Apparatus and process for continuous production of methyl n-methylcarbamate

Abstract

The application discloses a device and a process for continuously producing N-methyl methylcarbamate, wherein a tower reactor is adopted as a main body, heat exchange pipes are arranged on the upper half of the tower reactor, a flow guide cylinder is arranged on the lower half of the tower reactor, and a nozzle is used for feeding, so that the incompletely dissolved catalyst is fully mixed and dissolved in the tower reactor to form a homogeneous system, temperature is controlled through the heat exchange pipes, and the generation of by-products is reduced; the high-temperature and high-pressure gas-liquid two-phase flow flowing out of the tower reactor is reduced in pressure through a pressure reducing valve, dimethyl carbonate (DMC) is partially vaporized in a distillation tower, and the other part is heated through a reboiler of a tower kettle and then vaporized and separated, so that the continuous production and separation are realized, and energy consumption is reduced.

Description

Technical Field

[0001] This invention belongs to the field of N-methylcarbamate preparation technology, specifically relating to an apparatus and process for continuous production of N-methylcarbamate. Background Technology

[0002] Carbamates are important intermediates in organic synthesis. They can undergo various chemical reactions to produce a wide range of downstream products. For example, in pesticides, carbamates are low-toxicity insecticides, acaricides, and fungicides, and can also be used as herbicides. In pharmaceuticals, they can be used as sedatives and hypnotics, and also possess anticonvulsant and anticancer properties. In polymers, they are mainly used to synthesize polyurethanes. In fine chemical intermediates, they can be used to synthesize diisocyanates, dialkyl carbonates, melamine derivatives, etc., showing broad application prospects. Furthermore, carbamates also have certain applications in areas such as moth repellents for clothing, low-shrinkage cement, phenolic resin modification, and powder coatings.

[0003] Early methods for synthesizing carbamates involved reacting amines with phosgene. This process, besides being highly energy-intensive, also used highly corrosive and toxic phosgene and produced hydrochloric acid as a byproduct, failing to meet the requirements of building an environmentally friendly society and limiting the development and application of carbamates. Therefore, researchers proposed a new synthetic method: one molecule of a substituted urea and one molecule of a carbonate compound react under a catalyst to generate two molecules of a carbamate compound. This reaction is green and atom-economical. Based on this method, researchers used 1,3-dimethylurea (DMU) and dimethyl carbonate (DMC) for the highly efficient catalytic synthesis of methyl N-methylcarbamate (MMC).

[0004]

[0005] Currently, the production methods for N-methylcarbamate include:

[0006] The relevant patent reports that dimethyl carbonate, 1,3-dimethylurea, and DBTO are added to a stainless steel reactor in a molar ratio of 11:1, and the reaction is carried out at 150°C and 0.1 MPa under sealed conditions for 4 hours to obtain N-methylcarbamate with a yield of up to 99%. This patent-reported method is a laboratory batch production process with mild production conditions and a high product yield. However, there are currently no reports on continuous production methods for N-methylcarbamate. Batch production has the following drawbacks:

[0007] 1. The solid catalyst in this system needs to be dissolved at a high temperature and pretreated for a period of time to initiate a highly efficient catalytic reaction. Traditional jacketed heating systems with built-in stirred tanks result in slow catalyst dissolution, a heterogeneous initial reaction, poor mixing, and a slow reaction rate. 2. The reactor is a high-pressure vessel, operating under closed conditions of high temperature and pressure. The heat released during the reaction can cause excessively high temperatures, which can exacerbate the decomposition of dimethyl carbonate (DMC), leading to raw material waste. 3. The system suffers from low automation, slow reaction rate, long production cycle, and low production capacity. 4. After the reaction, product separation is not integrated with subsequent separation operations, resulting in energy waste and complex operation.

[0008] In view of this, it is currently necessary to design an apparatus and process that can efficiently and continuously produce and separate N-methylcarbamate and meet the different requirements at different stages of the reaction process. Summary of the Invention

[0009] To address the above-mentioned problems, the present invention aims to provide an apparatus and process for the continuous production of N-methylcarbamate.

