A reaction kettle device and preparation method for preparing ammonium acetate crystals

Abstract

This invention provides a reaction vessel apparatus and method for preparing ammonium acetate crystals. The reaction vessel apparatus includes a DCS control unit and an ammonium acetate solution preparation unit, a multi-stage crystallization unit, and a post-processing unit connected in sequence. The multi-stage crystallization unit includes an ultrasonic processor, an online particle size analyzer, and a primary crystallization vessel, a secondary crystallization vessel, and a tertiary crystallization vessel connected in sequence. The DCS control unit is signal-connected to each stage of the multi-stage crystallization unit, as well as to the ultrasonic processor and the online particle size analyzer. The ultrasonic processor is connected to the primary or tertiary crystallization vessel in the multi-stage crystallization unit via a circulation pipeline. The DCS control unit receives feedback signals from the online particle size analyzer and automatically adjusts the crystallization temperature of each stage of the multi-stage crystallization unit and the ultrasonic power of the ultrasonic processor according to the particle size distribution. This reaction vessel apparatus is used for the continuous preparation of ammonium acetate crystals, and can obtain ammonium acetate crystals with uniform particle size distribution and high purity, suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of ammonium acetate crystal preparation, specifically relating to a reaction vessel apparatus and preparation method for preparing ammonium acetate crystals. Background Technology

[0002] Ammonium acetate, as an important chemical raw material, is widely used in the preparation of ammonium salts, wood preservatives, mordants, and catalysts for the production of vinyl acetate and polyvinyl alcohol. High-purity ammonium acetate crystals are crucial for improving the performance and quality of downstream products.

[0003] In industrial crystallization production, traditional ammonium acetate crystallization processes typically employ batch operation or a simple single-stage crystallization method. These methods generally suffer from the following shortcomings: First, the crystallization process is difficult to control precisely, resulting in uneven crystal size distribution and a high content of fine crystals (usually referring to crystals with a particle size of less than 10 μm), affecting the purity, bulk density, and subsequent processing performance of the product; Second, production efficiency is low, energy consumption is high, and continuous and automated production is difficult to achieve.

[0004] Continuous gradient cooling crystallization technology, by progressively lowering the temperature in multiple crystallization vessels connected in series, allows for more precise control of crystallization supersaturation, contributing to improved uniformity of the crystal products. Meanwhile, ultrasonic technology exhibits unique advantages in enhancing the crystallization process. Studies show that the cavitation effect of ultrasound can effectively stimulate crystal nucleation, increase crystal growth rate, and control crystal size distribution by breaking down fine crystals, thereby improving product quality. Furthermore, applying ultrasound to the crystallization process can also prevent and remove scale, ensuring the heat exchange efficiency of the cooling system.

[0005] How to integrate continuous gradient crystallization, ultrasonic fine-grain crushing, and advanced process control technologies (such as online particle size monitoring and DCS control systems) into a device and method for the continuous and intelligent production of fine chemicals such as ammonium acetate, so as to achieve the integrated preparation of ammonium acetate crystals, is an urgent direction to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a reaction vessel apparatus and preparation method for preparing ammonium acetate crystals. It integrates continuous gradient crystallization, ultrasonic fine crystal crushing and advanced process control technology (such as online particle size monitoring and DCS control system) to achieve the continuous and intelligent production of fine chemicals such as ammonium acetate, thereby realizing the integrated preparation of ammonium acetate crystals.

[0007] To achieve this objective, the present invention adopts the following technical solution: The first aspect of the present invention is to provide a reaction vessel apparatus for preparing ammonium acetate crystals, the reaction vessel apparatus comprising a DCS control unit and an ammonium acetate solution preparation unit, a multi-stage crystallization unit and a post-processing unit connected in sequence; The multi-stage crystallization unit includes an ultrasonic processor, an online particle size analyzer, and a primary crystallization vessel, a secondary crystallization vessel, and a tertiary crystallization vessel connected in sequence. The DCS control unit is signal-connected to each crystallization vessel of the multi-stage crystallization unit, as well as the ultrasonic processor and the online particle size analyzer. The ultrasonic processor is connected to either the primary or tertiary crystallization vessel in the multi-stage crystallization unit via a circulation pipeline. The online particle size analyzer is located at the discharge end of the multi-stage crystallization unit and is used to detect the particle size distribution of the ammonium acetate crystallized product discharged from the discharge end in real time and output a feedback signal. The DCS control unit receives the feedback signal and automatically adjusts the crystallization temperature of each crystallization vessel of the multi-stage crystallization unit and the ultrasonic power of the ultrasonic processor according to the particle size distribution.

