Ionic liquid catalyst and preparation method therefor, methyl methylcarbamate and preparation method therefor, preparation system, and use

Abstract

The present invention provides an ionic liquid catalyst and a preparation method therefor, methyl methylcarbamate and a preparation method therefor, a preparation system, and the use. The structural formula of the ionic liquid catalyst is [Zn(CH3NHC(O)OCH3)2]2+•2(CH2COO)-. In the present invention, urea, methanol and dimethyl carbonate are used as raw materials, and methyl methylcarbamate is prepared under the catalytic action of the ionic liquid catalyst. Methanol, dimethyl carbonate and urea are subjected to multi-step alcoholysis and ammonolysis reactions, the target product selectivity is high, the raw material conversion rate is high, the methyl methylcarbamate product purity is high, without organic tin residues, and the catalyst cost is low.

Description

Ionic liquid catalysts and their preparation methods, methyl methyl carbamates and their preparation methods, preparation systems and applications

[0001] Cross-reference information

[0002] This application claims priority to Chinese Patent Application No. 202411535435.6, filed on October 30, 2024, entitled "Ionic Liquid Catalyst and Preparation Method Thereof, Methyl Methylcarbamate and Preparation Method Thereof, Preparation System and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to an ionic liquid catalyst and its preparation method, methyl methyl carbamate and its preparation method, preparation system and application, belonging to the field of methyl methyl carbamates. Background Technology

[0004] Methyl carbamates are an important class of fine chemical products with applications in the pharmaceutical, pesticide, and organic solvent fields. In the pharmaceutical field, they are used in applications such as trichloroethyl carbamate, physostigmine, and phenyl carbamate compounds. In the pesticide field, they are used in highly effective and low-toxicity pesticides such as methomyl, carbaryl, chlorfenapyr, cymoxanil, and ethoxysulfuron.

[0005] Currently, this product is still in the early stages of research and development. The three main synthesis methods described in the published literature are as follows:

[0006] Method 1: CN103524381A discloses a method for preparing N-methylcarbamate, which uses dimethyl carbonate and 1,3-dimethylurea as raw materials, mixes them in a molar ratio of 15 to 1:1, and reacts them under the action of dibutyltin oxide (DBTO) catalyst at a reaction temperature of 80-200℃ and a pressure of 0.1 MPa-5.0 MPa to obtain N-methylcarbamate.

[0007] Method 2: The paper "Synthesis of Methyl N-methylcarbamate" (Fine Chemicals, Vol. 31, No. 5, 2014) discloses a method for preparing methyl N-methylcarbamate, whose raw material route and process conditions are basically the same as those disclosed in CN103524381A.

[0008] Method 3: CN112409214A discloses a method for preparing N-methylcarbamate, which uses urea and methanol as raw materials, mixes them in a molar ratio of 1:10 to 20, and obtains N-methylcarbamate by alcoholysis reaction under the conditions of reaction temperature of 220-240℃ and pressure of 5.92Mpa-7.69Mpa.

[0009] However, both Method 1 and Method 2 require organotin catalysts, which are expensive and environmentally unfriendly, limiting their downstream applications. Since the dibutyltin oxide catalyst participates in the preparation of methyl methyl carbamate in a homogeneous reaction, subsequent separation is extremely difficult, and poor separation can affect product purity. Especially in the production of polyurethane materials, residual organotin in the product can catalyze and accelerate the cross-linking reaction between isocyanates and hydroxyl groups, resulting in a significant shortening of the activation period of the cross-linking system. Method 3 involves high reaction temperatures, high energy consumption, large raw material turnover, and high reaction pressure, leading to high technical requirements and large investments in industrial production equipment. In particular, this method only involves alcoholysis, resulting in a low raw material conversion rate.

[0010] Therefore, it is necessary to provide a new method for preparing N-methylcarbamate to improve the above-mentioned problems. Summary of the Invention

[0011] To address the aforementioned technical problems, the present invention aims to provide an ionic liquid catalyst and its preparation method, a methyl methyl carbamate and its preparation method, preparation system, and applications. The present invention uses urea, methanol, and dimethyl carbonate as raw materials to prepare methyl methyl carbamate under the catalysis of an ionic liquid catalyst. Methanol, dimethyl carbonate, and urea undergo multi-step alcoholysis and ammonolysis reactions, resulting in high selectivity for the target product, high raw material conversion rate, high purity of the methyl methyl carbamate product, absence of organotin residues, and low catalyst cost.

[0012] To achieve the above objectives, the present invention provides an ionic liquid catalyst with the structural formula [Zn(CH3NHC(O)OCH3)2]. 2+ ·2(CH2COO) - .

[0013] Compared to commonly used organotin catalysts, the catalyst of this invention exhibits superior catalytic performance in the subsequent chemical reaction of preparing methyl methyl carbamate from methanol, dimethyl carbonate, and urea. More importantly, it does not introduce additional impurities into the system, allowing for the acquisition of high-purity methyl methyl carbamate products through simple separation. Furthermore, it is lower in cost and leaves no organotin residue, resulting in better environmental friendliness and downstream applicability of the product.

[0014] The present invention also provides a method for preparing the aforementioned ionic liquid catalyst, which includes: mixing methyl methyl carbamate and zinc acetate to carry out a first chemical reaction to obtain the ionic liquid catalyst.

[0015] The ionic liquid catalyst prepared by this method does not introduce other impurity cations, and the reaction product system has a simple composition. The aforementioned ionic liquid catalyst product can be obtained through simple separation methods. Furthermore, the preparation method is simple, easy to implement, and uses simple, inexpensive, and readily available raw materials. Simultaneously, the preparation process generates no waste, making it economical, environmentally friendly, and easily scalable for industrial production.

[0016] Furthermore, the temperature of the first chemical reaction is 100–150°C.

[0017] Furthermore, the time for the first chemical reaction is 60–150 min.

[0018] Furthermore, the molar ratio of methyl methyl carbamate to zinc acetate is 6–10:1. MMC and zinc acetate are monodentately coordinated in this type of reaction, with a coordination molar ratio of 2:1. Excess MMC acts as a solvent to aid in the dissolution of zinc acetate during the synthesis of the ionic liquid catalyst. After preparation, excess methyl methyl carbamate (MMC) can be removed by vacuum distillation to purify the catalyst, thus obtaining the ionic liquid catalyst. Alternatively, purification can be omitted, and the catalyst can be directly used for subsequent preparation of methyl methyl carbamate. The degree of purification after catalyst synthesis does not affect the structure of the ionic liquid catalyst itself, and the presence of a small amount of free methyl methyl carbamate (MMC) does not affect the performance of the catalyst in subsequent applications of methyl methyl carbamate (MMC) preparation.

[0019] Furthermore, the first chemical reaction is carried out in an inert gas atmosphere, such as nitrogen.

[0020] The present invention also provides a method for preparing methyl methyl carbamate, which includes: mixing methanol, dimethyl carbonate, urea and the aforementioned ionic liquid catalyst to carry out a second chemical reaction to obtain methyl methyl carbamate.

[0021] This invention uses urea, methanol, and dimethyl carbonate as raw materials to prepare methyl methyl carbamate under the catalysis of the aforementioned ionic liquid catalyst. The main reaction processes and their equations are as follows:

[0022] Methanol reacts with urea in a catalytic alcoholysis reaction, producing methyl carbamate and ammonia.

[0023] Methyl carbamate further undergoes a catalytic alcoholysis reaction with methanol, producing dimethyl carbonate and ammonia.

[0024] Urea and dimethyl carbonate undergo simultaneous catalytic alcoholysis and ammonolysis to produce methyl methyl carbamate, ammonia, and carbon dioxide.

[0025] This preparation method improves the selectivity of target products and the conversion rate of raw materials in the multi-step alcoholysis and ammonolysis reactions of methanol, dimethyl carbonate, and urea. The preparation process is simple and the reaction conditions are relatively mild. Furthermore, the byproducts obtained in this preparation process, such as ammonia and carbon dioxide, can be recycled for the synthesis of urea, the raw material used in this invention, reducing production costs and avoiding environmental pollution, thus achieving green and environmentally friendly production. Moreover, this preparation process produces no waste, making it economical, environmentally friendly, and easily scalable for industrial production.

