Crystallization device and method for adipic acid

Abstract

The invention relates to an adipic acid crystallization process and crystallization device, and the crystallization process comprises the following steps: carrying out step-by-step reduced pressure evaporative crystallization on an adipic acid-containing primary slurry through an M-stage crystallization unit in a negative pressure environment to obtain an adipic acid-containing target slurry, steam generated by the front-stage crystallization unit provides heat for the adjacent rear-stage crystallization unit or the rear-stage crystallization units spaced by 1-2 stages; m > = 3. The crystallization device comprises M mutually independent crystallization chambers, the top of each crystallization chamber is provided with a gas phase outlet, the second crystallization chamber to the Mth crystallization chamber are provided with heat exchange mechanisms, and the gas phase outlet of the upper-stage crystallization chamber is connected with a negative pressure source through a communicating pipeline and a heat exchange medium channel of the lower-stage heat exchange mechanism; m > = 3. The adipic acid obtained by the process is high in quality, the used crystallization device is simple in structure and low in modification cost, scabbing in the crystallizer can be effectively avoided on the basis of realizing zero steam consumption and realizing crystallization of adipic acid slurry, and the operation cycle of the device is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and in particular to a device and method for crystallizing adipic acid. Background Art

[0002] Adipic acid belongs to aliphatic carboxylic acid, commonly known as fatty acid, with the molecular formula C6H 10 O4, a white crystalline powder, is stable and non-deliquescent. It is primarily used in the manufacture of nylon 66 (nylon 66) and polyurethane resins, and also in the production of plasticizers and lubricating greases. A small amount is used as a food acidifier and as a substitute for tartaric acid in baking powder. It can also be used in the manufacture of pesticides and adhesives, as well as in the production of pharmaceuticals and fragrances. Currently, the industries with the fastest growth in domestic usage include synthetic leather resins, polyurethane shoe sole resins, polyurethane adhesives, and polyols for TPU.

[0003] The production process for adipic acid involves oxidizing cyclohexanol / cyclohexanone with nitric acid in the presence of a copper-vanadium catalyst. The resulting oxidized solution undergoes a series of steps, including crystallization, concentration, dehydration, dissolution, decolorization, recrystallization, and drying, to produce the finished adipic acid. Large-scale industrial production of adipic acid requires crystallization.

[0004] Currently, adipic acid crystallization equipment is equipped with multiple continuous crystallization chambers, relying on vacuum evaporation and step-by-step cooling to form a supersaturated solution. However, because chemical companies typically use fixed specifications for chilled water and saturated steam, the use of chilled water and saturated steam to control step-by-step cooling is complex. This results in a large temperature difference between the heat exchange medium and the adipic acid slurry within the crystallization chamber. Under high vacuum conditions, the adipic acid slurry within the crystallization chamber boils violently, forming crusts at the bottom of the crystallization chamber, affecting the quality of the adipic acid crystals. Frequent maintenance downtime is also required, impacting production efficiency and significantly wasting heat.

[0005] Therefore, how to design a low-energy-consumption, long-operation-cycle adipic acid crystallization scheme is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] One of the purposes of the present invention is to address the deficiencies of the prior art and provide a method for crystallizing adipic acid, which does not require external steam heating and can crystallize for a long time at low cost to obtain a finished product slurry containing adipic acid, thereby meeting the production needs of enterprises.

[0007] The second object of the present invention is to provide a crystallization device for adipic acid, which has a simple structure and low modification cost. On the basis of achieving zero steam consumption to crystallize adipic acid slurry, it can effectively avoid scarring in the crystallizer and extend the operation cycle of the device.

[0008] A technical solution for achieving one of the objectives of the present invention is: a crystallization process for adipic acid, the crystallization process comprising: a primary slurry containing adipic acid is subjected to step-by-step reduced pressure evaporation and crystallization in M-stage crystallization units under negative pressure to obtain a target slurry containing adipic acid crystals, wherein the steam generated by the preceding crystallization unit provides heat to the adjacent subsequent crystallization unit or to the subsequent crystallization unit separated by 1 to 2 stages; M ≥ 3.

