Method for controlling temperature of high-performance carbon fiber precursor production high-efficiency acrylonitrile recovery demonomerisation tower

Abstract

The invention discloses a temperature control method for a high-performance carbon fiber precursor production efficient acrylonitrile recovery demonomerization tower, and belongs to the field of chemical equipment rectifying tower low-temperature control. Starting from actual production, acrylonitrile in the solution is recycled, the recycling efficiency reaches 99.95% or above, waste of acrylonitrile is avoided, pollution of acrylonitrile to the environment is reduced, the production cost is reduced, negative pressure operation is adopted on the tower top, the operation temperature is reduced, acrylonitrile self-polymerization is prevented, and energy is saved.

Description

Technical Field

[0001] The present invention belongs to the field of low temperature control of distillation towers in chemical equipment, and specifically relates to a method for controlling the temperature of a stripping tower for efficiently recovering acrylonitrile in the production of high-performance carbon fiber precursor. Background Art

[0002] Nowadays, many domestic carbon fiber companies do not have the process of solution monomer recovery. They directly discharge the solution containing acrylonitrile monomer into the sewage system by evaporation and condensation in a conventional distillation tower. This not only wastes acrylonitrile, but also causes acrylonitrile pollution to the environment and increases production costs. Solution solvent recovery and acrylonitrile monomer recovery are an important part of high-performance carbon fiber precursor production. Under the current production conditions, the production cost of domestic high-performance carbon fiber companies is relatively high. The recovery and recycling of solution acrylonitrile monomer is one of the important methods to effectively reduce the production cost of carbon fiber precursor. Generally, acrylonitrile is used as a polymerization monomer and dimethyl sulfoxide is used as a solvent in the production process of carbon fiber precursor.

[0003] In the production process of high-performance carbon fiber precursor, a mixed solution of acrylonitrile, water and dimethyl sulfoxide is produced. In order to reduce production costs, the dimethyl sulfoxide in the mixed solution needs to be dehydrated and distilled. In the production process of many domestic carbon fiber companies today, the acrylonitrile in the solution is not recovered, but directly discharged to the sewage treatment device along with the distillation condensate, and then the sewage is treated, which not only causes a waste of acrylonitrile, but also increases the sewage treatment cost for the sewage treatment device.

[0004] Therefore, the prior art has the following disadvantages:

[0005] (1) The effective utilization rate of acrylonitrile is low, which increases the production cost of carbon fiber precursor;

[0006] (2) It not only increases the cost and load of sewage treatment, but also greatly pollutes the environment;

[0007] (3) The temperature rise during the dehydration process of the solution distillation system can easily cause acrylonitrile to self-polymerize, resulting in blockage of the distillation system plates or packing, making it impossible to ensure the long-term stable operation of the solvent recovery device. Summary of the invention

[0008] The present invention mainly solves the technical problems existing in the above-mentioned prior art and provides a method for controlling the temperature of a stripping tower for efficiently recovering acrylonitrile in the production of high-performance carbon fiber precursor.

[0009] The above technical problem of the present invention is mainly solved by the following technical scheme: a method for controlling the temperature of an acrylonitrile stripping tower for efficiently recovering high-performance carbon fiber precursor, comprising vaporizing acrylonitrile and water in a mixed liquid by a reboiler using low-pressure steam to obtain mixed steam, distilling the mixed steam under reduced pressure through an acrylonitrile stripping tower, condensing the mixed steam in a condenser to obtain layered acrylonitrile and water, and recovering the upper layer of acrylonitrile in an acrylonitrile tank, the method comprising the following steps:

[0010] Solution vacuum distillation: The solution is fed into the acrylonitrile stripping tower through the feed port, and vacuum distillation is performed under negative pressure. Acrylonitrile and water are vaporized to obtain mixed steam, and the remaining liquid accumulates at the bottom of the kettle to form the bottom liquid of the tower;

[0011] Solution vapor condensation: Solution vapor rises from the acrylonitrile stripping tower to the condenser at the top of the tower. Under vacuum conditions, non-condensable gas enters the vacuum system, and water and acrylonitrile condense and flow into the condensate tank.

[0012] Liquid separation and recovery: Water and acrylonitrile are separated into layers in a condensate tank with a sight glass and a partition. The lower layer of water enters the separation water tank, and the upper layer of acrylonitrile enters the acrylonitrile tank through the overflow port to achieve acrylonitrile recovery.

[0013] Preferably, the solution vacuum distillation step further comprises forcibly circulating the bottom liquid of the tower through a tower bottom pump, heating it with steam from a reboiler, and then passing it into the acrylonitrile removal tower.