[0026] Furthermore, the temperature of the second chemical reaction is 200–220°C; the pressure of the second chemical reaction is 6.0–8.0 MPa; and the time of the second chemical reaction is 2–3 hours.

[0027] Furthermore, the molar ratio of methanol, dimethyl carbonate, and urea is 3–8:3–8:1.

[0028] Furthermore, the amount of ionic liquid catalyst used is 3 to 10% of the weight of urea.

[0029] Furthermore, the second chemical reaction is carried out in an inert gas atmosphere, such as nitrogen.

[0030] Furthermore, during the second chemical reaction, the reaction product system undergoes real-time or batch-wise gas-liquid separation to remove gaseous byproducts. Timely separation of gaseous byproducts during the reaction reduces reverse reactions and promotes the reaction towards the synthesis of methyl methyl carbamate. Removing byproduct gases such as ammonia and carbon dioxide from the reaction system in real-time or batches helps regulate the reaction equilibrium and further improves the conversion rate of urea to methyl methyl carbamate. Moreover, after removal, the byproducts such as ammonia and carbon dioxide can be entirely recycled into the urea production line as raw materials for further urea synthesis, thus achieving the beneficial effect of recycling byproduct gases, which is environmentally friendly and energy-saving.

[0031] Preferably, the reaction product system is subjected to gas-liquid separation in batches, for example, ammonia and carbon dioxide are extracted 2 to 4 times. It should be understood that the more times ammonia and carbon dioxide are extracted, the more beneficial it is to the forward reaction and the formation of the product methyl methyl carbamate, resulting in a higher overall yield of methyl methyl carbamate. However, frequent extraction of byproduct gases from the synthesis reaction process can cause fluctuations in pressure and temperature within the methyl methyl carbamate preparation vessel, which is detrimental to reaction stability. This invention does not impose a specific limit on the number of times byproduct gases are extracted; those skilled in the art can make corresponding adjustments according to their own technical needs, which is something they can implement themselves and will not be elaborated upon here.

[0032] The present invention also provides a system for preparing methyl methyl carbamate, comprising an ionic liquid catalyst preparation vessel and a methyl methyl carbamate preparation vessel connected in sequence; the ionic liquid catalyst preparation vessel is used to mix methyl methyl carbamate and zinc acetate to carry out a first chemical reaction to obtain an ionic liquid catalyst; the methyl methyl carbamate preparation vessel is used to mix methanol, dimethyl carbonate, the aforementioned ionic liquid catalyst and urea to carry out a second chemical reaction to obtain methyl methyl carbamate.

[0033] Furthermore, the ionic liquid catalyst preparation vessel has a feed port, through which methyl methyl carbamate and zinc acetate can be added to the ionic liquid catalyst preparation vessel.

[0034] Furthermore, the ionic liquid catalyst preparation vessel is controllably connected to the nitrogen generator, the thermal oil furnace, and the coolant via valves and pipelines.

[0035] Furthermore, the top of the methyl methyl carbamate preparation vessel and the bottom of the ionic liquid catalyst preparation vessel are connected by pipes and valves to controllably add the ionic liquid catalyst prepared in the ionic liquid catalyst preparation vessel to the methyl methyl carbamate preparation vessel in a quantitative manner during the feeding stage.

[0036] Furthermore, the methyl methyl carbamate preparation vessel has a feed port, through which reaction raw materials (such as methanol, dimethyl carbonate, and urea) can be added to the methyl methyl carbamate preparation vessel.

[0037] Furthermore, the methyl methyl carbamate preparation vessel is controllably connected to the nitrogen generator, the heat transfer oil furnace, and the coolant via valves and pipelines.

[0038] Furthermore, the aforementioned methyl methyl carbamate preparation vessel is a pressure-resistant batch reactor, possessing functions such as heating, cooling, sealing, and pressurizing of the materials inside the vessel. It is controllably connected to the feed manhole, methanol and dimethyl carbonate recovery device, condensation and reflux unit, and discharge port via valve opening and closing. The reaction pressure in the methyl methyl carbamate preparation vessel is self-generated pressure, resulting from the combined effects of nitrogen gas inside the vessel, heated and vaporized methanol and dimethyl carbonate, ammonia and carbon dioxide generated during the reaction, and the volume expansion of the reactants inside the vessel due to heating.

[0039] In a preferred embodiment, the system for preparing methyl methyl carbamate further includes a condensation and reflux unit; the condensation and reflux unit includes a first-stage packed demister, a first-stage vertical condenser, a second-stage packed demister, a second-stage vertical condenser, a horizontal tubular condenser, and a gas-liquid separator connected in sequence; the discharge port at the top of the methyl methyl carbamate preparation vessel is connected to the inlet of the first-stage packed demister; the liquid phase outlet of the gas-liquid separator is connected to the methyl methyl carbamate preparation vessel through a reflux pipe, and a reflux circulation pump is installed on the reflux pipe.

[0040] In this invention, before the horizontal tube-and-shell condenser, a vertical tower section is formed by first setting up a first-stage packed demister, a first-stage vertical condenser, a second-stage packed demister, and a second-stage vertical condenser. In the methyl methyl carbamate preparation vessel, some of the droplets from the reactants due to heating and stirring are blocked. A portion of the liquid in the droplets flows directly back into the synthesis reactor under gravity to continue participating in the reaction. Some of the unseparated methanol and dimethyl carbonate gases, along with byproducts ammonia and carbon dioxide, volatilize and rise for preliminary gas-liquid separation. Some of the droplets and gases are cooled into a liquid phase in the vertical tower section and flow directly back into the methyl methyl carbamate preparation vessel under gravity to continue participating in the reaction, maintaining the balance of reactants in the methyl methyl carbamate preparation vessel and improving the reaction conversion rate.

[0041] The phase separation of methanol, dimethyl carbonate, and reaction byproduct gases ammonia and carbon dioxide is carried out in a gas-liquid separator. The liquid phase outlet of the gas-liquid separator is connected to the methyl methyl carbamate preparation vessel via a reflux pipe. The condensed liquid phase collected in the gas-liquid separator can be refluxed (e.g., using a reflux circulation pump) back into the methyl methyl carbamate preparation vessel to maintain the balance of reactants and temperature within the vessel.

[0042] In the condensation and reflux unit, ammonia, carbon dioxide, and unreacted methanol and dimethyl carbonate enter the methyl methyl carbamate preparation vessel in gaseous form for gas-liquid separation. The ammonia and carbon dioxide then enter the reaction byproduct gas recovery unit in gaseous form. The unreacted methanol and dimethyl carbonate, in liquid form, flow downwards from the overflow port on the side of the gas-liquid separator, are connected to the inlet of the reflux pump through a pipeline, and are then transported to the methyl methyl carbamate preparation vessel by the reflux pump. The reflux circulation maintains the balance of reactants in the methyl methyl carbamate preparation vessel and improves the reaction conversion rate.

[0043] Furthermore, the packing in the packed demister is one or a combination of Raschig rings, Pall rings, or structured packing. Both vertical and horizontal shell-and-tube condensers have material flowing inside the tubes and coolant flowing between the tubes.

[0044] In a preferred embodiment, the system for preparing methyl methyl carbamate further includes a reaction byproduct gas recovery unit; the reaction byproduct gas recovery unit is connected to the gas phase outlet of the gas-liquid separator (e.g., the reaction byproduct gas recovery unit and the condensation and reflux unit can be controlled by opening and closing a valve). The reaction byproduct gas recovery unit is used to recover gases such as ammonia and carbon dioxide produced by the reaction. In the methyl methyl carbamate preparation vessel, the reaction material gases such as methanol and dimethyl carbonate, along with the generated ammonia and carbon dioxide gases, pass through the condensation and reflux unit, where the gas and liquid phases are separated. The methanol and dimethyl carbonate are completely condensed into liquid phases and returned to the methyl methyl carbamate preparation vessel for reuse, while the ammonia and carbon dioxide gases, as gaseous phases, are released under reduced pressure and enter the reaction byproduct gas recovery unit.