[0009] The crystallization process of the present invention utilizes the vapor phase heat generated by the preceding crystallization unit to supply heat to the succeeding crystallization unit. The temperature difference between the vapor phase heat of the preceding crystallization unit and the material in the succeeding crystallization unit is small, which can maintain stable evaporation of the material in each crystallization unit, achieving the goal of zero external steam use, reducing the cost of adipic acid production, and also allowing for intermittent heating according to actual needs. Zero external steam use can also avoid the problem of violent boiling of the material caused by a large temperature difference between the external steam and the material in the crystallization unit, thereby avoiding scarring caused by violent boiling of the material, and at the same time avoid uneven saturation distribution caused by the large temperature difference between the heat source and the material to be heated in the compartment, which can lead to a decrease in crystal quality.

[0010] In some preferred embodiments, the primary slurry is the oxidation product of cyclohexanol, cyclohexanone, and nitric acid. Preferably, the oxidation product undergoes a flash evaporation treatment. The flash evaporation temperature is preferably 85°C-90°C, and the flash evaporation time is preferably 20-40 minutes. The high-temperature oxidation liquid slurry (oxidation product) is first flash-evaporated in a flash evaporator before being transferred to the crystallization chamber. This lowers the temperature of the slurry entering the crystallization chamber, resulting in low-temperature multiple crystallization. This reduces the risk of scarring in the crystallization chamber and extends the equipment's operating cycle.

[0011] Preferably, the content of adipic acid in the primary slurry is 15-45 wt%, the content of other dibasic acids is 4-7 wt% of the mass of adipic acid, the other dibasic acids mainly include glutaric acid and succinic acid, the content of nitric acid is 15-40 wt%, no more than 5 wt% of monoacids, and the balance is water; Preferably, the processing flow rate of the primary slurry is 35-50m 3 / h, for example, 35 m 3 / h, 40 m 3 / h, 45 m 3 / h or 50m 3 / h.

[0012] Preferably, the temperature of the primary slurry is 80-100°C, for example 80°C, 85°C, 90°C, 95°C or 100°C, and the temperature of the target slurry is 20-45°C, for example 20°C, 25°C, 30°C, 35°C, 40°C or 45°C.

[0013] In some preferred embodiments, 5-20 wt% of the target slurry is refluxed to the crystal nucleus control crystallization unit to form a cycle, and a portion of the target slurry is refluxed back to the crystal nucleus control unit to regulate the crystallization process. The crystal nucleus control unit is generally the 2nd to M-2th crystallization unit.

[0014] In some preferred embodiments, each crystallization unit is equipped with a stirring mechanism, and the stirring mechanism has a rotational speed of 50-600 RPM, preferably 50-300 RPM. The stirring speed affects the uniformity of the material in the chamber, such as the uniformity of supersaturation and temperature. In this embodiment, the speed range above or a value within the above range can be selected to meet actual needs.

[0015] In some preferred embodiments, the pressure of the first-stage crystallization unit is 35-55 KPaA, preferably, the pressure is 35-45 KPaA, and the pressure of the tail-stage crystallization unit is 0-10 KPaA, preferably, the pressure is 4-6 KPaA; Preferably, M≥7.

[0016] The pressure drop from the first-stage crystallization unit to the N-stage crystallization unit is 20-30 kPaA, and the temperature drop is 15-30°C. The pressure drop from the N-stage crystallization unit to the M-stage crystallization unit is 10-20 kPaA, and the temperature drop is 15-30°C. 2≤N<M. For example, N=2, 3, 4, 5, or 6. The specific selection is based on actual operation and product conditions. Preferably, in the N-stage crystallization unit and before the N-stage crystallization unit, the pressure drop per stage is 5-15 kPaA, for example, 5, 8, 10, 12, or 15 kPaA, and the temperature drop per stage is 5-15°C, for example, 5, 8, 10, 12, or 15°C. From the N-stage crystallization unit to the M-stage crystallization unit, the pressure drop per stage is 1-6 kPaA, for example, 1, 2, 3, 4, or 6 kPaA, and the temperature drop per stage is 1-6°C, for example, 1, 2, 3, 4, or 6°C.

[0017] Preferably, the pressure drop is jointly adjusted by the steam supply from the preceding crystallization unit to the subsequent crystallization unit and the negative pressure source, or by adjusting the steam supply, the negative pressure source, and a condenser arranged upstream of the negative pressure source.

