A system and method for continuously producing dimethylol urea with high purity

Abstract

The invention belongs to the technical field of dimethylolurea synthesis, and specifically discloses a system and method for continuously producing dimethylolurea with high purity. The system comprises a dimethylolurea synthesis reactor, an aldehyde recovery tower, a dimethylolurea refining tower, a reaction circulation heater, an aldehyde recovery tower bottom heat exchanger, a product refining tower evaporator, an aldehyde recovery tower top condenser, a crude product recovery condenser, a product condenser, a crude product condenser, a crude product buffer tank, a product buffer tank, a reaction discharge pump, a crude product circulation pump, an aldehyde recovery pump, a refining tower circulation pump, a heavy component pump, a product pump, a reaction proportion feeding system, and a vacuum system. The system can realize high-intensity continuous production of dimethylolurea, achieve a total conversion rate of dimethylolurea of ​​more than 95%, and achieve a purity of 99.5% for the final product dimethylolurea. The system has the advantages of a simple process flow, easy device development, high dimethylolurea conversion rate, and high product purity.

Description

Technical Field

[0001] The invention relates to the technical field of dimethylol urea synthesis, in particular to a system and method for continuously producing dimethylol urea with high purity. Background Art

[0002] Over the years, the dimethylolurea industry has experienced significant growth. Its importance as a pharmaceutical raw material, feed additive, daily chemical raw material, pharmaceutical intermediate, and synthetic resin has been gradually recognized, and market demand for dimethylolurea is increasing. Currently, existing technologies mostly rely on batch production processes, often involving mixed product processes. Summary of the Invention

[0003] The object of the present invention is to provide a system and method for continuously producing dimethylol urea with high purity, so as to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solution: a system for continuously producing dimethylol urea with high purity, comprising a dimethylol urea synthesis reactor, an aldehyde recovery tower, a dimethylol urea refining tower, a reaction circulation heater, an aldehyde recovery tower bottom heat exchanger, a product refining tower evaporator, an aldehyde recovery tower top condenser, a crude product recovery condenser, a product condenser, a crude product condenser, a crude product buffer tank, a product buffer tank, a reaction discharge pump, a crude product circulation pump, an aldehyde recovery pump, a refining tower circulation pump, a heavy component pump, a product pump, a reaction proportion feeding system and a vacuum system; the dimethylol urea synthesis reactor is connected to the reaction proportion feeding system, and the dimethylol urea synthesis reactor is connected to the reaction proportion feeding system. The gas phase outlet of the reactor is connected to the middle part of the aldehyde recovery tower, the liquid phase outlet of the dimethylol urea synthesis reactor is connected to the reaction discharge pump, the reaction discharge pump outlet is connected to the reaction circulation heater and is connected to the middle part of the aldehyde recovery tower, the material outlet of the reaction circulation heater is connected to the top of the dimethylol urea synthesis reactor, the gas phase outlet of the aldehyde recovery tower is connected to the aldehyde recovery tower top condenser, and the aldehyde recovery tower top condenser outlet is connected to the crude product recovery condenser; the crude product recovery condenser gas phase outlet is connected to the non-condensable gas system, the crude product recovery condenser liquid phase outlet is connected to the aldehyde recovery pump, and the aldehyde recovery pump is connected to the top of the dimethylol urea synthesis reactor;

[0005] The liquid phase outlet of the aldehyde recovery tower is connected to the crude product circulation pump, the crude product circulation pump outlet is connected to the aldehyde recovery tower bottom heat exchanger and the crude product condenser, and the aldehyde recovery tower bottom heat exchanger is connected to the bottom of the aldehyde recovery tower;

[0006] The crude product condenser is connected to the top of the crude product buffer tank, the bottom of the crude product buffer tank is connected to the middle of the dimethylolurea refining tower, the top outlet of the dimethylolurea refining tower is connected to the product condenser, and the product condenser is connected to the top of the product buffer tank;