[0045] Furthermore, the reaction byproduct gas recovery unit is connected to the urea production line. The urea production line can be controllably connected to the reaction byproduct gas recovery unit via valves, so as to achieve the beneficial effect that the recovered ammonia and carbon dioxide can be reused for urea synthesis. The generated urea can continue to be used as a raw material for this method, further reducing production costs. The urea production line described above in this invention is a conventional urea production line and is not specifically limited thereto.

[0046] Furthermore, the reaction byproduct gas recovery unit includes two gas buffer tanks connected in sequence, and a pressure regulator is provided on each of the communication channels between the gas-liquid separator and the gas buffer tank, between the gas buffer tanks, and between the gas buffer tank and the urea production line.

[0047] In a preferred embodiment, the system further includes a synthesis mixture storage tank, which is located between the methyl methyl carbamate preparation vessel and the subsequent distillation vessel. After the reaction in the methyl methyl carbamate preparation vessel is terminated, the reactants are cooled to room temperature and depressurized to atmospheric pressure; then, through pipelines and valves, and finally through a synthesis mixture transfer pump, they are transported to the synthesis mixture storage tank for later use. The main components of the synthesis mixture are methanol, dimethyl carbonate, methyl methyl carbamate, an ionic liquid catalyst, and trace amounts of urea (mainly dissolved in methanol, dimethyl carbonate, and methyl methyl carbamate).

[0048] In a preferred embodiment, the above-described system for preparing methyl methyl carbamate further includes a purification unit; the purification unit includes a distillation vessel and a distillation column connected in sequence; the inlet of the distillation vessel is connected to the outlet of the product system of the methyl methyl carbamate preparation vessel (when the system includes a synthesis mixture storage tank, the inlet of the distillation vessel is connected to the outlet of the synthesis mixture storage tank); the distillation column has a purified methyl methyl carbamate outlet.

[0049] The refining unit of this invention employs a combination of distillation and rectification to obtain a high-purity methyl methyl carbamate product, and can effectively separate components such as methanol, dimethyl carbonate, and ionic liquid catalysts from the synthesis mixture, thereby achieving more efficient recycling.

[0050] First, because the boiling point difference between methanol, dimethyl carbonate, methyl methyl carbamate, and the ionic liquid catalyst is greater than 70°C, the low-boiling-point methanol (boiling range around 65°C) and dimethyl carbonate (boiling range around 90-91°C) in the synthesis mixture are heated and vaporized by steam in the distillation kettle. The vaporized vapor then rises to the vertical and horizontal condensers connected to the top of the distillation kettle, where it is condensed into a liquid and separated. The methanol and dimethyl carbonate mixture separated by distillation is analyzed for composition and then used as raw material in the synthesis reaction of this invention. The high-boiling-point methyl methyl carbamate, ionic liquid catalyst, and a small amount of urea do not undergo phase change and remain at the bottom of the distillation kettle as the distillation residue mixture. This residue mixture is pumped into the heavy component storage tank of the distillation kettle via a heavy component transfer pump. Subsequently, the distillation residue mixture enters a rectification column for continuous atmospheric pressure distillation separation of the methyl methyl carbamate, ionic liquid catalyst, and a small amount of urea. Methyl carbamate (distillation range around 167-168°C) is separated from the upper part of the rectification section (purity can reach 99.5% or higher), the ionic liquid catalyst is separated from the lower part of the stripping section (can be reused 6-7 times), and a small amount of urea is finally discharged from the bottom of the stripping section.

[0051] The production of methyl methyl carbamate in a distillation column is a continuous process. The heavy component mixture from the distillation vessel in the storage tank is pumped into the distillation column via a feed pump. It is first pumped into the feed preheating heat exchanger to exchange heat with the hot material exiting the distillation column, raising the temperature of the heavy component mixture. Then, it enters the first heat exchanger of the distillation column to continue exchanging heat with the heat transfer oil. After the heavy component mixture from the distillation vessel reaches a higher temperature, it is continuously added into the distillation column from the top of the stripping section. Some of the liquid methyl methyl carbamate at the bottom of the stripping section enters the top of the stripping section and mixes with the remaining distillate entering the distillation column, then flows down from the top of the stripping section. Simultaneously, the downstream liquid and the rising gas flow interact, transferring mass and heat, causing some of the volatile methyl methyl carbamate in the liquid to vaporize and rise. The gaseous methyl methyl carbamate is then distilled into the rectification section, while the liquid methyl methyl carbamate, the non-volatile ionic liquid catalyst, and a small amount of urea continue to descend to the bottom of the rectification section. There, it enters the heater in the stripping section for heating and is then transported back to the middle of the rectification section. Some of the heated methyl methyl carbamate, which has been converted from liquid to gas, rises to the rectification section and is continuously distilled and separated. Once the methyl methyl carbamate content of the ionic liquid catalyst and a small amount of urea is within acceptable limits, they are finally discharged from the bottom of the rectification section and enter the ionic liquid catalyst recovery and storage unit, where they will be used as raw materials again in the synthesis reaction of this invention. The gaseous methyl methyl carbamate rising to the top of the rectification section passes through the first condenser in the rectification section, resulting in a mixture of gaseous and liquid methyl methyl carbamate. This mixture then enters the gas-liquid separator in the rectification section to separate the gaseous methyl methyl carbamate, while the liquid methyl methyl carbamate is returned to the middle of the rectification section via a reflux pump. Once the methyl methyl carbamate reaches the required purity, it is cooled again in the second heat exchanger in the rectification section and then transported through pipelines to the methyl methyl carbamate storage unit.

[0052] This invention also provides a methyl methyl carbamate, which is prepared by the aforementioned method for preparing methyl methyl carbamate. The structural formula of this methyl methyl carbamate is as follows:

[0053] The present invention also provides an application of the aforementioned methyl methyl carbamate in electronic cleaning solvents, synthetic leather slurries, water-based coatings, water-based inks, water-based adhesives, leather finishing agents, organic solvents, and new energy battery electrolytes.

[0054] For the reasons stated above, the methyl methyl carbamate of this invention, when used as an electronic cleaning solvent, possesses excellent physicochemical properties, namely, superior solubility, suitable evaporation rate, and excellent non-toxicity, safety, and environmental friendliness. Furthermore, the methyl methyl carbamate of this invention is miscible with water in any proportion, making it widely applicable in industrial fields requiring water solubility, such as synthetic leather sizing agents, water-based coatings, water-based inks, water-based adhesives, and leather finishing agents. In addition, the methyl methyl carbamate of this invention is non-irritating, has very low or even no toxicity, and is safe and environmentally friendly. It can significantly replace ethylene glycol ether and propylene glycol ether solvents, and can also significantly replace xylene, butyl acetate, trimethylbenzene (S100 solvent oil), tetramethylbenzene (150 solvent oil), ethylene glycol ethyl ether acetate (CAC), propylene glycol methyl ether acetate (PMA), ethylene glycol diacetate (EGDA), and other organic solvents. More importantly, the methyl methyl carbamate of the present invention can be used in electrolytes for new energy batteries, replacing methyl carbamate (MC), dimethyl carbonate (DMC), N-methylpyrrolidone (NMP), etc., which are currently widely used in electrolytes for new energy batteries. Methyl methyl carbamate has more stable performance, is safer, more efficient, non-toxic, and non-irritating, and has broad application prospects.

[0055] In summary, the above-mentioned technical solution of the present invention has the following advantages:

[0056] The ionic liquid catalyst of this invention has a simple and easy-to-implement preparation process, and the reaction raw materials are simple, inexpensive, and readily available, resulting in low cost. The obtained ionic liquid catalyst has good stability and can be reused many times.

[0057] The ionic liquid catalyst of this invention exhibits high reactivity, short reaction time, high urea conversion rate, good selectivity in generating methyl methyl carbamate, and easy control of the reaction process.

