A continuous adipic acid crystallization system and process

Abstract

The application discloses a kind of adipic acid continuous crystallization system and process, belong to adipic acid production technical field.The adipic acid continuous crystallization system includes seed preparation tank and crystallizer, the guide vane is arranged in the inside of crystallizer along the axis, the guide vane is located in the lower part of crystallizer, the upper part of crystallizer is cylindrical evaporation part, the outer wall of evaporation part extends to the outside of guide vane and forms annular baffle, annular baffle and the sidewall between the lower part of crystallizer form annular clarification zone, the bottom of crystallizer is settling zone, and the center is provided with propelling type stirring paddle, the top of clarification zone is opened with circulating mother liquor outlet, and the top of evaporation part is opened with exhaust port.The adipic acid continuous crystallization system of the present application can realize the rapid and sufficient crystallization of adipic acid in a single device, and the unqualified fine crystals are recycled and utilized with the mother liquor, which greatly reduces the risk of crystallizer and heat exchanger fouling, and reduces the energy consumption of crystallizer.

Description

Technical Field

[0001] This invention belongs to the field of adipic acid production technology, specifically relating to a continuous crystallization system and process for adipic acid. Background Technology

[0002] Adipic acid is a highly valuable organic dicarboxylic acid in the industrial field, ranking second in production among all dicarboxylic acids. It is an important raw material for the production of polyamides, polyurethanes, nylon 66 fibers, engineering plastics, biodegradable plastics, polyurethane resins, synthetic leather (PU), and synthetic rubber. It is also widely used in national production and daily life as a food acidifier, textile treatment agent, high-grade lubricant, pharmaceutical intermediate, fragrance and flavor control agent, new single-crystal materials, and plastic foaming agent.

[0003] In the production of adipic acid, the crystallization stage is the core step that determines product quality and production efficiency. Traditional crystallization processes mainly include batch crystallization in a kettle and continuous crystallization in a horizontal manner.

[0004] The batch crystallization process is a traditional method that achieves solution supersaturation, crystal nucleation, and crystal growth through batch operation, ultimately obtaining the product through solid-liquid separation. Its core lies in precisely controlling supersaturation and crystallization time to optimize product quality. The main drawback of the batch crystallization process is its complex operation, requiring periodic loading, unloading, and cleaning operations. It involves significant manual intervention, from raw material preparation and temperature control to post-crystallization separation. This not only consumes a large amount of manpower and results in extremely low production efficiency, but also requires large equipment footprints and incurs high costs for construction and maintenance, making it difficult to meet the growing market demand. The most common horizontal continuous crystallization process uses a horizontal crystallizer with 12 compartments. Each compartment is connected by a siphon pipe, and a condenser and vacuum system are connected to the top of each compartment to maintain different vacuum levels. Under adiabatic evaporation operation, the crystallizer crystallizes adipic acid slurry through each compartment and discharges from the crystallizer. In this process, the crystallization process is controlled by varying the vacuum levels in each compartment. This process is complex; fluctuations in temperature and pressure in a single compartment can alter the crystal growth environment, affecting product performance and potentially leading to quality problems in subsequent processing, increasing the defect rate, wasting resources, and raising costs. Furthermore, the inner walls of the equipment are prone to scaling, forming an adhesion layer that compresses the crystallization space, reduces capacity, increases energy consumption, and shortens the equipment's operating cycle. Regular shutdowns for cleaning are required, further increasing time and labor costs and severely restricting the continuity and stability of production. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous crystallization system and process for adipic acid, so as to solve the problem that the existing adipic acid production crystallization process has unsatisfactory application effect as mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a continuous adipic acid crystallization system, comprising a crystallizer and a seed crystal preparation tank, wherein the seed crystal preparation tank is connected to the crystallizer via a seed crystal delivery pump pipeline; a guide tube is arranged along the axis inside the crystallizer, the guide tube being located at the lower part of the crystallizer; the upper part of the crystallizer is a cylindrical evaporation section, the diameter of which is smaller than the diameter of the lower part of the crystallizer but larger than the outer diameter of the guide tube; a circular baffle extends downward from the bottom of the outer wall of the evaporation section, the baffle extending to the upper outer side of the guide tube, forming a ring-shaped crystal growth zone between the two; the baffle of the evaporation section and the crystallizer... A ring-shaped clarification zone is formed between the lower sidewalls of the crystallizer. The bottom of the crystallizer is a crystal settling zone, and a propulsion agitator is set in the center. The agitator is connected to a drive motor located on the outside of the bottom of the crystallizer via a drive shaft. The agitator extends upward into the bottom of the guide tube. The bottom of the sidewall of the crystallizer has an inlet and an outlet on both sides. The inlet is connected to the inside of the guide tube through a pipe inside the crystallizer. The bottom of the crystallizer also has a circulating slurry inlet and a circulating slurry outlet on both sides, which are connected by a circulating pump pipeline. The crystallizer has a circulating mother liquor outlet at the top of the clarification zone, and an exhaust port at the top of the evaporation section.