[0007] The gas phase outlet at the top of the product buffer tank is connected to the vacuum system, the gas phase outlet of the vacuum system is connected to the middle of the aldehyde recovery tower, the liquid phase outlet of the vacuum system is connected to the sewage system, and the bottom of the product buffer tank is connected to the product pump;

[0008] The bottom outlet of the dimethylolurea refining tower is connected to the refining tower circulation pump, the outlet of the refining tower circulation pump is connected to the product refining tower evaporator, the material outlet of the product refining tower evaporator is connected to the bottom of the dimethylolurea refining tower, and the bottom outlet of the product refining tower evaporator is connected to the heavy component pump.

[0009] A method for continuously producing dimethylol urea with high purity, using the system as described above, the method comprising the following steps:

[0010] S1: Mix 37% wt formaldehyde and urea solution, and add an appropriate amount of sodium hydroxide to obtain a raw material;

[0011] S2: feeding the raw materials into the dimethylol urea synthesis reactor, and controlling the reaction temperature of the dimethylol urea synthesis reactor within the range of 25-65°C, the pressure within the range of 0.1-0.3 MPaG, and the pH value within the range of 8.5-10. After the reaction, a portion of the material is pumped into the aldehyde recovery tower via the reaction discharge pump, and the other portion of the material is heated by the reaction circulation heater and then returned to the top of the dimethylol urea synthesis reactor to maintain a stable reaction temperature, thereby completing the reaction and discharging;

[0012] S3: After the reaction material discharged by the reaction discharge pump is separated in an aldehyde recovery tower, its light component is discharged from the top of the aldehyde recovery tower to the aldehyde recovery tower top condenser. The temperature of the aldehyde recovery tower is controlled at 104-125°C and the pressure is controlled at 0.02-0.05 MPaG. The condensate is refluxed to the aldehyde recovery tower, and the non-condensable gas enters the crude product recovery condenser for secondary condensation to recover the crude product. The liquid phase discharge at the bottom of the crude product recovery condenser is refluxed to the dimethylol urea synthesis reactor through the aldehyde recovery pump to complete aldehyde recovery. The non-condensable gas after the secondary condensation is discharged to the non-condensable gas system;

[0013] The reaction material discharged from the reaction discharge pump (13) is separated in the aldehyde recovery tower (2), and its heavy components are discharged from the bottom of the tower to the crude product circulation pump, and are heated in the heat exchanger at the bottom of the aldehyde recovery tower, and then refluxed to the bottom of the aldehyde recovery tower. During this period, the temperature of the aldehyde recovery tower (2) is controlled at 95-104°C and the pressure is normal pressure. At the same time, the crude product is discharged into the crude product buffer tank through the outlet of the crude product circulation pump;

[0014] S4: The bottom of the crude product buffer tank is pumped to the middle of the dimethylolurea refining tower via a crude product delivery pump. The temperature is controlled at 95-104°C and the pressure is normal pressure. The product is discharged from the top of the dimethylolurea refining tower, cooled in a product condenser, and then enters a product buffer tank. After buffering, it is pumped out via a product pump.

[0015] The heavy component is discharged from the bottom of the dimethylolurea refining tower to the refining tower circulation pump, heated by the product refining tower evaporator and refluxed to the bottom of the dimethylolurea refining tower. The temperature is controlled at 120~156℃ and the pressure is normal pressure. At the same time, the heavy component product is discharged from the bottom of the product refining tower evaporator.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the present invention can realize high-intensity continuous production of dimethylol urea, and the total conversion rate of dimethylol urea reaches more than 95%, and the purity of the final product dimethylol urea reaches 99.5%. It has the advantages of simple process flow, easy device development, high dimethylol urea conversion rate, high product purity, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of the present invention.