[0058] The cationic component of the ionic liquid catalyst of the present invention is the reaction product methyl methyl carbamate, without introducing any other cations, and the composition of the reaction solution and subsequent separation are simple.

[0059] The synthesis reaction equipment of the present invention has simple connection, efficient gas-liquid separation of by-products in the preparation process, and simple and easy-to-control methods for reaction temperature, droplets in the reactor, and maintaining the balance of reactants in the reactor.

[0060] This invention controls the controlled removal of byproduct gases such as ammonia and carbon dioxide from the reaction system in batches during the preparation process, thereby regulating the reaction balance and improving the urea conversion rate. The byproducts, including ammonia and carbon dioxide, can all be used as raw materials in the urea production unit to further synthesize urea, and can also be recycled as raw materials for this invention, achieving the recycling of byproduct gases. This is an environmentally friendly green chemistry technology.

[0061] The synthesis of methyl methyl carbamate by this invention is a medium-pressure reaction with a short reaction time, a large difference in boiling points between the raw materials and the finished product, and simple separation.

[0062] The entire preparation process of this invention produces no waste, making it economical, environmentally friendly, and easy to scale up for industrial production. Attached Figure Description

[0063] Figure 1 is a process flow diagram for synthesizing methyl methyl carbamate according to an embodiment of the present invention.

[0064] Among them, 1-methyl methyl carbamate preparation vessel, 2-ionic liquid catalyst preparation vessel, 3-gas-liquid separator, 4-reflux circulation pump, 5-first-stage packed demister, 6-first-stage vertical condenser, 7-second-stage packed demister, 8-second-stage vertical condenser, 9-horizontal shell and tube condenser, 10-synthetic mixture transfer pump, 11-first gas buffer tank, 12-first pressure regulating valve 1, 13-second gas buffer tank, 14-second pressure regulating valve 2, 15-third pressure regulating valve 3, 16-synthetic mixture storage tank, 17-methanol and dimethyl carbonate mixture storage unit, 18-high-pressure steam supply unit, 19-distillation kettle feed pump, 20-distillation kettle, 21-distillation kettle vertical condenser, 22-distillation kettle Horizontal condenser, 23-distillation kettle gas-liquid separator, 24-condensate outlet, 25-distillation column feed pump, 26-distillation kettle heavy component storage tank, 27-rectification section, 28-distillation column, 29-distillation column first heat exchanger, 30-feed preheat exchanger, 31-rectification section first condenser, 32-rectification section gas-liquid separator, 33-rectification section reflux pump, 34-rectification section second heat exchanger, 35-stripping section, 36-stripping section heater, 37-methylcarbamate storage unit, 38-ionic liquid catalyst recovery and storage unit, 39-first vent pipe, 40-urea production line, 41-thermal oil furnace, 42-nitrogen generator, 43-second vent pipe, 44-coolant pipeline, 45-distillation kettle heavy component transfer pump.

[0065] Attached Figure Description

[0066] Figure 1 is a schematic diagram of a methyl methyl carbamate preparation system according to one embodiment of the present invention.

[0067] Figure 2 is a structural diagram of the ionic liquid catalyst in Example 1 of the present invention.

[0068] Figure 3 is an infrared test image of the ionic liquid catalyst in Example 1 of the present invention.

[0069] Figure 4 is a magnified view of a portion of Figure 3.

[0070] Figure 5 is a magnified view of a portion of Figure 3.

[0071] Main reference numerals: 1-Methyl methyl carbamate preparation vessel; 2-Ionic liquid catalyst preparation vessel; 3-Gas-liquid separator; 4-Reflux pump; 5-Stage 1 packed demister; 6-Stage 1 vertical condenser; 7-Stage 2 packed demister; 8-Stage 2 vertical condenser; 9-Horizontal tubular condenser; 10-Synthetic mixture transfer pump; 11-First gas buffer tank; 12-First pressure regulating valve 1; 13-Second gas buffer tank; 14-Second pressure regulating valve 2; 15-Third pressure regulating valve 3; 16-Synthetic mixture storage tank; 17-Methanol and dimethyl carbonate mixture storage unit; 18-High-pressure steam supply unit; 19-Distillation vessel feed pump; 20-Distillation vessel; 21-Distillation vessel vertical condenser; 22-Horizontal distillation vessel. 23-Gas-liquid separator for distillation kettle, 24-Condensate outlet, 25-Feed pump for distillation column, 26-Heavy component storage tank for distillation kettle, 27-Distillation section, 28-Distillation column, 29-First heat exchanger for distillation column, 30-Feed preheat exchanger, 31-First condenser for distillation section, 32-Gas-liquid separator for distillation section, 33-Reflux pump for distillation section, 34-Second heat exchanger for distillation section, 35-Stripping section, 36-Stripping section heater, 37-Methylcarbamate storage unit, 38-Ionic liquid catalyst recovery and storage unit, 39-First vent pipe, 40-Urea production line, 41-Heat transfer oil furnace, 42-Nitrogen generator, 43-Second vent pipe, 44-Coolant pipeline, 45-Heavy component transfer pump for distillation kettle. Detailed Implementation

[0072] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0073] Example 1

[0074] This invention provides a system for preparing methyl methyl carbamate, as shown in Figure 1 (all connections between devices in Figure 1 are pipe connections, and all arrows indicate the direction of movement of liquid or gaseous substances). The system includes:

[0075] (1) Methyl methyl carbamate preparation vessel 1, wherein,

[0076] The methyl methyl carbamate preparation vessel 1 is used to mix methanol, dimethyl carbonate, ionic liquid catalyst and urea to carry out a second chemical reaction to obtain methyl methyl carbamate.

[0077] The methyl methyl carbamate preparation vessel 1 has a volume of 5L and is controllably connected to the nitrogen generator 42, the thermal oil furnace 41, and the coolant pipeline 44 via valves and pipes.

[0078] The methyl methyl carbamate preparation vessel 1 includes a feed manhole for adding methanol, dimethyl carbonate and urea into the methyl methyl carbamate preparation vessel 1.

[0079] (2) Ionic liquid catalyst preparation vessel 2; wherein,

[0080] The ionic liquid catalyst preparation vessel 2 is used to mix methyl methyl carbamate and zinc acetate to carry out the first chemical reaction, thereby obtaining the ionic liquid catalyst.

[0081] The ionic liquid catalyst preparation vessel 2 has a capacity of 1L and is controllably connected to the nitrogen generator 42, the thermal oil furnace 41, and the coolant pipeline 44 via valves and pipes.

[0082] The ionic liquid catalyst preparation vessel 2 includes a feed port through which methyl methyl carbamate and zinc acetate are added to the ionic liquid catalyst preparation vessel 2.

[0083] The feed inlet at the top of the methyl methyl carbamate preparation vessel 1 and the discharge outlet at the bottom of the ionic liquid catalyst preparation vessel 2 are connected by pipes and valves to controllably add the ionic liquid catalyst prepared in the ionic liquid catalyst preparation vessel 2 to the methyl methyl carbamate preparation vessel 1 in a quantitative manner during the feeding stage.

[0084] (3) Condensation circulation reflux unit, wherein,

[0085] The condensation circulation reflux unit includes a first-stage packed demister 5, a first-stage vertical condenser 6, a second-stage packed demister 7, a second-stage vertical condenser 8, a horizontal shell-and-tube condenser 9, and a gas-liquid separator 3, which are connected in sequence.

[0086] The discharge port at the top of the methyl methyl carbamate preparation vessel 1 is connected to the inlet of the first-stage packing demister 5.

[0087] The liquid phase outlet of the gas-liquid separator 3 is connected to the methyl methyl carbamate preparation vessel 1 via a reflux pipe. The condensation circulation reflux unit also includes a circulation reflux pump 4, which is installed on the reflux pipe between the liquid phase outlet of the gas-liquid separator 3 and the methyl methyl carbamate preparation vessel 1.