[0007] Preferably, the circulating mother liquor outlet pipeline is connected to a mother liquor circulation pump and a circulating mother liquor heater, and the circulating mother liquor heater pipeline is connected to the feed pipeline of the crystallizer.

[0008] Preferably, the crystallizer has a seed inlet in the middle of the side of the evaporation section, the seed inlet is located at the flash liquid surface of the crystallization liquid in the evaporation section, and the seed inlet is connected to the seed preparation tank through a seed delivery pump pipeline.

[0009] Preferably, the exhaust port pipe at the top of the crystallizer is connected to a condenser, the outlet pipe of the condenser is connected to the condensate inlet at the top of the crystallization sealed tank, the condensate outlet at the bottom of the crystallization sealed tank is connected to the seed crystal preparation tank through a condensate collection pump pipe, the exhaust port pipe at the top of the crystallization sealed tank is connected to a vacuum unit, a branch pipe is provided on the connection pipe between the crystallization sealed tank and the vacuum unit to the atmosphere, and a regulating valve is provided on the branch pipe.

[0010] Preferably, the crystallizer has a detection port on the side near the discharge port, and an online particle size analyzer is installed at the detection port.

[0011] Preferably, the inlet pipe of the crystallizer is connected to a pre-processor, which includes a filter and an ion exchange resin.

[0012] This invention also provides a continuous crystallization process for adipic acid, wherein the continuous crystallization process is carried out using an adipic acid continuous crystallization system as described above, and the continuous crystallization process includes the following steps: (1) Raw material pretreatment: Adipic acid stock solution is first transported to the preprocessor for pretreatment. During the pretreatment process, the stock solution is first filtered to remove solid impurities. Then, the stock solution is treated with ion exchange resin to remove harmful metal ions. (2) Establish material circulation. The pretreated adipic acid stock solution enters the crystallizer through the crystallizer inlet. There is a pipe connecting the crystallizer inlet and the guide tube to guide the adipic acid stock solution into the guide tube. In the guide tube, the material is pushed upward to the top liquid surface of the evaporation section of the crystallizer by the action of the propulsion stirring paddle. Then it moves downward to the bottom of the crystallizer along the crystal growth zone between the guide tube and the baffle. Under the suction and pushing of the stirring paddle, it enters the guide tube again and moves upward to the top liquid surface of the evaporation section to start stable circulation. (3) Vacuum flash crystallization: Start the vacuum unit to gradually reduce the pressure inside the crystallizer, the material undergoes vacuum flash evaporation, the temperature drops rapidly, and adipic acid begins to crystallize. At the same time, start the seed crystal delivery pump to transport the seed crystals in the seed crystal preparation tank into the crystallizer through the seed crystal input port. The amount of seed crystals input is controlled by the crystal particle size data obtained by the online particle size analyzer. (4) Crystallization mother liquor circulation: In the clarification zone formed between the side wall and the baffle of the crystallizer, the stirring effect of the agitator has actually disappeared. Larger crystals in the liquid flow settle and separate from the mother liquor, while small crystals are discharged from the circulating mother liquor outlet at the top of the clarification zone with the mother liquor and are transported into the circulating mother liquor heater by the mother liquor circulation pump. The heated mother liquor has an increased temperature and increased solubility of adipic acid. The small crystals in the mother liquor redissolve into the mother liquor and are transported through pipelines and mixed with the pretreated adipic acid stock solution in proportion before re-entering the crystallizer. The temperature of the circulating mother liquor is controlled so that the temperature of the circulating mother liquor is about 0.5~10℃ higher than the crystallization temperature in the crystallizer. (5) Slurry extraction: After the crystallized particles grow to the qualified particle size, they are extracted from the discharge port at the bottom of the crystallizer by the slurry extraction pump and transported to the downstream centrifugal section.