[0010] The specific technical solution is as follows:

[0011] An apparatus for continuous production of N-methylcarbamate includes a batching device, a slurry pump, a heater, a tower reactor, a pressure reducing valve, a distillation column, a centrifugal pump, a continuous crystallizer, a filter, a cooler, and a gas-liquid separator. The upper part of the tower reactor is a homogeneous reaction zone containing heat exchange tubes. The outlet of the batching device is connected to the slurry pump. The outlet pipe of the slurry pump splits into two pipes, connecting to the heat exchange tubes and the heater respectively. The outlet pipe of the heat exchange tubes merges with the inlet pipe of the heater. The inlet pipe of the heater is equipped with a regulating valve to control the amount of material flowing through the heat exchange tubes. The bottom outlet pipe of the heater connects to the bottom of the tower reactor. The top outlet pipe of the tower reactor connects sequentially to the pressure reducing valve and the distillation column. The bottom outlet pipe of the distillation column connects sequentially to the centrifugal pump, the continuous crystallizer, and the filter. The top outlet pipe of the distillation column connects sequentially to the cooler and the gas-liquid separator.

[0012] Furthermore, the lower part of the tower reactor is a heterogeneous reaction zone, which is equipped with a guide tube. The bottom of the tower reactor is equipped with a nozzle, which is located at the center of the cross section of the guide tube. The upper end of the nozzle is flush with the lower end of the guide tube, and the nozzle is connected to the outlet pipe at the bottom of the heater.

[0013] A process for the continuous production of N-methylcarbamate using the above-mentioned apparatus includes the following steps: dimethylurea, dimethyl carbonate, and catalyst are added to a batching device in proportion and stirred into a uniform slurry. The raw material slurry is continuously pumped through a slurry pump, heated through a heat exchange tube and a heater, and then enters a tower reactor for reaction. The reacted material flows out from the top of the tower, is depressurized by a pressure reducing valve, and then enters a distillation tower for distillation separation. The low-boiling-point dimethyl carbonate and non-condensable gas flow out from the top of the distillation tower, are cooled by a cooler, and then enter a gas-liquid separator for separation. The non-condensable gas is discharged from the top of the gas-liquid separator and treated as waste gas. The dimethyl carbonate is discharged from the bottom and reused after post-treatment. The high-boiling-point N-methylcarbamate and dissolved catalyst flow out from the bottom of the tower, are pumped by a centrifugal pump, and then enter a continuous crystallizer. The catalyst precipitates in the continuous crystallizer and then enters a filter to remove the solid catalyst. The N-methylcarbamate is then subjected to subsequent purification.

[0014] Furthermore, the molar ratio of dimethylurea and dimethyl carbonate fed into the batching equipment is 1:3-1:20, the catalyst is dibutyltin oxide, and the amount of catalyst fed is 0.1-1% of the total mass of dimethylurea and dimethyl carbonate.

[0015] Furthermore, the raw material temperature is preheated to 40-60℃ by the heat exchange tubes, and then heated to 135-155℃ by the heater. The minimum heat exchange area of ​​the heat exchange tubes... Where X2 is the conversion rate of dimethylurea at the end of the reaction, and T r The reaction temperature inside the tower reactor is given in °C and F. A0 denoted as the molar flow rate of dimethylurea, mol / s; T0 is the feed temperature of the tower reactor (4), °C; Cp is the specific heat capacity of the feedstock, J / (g·℃); and n is the molar ratio of dimethyl carbonate to dimethylurea, M DMC M DMU ρ0 and ρ0 are the molar masses of dimethyl carbonate and dimethylurea, respectively, in g / mol, and K is the heat transfer coefficient in W / (m2). 2 ·℃), △H is the heat of reaction J / mol, △T is the heat transfer temperature difference, and the unit is ℃.

[0016] Solid catalysts need to dissolve and activate at temperatures above 120°C for a period of time. Therefore, the temperature of the tower reactor must be maintained at at least 120°C. The reaction is exothermic; excessively high temperatures will exacerbate the decomposition of dimethyl carbonate in the feedstock, producing non-condensable carbon dioxide and methanol as a byproduct, resulting in feedstock waste and increased pressure within the system. Therefore, while ensuring high temperatures, it is necessary to prevent the temperature in the tower reactor from becoming too high. Thus, heat exchange tubes are installed in the tower reactor, and feed liquid is circulated through the coils. The flow rate of the material entering the heat exchange tubes is regulated by a bypass regulating valve. To ensure that the temperature inside the tower reactor does not become too high (ensuring that the temperature inside the reactor is within the range of 145-165°C), the minimum heat exchange area of ​​the heat exchange tubes needs to be effectively designed. This minimum heat exchange area is calculated based on the maximum flow rate under the premise of a minimum temperature limit of 145°C in the tower reactor. If the temperature inside the tower reactor needs to be increased, only the flow rate needs to be adjusted.