[0014] Preferably, the solution reduced pressure distillation step further comprises introducing reflux liquid into the acrylonitrile removal tower, the reflux liquid is sprayed downward from a position near the top of the acrylonitrile removal tower through a distributor or nozzle in the tower, and contacts with the mixed steam in reverse direction for mass transfer, and the reflux liquid sprayed on the top of the tower transfers mass and heat with the rising mixed steam, thereby preventing dimethyl sulfoxide in the mixed steam from entering the top of the tower and reducing the amount of evaporation entering the top of the tower.

[0015] Preferably, the liquid separation and recovery step further comprises passing a portion of the water in the separation water tank into a distributor as reflux liquid through a separation water pump, and passing a portion of the water into a feed port of an acrylonitrile stripping tower to form a mixed liquid with the original liquid of acrylonitrile to be recovered for acrylonitrile recovery. Since the separation water contains a certain amount of acrylonitrile, a portion of the separation water is transported to the top of the tower as reflux liquid, and a portion of the separation water is transported to the feed port of the acrylonitrile stripping tower for acrylonitrile recovery.

[0016] Preferably, the bottom temperature of the acrylonitrile removal tower is 55-70°C, the top temperature is 40-50°C, the top pressure is 20-25 kPaA; and the cooling water temperature in the outer coil of the condensate tank is 7-11°C.

[0017] Preferably, the acrylonitrile removal tower is provided with tower internals, which are tower trays, fillers or combination thereof. The tower trays are formed by a combination of bubble trays, sieve plate trays, valve trays and baffle trays. The fillers are structured fillers, random fillers or a combination thereof.

[0018] The invention has the beneficial effects that the invention proceeds from the actual production and recovers acrylonitrile in the solution, the recovery efficiency reaches more than 99.95%, the waste of acrylonitrile is avoided, the pollution of acrylonitrile to the environment is reduced, the production cost is reduced, the tower top adopts negative pressure operation to reduce the operating temperature, which not only prevents acrylonitrile from self-polymerization, but also saves energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention.

[0020] In the figure: 1. stripping tower; 2. condenser; 3. reboiler; 4. bottom pump; 5. condensate tank; 6. separation water tank; 7. acrylonitrile tank; 8. separation water pump; 9. acrylonitrile pump; 10. thermometer; 11. pressure gauge; 12. flow regulating valve; 13. pressure regulating valve; 14. solenoid switch valve; 15. feed inlet; 16. condensate tank coil / jacket; 17. sight glass; 18. tower internals; 19. distributor; 20. nozzle; 21. level meter; 22. level regulating valve. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0022] Embodiment: A method for controlling the temperature of a stripping tower for efficiently recovering acrylonitrile in the production of high-performance carbon fiber precursor, such as Figure 1 As shown, the method comprises vaporizing acrylonitrile and water in the mixed liquid by using low-pressure steam through a reboiler 3 to obtain mixed steam, distilling the mixed steam under reduced pressure through an acrylonitrile stripping tower 1, condensing the mixed steam through a condenser 2 to obtain layered acrylonitrile and water, and recovering the upper layer of acrylonitrile in an acrylonitrile tank 7. The method comprises the following steps:

[0023] Solution vacuum distillation: The solution is fed into the acrylonitrile stripping tower 1 through the feed port 15, and vacuum distillation is performed under negative pressure conditions, acrylonitrile and water are vaporized to obtain mixed steam, and the remaining liquid accumulates at the bottom of the kettle to form the bottom liquid of the tower;

[0024] Solution vapor condensation: Solution vapor rises from the acrylonitrile stripping tower 1 to the condenser 2 at the top of the tower, non-condensable gas enters the vacuum system under vacuum conditions, and water and acrylonitrile condense and flow into the condensate tank 5;

[0025] Liquid separation and recovery: Water and acrylonitrile are separated into layers in the condensate tank 5 with a sight glass 17 and a partition. The lower layer of water enters the separation water tank 6, and the upper layer of acrylonitrile enters the acrylonitrile tank 7 through the overflow port to achieve acrylonitrile recovery.

[0026] The solution vacuum distillation step also includes forcibly circulating the bottom liquid of the tower through the bottom pump 4, heating it with the steam of the reboiler 3, and then passing it into the acrylonitrile removal tower 1.

[0027] The solution vacuum distillation step also includes introducing reflux liquid into the acrylonitrile removal tower 1, and the reflux liquid is sprayed downward from the acrylonitrile removal tower 1 near the top through the distributor 19 or the nozzle 20 in the tower, and contacts with the mixed steam in reverse direction for mass transfer. The reflux liquid sprayed on the top of the tower transfers mass and heat with the rising mixed steam, thereby preventing dimethyl sulfoxide in the mixed steam from entering the top of the tower and reducing the evaporation amount entering the top of the tower.