[0013] Furthermore, the water vapor and non-condensable gases generated during the flash evaporation process in the crystallizer are discharged from the exhaust port at the top of the crystallizer. After being condensed and cooled by the condenser, they are transported to the crystallization sealed tank through pipelines. The condensate is retained in the crystallization sealed tank, and the non-condensable gases are drawn into the vacuum unit through the exhaust port at the top of the crystallization sealed tank, and then transported to the downstream non-condensable gas treatment unit through the outlet pipeline of the vacuum unit.

[0014] Furthermore, a branch line is provided on the connecting pipeline between the crystallization sealing tank and the vacuum unit, which is connected to the atmosphere. The air flow into the vacuum unit is regulated by the regulating valve on the branch line, thereby controlling the pressure of the entire crystallization system.

[0015] Furthermore, when the liquid level of the condensate in the crystallization sealed tank reaches the set value, the condensate extraction pump is turned on, and the condensate is transported to the seed crystal preparation tank through the condensate outlet at the bottom of the crystallization sealed tank. Then, 50μm~100μm adipic acid particles are quantitatively added to the seed crystal preparation tank to prepare the seed crystal slurry. The seed crystal preparation tank is equipped with a stirring device to ensure the uniform distribution of the seed crystals in the liquid phase.

[0016] Furthermore, during the crystallization process in the crystallizer, the slurry circulation pump is turned on. The slurry at the bottom of the crystallizer is discharged from the circulating slurry outlet, transported by the slurry circulation pump, and returned to the bottom of the crystallizer from the circulating slurry inlet. Through slurry circulation, the distribution of slurry at the bottom of the crystallizer is improved, and large crystal particles are prevented from depositing and caking at the bottom of the crystallizer, which would affect the rotation of the stirring paddle and the crystallization effect.

[0017] Compared with the prior art, the advancements of the adipic acid continuous crystallization system and process provided by this invention are as follows: 1. The adipic acid continuous crystallization system of this invention is equipped with a guide tube inside the crystallizer and a baffle at the bottom of the evaporation section. A crystal growth zone is formed between the baffle and the guide tube, and a clarification zone is formed between the baffle and the side wall of the crystallizer. The adipic acid stock solution and slurry are continuously circulated to the evaporation section under the action of the propeller blades, the guide tube, and the crystal growth zone to complete the crystallization process of adipic acid. Large adipic acid crystals continuously settle to the crystal settling zone at the bottom of the crystallizer. In the clarification zone between the crystallizer and the baffle, due to the continuous crystallization and precipitation of adipic acid, the adipic acid content of the mother liquor is the lowest, and some tiny crystals also accumulate here. They are discharged from the crystallizer through the circulating mother liquor outlet and heated by the circulating mother liquor heater to dissolve the adipic acid microcrystals. Then, they are mixed with the adipic acid stock solution in proportion and sent back to the crystallizer for crystallization, realizing the full utilization of the adipic acid stock solution and reducing scaling.

[0018] 2. The adipic acid continuous crystallization system set up in this invention realizes continuous production. Compared with the traditional intermittent batch crystallization process and horizontal evaporation crystallization process, it does not require frequent shutdown, cleaning, feeding and other operations. The production process is smoother, more efficient and continuous material circulation and crystallization process, which greatly increases the output of adipic acid and significantly improves the production efficiency, and can better meet the growing market demand for adipic acid.

[0019] 3. The adipic acid continuous crystallization system of the present invention is equipped with a seed crystal addition device. The seed crystal inlet of the crystallizer is located near the flash liquid surface. The flash liquid surface is the point of highest supersaturation in the crystallizer, where fine crystals are most easily formed. The seed crystals delivered by the seed crystal delivery pump can effectively consume the supersaturation at the flash liquid surface, avoiding the excessive formation of fine crystals and effectively improving crystallization efficiency. An online particle size analyzer is also installed at the discharge end of the crystallizer to detect the particle size of the crystals in the collected slurry. Based on the detection results, the amount and timing of seed crystal addition by the seed crystal delivery pump are precisely controlled, and the seed crystal addition strategy is adjusted in real time, allowing crystal nuclei to form and grow under optimal conditions. This effectively improves the crystal growth rate and uniformity, reduces crystal agglomeration, and thus improves the quality and purity of the product.