[0018] By synergistically controlling the pressure drop from the first-stage crystallization unit process to the N-stage crystallization unit process through feedback from the evaporation gas phase supply and the negative pressure source, the pressure drop is 20-30Kpa A, and the pressure drop from the N-stage crystallization unit process to the M-stage crystallization unit process is 10-20Kpa A, ensuring that the temperature drop and pressure drop between the upstream crystallization units are large, while the temperature drop and pressure drop between the downstream crystallization units are small, so that the primary slurry quickly approaches the supersaturated crystallization precipitation point in the upstream crystallization unit, and the slurry crystallization in the downstream crystallization unit is uniform, which is beneficial to reducing impurity encapsulation and solvent residue, and improving the purity of the crystal product. In addition, it can also avoid the rapid growth and sedimentation of crystals or attachment to the equipment to form scars, extend the equipment operation cycle, and also facilitate the filtration and washing of crystals after the crystallization process. It has been found that the process of the present invention can make the material evaporate smoothly, and the precise control of the negative pressure makes the obtained adipic acid crystals high in quality and high in production efficiency. In addition, precise pressure control directly determines the precise boiling point temperature of each compartment, thereby more accurately controlling the evaporation amount, cooling rate, and supersaturation generation, which is conducive to obtaining adipic acid crystals with a narrower particle size distribution and more regular crystal shape.

[0019] Preferably, the amount of vaporized gas supplied can be automatically controlled. For example, a gas phase regulating valve and a pressure sensor are installed on the pipeline that supplies heat from the preceding crystallization unit to the subsequent crystallization unit. Both are communicatively connected to a central controller. The central controller receives signals from the pressure sensor to adjust the opening of the gas phase regulating valve. This allows for automatic and timely feedback adjustment of the pressure within the compartment in the event of fluctuations in process parameters.

[0020] Preferably, the negative pressure of each stage of crystallization units is provided by the same negative pressure source; preferably, M is 8-14, and N is 2-6.

[0021] The target slurry is used as a primary slurry and the crystallization process described in claim 1 is repeated once or twice. Preferably, before repeated crystallization, the target slurry is subjected to thickening, centrifugation, and decolorization. For details, reference can be made to existing processes, and the specific number of repetitions is selected based on product specifications. For example, if the color meets the requirements, decolorization may not be performed.

[0022] The technical solution for achieving the second object of the present invention is: a crystallization device for adipic acid, comprising M independent crystallization chambers, a connecting pipe is provided between two adjacent crystallization chambers, and the M independent crystallization chambers form a series structure through the connecting pipe, the upstream end of the connecting pipe is located below the liquid level of the upper crystallization chamber, and a gas phase outlet is provided at the top of each crystallization chamber. The second to Mth crystallization chambers are all provided with a heat exchange mechanism, and the gas phase outlet located in the upper crystallization chamber is connected to the heat exchange medium channel of the heat exchange mechanism located at the lower level through a connecting pipe and then connected to the negative pressure source; M≥3.

[0023] A connecting tube is installed between two adjacent crystallization chambers, forming a series structure. The upstream end of the connecting tube is located below the liquid level of the upstream crystallization chamber. The multiple independent crystallization chambers allow the adipic acid slurry to crystallize step by step, slowly generating crystals from the nuclei. This reduces the impurity content of the adipic acid crystals and improves product quality. The slurry in the adjacent upstream crystallization chamber can be transferred to the downstream crystallization chamber under the action of a pressure differential, reducing the power requirements of the device while meeting the requirements of multi-stage crystallization.

[0024] The heat exchange area of the heat exchange mechanism is adapted to the liquid level of the adipic acid slurry within the crystallization chamber. For example, the heat exchange area of the heat exchange mechanism extends from the bottom of the corresponding crystallization chamber to 1 / 5-1 / 2 of the crystallization chamber's height. Specifically, due to process characteristics, the material height within each crystallization chamber is not completely consistent, and the location of each heat exchange mechanism is aligned with the material height within each crystallization chamber. If the heat exchange structure is set too low, the liquid within the compartments will be unevenly heated, resulting in the formation of small crystals, which will affect subsequent filtration and washing processes. If it is set too high, heat utilization will be low. The heat exchange area of the heat exchange mechanism is adapted to the liquid level of the adipic acid slurry within the crystallization chamber. Due to the characteristics of the step-by-step evaporation crystallization process, the material height within each crystallization chamber is inconsistent. Adapting the heat exchange area of the heat exchange mechanism to the liquid level can effectively improve steam utilization. If the heat exchange area is too low, the slurry within the crystallization chamber will be unevenly heated, resulting in the formation of small crystals, which will affect subsequent filtration and washing processes. If the heat exchange area is too high, steam utilization will be low. The specific settings should be made according to the size of the device and the location of the feed liquid.