[0018] In the figure: 1. Dimethylolurea synthesis reactor; 2. Aldehyde recovery tower; 3. Dimethylolurea refining tower; 4. Reaction circulation heater; 5. Aldehyde recovery tower bottom heat exchanger; 6. Product refining tower evaporator; 7. Aldehyde recovery tower top condenser; 8. Crude product recovery condenser; 9. Product condenser; 10. Crude product condenser; 11. Crude product buffer tank; 12. Product buffer tank; 13. Reaction discharge pump; 14. Crude product circulation pump; 15. Aldehyde recovery pump; 16. Refining tower circulation pump; 17. Heavy component pump; 18. Product pump; 19. Reaction proportion feeding system; 20. Vacuum system. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be noted that the terms "vertical", "up", "down", "horizontal", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the present invention.

[0021] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0022] The present invention provides a high-purity continuous production system of dimethylolurea, comprising a dimethylolurea synthesis reactor 1, an aldehyde recovery tower 2, a dimethylolurea refining tower 3, a reaction circulation heater 4, an aldehyde recovery tower bottom heat exchanger 5, a product refining tower evaporator 6, an aldehyde recovery tower top condenser 7, a crude product recovery condenser 8, a product condenser 9, a crude product condenser 10, a crude product buffer tank 11, a product buffer tank 12, a reaction discharge pump 13, a crude product circulation pump 14, an aldehyde recovery pump 15, a refining tower circulation pump 16, a heavy component pump 17, a product pump 18, a reaction proportion feeding system 19 and a vacuum system 20; the dimethylolurea synthesis reactor 1 is connected to the reaction proportion feeding system 19, and the dimethylolurea synthesis reactor 1 is connected to the reaction proportion feeding system 19. The gas phase outlet of the reactor 1 is connected to the middle part of the aldehyde recovery tower 2, the liquid phase outlet of the dimethylol urea synthesis reactor 1 is connected to the reaction discharge pump 13, the outlet of the reaction discharge pump 13 is connected to the reaction circulation heater 4, and is connected to the middle part of the aldehyde recovery tower 2, the material outlet of the reaction circulation heater 4 is connected to the top of the dimethylol urea synthesis reactor 1, the gas phase outlet of the aldehyde recovery tower 2 is connected to the aldehyde recovery tower top condenser 7, and the condenser outlet of the aldehyde recovery tower 2 is connected to the crude product recovery condenser 8; the gas phase outlet of the crude product recovery condenser 8 is connected to the non-condensable gas system, the liquid phase outlet of the crude product recovery condenser 8 is connected to the aldehyde recovery pump 15, and the aldehyde recovery pump 15 is connected to the top of the dimethylol urea synthesis reactor 1.

[0023] Furthermore, the liquid phase outlet of the aldehyde recovery tower 2 is connected to the crude product circulation pump 14 , the outlet of the crude product circulation pump 14 is connected to the aldehyde recovery tower bottom heat exchanger 5 and the crude product condenser 10 , and the aldehyde recovery tower bottom heat exchanger is connected to the bottom of the aldehyde recovery tower 2 .

[0024] Furthermore, the crude product condenser 10 is connected to the top of the crude product buffer tank 11, the bottom of the crude product buffer tank 11 is connected to the middle of the dihydroxymethylurea refining tower 3, the top outlet of the dihydroxymethylurea refining tower 3 is connected to the product condenser 9, and the product condenser 9 is connected to the top of the product buffer tank 12.

[0025] Furthermore, the gas phase outlet at the top of the product buffer tank 12 is connected to the vacuum system 20, the gas phase outlet of the vacuum system 20 is connected to the middle of the aldehyde recovery tower 2, the liquid phase outlet of the vacuum system 20 is connected to the sewage, and the bottom of the product buffer tank 12 is connected to the product pump 18.

[0026] Furthermore, the bottom outlet of the dimethylol urea refining tower 3 is connected to the refining tower circulation pump 16, the outlet of the refining tower circulation pump 16 is connected to the product refining tower evaporator, the material outlet of the product refining tower evaporator 6 is connected to the bottom of the dimethylol urea refining tower 3, and the bottom outlet of the product refining tower evaporator 6 is connected to the heavy component pump 17.