[0020] 4. The adipic acid continuous crystallization system of this invention employs vacuum flash cooling, eliminating the need for heat exchange surfaces. Simultaneously, the forced circulation of the crystallizing material avoids the scaling problem common in traditional crystallization processes. Scaling in traditional processes not only affects crystallization efficiency and product quality but also requires periodic shutdowns for cleaning and maintenance, consuming significant time and labor costs. This crystallization system eliminates scaling issues, enabling the equipment to operate stably for extended periods, reducing maintenance frequency and costs, and improving equipment utilization and production continuity.

[0021] 5. Compared with traditional batch reactor crystallization and horizontal evaporation crystallization processes, the adipic acid continuous crystallization system of this invention requires only one vertical crystallizer to achieve high-quality and stable crystallization of adipic acid under the same production capacity. The process flow is shorter, control is simpler, and equipment investment is significantly reduced. Furthermore, due to the shorter process flow, fewer auxiliary equipment is needed, and compared to horizontal crystallizers, the vertical crystallizer used in this process has higher crystallization space utilization and a smaller equipment footprint. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of an adipic acid continuous crystallization system according to the present invention; In the diagram: 1-Seed crystal preparation tank, 2-Seed crystal transfer pump, 3-Crystallizer, 4-Mother liquor circulation pump, 5-Circulating mother liquor heater, 6-Crystallization condenser, 7-Crystallization sealed tank, 8-Vacuum unit, 10-Slurry collection pump, 11-Slurry circulation pump, 12-Condensate collection pump, 13-Online particle size analyzer, 31-Agitator, 32-Baffle, 33-Guide tube, 34-Detection port, 35-Evaporation section. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1 As shown, this invention provides an embodiment of a continuous adipic acid crystallization system. In this embodiment, the continuous adipic acid crystallization system includes a seed crystal preparation tank 1, a crystallizer 3, a mother liquor circulation pump 4, a circulating mother liquor heater 5, a crystallization condenser 6, a crystallization sealed tank 7, and a vacuum unit 8. A guide tube 33 is arranged along the axis inside the crystallizer 3, located at the lower part of the crystallizer 3. The upper part of the crystallizer 3 is a cylindrical evaporation section 35, the diameter of which is smaller than the diameter of the lower part of the crystallizer 3 but larger than the outer diameter of the guide tube 33. An annular baffle 32 extends downward from the bottom of the outer wall of the evaporation section 35, extending to the outside of the guide tube 33, forming an annular crystal growth zone between them. An annular clarification zone is formed between the outer side of the baffle 32 of the evaporation section 35 and the side wall of the lower part of the crystallizer 3. The bottom of the crystallizer 3 is a crystal settling zone, and a propulsion agitator 31 is set in the center. The agitator 31 is connected to a drive motor located on the outside of the bottom of the crystallizer 3 via a drive shaft. The agitator 31 extends upward into the bottom of the inner side of the guide tube 33. The rotation of the agitator 31 can push the slurry in the guide tube 33 upward, and at the same time suck the slurry on the outside of the bottom of the guide tube 33 into the guide tube 33.

[0025] The bottom sidewalls of crystallizer 3 are symmetrically equipped with inlet N1 and outlet N5. Inlet N1 is connected to the inside of guide cylinder 33 via a pipe inside crystallizer 3, and to a pretreatment device for adipic acid solution via a pipe outside crystallizer 3. The adipic acid crystallization stock solution is directly fed into guide cylinder 3 through inlet N1. Outlet N5 is connected to slurry pump 10, which transports the adipic acid crystal slurry to the slurry centrifugation section.

[0026] The bottom of the crystallizer 3 is symmetrically equipped with a circulating slurry inlet N7 and a circulating slurry outlet N6, which are connected by a slurry circulation pump 11. The slurry circulation pump 11 provides power to realize the self-circulation of the slurry in the settling zone at the bottom of the crystallizer 3. Through slurry circulation, the distribution of slurry at the bottom of the crystallizer is improved, and large crystal particles are prevented from depositing and caking at the bottom of the crystallizer, which would affect the rotation of the stirring paddle and the crystallization effect.

[0027] The crystallizer 3 has a circulating mother liquor outlet N4 at the top side wall of the clarification zone. The circulating mother liquor outlet N4 is connected to the circulating mother liquor heater 5 through the mother liquor circulation pump 4. The circulating mother liquor heater 5 is heated by steam. The discharge end of the circulating mother liquor heater 5 is connected to the feed pipeline of the crystallizer 3 through a pipeline.