[0017] Furthermore, the residence time of materials in the tower reactor is controlled at 3-10 hours.

[0018] Furthermore, the size of the heterogeneous reaction zone in the tower reactor is determined by... The calculation yields F. A0 X1 is the molar flow rate of dimethylurea in the feed solution, X2 is the conversion rate of the heterogeneous reaction section, and -r A1 The reaction rate of dimethylurea in the heterogeneous reaction zone is expressed in mol / (L·s); the size of the homogeneous reaction zone in the tower reactor is determined by... The calculations show that X2 represents the dimethylurea conversion rate in the homogeneous reaction section, and -r A denoted as the reaction rate in the homogeneous reaction zone, expressed in mol / (L·s).

[0019] Furthermore, the height-to-diameter ratio of the tower reactor is 8-15, the ratio of the inner diameter of the guide tube of the heterogeneous reaction zone to that of the tower reactor is 0.5-0.8, and the height of the guide tube is 0.8-0.9 of the height of the heterogeneous reaction zone.

[0020] Furthermore, the temperature inside the distillation column is controlled at 95-120℃, and the temperature of the gas-liquid separator is 40-60℃.

[0021] The beneficial effects of this invention are as follows:

[0022] 1) The main body of the device of the present invention uses a tower reactor, with a guide tube in the lower half and a nozzle for feeding. When the catalyst enters the reactor, the undissolved catalyst is fully mixed and dissolved in the tower reactor section to form a homogeneous system, which is conducive to the efficient catalytic reaction, improves the utilization rate of raw materials, and replaces the mechanical stirring device of the traditional batch reactor, making the overall process more airtight.

[0023] 2) This invention uses an external heater instead of the traditional jacket heating method to heat the material to the temperature required to initiate the reaction. The upper part of the tower reactor is equipped with heat exchange tubes, and the flow rate of the raw material liquid flowing through the coil can be adjusted by the bypass regulating valve to remove the excess heat released by the reaction, maintain the stability of the reaction, reduce the occurrence of side reactions (decomposition of dimethyl carbonate), and at the same time achieve the effect of preheating the raw material liquid, reducing energy consumption and improving production safety.

[0024] 3) The high-temperature and high-pressure gas-liquid two-phase flow from the reactor of this invention is depressurized by a pressure reducing valve. Part of the solvent DMC forms a superheated liquid and is partially vaporized in the distillation column. The other part is heated by the reboiler in the column bottom and then vaporized and separated. This design makes full use of the sensible heat of the material, realizes continuous production and separation, and reduces energy consumption.

[0025] 4) After the material of the present invention is preheated by the heat exchange tube and heated by the external heater, the solid reactants in the raw material can be completely dissolved, and a small amount of incompletely dissolved catalyst will not cause blockage, making the conveying smoother.

[0026] 5) Compared with traditional batch processes, this invention combines unit modules such as batching, heating, reaction, and separation, and uses continuous feeding and continuous discharging to connect the production and separation of MMC in series, achieving high-efficiency production and refining; the reaction of this invention has vigorous flow in the reactor, fast mass and heat transfer, and high production efficiency; at the same time, it can be used with a computer control system for remote control, high degree of automation, and fewer on-site operators. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process of the present invention.