[0027] A method for continuously producing dimethylol urea with high purity comprises the following steps:

[0028] S1: Mix 37% wt formaldehyde and urea solution, and add an appropriate amount of sodium hydroxide to obtain a raw material;

[0029] S2: adding raw materials into the dimethylol urea synthesis reactor 1, and controlling the reaction temperature of the dimethylol urea synthesis reactor 1 to be within 25-65° C., the pressure to be controlled to be 0.1-0.3 MPaG, and the pH value to be adjusted to be 8.5-10. After the reaction, a portion of the material enters the aldehyde recovery tower 2 via the reaction discharge pump 13, and the other portion of the material is heated by the reaction circulation heater 4 and then returned to the top of the dimethylol urea synthesis reactor 1 to maintain the reaction temperature stable, thereby completing the reaction and discharging;

[0030] S3: After the reaction material discharged by the reaction discharge pump 13 is separated by the aldehyde recovery tower 2, the light component is discharged from the top of the aldehyde recovery tower 2 to the aldehyde recovery tower top condenser 7. The temperature of the aldehyde recovery tower 2 is controlled at 104-125° C. and the pressure is controlled at 0.02-0.05 MPaG. The condensate is refluxed to the aldehyde recovery tower 2, and the non-condensable gas enters the crude product recovery condenser 8 for secondary condensation. The crude product is recovered, and the liquid phase discharge at the bottom of the crude product recovery condenser is refluxed to the dimethylol urea synthesis reactor 1 through the aldehyde recovery pump 15 to complete the aldehyde recovery. The non-condensable gas after the secondary condensation is discharged to the non-condensable gas system;

[0031] The reaction material discharged from the reaction discharge pump (13) is separated by the aldehyde recovery tower (2), and its heavy components are discharged from the bottom of the tower to the crude product circulation pump 14. After being heated by the aldehyde recovery tower bottom heat exchanger 5, it refluxes to the bottom of the aldehyde recovery tower 2. During this period, the aldehyde recovery tower (2) is controlled at a temperature of 95-104°C and a pressure of normal pressure. At the same time, it enters the crude product buffer tank 11 through the outlet of the crude product circulation pump 14;

[0032] S4: The bottom of the crude product buffer tank 11 is transported to the middle of the dimethylolurea refining tower 3 via the crude product delivery pump, the temperature is controlled at 95-104°C, and the pressure is normal pressure. The product is discharged from the top of the dimethylolurea refining tower 3, cooled by the product condenser 9, and then enters the product buffer tank 12. After buffering, it is delivered by the product pump 18;

[0033] The heavy component is discharged from the bottom of the dimethylolurea refining tower 3 to the refining tower circulation pump 16, heated by the product refining tower evaporator 6, and then refluxed to the bottom of the dimethylolurea refining tower 3. The temperature is controlled at 120~156℃ and the pressure is normal pressure. At the same time, the heavy component product is discharged from the bottom of the product refining tower evaporator 6.

[0034] Example 1:

[0035] A high-purity continuous production system for dimethylolurea, as shown in the figure, includes a dimethylolurea synthesis reactor 1, an aldehyde recovery tower 2, a dimethylolurea refining tower 3, a reaction circulation heater 4, an aldehyde recovery tower bottom heat exchanger 5, a product refining tower evaporator 6, an aldehyde recovery tower top condenser 7, a crude product recovery condenser 8, a product condenser 9, a crude product condenser 10, a crude product buffer tank 11, a product buffer tank 12, a reaction discharge pump 13, a crude product circulation pump 14, an aldehyde recovery pump 15, a refining tower circulation pump 16, a heavy component pump 17, a product pump 18, a reaction ratio feeding system 19, and a vacuum system 20, which are connected in sequence.