[0028] The liquid separation and recovery step also includes passing a portion of the water in the separation water tank 6 into the distributor 19 as reflux liquid through the separation water pump 8, and a portion of the water into the feed port 15 of the acrylonitrile removal tower 1 to form a mixed liquid with the original liquid of acrylonitrile to be recovered for acrylonitrile recovery. Since the separation water contains a certain amount of acrylonitrile, a portion of the separation water is transported to the top of the tower as reflux liquid, and a portion of the separation water is transported to the acrylonitrile removal tower feed for acrylonitrile recovery.

[0029] The bottom temperature of the acrylonitrile removal tower 1 is 55-70°C, the top temperature is 40-50°C, and the top pressure is 20-25kPaA; the cooling water temperature in the outer coil of the condensate tank 5 is 7-11°C.

[0030] The acrylonitrile removal tower 1 is provided with a tower internal 18, which is a tower tray, a filler or a combination thereof. The tower tray is formed by a combination of bubble trays, sieve plate trays, float valve trays, and baffle trays. The filler is a structured filler, a random filler or a combination thereof.

[0031] The acrylonitrile concentration of the feed solution treated by the acrylonitrile removal tower 1 is 5% to 10%. In order to prevent acrylonitrile from self-polymerizing and save energy, the top of the tower is operated at a negative pressure to reduce the temperature of the top and bottom of the tower. The feed in the tower is in contact with the heated and rising gas phase in the tower bottom for mass transfer, so that the acrylonitrile and part of the water therein are converted into rising gas phase under reduced pressure conditions. The top condenser 2 uses chilled water for condensation, and the condensate tank 5, separation water tank 6 and acrylonitrile tank 7 are cooled with chilled water to increase the cooling effect and prevent acrylonitrile from self-polymerizing. The tower bottom temperature is directly related to the concentration of dimethyl sulfoxide in the tower bottom. After heating treatment, the concentration of acrylonitrile in the tower bottom liquid reaches the ppm level or even the trace level;

[0032] The invention comprises an acrylonitrile desinging tower 1 and a reboiler 3 for vacuum distillation, wherein the liquid inlet of the reboiler 3 is connected to the bottom liquid outlet of the acrylonitrile desinging tower 1 through a bottom pump 4, the heat source of the reboiler 3 is low-pressure steam, the low-pressure steam is introduced into the reboiler 3 through an electromagnetic switch valve 14 and a flow regulating valve 12, the gas outlet of the steam obtained after heating is connected to the acrylonitrile desinging tower 1, the feed inlet 15 of the acrylonitrile desinging tower 1 is located in the middle or upper part of the tower body, the gas phase outlet of the acrylonitrile desinging tower 1 is connected to the gas phase inlet of the condenser 2, the condensate outlet of the condenser 2 is connected to the liquid inlet of the condensate tank 5, the condenser 2 is connected to the vacuum system, and the vacuum system regulates the pressure between the condenser 2 and the acrylonitrile through the pressure regulating valve 13 The gas phase channel between the acrylonitrile desing towers 1 is automatically controlled, and the acrylonitrile desing tower 1 is evacuated to form a negative pressure set by the process, thereby ensuring the temperature control of the acrylonitrile desing tower 1, so that the mixed steam in the acrylonitrile desing tower 1 flows into the condenser 2 for condensation, and the vacuum system extracts the non-condensable gas mixed between the acrylonitrile steam and the water vapor; the condensate tank 5 is kept cold by a coil (external coil and / or internal coil), a jacket or a combination thereof to ensure stratification; an overflow port and a liquid outlet are provided on the condensate tank 5, the overflow port of the condensate tank 5 is connected to the acrylonitrile tank 7, and the liquid outlet of the condensate tank 5 is connected to the separation water tank 6; acrylonitrile is extracted from the acrylonitrile tank 77 by an acrylonitrile pump 9 for finished product output.

[0033] A sight glass 17 for observing the reaction state in the tower kettle is provided on the side wall of the acrylonitrile desingene tower 1, and a tower internal 18 is provided inside; the tower internal 18 is a tower plate, a filler or a combination thereof; preferably, the tower internal 18 above the feed inlet 15 of the acrylonitrile desingene tower 1 is a filler, and the tower internal 18 below is a tower plate. The tower plate is one or more combinations of sieve plate plates, float valve plates, bubble cap plates, tongue-shaped plates, mesh plates, and flow-through plates; the filler is a regular filler, a random filler or a combination thereof; the tower internal 18 is made of stainless steel, carbon steel lined plastic material, or fiberglass. A reflux liquid distributor 19 and a nozzle 20 are provided near the top of the acrylonitrile desingene tower 1; the water inlet pipe of the distributor 19 is connected to the separation water tank 6 through the separation water pump 8; part of the separation water drawn from the separation water tank 6 by the separation water pump 8 flows into the distributor 19, and part flows into the feed inlet 15 of the acrylonitrile desingene tower 1;

[0034] Acrylonitrile stripping tower 1 feed volume 4.5m 3 / h; tower bottom output 4.4m 3 / h; reflux volume 14m 3 / h, 99.95% acrylonitrile product 0.1m 3 / h, reflux ratio 70-140; control steam heating capacity 200-500kg / h.