[0028] In the diagram: 1. Batching equipment; 2. Slurry pump; 3. Heater; 4. Tower reactor; 41. Heat exchange tube; 42. Flow guide tube; 43. Nozzle; 5. Pressure reducing valve; 6. Distillation column; 7. Centrifugal pump; 8. Continuous crystallizer; 9. Filter; 10. Cooler; 11. Gas-liquid separator. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] like Figure 1As shown, an apparatus for the continuous production of N-methylcarbamate includes a batching device 1, a slurry pump 2, a heater 3, a tower reactor 4, a pressure reducing valve 5, a distillation column 6, a centrifugal pump 7, a continuous crystallizer 8, a filter 9, a cooler 10, and a gas-liquid separator 11. The upper part of the tower reactor 4 is a homogeneous reaction zone, within which heat exchange tubes 41 are installed. The lower part of the tower reactor 4 is a heterogeneous reaction zone, within which a guide tube 42 is installed. The outlet of the batching device 1 is connected to the slurry pump 2. The outlet pipe of the slurry pump 2 splits into two pipes, one connected to the heat exchange tube 41 and the other to the heater 3. The outlet pipe of the heat exchange tube 41... The inlet pipe of the heater 3 is connected to the inlet pipe of the heat exchange tube 41. The inlet pipe of the heater 3 is equipped with a regulating valve for controlling the amount of material flowing through the heat exchange tube 41. The bottom of the tower reactor 4 is equipped with a nozzle 43, which is located at the center of the cross section of the guide tube 42. The upper end of the nozzle 43 is flush with the lower end of the guide tube 42. The nozzle 43 is connected to the outlet pipe at the bottom of the heater 3. The top outlet pipe of the tower reactor 4 is connected to the pressure reducing valve 5 and the distillation column 6 in sequence. The bottom outlet pipe of the distillation column 6 is connected to the centrifugal pump 7, the continuous crystallizer 8 and the filter 9 in sequence. The top outlet pipe of the distillation column 6 is connected to the cooler 10 and the gas-liquid separator 11 in sequence.

[0031] In the embodiments of the present invention, the tower reactor 4 has an inner diameter of 0.5m and a height of 5m, wherein the guide tube 42 has an inner diameter of 0.4m and a height of 2m, and the heat transfer coefficient of the heat exchange tube 41 is taken as K = 250W / (m²). 2 (℃), the area A of the heat exchange tube is approximately 0.87m². 2 When the flow rate through the heat exchange tube is fully open, all the heat released by the reaction can be removed. During operation, the flow rate of the cold material through the heat exchange tube can be adjusted according to actual needs through the bypass regulating valve to achieve the temperature control requirements.

[0032] Example 1

[0033] Dimethyl urea (DMU) and dimethyl carbonate (DMC) are added to batching equipment 1 in a 1:5 ratio, followed by 0.7% (by weight of the total raw materials) of the catalyst dibutyltin oxide. The mixture is stirred at a stirring speed of 700 r / min until homogeneous, and then pumped at a flow rate of 0.20 m³ / min using slurry pump 2. 3The material is conveyed at a rate of / h, and the flow rate of the material passing through heat exchanger 41 is adjusted to preheat it from room temperature to 41℃. It is then fed into heater 3, where high-temperature steam heats the raw material to 150℃ before it enters tower reactor 4 for dissolution and mixing. In tower reactor 4, the reaction pressure is controlled at 5.0 bar, the reaction temperature at 150℃, and the total reaction time is 5 hours. Gas phase analysis of samples taken from the heterogeneous region shows that the conversion rate of the raw material dimethylurea (DMU) is 38.1%. The main components of the reacted material are excess dimethyl carbonate (DMC) and the generated N-methylcarbamate (MM). C) After flowing out from the top of the column, the pressure is reduced to 1 bar by the pressure reducing valve 5 and enters the distillation column 6, where dimethyl carbonate (DMC) forms a superheated liquid. The sensible heat causes it to partially vaporize, and the unvaporized dimethyl carbonate (DMC) settles into the bottom of the column. The reboiler in the bottom of the column distills the dimethyl carbonate (DMC). The distillation column 6 operates at a pressure of 1 bar and a temperature of 100°C, with 10 trays. Dimethyl carbonate vapor (DMC) and other non-condensable gases flow out from the top of the distillation column 6 and are cooled to 50°C by the cooler 10 before entering the gas-liquid separator 11 for separation at a temperature of 40°C. Non-condensable gases are treated from the top, and condensates such as dimethyl carbonate (DMC) are recycled after post-treatment. The N-methylcarbamate (MMC) in the bottom of the tower contains dissolved catalyst with a purity of 99.5%. It is pumped by centrifugal pump 7 into continuous crystallizer 8, where the catalyst precipitates. Then it enters filter 9 to filter out the solid catalyst. The N-methylcarbamate (MMC) is then purified to a yield of 92.3%.