[0028] The top of the evaporation section 35 of the crystallizer 3 has an exhaust port N2. The exhaust port N2 is connected to the crystallization condenser 6. The crystallization condenser 6 is connected to the chilled water circulation system to cool and condense the exhaust. The outlet of the crystallization condenser 6 is connected to the condensate inlet N71 at the top of the crystallization sealed tank 7. The condensate outlet N73 at the bottom of the crystallization sealed tank 7 is connected to the seed crystal preparation tank 1 through the condensate collection pump 12. The exhaust port N72 at the top of the crystallization sealed tank 7 is connected to the vacuum unit 8. The seed crystal preparation tank 1 is equipped with a stirring device, and its top also has an adipic acid granule addition port, and its bottom has a seed crystal outlet. It is connected to the seed crystal inlet N3 of the evaporation section 35 of the crystallizer 3 through the seed crystal delivery pump 2. The seed crystal inlet N3 is located at the flash liquid surface of the evaporation section 35.

[0029] The crystallizer 3 has a detection port 34 on the side near the discharge port N5. An online particle size analyzer 13 is installed through the detection port. The online particle size analyzer 13 detects the particle size of adipic acid crystals in the crystallizer 3 and controls the working status of the seed crystal delivery pump 2 through the controller.

[0030] The production process of the adipic acid continuous crystallization system provided in this embodiment includes the following steps. (1) Raw material pretreatment: Adipic acid stock solution is first transported to the pretreatment equipment. During the pretreatment process, the stock solution is first filtered to remove solid impurities. Then, the stock solution is subjected to ion exchange treatment using ion exchange resin to remove metal ions and other harmful impurities, ensuring that the purity of the stock solution entering the crystallizer meets the requirements, thus laying the foundation for a high-quality crystallization process.

[0031] (2) Establishing material circulation: The pretreated adipic acid stock solution and the adipic acid mother liquor heated by the circulating mother liquor heater to eliminate fine crystals are mixed in proportion and then enter the crystallizer 3 through the crystallizer inlet N1. There is a pipe connecting the crystallizer inlet N1 and the guide tube 33 to guide the mixed liquid into the guide tube 33. The temperature of the circulating mother liquor is controlled so that the temperature of the mixed material is about 0.5~10℃ higher than the crystallization temperature in the crystallizer 3. In the guide tube 33, the material is pushed upward to the top liquid surface of the evaporation section 35 of the crystallizer 3 by the action of the propulsion stirring paddle 31, and then moves downward to the bottom of the crystallizer 3 along the crystal growth zone formed by the guide tube 33 and the baffle 32. Under the suction and pushing of the stirring paddle 31, it enters the guide tube 33 again and moves upward to the top liquid surface of the crystallizer 3 again to start stable circulation.

[0032] (3) Vacuum flash crystallization: The vacuum unit is started, and the pressure inside crystallizer 3 gradually decreases. The material undergoes vacuum flash evaporation, and the temperature drops rapidly, causing adipic acid to begin crystallization. During the crystallization process, the pressure inside the crystallizer is precisely controlled to keep the temperature within a specific range, ensuring the smooth progress of the crystallization process. At the same time, pressure changes are monitored in real time to ensure pressure stability and avoid instability in the crystallization process due to pressure fluctuations, which could affect the crystal quality. The water vapor and non-condensable gases generated by flash evaporation are discharged from the exhaust port N2 at the top of the crystallizer. After being condensed and cooled by the crystallization condenser 6, they enter the crystallization sealed tank 7 through the condensate inlet N71 at the top of the crystallization sealed tank 7. The condensate remains in the crystallization sealed tank 7, and the non-condensable gases are drawn into the vacuum unit 8 through the exhaust port N72 at the top of the crystallization sealed tank, and then transported to the downstream non-condensable gas treatment unit through the outlet pipeline of the vacuum unit 8. A branch pipeline is provided on the connecting pipeline between the crystallization sealed tank 7 and the vacuum unit 8 to connect with the atmosphere. The air flow rate entering the vacuum unit is adjusted by the regulating valve on the branch pipeline, thereby controlling the pressure of the entire crystallization system. The crystallization sealed tank 7 can buffer the pressure fluctuations of the entire system and ensure the stability of the crystallization environment.