[0088] The vertical tower section, consisting of a first-stage packed demister 5, a first-stage vertical condenser 6, a second-stage packed demister 7, and a second-stage vertical condenser 8, can perform preliminary gas-liquid separation of the volatile and rising droplets and gaseous materials in the methyl methyl carbamate preparation vessel 1. Some of the droplets and gaseous materials are cooled into liquid phase in the vertical tower section and flow directly back into the methyl methyl carbamate preparation vessel 1 under gravity to continue participating in the reaction, maintaining the balance of reactants in the methyl methyl carbamate preparation vessel 1 and improving the conversion rate of the reaction.

[0089] The phase separation of methanol, dimethyl carbonate, and reaction byproduct gases ammonia and carbon dioxide is carried out in gas-liquid separator 3. Ammonia, carbon dioxide, and unreacted methanol and dimethyl carbonate enter the gas-liquid separator 3 in gaseous state from the methyl methyl carbamate preparation vessel 1 for gas-liquid separation. Ammonia and carbon dioxide then enter the subsequent reaction byproduct gas recovery unit in gaseous state. Unreacted methanol and dimethyl carbonate, in liquid state, flow downwards from the overflow port on the side of the gas-liquid separator 3 through a pipeline into the inlet of the reflux pump 4, and are then transported to the methyl methyl carbamate preparation vessel 1 by the reflux pump 4. The reflux circulation maintains the balance of reactants in the methyl methyl carbamate preparation vessel 1, thereby improving the reaction conversion rate.

[0090] (4) A reaction byproduct gas recovery unit, wherein...

[0091] The gas phase outlet of the gas-liquid separator 3 can be controllably connected to the reaction by-product gas recovery unit to recover the ammonia and carbon dioxide produced by the reaction.

[0092] The reaction byproduct gas recovery unit is connected to the urea production line 40 so that the recovered ammonia and carbon dioxide can be used for urea synthesis.

[0093] The reaction byproduct gas recovery unit includes a first gas buffer tank 11 and a second gas buffer tank 13 connected in sequence. A first pressure regulating valve 12 is provided on the communication channel between the gas-liquid separator 3 and the first gas buffer tank 11. A second pressure regulating valve 14 is provided on the communication channel between the first gas buffer tank 11 and the second gas buffer tank 13. A third pressure regulating valve 15 is provided on the communication channel between the second gas buffer tank 13 and the urea production line 40.

[0094] (5) Synthetic mixture storage tank 16, wherein...

[0095] The synthesis mixture storage tank 16 is located between the methyl methyl carbamate preparation vessel 1 and the subsequent distillation vessel 20.

[0096] After the reaction is terminated, the reactants in the methyl methyl carbamate preparation vessel 1 are cooled and depressurized, and then transported through pipelines and valves to the synthesis mixture transfer pump 10 and stored in the synthesis mixture storage tank 16 for later use. Its main components are methanol, dimethyl carbonate, methyl methyl carbamate, ionic liquid catalyst and trace amounts of urea (mainly dissolved in methanol, dimethyl carbonate and methyl methyl carbamate).

[0097] (6) Refining unit, wherein,

[0098] The refining unit includes: a methanol and dimethyl carbonate mixture storage unit 17, a high-pressure steam supply unit 18, a distillation kettle feed pump 19, a condensate outlet 24, a distillation kettle 20, a vertical distillation kettle condenser 21, a horizontal distillation kettle condenser 22, a distillation kettle gas-liquid separator 23, a distillation kettle heavy component storage tank 26, a distillation kettle heavy component transfer pump 45, a distillation column 28 (with a rectification section 27 and a stripping section 35), a distillation column feed pump 25, a first heat exchanger for the distillation column 29, a feed preheater 30, a first condenser for the rectification section 31, a gas-liquid separator for the rectification section 32, a reflux pump for the rectification section 33, a second heat exchanger for the rectification section 34, a stripping section heater 36, a coolant pipeline 44, a thermal oil furnace 41, an ionic liquid catalyst recovery and storage unit 38, and a methyl methyl carbamate storage unit 37.

[0099] The inlet of the distillation kettle 20 is connected to the outlet of the synthesis mixture storage tank 16. Since the boiling point difference between methanol, dimethyl carbonate, methyl methyl carbamate, and the ionic liquid catalyst is greater than 70°C, the low-boiling-point methanol and dimethyl carbonate in the synthesis mixture are heated and vaporized by steam in the distillation kettle 20. These vaporized vapors then rise to the horizontal condenser 22 connected to the top of the distillation kettle, where they are condensed into liquid and separated. The distilled methanol and dimethyl carbonate mixture, after component analysis, will be used as raw material again in the synthesis reaction of this invention. The high-boiling-point methyl methyl carbamate, ionic liquid catalyst, and a small amount of urea do not undergo phase change and remain at the bottom of the distillation kettle 20 as the distillation residue mixture. This mixture is pumped into the distillation kettle heavy component storage tank 26 via the distillation kettle heavy component transfer pump 45. Subsequently, the distillation residue mixture in the distillation kettle heavy component storage tank 26 continues to enter the rectification column 28 for continuous atmospheric pressure distillation separation of the methyl methyl carbamate, ionic liquid catalyst, and a small amount of urea. Methyl methyl carbamate is separated from the upper part of the rectification section 27, the ionic liquid catalyst is separated from the lower part of the stripping section 35, and a small amount of urea is finally discharged from the bottom of the stripping section 35.

[0100] The process of producing methyl methyl carbamate in distillation column 27 is continuous. The heavy component mixture from the distillation vessel in the heavy component storage tank 26 is pumped into the distillation column feed pump 25. It is first pumped into the feed preheater 30 to exchange heat with the hot material exiting the distillation column, raising the temperature of the heavy component mixture. Then, it enters the first heat exchanger 29 of the distillation column to continue exchanging heat with the heat transfer oil. After the heavy component mixture from the distillation vessel reaches a higher temperature, it is continuously added into the distillation column 28 from the top of the stripping section 35. Some of the liquid methyl methyl carbamate at the bottom of the distillation section 27 enters the top of the stripping section 35 and mixes with the remaining distillation mixture entering the distillation column 28. Then, it flows down from the top of the stripping section 35. Simultaneously, the downstream liquid and the rising gas flow interact, transferring mass and heat, causing some of the volatile methyl methyl carbamate in the liquid to vaporize and rise. The gaseous methyl methyl carbamate is distilled into the rectification section 27, while the liquid methyl methyl carbamate, the non-volatile ionic liquid catalyst, and a small amount of urea continue to descend to the bottom of the stripping section 35, enter the stripping section heater 36 for heating, and are then transported back to the middle of the stripping section 35. Some of the heated methyl methyl carbamate, which has been converted from liquid to gas, rises to the rectification section 27 and is continuously refined and separated. The ionic liquid catalyst and a small amount of urea, after the methyl methyl carbamate content is qualified, are finally discharged from the bottom of the stripping section 35 and enter the ionic liquid catalyst recovery and storage unit 38, where they will be used as raw materials again in the synthesis reaction of this invention. The gaseous methyl methyl carbamate rising to the top of the rectification section 27 passes through the first condenser 31 of the rectification section, resulting in a mixture of gaseous and liquid methyl methyl carbamate. This mixture then enters the gas-liquid separator 32 of the rectification section to separate the gaseous methyl methyl carbamate, while the liquid methyl methyl carbamate is returned to the middle of the rectification section via the reflux pump 33. Once the methyl methyl carbamate reaches the required purity, it is cooled again by the second heat exchanger 34 of the rectification section and then transported through pipelines to the methyl methyl carbamate storage unit 37.

[0101] (7) The first vent pipe 39 and the second vent pipe 43 are used for system venting operations.