[0025] Preferably, the heat exchange mechanism is a heat exchange jacket, and the heat exchange jacket is arranged on the outer wall of the corresponding crystallization chamber; Preferably, each crystallization chamber is provided with an agitator, and the upstream end of each connecting pipe is higher than the downstream end; Preferably, a gas phase regulating valve is provided on the connecting pipeline; preferably, the opening of the gas phase regulating valve is 5%~100%; more preferably, a pressure sensor is provided on the connecting pipeline, and the device is also provided with a central controller which is respectively communicated with the gas phase regulating valve and the pressure sensor.

[0026] Preferably, the heat exchange medium channel outlets of each heat exchange mechanism are connected to the same negative pressure source.

[0027] The gas phase outlet of the upper crystallization chamber is connected to the negative pressure source through the heat exchange medium channel of the heat exchange mechanism of the adjacent lower crystallization chamber; or, the gas phase outlet of the upper crystallization chamber is connected to the negative pressure source through the heat exchange medium channel of the heat exchange mechanism separated by one crystallization chamber; the heat exchange medium channel outlet of each heat exchange mechanism is connected to the negative pressure source through a condenser, and the steam generated by boiling is mainly nitric acid and water, which are recovered as nitric acid after condensation.

[0028] Preferably, the heat exchange medium channel outlet of each heat exchange mechanism is connected to the negative pressure source through a condenser; for example, if the temperature after heat exchange is too high, additional surface cooling and heat exchange are required to achieve the required vacuum pressure gradient, which is a general choice for completing pressure gradient control.

[0029] Preferably, the condenser is a surface cooler, and the condensed water outlets of the surface coolers are connected in parallel to feed the mother liquor system, which refers to a liquid recovery system containing nitric acid aqueous solution.

[0030] Preferably, the system further comprises a flash tank, the feed port of which is connected to a source of oxidizing liquid, and the discharge port of which supplies the crystallization chamber. The oxidizing liquid source is the oxidation product of the reaction of cyclohexanol, cyclohexanone, and nitric acid. The feed port of the flash tank is connected to the source of oxidizing liquid, and the discharge port of the flash tank supplies the crystallization chamber at the upstream end. Preferably, the system further comprises a reflux pipe, the upstream end of which is connected to the final crystallization chamber, and the downstream end of which supplies the first crystallization chamber.

[0031] The method comprises at least two of any one of the above crystallization devices, wherein at least two crystallization devices are connected in series, and a thickening mechanism, a centrifugal mechanism and a decolorization mechanism are arranged between two adjacent crystallization devices.

[0032] The above technical solution has the following beneficial effects: 1. The crystallization process of the present invention utilizes the vapor phase heat generated by the preceding crystallization unit to heat the subsequent crystallization unit. The temperature difference between the vapor phase heat of the preceding crystallization unit and the material in the subsequent crystallization unit is small, which can maintain stable evaporation of the material in each crystallization unit, achieving the goal of zero external steam use and reducing the cost of adipic acid production. Zero external steam use can also avoid the problem of violent boiling of the material caused by a large temperature difference between the external steam and the material in the crystallization unit, thereby avoiding scarring caused by violent boiling of the material, and at the same time avoid uneven saturation distribution caused by the large temperature difference between the heat source and the heated material in the compartment, which leads to a decrease in crystal quality.

[0033] 2. The crystallization process of the present invention coordinates the pressure drop from the first-stage crystallization unit process to the N-stage crystallization unit process by feedback control of the evaporation gas supply and the negative pressure source, and the pressure drop from the N-stage crystallization unit process to the M-stage crystallization unit process is 10-20Kpa A, ensuring that the temperature drop and pressure drop between the upstream crystallization units are large, while the temperature drop and pressure drop between the downstream crystallization units are small, so that the primary slurry quickly approaches the supersaturated crystallization precipitation point in the upstream crystallization unit, and the slurry crystallization in the downstream crystallization unit is uniform, which is beneficial to reducing impurity encapsulation and solvent residue, and improving the purity of the crystal product. In addition, it can also avoid the rapid growth and sedimentation of crystals or attachment to the equipment to form scars, extend the equipment operation cycle, and also facilitate the filtration and washing of crystals after the crystallization process. It has been found that the process of the present invention can make the material evaporate smoothly, and the precise control of the negative pressure makes the obtained adipic acid crystals high in quality and high in production efficiency.