[0036] Wherein, the reaction system: the reaction ratio feeding system 19 is connected to the dimethylol urea synthesis reactor 1, the top discharge of the dimethylol urea synthesis reactor 1 is connected to the middle of the aldehyde recovery tower 2, the bottom discharge is connected to the inlet of the reaction discharge pump 13, the outlet of the reaction discharge pump 13 is respectively connected to the reaction circulation heater 4 and the middle of the aldehyde recovery tower 2, and the material outlet of the reaction circulation heater 4 is connected to the top of the dimethylol urea synthesis reactor to complete the reaction;

[0037] Aldehyde recovery: the gas phase outlet of the aldehyde recovery tower 2 is connected to the aldehyde recovery tower top condenser 7, the outlet of the aldehyde recovery tower top condenser 7 is connected to the crude product recovery condenser 8, the gas phase outlet of the crude product recovery condenser 8 is connected to the non-condensable gas system to remove the tail gas treatment, the liquid phase outlet of the crude product recovery condenser 8 is connected to the aldehyde recovery pump 15, and the outlet of the aldehyde recovery pump 15 is refluxed to the dimethylol urea synthesis reactor 1 to complete the aldehyde recovery;

[0038] The liquid phase outlet of the aldehyde recovery tower 2 is connected to the crude product circulation pump 14, the outlet of the crude product circulation pump 14 is connected to the aldehyde recovery tower bottom heat exchanger 5 and the crude product condenser 10, the aldehyde recovery tower bottom heat exchanger 5 is connected to the bottom of the aldehyde recovery tower 2, the crude product condenser 10 is connected to the top of the crude product buffer tank 11, and the bottom of the crude product buffer tank 11 is connected to the middle of the dimethylolurea refining tower 3;

[0039] Product refining: The top outlet of the dimethylol urea refining tower 3 is connected to the product condenser 9, and the outlet of the product condenser 9 is connected to the top of the product buffer tank 12; the gas phase outlet of the product buffer tank 12 is connected to the vacuum system 20, and the vacuum system 20 is connected to the non-condensable steam treatment system. The liquid phase outlet at the bottom of the product buffer tank 12 is connected to the product pump 18 to complete the product refining process;

[0040] The bottom outlet of the dimethylolurea refining tower 3 is connected to the refining tower circulation pump 16; the outlet of the refining tower circulation pump 16 is connected to the product refining tower evaporator 6; the material outlet of the product refining tower evaporator 6 is connected to the bottom of the dimethylolurea refining tower 3; the liquid phase outlet at the bottom of the product refining tower evaporator 6 is connected to the heavy component pump 17 to complete the heavy component product transportation process.

[0041] Example 2:

[0042] A method for continuously producing dimethylol urea with high purity comprises the following steps:

[0043] 1. The raw materials composed of formaldehyde and urea are strictly controlled in proportion while the reaction pH value is strictly controlled, and are fed into the reactor and the dimethylol urea reactor. The reaction temperature in the dimethylol urea thermal decomposition reactor is controlled to be 45°C-75°C, and the pressure is controlled to be 0.2-0.5MPaG. After reacting for 5-30s, the gas discharged from the top of the reactor enters the aldehyde recovery tower 2 with a discharge temperature of 45°C-75°C. At the same time, the liquid material at the bottom is simultaneously fed into the reaction circulation heater 4 for heat exchange to maintain the reaction temperature at 45°C-75°C. The reaction extraction line is connected to the aldehyde recovery tower 2 to complete the reaction feeding and discharging;

[0044] 2. The material from the dimethylol urea synthesis reactor 1 is sent to the aldehyde recovery tower 2. The tower temperature is controlled at 125°C-150°C and the pressure is controlled at 0.02-0.05 MPaG. The aldehyde gas mixture discharged from the top discharge port is passed through the aldehyde recovery tower top condenser at 85°C-135°C and the pressure is 0.02-0.05 MPaG. After condensation, the liquid refluxes to the aldehyde recovery tower 2, and the gas is sent to the crude product recovery condenser 8 at a temperature of 45°C-85°C. The liquid is refluxed to the dimethylol urea synthesis reaction through the aldehyde recovery pump 15 to complete the aldehyde recovery, and the gas is discharged to the non-condensable gas treatment system;