[0033] (4) Seed preparation: When the liquid level of the condensate in the crystallization sealed tank 7 reaches the set value, the condensate extraction pump 12 is turned on. The condensate is transported to the seed preparation tank 1 through the condensate outlet N73 at the bottom of the crystallization sealed tank 7. Then, 50μm~100μm adipic acid particles are quantitatively added to the seed preparation tank to prepare a seed slurry with a certain solid content. The seed preparation tank 1 is equipped with a stirring device to ensure the uniform distribution of the seed in the liquid phase. After being metered, the prepared seed slurry is transported by the seed delivery pump 2 through the seed inlet N3 into the crystallizer 3 near the flash liquid surface. The flash liquid surface is the point with the highest supersaturation in the crystallizer, and it is easiest to form fine crystals. The seed delivered by the seed delivery pump 2 can effectively consume the supersaturation at the flash liquid surface, avoid the large-scale generation of fine crystals, and effectively improve the crystallization effect. The input amount of seed needs to be adjusted and controlled according to the crystal particle size data obtained by the online particle size analyzer 13 at the extraction end.

[0034] (5) Mother liquor circulation: In the clarification zone formed by the outer shell of crystallizer 3 and baffle 32, the stirring effect of the stirring paddle 31 has actually disappeared. Larger crystals settle and separate from the mother liquor, while small crystals are discharged from the circulating mother liquor outlet N4 at the top of the clarification zone along with the mother liquor. They are then transported into the circulating mother liquor heater 5 by the mother liquor circulation pump 4. The heated mother liquor has an increased temperature, and the microcrystals in the mother liquor redissolve and re-enter the mother liquor. After being mixed with the feed raw liquor in proportion, it re-enters the crystallizer.

[0035] Fine crystals are discharged with the mother liquor and redissolved, which can reduce the risk of scaling on the crystallizer wall and heat exchanger, extend the cleaning cycle, and reduce the hydraulic resistance of the built-in agitator, thus reducing the energy consumption of the crystallizer.

[0036] (6) Slurry circulation: The slurry at the bottom of the crystallizer 3 is discharged from the circulating slurry outlet N6, transported by the slurry circulation pump 11, and returned to the bottom of the crystallizer from the circulating slurry inlet N7. Through slurry circulation, the distribution of slurry at the bottom of the crystallizer is improved, and large particles of crystals are prevented from depositing and caking at the bottom of the crystallizer, which would affect the rotation of the stirring paddle and the crystallization effect.

[0037] (7) Slurry extraction: When the crystallized particles grow to the qualified particle size, start the slurry extraction pump 10 to extract the slurry from the bottom slurry outlet N5 of the crystallizer 3 and transport it to the downstream centrifugal section.

[0038] Example 1 The adipic acid crystallization production process according to the above-described continuous crystallization process provided by this invention is as follows: Raw material preparation: Prepare adipic acid stock solution with an initial concentration of 35%. The impurity content (including metal ions and other organic impurities) must meet industry standards after testing. Specifically, the metal ion content should be below 10 mg / kg for iron ions, below 10 mg / kg for copper ions, and below 20 mg / kg for vanadium ions. The stock solution temperature should be controlled at 85~90℃ to ensure its stability during transportation and pretreatment. In the pretreatment stage, the adipic acid stock solution is first fed into a filtration system using a diatomaceous earth filter, which effectively removes solid impurities and decolorizes the solution. After filtration, the stock solution enters an ion exchange resin column filled with strongly acidic cation exchange resin and strongly basic anion exchange resin. Through ion exchange reactions, metal ions in the stock solution are removed. The pretreated adipic acid stock solution exhibits significantly reduced impurity content, with metal ions becoming virtually undetectable, providing a high-purity raw material for the subsequent crystallization process. In the crystallization process, the pretreated adipic acid stock solution is pumped into the crystallizer. The crystallization temperature inside the crystallizer is set at 25℃ and the pressure at 9 kPa. The rotation speed of the propeller-type agitator is set at 150 r / min, and the ratio of mother liquor circulation rate to stock solution feed rate is 100. During the crystallization process, temperature and pressure changes inside the crystallizer are monitored in real time using temperature and pressure sensors, and the opening of the vacuum system valves is adjusted to ensure that the temperature and pressure remain within the set range. The particle size data of the crystals measured by an online particle size analyzer is used to adjust the amount of seed crystals injected into the crystallizer to improve the crystallization effect in a timely manner.