[0034] 3. The adipic acid crystallization apparatus includes multiple independent crystallization chambers connected in series via a connecting pipe. A vapor phase outlet is provided at the top of each crystallization chamber. Each of the second to final crystallization chambers is provided with a heat exchange mechanism. The vapor phase outlet of the upper crystallization chamber is connected to the heat exchange medium channel of the lower heat exchange mechanism via a connecting pipe and then to a negative pressure source to adapt to the crystallization process of the present application. Preferably, the steam generated by the upper crystallization chamber directly provides heat to the adjacent lower crystallization chamber, thereby improving the utilization rate of the generated steam. Furthermore, the temperature difference between the upper crystallization chamber and the slurry in the lower descending crystallization chamber is small, thereby avoiding violent boiling of the slurry and ensuring the quality of crystallization in each crystallization chamber.

[0035] 4. A gas phase regulating valve is provided on each connecting pipe in the crystallization device. The opening of the gas phase regulating valve is 5% to 100%. The pressure drop from the first stage crystallization unit process to the N stage crystallization unit process is coordinated and controlled by the feedback of the negative pressure source to be 20-30 kPa A, and the pressure drop from the N stage crystallization unit process to the M stage crystallization unit process is 10-20 kPa A, so as to adapt to the preferred crystallization process of this application. In addition, the independent control of the gas phase regulating valve can effectively prevent the abnormal pressure in a certain compartment from causing the liquid to flow into the adjacent low-pressure compartment or mix, affecting the liquid flow and destroying the preset temperature gradient and pressure gradient.

[0036] 5. The outlet of the heat exchange medium channel of each heat exchange mechanism is connected to the same negative pressure source, which not only reduces the control difficulty and use cost of the device, but also controls the heat exchange amount of each crystallization chamber by controlling the opening of the gas phase regulating valve. In combination with the condenser arranged between the outlet of the heat exchange medium channel and the negative pressure source, the crystallization device can achieve the required vacuum gradient.

[0037] The applicant's experiments have verified that the crystallization method of the present invention can achieve zero steam input crystallization to obtain finished slurry, the maintenance cycle of the crystallization device reaches more than 85 days, and the impurity content (glutaric acid and succinic acid) of the adipic acid product obtained by crystallization is less than 10ppm.

[0038] The following is a further description with reference to the accompanying drawings and specific implementations. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a connection diagram of Example 1; Figure 2 This is a connection diagram of Example 2.

[0040] In the accompanying drawings, 1 is a crystallization chamber, 2 is a connecting pipe, 3 is a gas phase outlet, 4 is a heat exchange mechanism, 5 is a condenser, and 6 is a stirrer. DETAILED DESCRIPTION Example 1

[0041] See also Figure 1 The adipic acid crystallization apparatus includes twelve independent crystallization units. In this embodiment, each crystallization unit is represented by a crystallization chamber 1. Each crystallization chamber 1 is equipped with an agitator 6. A connecting pipe 2 is provided between two adjacent crystallization chambers, forming a series structure. The upstream end of the connecting pipe 2 is located below the liquid level of the upstream crystallization chamber, and the upstream end of each connecting pipe 2 is higher than the downstream end. Each crystallization chamber 1 is equipped with a heat exchange mechanism 4. Specifically, the heat exchange mechanism 4 is a heat exchange jacket provided on the outer wall of the corresponding crystallization chamber, and the height of the heat exchange jacket is adapted to the liquid level of the adipic acid slurry in the crystallization chamber. A gas phase outlet 3 is provided at the top of each crystallization chamber 1. The gas phase outlet of the upstream crystallization chamber is connected to a negative pressure source via a connecting pipe, a heat exchange medium channel of the adjacent downstream heat exchange mechanism, and a condenser 5. That is, the gas phase outlet of the first crystallization chamber is connected to the heat exchange medium channel inlet of the heat exchange jacket in the second crystallization chamber, and the gas phase outlet of the second crystallization chamber is connected to the heat exchange medium channel inlet of the heat exchange jacket in the third crystallization chamber, and so on. Condenser 5 is a surface cooler, and the condensate outlets of each cooler are connected in parallel to feed the mother liquor system. A gas-phase regulating valve is installed in the connecting pipeline. By adjusting the opening of the gas-phase regulating valve, the absolute pressure of each compartment is independently controlled to a preset target value. To facilitate industrial operation, a pressure sensor is also installed in the connecting pipeline. The gas-phase regulating valve and pressure sensor are communicatively connected to a central controller that is evenly externally located. The central controller is used to receive signals from the pressure sensor and adaptively adjust the opening of the gas-phase regulating valve between 5% and 100% to accurately control the pressure of each crystallization chamber within the preset target value.