[0034] Example 2

[0035] Dimethyl urea (DMU): dimethyl carbonate (DMC) is added to batching equipment 1 at a ratio of 1:5, followed by 0.7% (by weight of the total raw materials) of the catalyst dibutyltin oxide. The mixture is stirred at a stirring speed of 700 r / min until homogeneous. A slurry pump 2 is then used to pump the mixture at a flow rate of 0.33 m³ / min. 3The material is conveyed at a rate of / h, and the flow rate of the material passing through the heat exchange tube 41 is adjusted to preheat it from room temperature to 39°C. Then it is fed into the heater 3, where high-temperature steam heats the raw material to 150°C before it enters the tower reactor 4 for dissolution and mixing. In tower reactor 4, the reaction pressure was controlled at 5.0 bar, the reaction temperature at 150°C, and the total reaction time at 5 h. Gas phase analysis of samples taken from the heterogeneous region revealed a conversion rate of 29.3% for the raw material dimethyl urea (DMU). The main components of the reacted material were excess dimethyl carbonate (DMC) and generated N-methylcarbamate (MMC). After flowing out from the top of the tower, the pressure was reduced to 1 bar by pressure reducing valve 5 and then entered distillation tower 6. In this distillation tower, the dimethyl carbonate (DMC) formed a superheated liquid, and its sensible heat caused partial vaporization. The unvaporized dimethyl carbonate (DMC) settled into the bottom of the tower. The reboiler in the bottom of the tower distilled the dimethyl carbonate (DMC). The distillation tower 6 operated at 1 bar and 100°C, with 5 trays. Dimethyl carbonate vapor (DMC) and other non-condensable gases flowed out from the top of distillation tower 6, were cooled to 50°C by cooler 10, and then entered gas-liquid separator 11 for separation at an operating temperature of 40°C. Non-condensable gases are treated from the top, and condensates such as dimethyl carbonate (DMC) are recycled after post-treatment. The N-methylcarbamate (MMC) in the bottom of the tower contains dissolved catalyst with a purity of 93.2%. It is pumped by centrifugal pump 7 into continuous crystallizer 8, where the catalyst precipitates. Then it enters filter 9 to remove the solid catalyst. The N-methylcarbamate (MMC) is then purified to a yield of 62.1%.

[0036] Example 3

[0037] Dimethyl urea (DMU) and dimethyl carbonate (DMC) were added to batching equipment 1 at a ratio of 1:5, followed by 0.7% (by weight of the total raw materials) of the catalyst dibutyltin oxide. The mixture was stirred at a stirring speed of 700 r / min until homogeneous, and then pumped at a flow rate of 0.20 m³ / min using slurry pump 2. 3The material is conveyed at a rate of / h, and the flow rate of the material passing through heat exchanger 41 is adjusted to preheat it from room temperature to 39℃. It is then fed into heater 3, where high-temperature steam heats the raw material to 160℃ before it enters tower reactor 4 for dissolution and mixing. In tower reactor 4, the reaction pressure is controlled at 6.2 bar, the reaction temperature at 160℃, and the total reaction time is 5 hours. Gas phase analysis of samples taken from the heterogeneous region shows that the conversion rate of the raw material dimethylurea (DMU) is 43.4%. The main components of the reacted material are excess dimethyl carbonate (DMC) and the generated N-methylcarbamate (MM). C) After flowing out from the top of the column, the pressure is reduced to 1 bar by the pressure reducing valve 5 and enters the distillation column 6, where dimethyl carbonate (DMC) forms a superheated liquid. The sensible heat causes it to partially vaporize, and the unvaporized dimethyl carbonate (DMC) settles into the bottom of the column. The reboiler in the bottom of the column distills the dimethyl carbonate (DMC). The operating pressure of the distillation column 6 is 1 bar, the operating temperature is 105°C, and there are 2 trays. The dimethyl carbonate vapor (DMC) and other non-condensable gases flow out from the top of the distillation column 6 and are cooled to 50°C by the cooler 10. Then they enter the gas-liquid separator 11 for separation, with an operating temperature of 50°C. Non-condensable gases are treated from the top, and condensates such as dimethyl carbonate (DMC) are recycled after post-treatment. The N-methylcarbamate (MMC) in the bottom of the tower contains dissolved catalyst with a purity of 68%. It is pumped by centrifugal pump 7 into continuous crystallizer 8, where the catalyst precipitates. Then it enters filter 9 to filter out the solid catalyst. The N-methylcarbamate (MMC) is then purified to obtain a yield of 88.7%.