[0045] The crude product material at the bottom of the aldehyde recovery tower 2 enters the aldehyde recovery tower bottom heat exchanger at 135°C-160°C and the pressure is controlled at 0.2-0.3 MPaG and the crude product condenser 10 through the crude product circulation pump 14, with the temperature at 130°C-145°C and the pressure controlled at 0.2-0.3 MPaG. The aldehyde recovery tower bottom heat exchanger 5 is used to control the tower bottom temperature, the crude product condenser 10 is used to control the crude product temperature, and the crude product buffer tank 11 is controlled at a temperature of 125-140°C and a pressure of -0.025 / -0.045 MPaG to complete the discharge of the crude product;

[0046] 3. The crude product from the crude product buffer tank at 125-150°C and pressure controlled at -0.025 / -0.045MPaG is sent to the dimethylolurea refining tower at 160-225°C and pressure controlled at -0.085 / -0.095MPaG for product refining. The top gaseous product passes through the product condenser at 160-190°C and pressure controlled at -0.085 / -0.095MPaG to condense the product. The liquid product enters the product buffer tank at 130-140°C and pressure controlled at -0.015 / -0.025MPaG. The product with a purity of up to 99.5% is sent out through pump 18. The gas phase space of the product buffer tank 12 is connected to the vacuum system at a temperature of 130-150°C and pressure controlled at -0.088 / -0.097MPaG to ensure the vacuum degree of the refining system.

[0047] The heavy component material at the bottom of the dimethylolurea refining tower 3 enters the product refining tower evaporator 6 through the refining tower circulation pump 16, maintaining the temperature at 160-225°C and the pressure at 0.1-0.3 MPaG. The heat exchanger at the bottom of the dimethylolurea refining tower 3 is used to control the bottom temperature; the bottom of the product refining tower evaporator 6 is the heavy component mixed material, which is discharged through the heavy component pump 17.

[0048] Application Example 1:

[0049] Based on a design capacity of 80 t / a of dimethylolurea (calculated as dimethylolurea, with an annual operating time of 8,000 h), a single-pass dimethylolurea conversion of 10%, and a residence time of 12 seconds, 25.398 kg / h of dimethylolurea, consisting of formaldehyde and urea, enters dimethylolurea pyrolysis reactor 1 at a reaction temperature of 65°C and a pressure of 0.35 MPaG. The pressure in aldehyde recovery column 2 is controlled at 0.04 MPaG and a temperature of 135°C. The pressure in dimethylolurea refining column 3 is maintained at -0.085 MPaG and a temperature of 185°C. After system equilibrium, the fresh formaldehyde (37% wt) feed rate is 18.701 kg / h, the solution feed rate is 6.697 kg / h, the ethylene dimethylolurea production is 9.998 kg / h, and the heavy component yield is 0.0022 kg / h. 15.398 kg / h of wastewater is generated. The reaction equation is: 2H2CO+H4N2CO—H8N2C3O3.

[0050] Application Example 2:

[0051] Based on a design capacity of 40 tons / year of dimethylolurea production (measured as dimethylolurea, with an annual operating time of 8,000 hours), a single-pass conversion of 10%, and a residence time of 10 seconds, the feedstock, consisting of formaldehyde and urea, is fed to dimethylolurea pyrolysis reactor 1 at a reaction temperature of 55°C and a pressure of 0.25 MPaG. The pressure in aldehyde recovery column 2 is controlled at 0.03 MPaG and the temperature at 140°C. The pressure in dimethylolurea refining column 3 is maintained at -0.087 MPaG and the temperature at 195°C. After system equilibrium, the fresh formaldehyde (37% wt) feed rate is 9.35 kg / hour, the solution feed rate is 3.35 kg / hour, the ethylene dimethylolurea production is approximately 5 kg / hour, the heavy component yield is 0.0011 kg / hour, and 7.7 kg / hour of wastewater is generated. The reaction equation is: 2H2CO+H4N2CO—H8N2C3O3.