[0042] The twelfth crystallization chamber also supplies material to the third crystallization chamber through a reflux pipe. Obviously, the reflux pipe is provided with a valve and a pump.

[0043] The crystallization device also includes a flash tank, the feed port of the flash tank is connected to the oxidizing liquid source, and the discharge port of the flash tank supplies material to the crystallization chamber at the upstream end. Example 2

[0044] See also Figure 2 , which is different from Example 1 in that the gas phase outlet of the upstream crystallization chamber is connected to the negative pressure source through the heat exchange medium channel of the heat exchange mechanism separated by one crystallization chamber, the condenser, that is, the gas phase outlet of the first crystallization chamber is connected to the heat exchange medium channel inlet of the heat exchange jacket in the third crystallization chamber, the gas phase outlet of the second crystallization chamber is connected to the heat exchange medium channel inlet of the heat exchange jacket in the fourth crystallization chamber, and so on. The other structures are the same. Example 3

[0045] In this embodiment, two sets of adipic acid crystallization apparatuses of Example 1 are included. The finished slurry produced by the first set of crystallization apparatuses is thickened, centrifuged, and decolorized before being used as the primary slurry for the second set of crystallization apparatuses. Comparative Example 1

[0046] The heat exchange jackets of each crystallization chamber are heated separately, and each crystallization chamber is directly connected to the negative pressure source, and 0.5MPaG saturated steam is used to heat the heat exchange jackets of each crystallization chamber. Comparative Example 2

[0047] In this embodiment, there are two sets of apparatuses of Comparative Example 1. The finished slurry produced by the first set of crystallization apparatus is used as the primary slurry of the second set of crystallization apparatus after thickening, centrifugation and decolorization. Application Example 1

[0048] A method for crystallizing adipic acid using the crystallization apparatus of Example 1, with M=12 and N=4.

[0049] The following steps are involved: 1) The primary slurry containing the target product (composed of 25 wt% adipic acid, 1.12 wt% glutaric acid, 0.375 wt% succinic acid, approximately 30 wt% nitric acid, no more than 5 wt% monoacid, and the remainder water) is sent to a flash tank at a flash temperature of 90°C for 20-40 min. The flashed slurry is then sent to the first crystallization chamber at a temperature of 90°C. The primary slurry flow rate is 40 m 3 / h; 2) Through the coordinated control of the negative pressure source, the surface cooler and the opening of the gas phase regulating valve, the pressure in each crystallization chamber is controlled to be negative pressure, and the pressure decreases in sequence to 48KPaA, 38KPaA, 30KPaA, 22KPaA, 20KPaA, 19KPaA, 16KPaA, 13KPaA, 11KPaA, 9KPaA, 6KPaA, and 4KPaA, and the temperature is 75℃, 68℃, 60℃, 52℃, 50℃, 48℃, 45℃, 42℃, 39℃, 36℃, 33℃, and 30℃, and the stirring speed in each crystallization chamber is controlled to 350RPM; 3) The target slurry containing adipic acid crystals is discharged from the twelfth crystallization chamber. 10 wt% of this target slurry is returned to the third crystallization chamber for a recirculation. After system equilibrium is reached, the primary target slurry containing adipic acid crystals has a temperature of 25°C and a composition of 38 wt% adipic acid, 2.2 wt% by-product dibasic acids (glutaric and succinic acid), 30 wt% nitric acid, and the remainder water. The entire crystallization process consumes no external steam, and the crystallization unit operates for a period of more than 85 days, meaning it remains operational even after 85 days. Application Example 2

[0050] The method for crystallizing adipic acid using the crystallization apparatus of Example 2 comprises the following steps: 1) The primary slurry containing the target product (composition of 35 wt% adipic acid, 1.26 wt% glutaric acid, 0.74 wt% succinic acid, about 25 wt% nitric acid, no more than 5 wt% monoacid, and the balance water) is sent to a flash tank. The flash temperature is 85°C and the time is 20-40 min. The slurry obtained after flashing is sent to the first crystallization chamber at 90°C. The flow rate of the primary slurry is 45m 3 / h; 2) Control the pressure in each crystallization chamber to negative pressure. The pressure control is the same as in Application Example 1. Control the stirring speed in each crystallization chamber to 350 RPM. 3) The target slurry containing adipic acid crystals is discharged from the twelfth crystallization chamber. 10 wt% of this target slurry is then recycled to the third crystallization chamber. After system equilibrium is reached, the primary target slurry containing adipic acid crystals has a temperature of 23°C and a composition of 39 wt% adipic acid, 2.4 wt% by-product dibasic acids (glutaric and succinic acid), 30 wt% nitric acid, and the remainder water. The entire crystallization process consumes no external steam, and the crystallization unit operates for a period of more than 85 days, meaning it remains operational even after 85 days. Application Example 3