[0102] This embodiment also provides a method for preparing methyl methyl carbamate, which includes:

[0103] The system shown in Figure 1 was used for preparation. In the system shown in Figure 1, 372.1 g (4.181 mol) of methyl methyl carbamate and 127.9 g (0.697 mol) of zinc acetate (molar ratio of 6:1) were added to the ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and the heat transfer oil furnace was turned on for heating. After reacting at 150°C for 60 min, the temperature was lowered to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0104] The synthesized ionic liquid catalyst was further purified by removing free MMC through vacuum distillation (heating temperature 135–138 °C, pressure -0.06–0.09 MPa). The structure of the synthesized ionic liquid catalyst (as shown in Figure 2) was illustrated by infrared characterization of the purified catalyst and the raw materials before synthesis (i.e., a homogeneous solution of physically dissolved MMC and zinc acetate at room temperature). The infrared characterization results show that the catalyst retained all characteristic peaks of MMC before synthesis and after purification (as shown in Figure 3), indicating that the basic structural framework of MMC remained unchanged. However, at 2200 cm⁻¹… -1 New characteristic peaks appeared on both sides (as shown in Figure 4), corresponding to a triple bond or cumulative double bond structure formed by carbon and nitrogen atoms. Since there are no terminal nitrogen atoms and adjacent carbon atoms in the structure, a triple bond structure cannot be formed; therefore, it should be a cumulative double bond structure. Another major change was observed at 1690 cm⁻¹. -1 The characteristic peaks on the left and right (as shown in Figure 5) correspond to the carbonyl structure. It can be seen that the catalyst structure consists of a chelate bond between zinc ions and carbonyl oxygen, while the electron cloud of the nearby nitrogen atom strengthens the bond between the carbonyl carbon atom, balancing the influence of the chelate bond between zinc ions and carbonyl carbon atoms on the carbonyl group. This is consistent with the expected coordination mode in the target ionic liquid catalyst structure and the electronic effect induced by zinc ion coordination. Furthermore, the remaining characteristic peaks all conform to the trends resulting from the determination of the catalyst structure. Simultaneously, the solution conductivity was 0.07 S / m before catalyst synthesis, decreasing to 0.04 S / m after synthesis. The reason for this is attributed to the formation of chelate ions, which increases the ion volume and reduces the ion migration rate, thereby decreasing the conductivity. This result further confirms the ionic liquid structure of the catalyst obtained by the preparation method.

[0105] 374.8 g (11.7 mol) of methanol, 1053.9 g (11.7 mol) of dimethyl carbonate, 234.2 g (3.9 mol) of urea (molar ratio 3:3:1), and 7.03 g (based on 3% of the urea feed amount) of the prepared ionic liquid catalyst were added to methyl methyl carbamate preparation vessel 1. The vessel was sealed, and stirring was started to dissolve the materials. The air inside the vessel was evacuated by applying a vacuum, and then nitrogen was introduced to pressurize the vessel to 0.7 MPa. The heat transfer oil heater was turned on to heat the vessel to 200°C, at which point the pressure inside the vessel was 6.0 MPa. Under these conditions, some of the reactants inside the vessel vaporized and rose to the condensation and reflux unit, forming a normal reflux. The condensed methanol and dimethyl carbonate liquids flowed back into the vessel normally. The reaction was carried out at this temperature and pressure for 40 minutes. The control valve 15 of the reaction byproduct gas recovery unit was opened, and ammonia and carbon dioxide were slowly released once to the reaction byproduct gas recovery unit. The pressure inside the methyl methyl carbamate preparation vessel decreased; after the ammonia and carbon dioxide were discharged, valve 15 was closed. At 60 minutes of reaction, the pressure inside the vessel was 7.2 MPa; ammonia and carbon dioxide were released and discharged once more. When the reactants in the vessel continued to react at 220℃ for 2 hours, the pressure inside the vessel was controlled at 8.0 MPa, indicating the reaction was complete. Heating was stopped, and cooling liquid was introduced to lower the temperature until it dropped below 50℃. Then, all the reactants were transferred to distillation vessel 20, where steam heating was used for distillation to completely separate methanol and dimethyl carbonate. The distillation residue was then transferred to rectification column 28 for rectification. 241.7 g of methyl methyl carbamate was obtained. Calculations showed a urea conversion rate of 99.8% and a methyl methyl carbamate selectivity of 69.6%.

[0106] Example 2

[0107] This embodiment provides a method for preparing methyl methyl carbamate, which includes:

[0108] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 397.5 g (4.466 mol) of methyl methyl carbamate and 102.5 g (0.559 mol) of zinc acetate (molar ratio of 8:1) were added to the ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 100 °C for 105 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0109] 374.8 g (11.7 mol) of methanol, 1053.9 g (11.7 mol) of dimethyl carbonate, 234.2 g (3.9 mol) of urea (molar ratio 3:3:1), and 15.22 g (based on 6.5% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 243.2 g of methyl methyl carbamate was obtained.

[0110] Example 3

[0111] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 414.5 g (4.657 mol) of methyl methyl carbamate and 85.5 g (0.466 mol) of zinc acetate (molar ratio 10:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 125 °C for 150 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0112] 374.8 g (11.7 mol) of methanol, 1053.9 g (11.7 mol) of dimethyl carbonate, 234.2 g (3.9 mol) of urea (molar ratio 3:3:1), and 23.42 g (based on 10% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts during the synthesis reaction three times. Other reaction conditions were the same as in Example 1. 241.3 g of methyl methyl carbamate was obtained.

[0113] Example 4

[0114] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 372.1 g (4.181 mol) of methyl methyl carbamate and 127.9 g (0.697 mol) of zinc acetate (molar ratio 6:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 150 °C for 105 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis and ammonolysis reactions of urea with methanol and dimethyl carbonate.

[0115] 246.1 g (7.68 mol) of methanol, 1268.3 g (14.08 mol) of dimethyl carbonate, 153.8 g (2.56 mol) of urea (molar ratio 3:5.5:1), and 15.38 g (based on 10% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 169.3 g of methyl methyl carbamate was obtained.

[0116] Example 5

[0117] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 397.5 g (4.466 mol) of methyl methyl carbamate and 102.5 g (0.559 mol) of zinc acetate (molar ratio of 8:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 100 °C for 150 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0118] 246.1 g (7.68 mol) of methanol, 1268.3 g (14.08 mol) of dimethyl carbonate, 153.8 g (2.56 mol) of urea (molar ratio 3:5.5:1), and 10 g (based on 6.5% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 170.7 g of methyl methyl carbamate was obtained.

[0119] Example 6

[0120] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 414.5 g (4.657 mol) of methyl methyl carbamate and 85.5 g (0.466 mol) of zinc acetate (molar ratio 10:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 125 °C for 60 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0121] 246.1 g (7.68 mol) of methanol, 1268.3 g (14.08 mol) of dimethyl carbonate, 153.8 g (2.56 mol) of urea (molar ratio 3:5.5:1), and 4.61 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 167.7 g of methyl methyl carbamate was obtained.

[0122] Example 7

[0123] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 372.1 g (4.181 mol) of methyl methyl carbamate and 127.9 g (0.697 mol) of zinc acetate (molar ratio 6:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 150 °C for 150 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis and ammonolysis reactions of urea with methanol and dimethyl carbonate.

[0124] 182.7 g (5.7 mol) of methanol, 1369.3 g (15.2 mol) of dimethyl carbonate, 114.2 g (1.9 mol) of urea (molar ratio 3:8:1), and 7.42 g (based on 6.5% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 122 g of methyl methyl carbamate was obtained.

[0125] Example 8

[0126] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 397.5 g (4.466 mol) of methyl methyl carbamate and 102.5 g (0.559 mol) of zinc acetate (molar ratio of 8:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 100 °C for 60 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0127] 182.7 g (5.7 mol) of methanol, 1369.3 g (15.2 mol) of dimethyl carbonate, 114.2 g (1.9 mol) of urea (molar ratio 3:8:1), and 3.426 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 124.3 g of methyl methyl carbamate was obtained.

[0128] Example 9

[0129] Using the methyl methyl carbamate preparation system described in Example 1, in the apparatus shown in Figure 1, 414.5 g (4.657 mol) of methyl methyl carbamate and 85.5 g (0.466 mol) of zinc acetate (molar ratio 10:1) were added to a 1 L ionic liquid catalyst preparation vessel 2. Nitrogen gas was introduced into the vessel, stirring was started and heating was initiated. The reaction was carried out at 125 °C for 105 min, and then cooled to room temperature to obtain a colorless and transparent liquid, which is the ionic liquid catalyst for the multi-step alcoholysis reaction and ammonolysis reaction of urea with methanol and dimethyl carbonate.