[0038] Example 4

[0039] Dimethyl urea (DMU) and dimethyl carbonate (DMC) were added to batching equipment 1 at a ratio of 1:5, followed by 0.7% (by weight of the total raw materials) of the catalyst dibutyltin oxide. The mixture was stirred at a stirring speed of 700 r / min until homogeneous, and then pumped at a flow rate of 0.10 m³ / min using slurry pump 2. 3The material is conveyed at a rate of / h, and the flow rate of the material passing through heat exchanger 41 is adjusted to preheat it from room temperature to 38℃. It is then fed into heater 3, where high-temperature steam heats the raw material to 150℃ before it enters tower reactor 4 for dissolution and mixing. In tower reactor 4, the reaction pressure is controlled at 5.0 bar, the reaction temperature at 150℃, and the total reaction time is 10 hours. Gas phase analysis of samples taken from the heterogeneous region shows that the conversion rate of the raw material dimethylurea (DMU) is 19.8%. The main components of the reacted material are excess dimethyl carbonate (DMC) and the generated N-methylcarbamate (M...). Dimethyl carbonate (DMC) flows out from the top of the column, and after passing through pressure reducing valve 5 to reduce the pressure to 1 bar, it enters distillation column 6. In this column, DMC forms a superheated liquid, and its sensible heat causes it to partially vaporize. The unvaporized DMC settles into the bottom of the column, where the reboiler distills the DMC. The distillation column 6 operates at a pressure of 1 bar and a temperature of 105°C, with 10 trays. DMC vapor and other non-condensable gases flow out from the top of distillation column 6, are cooled to 50°C by cooler 10, and then enter gas-liquid separator 11 for separation at a temperature of 40°C. Non-condensable gases are treated from the top, and condensates such as dimethyl carbonate (DMC) are recycled after post-treatment. The N-methylcarbamate (MMC) in the bottom of the tower contains dissolved catalyst with a purity of 68%. It is pumped by centrifugal pump 7 into continuous crystallizer 8, where the catalyst precipitates. Then it enters filter 9 to remove the solid catalyst. The N-methylcarbamate (MMC) is then purified to a yield of 92.6%.

[0040] From Examples 1 to 4, it can be concluded that the prepared raw materials are mixed at a concentration of 0.20 mg / L. 3 The material is conveyed at a rate of / h, and reacted in tower reactor 4 at 150℃ for 5h, resulting in a good MMC yield. Too low a temperature or too high a flow rate will lead to incomplete reaction; a low flow rate may achieve the desired yield, but the reaction time will be too long; and too high a temperature will cause the raw materials to decompose.

Claims

1. An apparatus for continuous production of N-methylcarbamate, characterized in that, The reactor includes a batching device (1), a slurry pump (2), a heater (3), a tower reactor (4), a pressure reducing valve (5), a distillation column (6), a centrifugal pump (7), a continuous crystallizer (8), a filter (9), a cooler (10), and a gas-liquid separator (11). The upper part of the tower reactor (4) is a homogeneous reaction zone, and a heat exchange tube (41) is installed in the homogeneous reaction zone. The outlet of the batching device (1) is connected to the slurry pump (2). The outlet pipeline of the slurry pump (2) is divided into two pipelines, which are connected to the heat exchange tube (41) and the heater (3) respectively. The outlet of the heat exchange tube (41) is... The pipeline is connected to the inlet pipeline of the heater (3). The inlet pipeline of the heater (3) is equipped with a regulating valve for controlling the amount of material flowing through the heat exchange tube (41). The bottom outlet pipeline of the heater (3) is connected to the bottom of the tower reactor (4). The top outlet pipeline of the tower reactor (4) is connected to the pressure reducing valve (5) and the distillation tower (6) in sequence. The bottom outlet pipeline of the distillation tower (6) is connected to the centrifugal pump (7), the continuous crystallizer (8) and the filter (9) in sequence. The top outlet pipeline of the distillation tower (6) is connected to the cooler (10) and the gas-liquid separator (11) in sequence. The lower part of the tower reactor (4) is a heterogeneous reaction zone, and a guide tube (42) is provided in the heterogeneous reaction zone. A nozzle (43) is provided at the bottom of the tower reactor (4). The nozzle (43) is located at the center of the cross section of the guide tube (42). The upper end of the nozzle (43) is flush with the lower end of the guide tube (42). The nozzle (43) is connected to the outlet pipe at the bottom of the heater (3).