[0051] A method for crystallizing adipic acid using the adipic acid crystallization apparatus of Example 3 comprises the following steps: 1) The primary target slurry obtained in Application Example 1 was subjected to thickening, centrifugation, dissolution and decolorization treatment to obtain a primary slurry. The primary slurry had a composition of 40 wt % adipic acid, 2.4 wt % by-product dibasic acid, 1 wt % nitric acid, and the remainder being water; 2) The first-stage slurry is sent to the first crystallization chamber of the second crystallization device (M=12, N=3), the temperature is 92℃, and the flow rate of the first-stage slurry is 35m 3 / h; 3) Through the coordinated control of the negative pressure source, the surface cooler and the opening of the gas phase regulating valve, the pressure in each crystallization chamber of the second crystallization device is controlled to be negative pressure, and the pressure decreases in sequence to 50KPaA, 40KPaA, 30KPaA, 27KPaA, 24KPaA, 21KPaA, 18KPaA, 15KPaA, 11KPaA, 9KPaA, 7KPaA, and 5KPaA, and the temperature is 80℃, 70℃, 60℃, 58℃, 56℃, 53℃, 50℃, 49℃, 45℃, 39℃, 33℃, and 27℃, and the stirring shaft speed is 450RPM; 4) The twelfth crystallization chamber of the second crystallization device discharges the finished slurry containing the target product at a flow rate of 30m 3 / h; the temperature is 30°C, the component content is 42wt% of adipic acid, the content of by-product dibasic acids (glutaric acid and succinic acid) is less than 1wt%, the content of nitric acid is less than 0.5wt%, and the rest is water.

[0052] 5) The finished slurry is thickened and dehydrated, and then sent to a fluidized bed for drying to obtain adipic acid powder. Testing shows that the impurity content (glutaric acid and succinic acid) in the adipic acid powder is less than 10 ppm, and the particle size distribution of the adipic acid powder is D50 = 100 ± 10 μm. Application Example 4

[0053] The adipic acid crystallization device of Example 3 is different from that of Application Example 3 in that: The steam generated by the front-stage crystallization unit is used to heat the adjacent rear-stage crystallization unit. The pressure drop is controlled by the negative pressure source, and the pressure drop of adjacent crystallization chambers is maintained at 3~10KPaA to ensure that each crystallization unit can pass the material normally.

[0054] After testing, the impurity content (glutaric acid and succinic acid) in the adipic acid powder is less than 15ppm, and the particle size distribution of the adipic acid powder is D50=110±15μm. Comparative Application Example 1

[0055] The apparatus of Comparative Example 1 was used, and the process of Example 1 was applied. Under steady state, 0.5 MPaG saturated steam was consumed at about 2.8 t / h. After 30 days of operation, obvious scarring appeared in the crystallization chamber, which required scar removal, affecting production efficiency. Comparative Application Example 2

[0056] Using the apparatus of Comparative Example 2 and the process of Example 2, the steady-state saturated steam consumption was approximately 4.1 t / h at 0.5 MPaG, and the resulting adipic acid powder contained approximately 100 ppm of impurities (glutaric acid and succinic acid). The adipic acid powder had a particle size distribution of D50 = 80 ± 40 μm.

Claims

1. A crystallization process for adipic acid, characterized in that: The crystallization process is as follows: a primary slurry containing adipic acid is subjected to step-by-step decompression evaporation and crystallization in M-stage crystallization units under negative pressure to obtain a target slurry containing adipic acid crystals. The steam generated by the preceding crystallization unit provides heat to the adjacent subsequent crystallization unit or to the subsequent crystallization unit separated by 1 to 2 stages; M ≥ 3.

2. The crystallization process according to claim 1, characterized in that The primary slurry is an oxidation product of cyclohexanol, cyclohexanone and nitric acid, and preferably, the oxidation product is obtained by flash distillation; Preferably, the content of adipic acid in the primary slurry is 15-45 wt%, the content of other dibasic acids is 4-7 wt% of the mass of adipic acid, the content of nitric acid is 15-40 wt%, the content of monoacids does not exceed 5 wt%, and the balance is water; Preferably, the processing flow rate of the primary slurry is 35-50m 3 / h; Preferably, the temperature of the primary slurry is 80-100°C, and the temperature of the target slurry is 20-45°C.