[0130] 182.7 g (5.7 mol) of methanol, 1369.3 g (15.2 mol) of dimethyl carbonate, 114.2 g (1.9 mol) of urea (molar ratio 3:8:1), and 11.42 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 123 g of methyl methyl carbamate was obtained.

[0131] Example 10

[0132] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 1.

[0133] 581.6 g (18.15 mol) of methanol, 891.8 g (9.9 mol) of dimethyl carbonate, 198.2 g (3.3 mol) of urea (molar ratio 5.5:3:1), and 12.88 g (based on 6.5% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 218.6 g of methyl methyl carbamate was obtained.

[0134] Example 11

[0135] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 2.

[0136] 581.6 g (18.15 mol) of methanol, 891.8 g (9.9 mol) of dimethyl carbonate, 198.2 g (3.3 mol) of urea (molar ratio 5.5:3:1), and 5.95 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 220.9 g of methyl methyl carbamate was obtained.

[0137] Example 12

[0138] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 3.

[0139] 581.6 g (18.15 mol) of methanol, 891.8 g (9.9 mol) of dimethyl carbonate, 198.2 g (3.3 mol) of urea (molar ratio 5.5:3:1), and 19.82 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 221.8 g of methyl methyl carbamate was obtained.

[0140] Example 13

[0141] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 4.

[0142] 401.8 g (12.54 mol) of methanol, 1129.6 g (12.54 mol) of dimethyl carbonate, 137 g (2.28 mol) of urea (molar ratio 5.5:5.5:1), and 4.11 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 151.6 g of methyl methyl carbamate was obtained.

[0143] Example 14

[0144] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 5.

[0145] 401.8 g (12.54 mol) of methanol, 1129.6 g (12.54 mol) of dimethyl carbonate, 137 g (2.28 mol) of urea (molar ratio 5.5:5.5:1), and 8.91 g (based on 6.5% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 155.5 g of methyl methyl carbamate was obtained.

[0146] Example 15

[0147] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 6.

[0148] 401.8 g (12.54 mol) of methanol, 1129.6 g (12.54 mol) of dimethyl carbonate, 137 g (2.28 mol) of urea (molar ratio 5.5:5.5:1), and 13.7 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 156.9 g of methyl methyl carbamate was obtained.

[0149] Example 16

[0150] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 7.

[0151] 307.6 g (9.6 mol) of methanol, 1257.5 g (13.96 mol) of dimethyl carbonate, 104.8 g (1.745 mol) of urea (molar ratio 5.5:8:1), and 3.14 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 120.3 g of methyl methyl carbamate was obtained.

[0152] Example 17

[0153] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 8.

[0154] 307.6 g (9.6 mol) of methanol, 1257.5 g (13.96 mol) of dimethyl carbonate, 104.8 g (1.745 mol) of urea (molar ratio 5.5:8:1), and 6.81 g (based on 6.5% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 119.3 g of methyl methyl carbamate was obtained.

[0155] Example 18

[0156] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 9.

[0157] 307.6 g (9.6 mol) of methanol, 1257.5 g (13.96 mol) of dimethyl carbonate, 104.8 g (1.745 mol) of urea (molar ratio 5.5:8:1), and 10.48 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 120.7 g of methyl methyl carbamate was obtained.

[0158] Example 19

[0159] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 1.

[0160] 730.5 g (22.8 mol) of methanol, 770.2 g (8.55 mol) of dimethyl carbonate, 171.2 g (2.85 mol) of urea (molar ratio 8:3:1), and 11.128 g (based on 6.5% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 191.6 g of methyl methyl carbamate was obtained.

[0161] Example 20

[0162] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 2.

[0163] 730.5 g (22.8 mol) of methanol, 770.2 g (8.55 mol) of dimethyl carbonate, 171.2 g (2.85 mol) of urea (molar ratio 8:3:1), and 17.12 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 193.3 g of methyl methyl carbamate was obtained.

[0164] Example 21

[0165] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 3.

[0166] 730.5 g (22.8 mol) of methanol, 770.2 g (8.55 mol) of dimethyl carbonate, 171.2 g (2.85 mol) of urea (molar ratio 8:3:1), and 5.136 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 192.6 g of methyl methyl carbamate was obtained.

[0167] Example 22

[0168] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 4.

[0169] 525.5 g (16.4 mol) of methanol, 1015.6 g (11.275 mol) of dimethyl carbonate, 123.1 g (2.05 mol) of urea (molar ratio 8:5.5:1), and 1.23 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 139.4 g of methyl methyl carbamate was obtained.

[0170] Example 23

[0171] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 5.

[0172] 525.5 g (16.4 mol) of methanol, 1015.6 g (11.275 mol) of dimethyl carbonate, 123.1 g (2.05 mol) of urea (molar ratio 8:5.5:1), and 3.69 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 138.5 g of methyl methyl carbamate was obtained.

[0173] Example 24

[0174] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 6.

[0175] 525.5 g (16.4 mol) of methanol, 1015.6 g (11.275 mol) of dimethyl carbonate, 123.1 g (2.05 mol) of urea (molar ratio 8:5.5:1), and 8 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 138.9 g of methyl methyl carbamate was obtained.

[0176] Example 25

[0177] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 7.

[0178] 412.7 g (12.88 mol) of methanol, 1160.2 g (12.88 mol) of dimethyl carbonate, 96.7 g (1.61 mol) of urea (molar ratio 8:8:1), and 2.901 g (based on 3% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 200 °C, and ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. Other reaction conditions were the same as in Example 1. 111.9 g of methyl methyl carbamate was obtained.

[0179] Example 26

[0180] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 8.

[0181] 412.7 g (12.88 mol) of methanol, 1160.2 g (12.88 mol) of dimethyl carbonate, 96.7 g (1.61 mol) of urea (molar ratio 8:8:1), and 6.286 g (based on 6.5% of the urea feed amount) of the aforementioned prepared ionic liquid catalyst were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 112.4 g of methyl methyl carbamate was obtained.

[0182] Example 27

[0183] The methyl methyl carbamate preparation system of Example 1 was used, and the ionic liquid catalyst preparation method was the same as in Example 9.

[0184] 412.7 g (12.88 mol) of methanol, 1160.2 g (12.88 mol) of dimethyl carbonate, 96.7 g (1.61 mol) of urea (molar ratio 8:8:1), and 9.67 g (based on 10% of the urea feed amount) of the ionic liquid catalyst prepared above were added to reactor 1 for the preparation of methyl methyl carbamate. The reaction temperature was controlled at 220 °C, and ammonia and carbon dioxide were released as byproducts four times during the synthesis reaction. Other reaction conditions were the same as in Example 1. 112.5 g of methyl methyl carbamate was obtained.

[0185] Comparative Example

[0186] Referring to the catalyst in Chinese Invention Patent Application Publication No. CN103524381A, which is dibutyltin oxide (DBTO), the comparative examples all use dibutyltin oxide to replace the ionic liquid catalyst of the present invention. The amount added is 1-12 mol% of the raw material substituted urea in Chinese Invention Patent Application Publication No. CN103524381A. Other process conditions and methods are the same as those in the implementation method of the present invention. Methyl methyl carbamate is obtained by reaction.