[0035] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention should be considered to belong to the protection scope of the present invention.

Claims

1. A method for controlling the temperature of an acrylonitrile stripping tower for producing high-performance carbon fiber precursor with high efficiency recovery, characterized in that: The method comprises the following steps: vaporizing acrylonitrile and water in a mixed liquid by using low-pressure steam through a reboiler (3) to obtain mixed steam; distilling the mixed steam under reduced pressure through an acrylonitrile stripping tower (1); condensing the mixed steam through a condenser (2) to obtain layered acrylonitrile and water; and recovering the upper layer of acrylonitrile through an acrylonitrile tank (7). The method comprises the following steps: Solution vacuum distillation: The solution is fed into the acrylonitrile removal tower (1) through the feed port (15), and vacuum distillation is performed under negative pressure conditions, acrylonitrile and water are vaporized to obtain mixed steam, and the remaining liquid accumulates at the bottom of the reactor to form the bottom liquid of the tower; Solution vapor condensation: Solution vapor rises from the acrylonitrile stripping tower (1) to the condenser (2) at the top of the tower, non-condensable gas enters the vacuum system under vacuum conditions, and water and acrylonitrile condense and flow into the condensate tank (5); Liquid separation and recovery: Water and acrylonitrile are separated into layers in a condensate tank (5) having a sight glass (17) and a partition. The lower layer of water enters a separation water tank (6), and the upper layer of acrylonitrile enters an acrylonitrile tank (7) through an overflow port to achieve acrylonitrile recovery.

2. The method for controlling the temperature of an acrylonitrile stripping tower (1) for producing high-performance carbon fiber precursor with high efficiency recovery according to claim 1, characterized in that: The solution vacuum distillation step also includes forcibly circulating the bottom liquid of the tower through a tower bottom pump (4), heating it with steam from a reboiler (3), and then passing it into the acrylonitrile removal tower (1).

3. The method for controlling the temperature of an acrylonitrile stripping tower (1) for producing high-performance carbon fiber precursor with high efficiency recovery according to claim 1, characterized in that: The solution reduced pressure distillation step also includes introducing reflux liquid into the acrylonitrile removal tower (1), wherein the reflux liquid is sprayed downward from a position near the top of the acrylonitrile removal tower (1) through a distributor (19) or a nozzle (20) in the tower, and contacts with the mixed steam in a countercurrent manner for mass transfer. The reflux liquid sprayed from the top of the tower transfers mass and heat with the rising mixed steam, thereby preventing dimethyl sulfoxide in the mixed steam from entering the top of the tower and reducing the amount of evaporation entering the top of the tower.

4. The method for controlling the temperature of an acrylonitrile stripping tower (1) for producing high-performance carbon fiber precursor with high efficiency recovery according to claim 1, characterized in that: The liquid separation and recovery step also includes passing a portion of the water in the separation water tank (6) into a distributor (19) as reflux liquid through a separation water pump (8), and passing a portion of the water into a feed port (15) of an acrylonitrile removal tower (1) to form a mixed liquid with the original liquid of acrylonitrile to be recovered for acrylonitrile recovery. Since the separation water contains a certain amount of acrylonitrile, a portion of the separation water is transported to the top of the tower as reflux liquid, and a portion of the separation water is transported to the acrylonitrile removal tower for feeding, and acrylonitrile is recovered again.

5. The method for controlling the temperature of an acrylonitrile stripping tower (1) for producing high-performance carbon fiber precursor with high efficiency recovery according to claim 1, characterized in that: The bottom temperature of the acrylonitrile removal tower (1) is 55-70°C, the top temperature is 40-50°C, and the top pressure is 20-25 kPaA; the cooling water temperature in the outer coil of the condensate tank (5) is 7-11°C.

6. The method for controlling the temperature of an acrylonitrile stripping tower (1) for producing high-performance carbon fiber precursor with high efficiency recovery according to claim 1, characterized in that: The acrylonitrile removal tower (1) is provided with a tower internal (18), which is a tower tray, a filler or a combination thereof. The tower tray is a combination of bubble tray, sieve tray, valve tray and baffle tray. The filler is a structured filler, a random filler or a combination thereof.

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