3. The crystallization process according to claim 1, characterized in that 5-20 wt% of the obtained target slurry is refluxed to the crystal nucleus controlled crystallization unit to form a cycle; Preferably, each crystallization unit is provided with a stirring mechanism, and the rotation speed of the stirring mechanism is 50-600 RPM.

4. The crystallization process according to claim 1, characterized in that The pressure of the first-stage crystallization unit is 35-55KpaA, and the pressure of the tail-stage crystallization unit is 0-10KpaA; Preferably, M≥7.

5. The crystallization process according to claim 4, characterized in that The pressure drop from the first-stage crystallization unit to the N-stage crystallization unit is 20-30KpaA, and the temperature drop is 15-30°C; the pressure drop from the N-stage crystallization unit to the M-stage crystallization unit is 10-20KpaA, and the temperature drop is 15-30°C, 2≤N<M; Preferably, the pressure drop is jointly adjusted by the steam supply from the preceding crystallization unit to the subsequent crystallization unit and the negative pressure source, or by adjusting the steam supply, the negative pressure source, and a condenser provided upstream of the negative pressure source; Preferably, the negative pressure of each stage of crystallization units is provided by the same negative pressure source; preferably, M is 8-14, and N is 2-6.

6. The crystallization process according to claim 1, characterized in that The target slurry is used as a primary slurry to repeat the crystallization process described in claim 1 once or twice; preferably, before repeated crystallization, the target slurry is thickened, centrifuged, and decolorized.

7. A crystallization device for adipic acid, comprising M mutually independent crystallization chambers (1), a connecting pipe (2) being provided between two adjacent crystallization chambers, the M mutually independent crystallization chambers forming a series structure through the connecting pipe (2), the upstream end of the connecting pipe (2) being located below the liquid level of the upper crystallization chamber, characterized in that: A gas phase outlet (3) is provided at the top of each crystallization chamber (1), and a heat exchange mechanism (4) is provided in each of the second to Mth crystallization chambers (1). The gas phase outlet of the upper crystallization chamber is connected to a negative pressure source via a connecting pipeline and a heat exchange medium channel of a lower heat exchange mechanism; M≥3.

8. The crystallization device for adipic acid according to claim 7, characterized in that: The heat exchange area of the heat exchange mechanism (4) is adapted to the liquid level of the adipic acid slurry in the crystallization chamber; Preferably, the heat exchange mechanism (4) is a heat exchange jacket, and the heat exchange jacket is arranged on the outer wall of the corresponding crystallization chamber; Preferably, each crystallization chamber (1) is provided with a stirrer (6), and the upstream end of each connecting pipe (2) is higher than the downstream end; Preferably, a gas phase regulating valve is provided on the connecting pipeline; preferably, the opening of the gas phase regulating valve is 5% to 100%; Preferably, the heat exchange medium channel outlets of each heat exchange mechanism are connected to the same negative pressure source.

9. The crystallization device for adipic acid according to claim 7, characterized in that: The gas phase outlet of the upper crystallization chamber is connected to the negative pressure source through the heat exchange medium channel of the heat exchange mechanism of the adjacent lower crystallization chamber; or, the gas phase outlet of the upstream crystallization chamber is connected to the negative pressure source through the heat exchange medium channel of the heat exchange mechanism of the crystallization chamber separated by one; Preferably, the heat exchange medium channel outlet of each heat exchange mechanism (4) is connected to the negative pressure source via the condenser (5); Preferably, the condenser (5) is a surface cooler, and the condensed water outlets of the surface coolers are connected in parallel to feed the mother liquor system; Preferably, the method further comprises a flash tank, wherein the feed port of the flash tank is connected to the oxidizing liquid source, and the discharge port of the flash tank supplies the crystallization chamber; Preferably, the method further comprises a reflux pipe, wherein the upstream end of the reflux pipe is connected to the final crystallization chamber, and the downstream end of the reflux pipe supplies materials to the crystal nucleus control crystal chamber.

10. A crystallization system for adipic acid, characterized in that: The method comprises at least two crystallization devices according to any one of claims 7 to 9, wherein the at least two crystallization devices are connected in series.

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