[0187] Comparative Example 1

[0188] Add 374.8 g (11.7 mol) of methanol, 1053.9 g (11.7 mol) of dimethyl carbonate, 234.2 g (3.9 mol) of urea (molar ratio 3:3:1), and 9.71 g (1% of the urea feed amount) of dibutyltin oxide to a 5 L methyl methyl carbamate preparation vessel. Seal the methyl methyl carbamate preparation vessel and start stirring to dissolve the materials. Evacuate the vessel by applying a vacuum, then pressurize it with nitrogen to 0.7 MPa. Turn on the heat transfer oil to heat the vessel. Raise the temperature to 200°C, at which point the pressure inside the vessel is 6.0 MPa. Under these conditions, some of the reactants in the vessel vaporize and rise to the condenser circulation reflux device, forming a normal reflux. The condensed methanol and dimethyl carbonate liquids flow back into the vessel normally. The reaction was carried out at this temperature and pressure for 40 minutes. The control valve of the by-product gas recovery device was opened, and ammonia and carbon dioxide were slowly released once to the reaction by-product gas recovery unit. The pressure inside the methyl methyl carbamate preparation vessel decreased; after the ammonia and carbon dioxide were discharged, the valve was closed. At 60 minutes of reaction, the pressure inside the vessel was 6.7 MPa; ammonia and carbon dioxide were released and discharged once more. When the reactants in the vessel continued to react at 220℃ for 2 hours, the pressure inside the vessel was controlled at 7.3 MPa, indicating the reaction was complete. Heating was stopped, and cooling liquid was introduced to lower the temperature until it dropped below 50℃. Then, all the reactants were transferred to a distillation vessel, and distillation was performed using steam heating to completely separate methanol and dimethyl carbonate. The distillation residue was then transferred to a rectification column, and 106.5 g of methyl methyl carbamate was obtained through rectification. The calculated urea conversion rate was 44.0%, and the methyl methyl carbamate selectivity was 30.7%.

[0189] Comparative Example 2

[0190] Except that the catalyst is replaced by dibutyltin oxide instead of the ionic liquid catalyst of the present invention, the other process conditions and methods are the same as in Example 14, and the composition and control conditions of the added raw materials are as follows:

[0191] 401.8 g (12.54 mol) of methanol, 1129.6 g (12.54 mol) of dimethyl carbonate, 137 g (2.28 mol) of urea (molar ratio 5.5:5.5:1), and 36.9 g (based on 6.5% of the urea feed amount) of dibutyltin oxide were added. The reaction temperature was controlled at 210 °C. Ammonia and carbon dioxide were released twice as byproducts during the synthesis reaction. 70.8 g of methyl methyl carbamate was obtained. The urea conversion rate was calculated to be 45.4%, and the selectivity of methyl methyl carbamate was 34.9%.

[0192] Comparative Example 3

[0193] Except that the catalyst is replaced by dibutyltin oxide instead of the ionic liquid catalyst of the present invention, the other process conditions and methods are the same as in Example 26, and the composition and control conditions of the added raw materials are as follows:

[0194] 412.7 g (12.88 mol) of methanol, 1160.2 g (12.88 mol) of dimethyl carbonate, 96.7 g (1.61 mol) of urea (molar ratio 8:8:1), and 48.1 g (based on 12% of the urea feed amount) of dibutyltin oxide were added. The reaction temperature was controlled at 210 °C, and ammonia and carbon dioxide were released as byproducts three times during the synthesis reaction. 52.7 g of methyl methyl carbamate was obtained. The urea conversion rate was calculated to be 46.8%, and the selectivity of methyl methyl carbamate was 36.8%.

[0195] The reaction conditions and comparative data for the preparation of ionic liquid catalysts in the above embodiments are shown in Table 1 below.

[0196] Table 1

[0197] The reaction conditions for the preparation of methyl methyl carbamates in the above examples and comparative examples are shown in Table 2 below.

[0198] Table 2

[0199] In Table 2, the molar ratio of methanol to dimethyl carbonate to urea is given; the amount of catalyst added is based on 100% of the weight of urea added; the unit of reaction temperature is °C; the unit of reaction pressure is MPa; the unit of reaction time is h; and the byproduct gases are ammonia and carbon dioxide.

[0200] The above embodiments and comparative data are shown in Table 3 below.

[0201] Table 3

[0202] Table 3 shows that when the molar ratio of methanol, dimethyl carbonate, and urea is 3–8:3–8:1, and the amount of the aforementioned ionic liquid catalyst (based on urea dosage) is 3–10%, the reaction temperature is 200–220℃, and the reaction pressure is 6.0–8.0 MPa, the urea conversion rate is close to 100%, and the selectivity of methyl methyl carbamate is 69.5–78.5%. In contrast, the comparative example, with a catalyst dosage of 1–12% (based on urea dosage), a reaction temperature of 200–220℃, and a reaction pressure of 6.0–8.0 MPa, shows a urea conversion rate of 44.0–46.8% and a selectivity of methyl methyl carbamate of 30.7–36.8%. Therefore, using butyltin oxide as a catalyst has no significant effect on the preparation method of methyl methyl carbamate from methanol, dimethyl carbonate, and urea.

Claims

1. An ionic liquid catalyst, wherein, The structural formula of the ionic liquid catalyst is [Zn(CH3NHC(O)OCH3)2]. 2+ ·2(CH2COO) - .

2. A method for preparing the ionic liquid catalyst according to claim 1, wherein, A first chemical reaction was carried out by mixing methyl methyl carbamate and zinc acetate to obtain an ionic liquid catalyst.

3. The method for preparing the ionic liquid catalyst according to claim 2, wherein, The temperature of the first chemical reaction is 100–150°C, and the time is 60–150 min.

4. The method for preparing the ionic liquid catalyst according to claim 2, wherein, The molar ratio of the methyl methyl carbamate to the zinc acetate is 6 to 10:

1.

5. A method for preparing a methyl methyl carbamate, wherein, include: Methanol, dimethyl carbonate, and urea are mixed and subjected to a second chemical reaction under the catalysis of the ionic liquid catalyst described in claim 1 to obtain methyl methyl carbamate.

6. The method for preparing methyl methyl carbamate according to claim 5, wherein, The second chemical reaction takes place at a temperature of 200–220°C, a pressure of 6.0–8.0 MPa, and a time of 2–3 hours.

7. The method for preparing methyl methyl carbamate according to claim 5, wherein, The molar ratio of methanol, dimethyl carbonate and urea is 3-8:3-8:1; The amount of the ionic liquid catalyst used is 3 to 10% of the weight of the urea.

8. The method for preparing methyl methyl carbamate according to claim 5, wherein, During the second chemical reaction, gaseous byproducts in the reaction product system are discharged.

9. A system for preparing methyl methyl carbamate, wherein, This includes a reactor for preparing ionic liquid catalysts and a reactor for preparing methyl methyl carbamates that are connected in sequence. The ionic liquid catalyst preparation vessel is used to mix methyl methyl carbamate and zinc acetate to carry out a first chemical reaction to obtain the ionic liquid catalyst. The methyl methyl carbamate preparation vessel is used to mix methanol, dimethyl carbonate, the ionic liquid catalyst, and urea to carry out a second chemical reaction to obtain methyl methyl carbamate.

10. The system for preparing methyl methyl carbamate according to claim 9, wherein, It also includes a condensation circulation reflux unit; The condensation circulation reflux unit includes a first-stage packed demister, a first-stage vertical condenser, a second-stage packed demister, a second-stage vertical condenser, a horizontal tube-and-shell condenser, and a gas-liquid separator connected in sequence. The discharge port at the top of the methyl methyl carbamate preparation vessel is connected to the inlet of the first-stage packing demister; The liquid phase outlet of the gas-liquid separator is connected to the methyl methyl carbamate preparation vessel via a reflux pipe.

11. The system for preparing methyl methyl carbamate according to claim 10, wherein, It also includes a reaction byproduct gas recovery unit; The gas phase outlet of the gas-liquid separator is connected to the reaction by-product gas recovery unit.

12. The system for preparing methyl methyl carbamate according to claim 10, wherein, It also includes a refining unit; The refining unit includes a distillation vessel and a distillation column connected in sequence; The feed inlet of the distillation vessel is connected to the discharge outlet at the bottom of the methyl methyl carbamate preparation vessel; The distillation column has a refined methyl methyl carbamate outlet.

13. A methyl methyl carbamate, wherein, It is prepared by the method for preparing methyl methyl carbamate according to any one of claims 5 to 8.

14. The application of the methyl methyl carbamate of claim 13 in electronic cleaning solvents, synthetic leather slurries, water-based coatings, water-based inks, water-based adhesives, leather finishing agents, organic solvents, and new energy battery electrolytes.

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