[0039] The slurry is collected when the average particle size of the crystals grows to 500 μm. It is then pumped to a centrifuge for solid-liquid separation. The separated crystals are then dried in a vacuum dryer at 120°C to obtain the final crystalline adipic acid product. Quality Inspection Results: A comprehensive quality inspection was conducted on the obtained crystalline adipic acid product. High-performance liquid chromatography (HPLC) was used to determine its purity, which was found to be above 99.9%. Laser particle size analyzer was used to analyze the crystal size distribution, showing an average particle size of 600 μm and uniform distribution. Chemical analysis was used to determine the impurity content, finding iron ion content to be 1 mg / kg, copper ion content to be below 1.5 mg / kg, and other impurities to be at extremely low levels. The product exhibits white, uniform crystal particles with good flowability, meeting the quality requirements of the high-end market for adipic acid products.

[0040] Example 2 Compared to Example 1, in this implementation, the online particle size analyzer and seed pump were shut down, and no more seed crystals were added to the crystallizer. All other operating parameters and procedures remained identical. A comprehensive quality test was performed on the obtained crystalline adipic acid product. High-performance liquid chromatography (HPLC) was used to determine its purity, which showed a purity of over 99%. A laser particle size analyzer was used to determine the crystal size distribution, showing an average particle size of 400 μm and a relatively wide distribution. Chemical analysis was used to determine the impurity content in the product, revealing an iron ion content of 2 mg / kg and a copper ion content of approximately 3 mg / kg. The product had a white appearance and good flowability, but the crystal particles were uneven and small in size, failing to meet the quality requirements of the high-end market for adipic acid products.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A continuous crystallization system for adipic acid, characterized in that, The adipic acid continuous crystallization system includes a crystallizer and a seed crystal preparation tank. The seed crystal preparation tank is connected to the crystallizer via a seed crystal delivery pump pipeline. A guide tube is arranged along the axis inside the crystallizer, located at the lower part of the crystallizer. The upper part of the crystallizer is a cylindrical evaporation section. The diameter of the evaporation section is smaller than the diameter of the lower part of the crystallizer but larger than the outer diameter of the guide tube. A circular baffle extends downwards from the outer wall of the evaporation section, reaching the upper outer side of the guide tube. An annular crystal growth zone is formed between the baffle and the guide tube. An annular crystal growth zone is formed between the baffle of the evaporation section and the side wall of the lower part of the crystallizer. The crystallizer has a crystal settling zone at its bottom, with a propulsion agitator at its center. The agitator is connected to a drive motor located on the outside of the bottom of the crystallizer via a drive shaft. The agitator extends upwards into the bottom of the guide tube. The bottom side wall of the crystallizer has an inlet and an outlet on both sides. The inlet is connected to the inside of the guide tube via a pipe inside the crystallizer. The bottom of the crystallizer also has a circulating slurry inlet and a circulating slurry outlet on symmetrical sides, which are connected by a circulating pump pipeline. The crystallizer has a circulating mother liquor outlet at the top of the clarification zone, and an exhaust port at the top of the evaporation section.

2. The adipic acid continuous crystallization system according to claim 1, characterized in that: The circulating mother liquor outlet pipeline is connected to a mother liquor circulation pump and a circulating mother liquor heater, and the circulating mother liquor heater outlet pipeline is connected to the crystallizer feed pipeline.

3. The adipic acid continuous crystallization system according to claim 2, characterized in that: The crystallizer has a seed inlet located in the middle of the side of the evaporation section. The seed inlet is located at the flash evaporation liquid surface of the crystallizing liquid in the evaporation section. The seed inlet is connected to the seed preparation tank through a seed delivery pump pipeline.

4. The adipic acid continuous crystallization system according to claim 3, characterized in that: The exhaust pipe at the top of the crystallizer is connected to a condenser. The outlet pipe of the condenser is connected to the condensate inlet at the top of the crystallization sealed tank. The condensate outlet at the bottom of the crystallization sealed tank is connected to the seed crystal preparation tank via a condensate collection pump pipe. The exhaust pipe at the top of the crystallization sealed tank is connected to a vacuum unit. A branch pipe is provided on the connection pipe between the crystallization sealed tank and the vacuum unit to the atmosphere. A regulating valve is provided on the branch pipe.

5. The adipic acid continuous crystallization system according to claim 4, characterized in that: The crystallizer has a detection port on the side near the discharge port, and an online particle size analyzer is installed at the detection port.