[0052] It is worth noting that the entire device is controlled by a master control button. Since the devices matched with the control button are commonly used devices and belong to existing common knowledge technology, their electrical connection relationship and specific circuit structure will not be described in detail here.

[0053] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A system for continuously producing dimethylol urea with high purity, characterized in that: The invention comprises a dimethylolurea synthesis reactor (1), an aldehyde recovery tower (2), a dimethylolurea refining tower (3), a reaction circulation heater (4), an aldehyde recovery tower bottom heat exchanger (5), a product refining tower evaporator (6), an aldehyde recovery tower top condenser (7), a crude product recovery condenser (8), a product condenser (9), a crude product condenser (10), a crude product buffer tank (11), a product buffer tank (12), a reaction discharge pump (13), a crude product circulation pump (14), an aldehyde recovery pump (15), a refining tower circulation pump (16), a heavy component pump (17), a product pump (18), a reaction ratio feeding system (19), and a vacuum system (20); the dimethylolurea synthesis reactor (1) is connected to the reaction ratio feeding system (19), and the gas of the dimethylolurea synthesis reactor (1) is The phase outlet is connected to the middle of the aldehyde recovery tower (2), the liquid phase outlet of the dimethylol urea synthesis reactor (1) is connected to the reaction discharge pump (13), the outlet of the reaction discharge pump (13) is connected to the reaction circulation heater (4), and is also connected to the middle of the aldehyde recovery tower (2), the material outlet of the reaction circulation heater (4) is connected to the top of the dimethylol urea synthesis reactor (1), the gas phase outlet of the aldehyde recovery tower (2) is connected to the aldehyde recovery tower top condenser (7), the outlet of the aldehyde recovery tower top condenser (7) is connected to the crude product recovery condenser (8), the gas phase outlet of the crude product recovery condenser (8) is connected to the non-condensable gas system, the liquid phase outlet of the crude product recovery condenser (8) is connected to the aldehyde recovery pump (15), and the aldehyde recovery pump (15) is connected to the top of the dimethylol urea synthesis reactor (1); The liquid phase outlet of the aldehyde recovery tower (2) is connected to the crude product circulation pump (14), the outlet of the crude product circulation pump (14) is connected to the aldehyde recovery tower bottom heat exchanger (5) and the crude product condenser (10), and the aldehyde recovery tower bottom heat exchanger (5) is connected to the bottom of the aldehyde recovery tower (2); The crude product condenser (10) is connected to the top of the crude product buffer tank (11), the bottom of the crude product buffer tank (11) is connected to the middle of the dimethylolurea refining tower (3), the top outlet of the dimethylolurea refining tower (3) is connected to the product condenser (9), and the product condenser (9) is connected to the top of the product buffer tank (12); The gas phase outlet at the top of the product buffer tank (12) is connected to the vacuum system (20), the gas phase outlet of the vacuum system (20) is connected to the middle of the aldehyde recovery tower (2), the liquid phase outlet of the vacuum system (20) is connected to the sewage system, and the bottom of the product buffer tank (12) is connected to the product pump (18); The bottom outlet of the dimethylolurea refining tower (3) is connected to the refining tower circulation pump (16), the outlet of the refining tower circulation pump (16) is connected to the product refining tower evaporator, the material outlet of the product refining tower evaporator (6) is connected to the bottom of the dimethylolurea refining tower (3), and the bottom outlet of the product refining tower evaporator (6) is connected to the heavy component pump (17).