2. A process for the continuous production of N-methylcarbamate using the apparatus as described in claim 1, characterized in that, The process includes the following steps: dimethyl urea, dimethyl carbonate, and catalyst are added to the batching equipment (1) in proportion and stirred into a uniform slurry. The raw material slurry is continuously transported by the slurry pump (2), heated through the heat exchange tube (41) and heater (3), and then enters the tower reactor (4) for reaction. The reacted material flows out from the top of the tower, is depressurized by the pressure reducing valve (5), and then enters the distillation tower (6) for distillation separation. The low-boiling-point dimethyl carbonate and non-condensable gas flow out from the top of the distillation tower (6) and are cooled by the cooler ( 10) After cooling, it enters the gas-liquid separator (11) for separation. The non-condensable gas is discharged from the top of the gas-liquid separator (11) and then treated as waste gas. Dimethyl carbonate is discharged from the bottom and reused after post-treatment. High-boiling-point N-methylcarbamate and dissolved catalyst flow out from the bottom of the tower and are transported by centrifugal pump (7) and enter the continuous crystallizer (8). The catalyst is precipitated in the continuous crystallizer (8) and then enters the filter (9). After filtering out the solid catalyst, N-methylcarbamate is further purified.

3. The process as described in claim 2, characterized in that, The molar ratio of dimethylurea and dimethyl carbonate in the batching equipment (1) is 1:3-1:20, the catalyst is dibutyltin oxide, and the amount of catalyst fed is 0.1-1% of the total mass of dimethylurea and dimethyl carbonate.

4. The process as described in claim 2, characterized in that, The raw material temperature is preheated to 40-60℃ by the heat exchange tube (41), and then heated to 135-155℃ by the heater (3). The minimum heat exchange area of ​​the heat exchange tube (41) is... Where X2 is the conversion rate of dimethylurea at the end of the reaction, and T r The reaction temperature inside the tower reactor is in °C and F. A0 denoted as the molar flow rate of dimethylurea, mol / s; T0 is the feed temperature of the tower reactor (4), °C; Cp is the specific heat capacity of the feedstock, J / (g·℃); and n is the molar ratio of dimethyl carbonate to dimethylurea, M DMC M DMU ρ0 and ρ0 are the molar masses of dimethyl carbonate and dimethylurea, respectively, in g / mol, and K is the heat transfer coefficient in W / (m2). 2 ·℃), △H is the heat of reaction J / mol, △T is the heat transfer temperature difference, and the unit is ℃.

5. The process as described in claim 2, characterized in that, The residence time of materials in the tower reactor (4) is controlled at 3-10h.

6. The process as described in claim 2, characterized in that, The size of the heterogeneous reaction zone of the tower reactor (4) is determined by The calculation yields F. A0 X1 is the molar flow rate of dimethylurea in the feed solution, X2 is the conversion rate of dimethylurea in the heterogeneous reaction section, and -r A1 The reaction rate in the heterogeneous reaction zone is mol / (L·s); the size of the homogeneous reaction zone in the tower reactor (4) is determined by... The calculations show that X2 represents the conversion rate of dimethylurea in the homogeneous reaction section, and -r A denoted as the reaction rate in the homogeneous reaction zone, in mol / (L·s).

7. The process as described in claim 6, characterized in that, The height-to-diameter ratio of the tower reactor (4) is 8-15, the diameter of the guide tube (42) in the heterogeneous reaction zone is 0.5-0.8 to the inner diameter of the tower reactor (4), and the height of the guide tube (42) is 0.8-0.9 to the height of the heterogeneous reaction zone.

8. The process as described in claim 2, characterized in that, The temperature inside the distillation column (6) is controlled at 95-120℃, and the temperature of the gas-liquid separator (11) is 40-60℃.

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