6. The adipic acid continuous crystallization system according to claim 5, characterized in that: The crystallizer's inlet pipe is connected to a pre-processor, which includes a filter and an ion exchange resin.

7. A continuous crystallization process for adipic acid, characterized in that: The continuous crystallization process is carried out using the adipic acid continuous crystallization system as described in claim 6, and the continuous crystallization process includes the following steps: (1) Raw material pretreatment: Adipic acid stock solution is first transported to the preprocessor for pretreatment. During the pretreatment process, the stock solution is first filtered to remove solid impurities. Then, the stock solution is treated with ion exchange resin to remove harmful metal ions. (2) Establish material circulation. The pretreated adipic acid stock solution enters the crystallizer through the crystallizer inlet. There is a pipe connecting the crystallizer inlet and the guide tube to guide the adipic acid stock solution into the guide tube. In the guide tube, the material is pushed upward to the top liquid surface of the evaporation section of the crystallizer by the action of the propulsion stirring paddle. Then it moves downward to the bottom of the crystallizer along the crystal growth zone between the guide tube and the baffle. Under the suction and pushing of the stirring paddle, it enters the guide tube again and moves upward to the top liquid surface of the evaporation section to start stable circulation. (3) Vacuum flash crystallization: Start the vacuum unit to gradually reduce the pressure inside the crystallizer, the material undergoes vacuum flash evaporation, the temperature drops rapidly, and adipic acid begins to crystallize. At the same time, start the seed crystal delivery pump to deliver the seed crystals in the seed crystal preparation tank into the crystallizer through the seed crystal input port. The amount of seed crystals input is controlled by the crystal particle size data obtained by the online particle size analyzer. During the crystallization process in the crystallizer, start the slurry circulation pump. The slurry at the bottom of the crystallizer is discharged from the circulating slurry outlet, transported by the slurry circulation pump, and returned to the bottom of the crystallizer from the circulating slurry inlet. (4) Crystallization mother liquor circulation: In the clarification zone formed between the side wall and the baffle of the crystallizer, the stirring effect of the agitator has actually disappeared. Larger crystals in the liquid flow settle and separate from the mother liquor, while small crystals are discharged from the circulating mother liquor outlet at the top of the clarification zone with the mother liquor and are transported into the circulating mother liquor heater by the mother liquor circulation pump. The heated mother liquor has an increased temperature and increased solubility of adipic acid. The small crystals in the mother liquor redissolve into the mother liquor and are transported through pipelines and mixed with the pretreated adipic acid stock solution in proportion before re-entering the crystallizer. The temperature of the circulating mother liquor is controlled so that the temperature of the circulating mother liquor is about 0.5~10℃ higher than the crystallization temperature in the crystallizer. (5) Slurry extraction: After the crystallized particles grow to the qualified particle size, they are extracted from the discharge port at the bottom of the crystallizer by the slurry extraction pump and transported to the downstream centrifugal section.

8. The continuous crystallization process for adipic acid according to claim 7, characterized in that: The water vapor and non-condensable gases generated during the flash evaporation process in the crystallizer are discharged from the exhaust port at the top of the crystallizer. After being condensed and cooled by the condenser, they are transported to the crystallization sealed tank through pipelines. The condensate is retained in the crystallization sealed tank, and the non-condensable gases are drawn into the vacuum unit through the exhaust port at the top of the crystallization sealed tank, and then transported to the downstream non-condensable gas treatment unit through the outlet pipeline of the vacuum unit.

9. The continuous crystallization process for adipic acid according to claim 8, characterized in that: Once the condensate level in the crystallization tank reaches the set value, the condensate extraction pump is turned on, and the condensate is transported to the seed crystal preparation tank through the condensate outlet at the bottom of the crystallization tank. Then, 50μm~100μm adipic acid particles are quantitatively added to the seed crystal preparation tank to prepare the seed crystal slurry. The seed crystal preparation tank is equipped with a stirring device to ensure the uniform distribution of the seed crystals in the liquid phase.

10. A continuous crystallization process for adipic acid according to claim 9, characterized in that: The connecting pipeline between the crystallization sealed tank and the vacuum unit is equipped with a branch pipeline that is connected to the atmosphere. The air flow into the vacuum unit is regulated by the regulating valve on the branch pipeline, thereby controlling the pressure of the entire crystallization system.

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