaction was carried out at this temperature for 8 minutes. The concentration of N-methylimidazole was detected to be 12.3%.

[0035] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 70 °C, the vacuum is maintained at 80 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 150 °C, the vacuum is maintained at 96 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 94.2% after detection.

[0036] (3) The crude product in the distillation system's raw material tank was flowed into the distillation unit. The bottom temperature of the distillation unit was adjusted to 60°C, the distillation vacuum was controlled to 97 kPa, and the reflux ratio was adjusted to 1.6. The distillation operation was carried out. The N-methylimidazole remained at the bottom of the unit after distillation, with a concentration of 98.7%.

[0037] Example 7 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:1.2) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1.5:1.5) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 80°C. A high-precision metering pump was turned on to control the flow rate of the mixed ammonia at 50 mL / min and the flow rate of the mixed aldehyde at 50 mL / min. The reaction was carried out at this temperature for 3 minutes. The concentration of N-methylimidazole was detected to be 13.2%.

[0038] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 60 °C, the vacuum degree is maintained at 85 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the water collection tank until no distillate is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 150 °C, the vacuum degree is maintained at 95 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no distillate is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 95.5% after detection.

[0039] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 60°C, the distillation vacuum is controlled to 95 kPa, and the reflux ratio is adjusted to 2.1. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 99.5%.

[0040] Example 8 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:2) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1:1.4) were mixed to obtain a mixed aldehyde solution. The circulating oil bath in the microchannel reactor was turned on and the oil bath temperature was controlled at 80°C. A high-precision metering pump was turned on to control the mixed ammonia flow rate to 60 mL / min and the mixed aldehyde flow rate to 55 mL / min. The reaction was carried out at this temperature for 5 minutes. The concentration of N-methylimidazole was detected to be 13.5%.

[0041] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 70 °C, the vacuum is maintained at 85 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 130 °C, the vacuum is maintained at 97 kPa, and the temperature of the circulating condensing water is 10 °C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 95.4% after detection.

[0042] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 65°C, the distillation vacuum is controlled to 97 kPa, and the reflux ratio is adjusted to 2.2. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 99.6%.

[0043] Example 9 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:1.5) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1.3:1.5) were mixed to obtain a mixed aldehyde solution. The circulating oil bath of the microchannel reactor was turned on and the oil bath temperature was controlled at 70°C. A high-precision metering pump was turned on to control the flow rate of the mixed ammonia at 50 mL / min and the flow rate of the mixed aldehyde at 60 mL / min. The reaction was carried out at this temperature for 7 minutes. The concentration of N-methylimidazole was detected to be 13.3%.

[0044] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 65°C, the vacuum degree is maintained at 90kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 140°C, the vacuum degree is maintained at 95kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 94.7% after testing.

[0045] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 65°C, the distillation vacuum is controlled to 98 kPa, and the reflux ratio is adjusted to 1.8. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 99.2%.

[0046] Example 10 (1) A 40% methylamine solution and aqueous ammonia (molar ratio of 1:2) were mixed to obtain a mixed ammonia solution. Then, formaldehyde and glyoxal solutions (molar ratio of 1.4:3) were mixed to obtain a mixed aldehyde solution. The circulating oil bath in the microchannel reactor was turned on and the oil bath temperature was controlled at 65°C. A high-precision metering pump was turned on to control the mixed ammonia flow rate to 50 mL / min and the mixed aldehyde flow rate to 55 mL / min. The reaction was carried out at this temperature for 9 minutes. The concentration of N-methylimidazole was detected to be 11.2%.

[0047] (2) After the reaction is completed, the reaction unit is connected to the vacuum distillation and condensation system. First, the temperature of the circulating oil bath of the reaction unit is raised to 70°C, the vacuum is maintained at 85kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the water collection tank until no fraction is evaporated. Then, the condensation collection tank is switched, the temperature of the circulating oil bath of the reaction unit is raised to 150°C, the vacuum is maintained at 93kPa, and the temperature of the circulating condensing water is 10°C for distillation and condensation. The condensate is collected and put into the crude product collection tank until no fraction is evaporated. The pressure of the reaction unit is restored to normal pressure, and the water mixture containing a large amount of N-methylimidazole in the crude product collection tank is put into the raw material tank of the distillation system. The concentration of N-methylimidazole is 93.7% after testing.

[0048] (3) The crude product in the distillation system raw material tank flows into the distillation unit. The bottom temperature of the distillation unit is adjusted to 60°C, the distillation vacuum is controlled to 95 kPa, and the reflux ratio is adjusted to 1.4. The distillation operation is carried out. The N-methylimidazole remains at the bottom of the unit after distillation, with a concentration of 98.1%.

[0049] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, it is of course possible to easily make other implementation methods by replacing or changing the technical content disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A method for efficiently preparing N-methylimidazole using a microchannel reactor, characterized in that: The following steps are involved: 1) mixing a 40% methylamine solution and aqueous ammonia to obtain a mixed ammonia solution, and then mixing a formaldehyde solution and a glyoxal solution to obtain a mixed aldehyde solution; 2) the mixed ammonia solution and the mixed aldehyde solution obtained in step 1) are introduced into a microchannel reactor through a high-precision metering pump to react to obtain a crude product containing N-methylimidazole; 3) The crude product obtained in step 2) is connected to a vacuum distillation and condensation system. The distillate is distilled into different collection tanks through a two-step vacuum distillation and condensation process with variable temperature and pressure. After returning to normal pressure, the water mixture containing a large amount of N-methylimidazole is flowed into a distillation feed tank. 4) Connecting the distillation raw material tank in step 3) to the refining system to distill off excess water to obtain N-methylimidazole with a concentration greater than 98%.

2. The method according to claim 1, characterized in that In step 1), the molar ratio of 40% methylamine, ammonia water, formaldehyde and glyoxal is 1:(1-3):(1-2):(1-3).

3. The method according to claim 1, characterized in that In step 2), the reaction temperature is 50-80° C., the reaction time is 3-10 min, the mixed ammonia flow rate is controlled at 30-80 mL / min, and the mixed aldehyde flow rate is controlled at 30-80 mL / min.

4. The method according to claim 1, wherein Step 3) The specific steps are as follows: 1) raising the temperature of the circulating oil bath of the reaction unit to 60-70°C, maintaining the vacuum degree at 80-90 kPa, and collecting the condensate at a circulating condensing water temperature of 10°C into a water collection tank until no distillate is evaporated; 2) switching the condensate collection tank, raising the temperature of the circulating oil bath of the reaction unit to 130-150°C, maintaining the vacuum degree at 90-99 kPa, and collecting the condensate at a circulating condensing water temperature of 10°C into a crude product collection tank until no distillate is evaporated, restoring the pressure of the reaction unit to normal pressure, and sending the water mixture containing a large amount of N-methylimidazole in the crude product collection tank into the raw material tank of the distillation system.

5. The method according to claim 1 or 4, characterized in that Step 3) After the medium-coarse product is connected to the vacuum distillation and condensation system, the distillation parameters are dynamically adjusted step by step according to the required distilled condensate.

6. The method according to claim 1, characterized in that In step 4), the temperature of the refining system is 50-80°C and the vacuum degree is 90-97 kPa.

7. The method according to claim 1 or 6, characterized in that In step 4), after the distillation raw material tank is connected to the refining system, the distillation parameters are dynamically adjusted in real time according to the raw material concentration and the concentration of the product N-methylimidazole.