2. A method for continuously producing dimethylol urea with high purity, characterized in that: Using the system according to claim 1, the method comprises the following steps: S1: Mix 37% wt formaldehyde and urea solution, and add an appropriate amount of sodium hydroxide to prepare a raw material; S2: The raw materials are fed into the dimethylolurea synthesis reactor (1), and the reaction temperature of the dimethylolurea synthesis reactor (1) is controlled within the range of 25-65°C, the pressure is controlled within the range of 0.1-0.3 MPaG, and the pH value is adjusted to 8.5-10. After the reaction, a portion of the material enters the aldehyde recovery tower (2) via the reaction discharge pump (13), and the other portion of the material is heated by the reaction circulation heater (4) and then returned to the top of the dimethylolurea synthesis reactor (1), thereby maintaining the reaction temperature stable, thereby completing the reaction and discharging; S3: After the reaction material discharged from the reaction discharge pump (13) is separated by the aldehyde recovery tower (2), the light component is discharged from the top of the aldehyde recovery tower (2) to the aldehyde recovery tower top condenser (7). The temperature of the aldehyde recovery tower (2) is controlled to be 104~125℃, and the pressure is controlled to be 0.02~0.05MPaG. The condensate is refluxed to the aldehyde recovery tower (2), and the non-condensable gas enters the crude product recovery condenser (8) for secondary condensation. The crude product is recovered, and the liquid phase discharge at the bottom of the crude product recovery condenser (8) is refluxed to the dimethylol urea synthesis reactor (1) through the aldehyde recovery pump (15) to complete the aldehyde recovery. The non-condensable gas after the secondary condensation is discharged to the non-condensable gas system; The reaction material discharged from the reaction discharge pump (13) is separated in the aldehyde recovery tower (2), and its heavy components are discharged from the bottom of the tower to the crude product circulation pump (14), heated in the aldehyde recovery tower bottom heat exchanger (5), and then refluxed to the bottom of the aldehyde recovery tower (2). During this period, the aldehyde recovery tower (2) is controlled at a temperature of 95-104°C and a pressure of normal pressure. The heavy components separated in the aldehyde recovery tower (2) are simultaneously discharged into the crude product buffer tank (11) through the outlet of the crude product circulation pump (14); S4: The crude product at the bottom of the crude product buffer tank (11) is transported to the middle of the dimethylolurea refining tower (3), the temperature is controlled at 95~104℃, the pressure is normal pressure, the light component is discharged from the top of the dimethylolurea refining tower (3), cooled by the product condenser (9), and then enters the product buffer tank (12). After buffering, it is sent out through the product pump (18); the heavy component is discharged from the bottom of the dimethylolurea refining tower (3) to the refining tower circulation pump (16), heated by the product refining tower evaporator (6), and refluxed to the bottom of the dimethylolurea refining tower (3). The temperature is controlled at 120~156℃, the pressure is normal pressure, and the heavy component product is discharged from the bottom of the product refining tower evaporator (6).

3. A method for continuously producing dimethylol urea with high purity according to claim 2, characterized in that: In the step S2, the reaction temperature in the dimethylolurea synthesis reactor (1) is 65°C and the pressure is controlled to be 0.15 MPaG.

4. A method for continuously producing dimethylol urea with high purity according to claim 2, characterized in that: In the step S2, the wall of the dimethylol urea synthesis reactor (1) adopts an internal hot water jacket structure and the wall temperature is controlled at 65°C.

5. A method for continuously producing dimethylol urea with high purity according to claim 2, characterized in that: In the step S3, the reaction material discharged from the reaction discharge pump (13) is separated in the aldehyde recovery tower (2), and the heavy components are discharged from the bottom of the tower to the crude product circulation pump (14), heated in the aldehyde recovery tower bottom heat exchanger (5), and then refluxed to the bottom of the aldehyde recovery tower (2). During this period, the temperature in the aldehyde recovery tower (2) is controlled at 104°C at the bottom and the pressure is controlled at normal pressure, and the temperature at the top is controlled at 95°C and the pressure is controlled at normal pressure. In the step S4, the crude product at the bottom of the crude product buffer tank (11) is transported to the middle of the dimethylolurea refining tower (3), and the temperature in the dimethylolurea refining tower (3) is controlled to be 104°C at the bottom and the pressure is controlled to be normal pressure, and the temperature at the top is controlled to be 95°C and the pressure is controlled to be normal pressure.

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