[0008] This invention is the first to systematically integrate three-stage continuous gradient crystallization, ultrasonic fine-grain online crushing, online real-time particle size monitoring, and DCS intelligent control, constructing a continuous and intelligent crystallization reactor device suitable for material crystallization. It overcomes the technical defects of traditional intermittent crystallization operations, such as difficulty in precise control and large batch-to-batch product differences.

[0009] This invention adopts a closed-loop control strategy of "online particle size detection signal → DCS control unit → crystallization temperature and ultrasonic power linkage adjustment in crystallization vessel". It takes the product particle size distribution as the direct control target and realizes the automated regulation of the dynamic balance of "nucleation-growth-crushing" during the crystallization process, ensuring that the product particle size can be controlled in a directional manner as needed.

[0010] In this invention, the ultrasonic processor is preferably connected to the primary crystallizer. The ultrasonic processor is placed on the external circulation pipeline of the primary crystallizer to circulate and extract the crystal slurry, break it up with ultrasound, and then return it. This allows the broken fine crystals to participate in the subsequent growth process within the primary crystallizer. After three-stage gradient cooling, uniform large crystals are formed. This method achieves high fine crystal processing efficiency without affecting the continuity of the main crystallization process.

[0011] As a preferred embodiment of the present invention, the ammonium acetate solution preparation unit is used to prepare an ammonium acetate solution; the inlet of the multi-stage crystallization unit is connected to the outlet of the ammonium acetate solution preparation unit, and is used to crystallize the ammonium acetate reaction solution to obtain a crystal slurry; the ultrasonic processor is used to selectively crush fine crystals with a particle size of less than 10 μm; the post-processing unit is used to separate the crystal slurry into ammonium acetate crystal product and waste liquid.

[0012] As a preferred technical solution of the present invention, the crystallization kettle device further includes a mother liquor circulation unit, which includes a nanofiltration membrane; The crystal slurry flowing out of the multi-stage crystallization unit after crystallization is processed by the post-processing unit to obtain ammonium acetate crystal product and waste liquid. The waste liquid is introduced into the mother liquor recycling unit and treated by the nanofiltration membrane to separate it into permeate and concentrate. The permeate and concentrate are returned to the multi-stage crystallization unit and the ammonium acetate solution preparation unit, respectively. The primary, secondary, and tertiary crystallization reactors are all equipped with a combined agitator. The blades of the combined agitator include a propeller and a turbine, and the inner wall is provided with an inner wall baffle with turbulence holes.

[0013] This invention combines a nanofiltration membrane separation unit with a crystallization post-treatment unit. By using a nanofiltration membrane with a specific molecular weight cutoff (50~300Da) and operating parameters, it achieves precise separation of effective components and impurities in ammonium acetate waste liquid. The separated permeate and concentrate are then sent back to the crystallization unit and the ammonium acetate solution preparation unit, respectively, forming a closed-loop material circulation path of "crystallization-separation-mother liquor recovery-raw material preparation", which significantly reduces raw material consumption and wastewater treatment load.

[0014] The crystallization vessel of this invention employs a stirrer combining a propeller and a turbine propeller, along with an inner wall baffle with turbulence holes. This ensures the uniformity of crystal slurry suspension, enhances wall heat exchange and fluid shearing effects, helps prevent scaling and deposition of crystals on the vessel wall, and guarantees stability and heat exchange efficiency during long-term continuous operation.

[0015] As a preferred technical solution of the present invention, the DCS control unit receives the crystallization temperature, liquid level and flow rate signals of each crystallizer of the multi-stage crystallization unit, and automatically adjusts the heat exchange medium flow rate of each crystallizer, the stirring speed of each crystallizer, the flow rate of the circulating pump and the opening degree of each regulating valve.

[0016] The flow rate signal in this invention refers to the flow rate of the main material entering and exiting each stage of the crystallizer and the material transfer between stages, used to maintain material balance and constant residence time. A circulating pump is installed on the external circulation pipeline between the crystallizer and the ultrasonic processor, responsible for driving the slurry to flow through the ultrasonic processor for processing. The DCS system optimizes the crystallization particle size distribution by regulating the flow rate of this circulating pump in conjunction with ultrasonic power adjustment.

[0017] As a preferred embodiment of the present invention, the preparation method uses the reaction vessel apparatus as described in the first aspect, and the method includes the following steps: (1) The ammonium acetate solution obtained by the ammonium acetate solution preparation unit enters the multi-stage crystallization unit and is sequentially fed into the first-stage crystallization kettle, the second-stage crystallization kettle and the third-stage crystallization kettle for three-stage continuous gradient cooling crystallization. During the crystallization process, the crystal slurry in the first-stage crystallization kettle or the third-stage crystallization kettle is continuously introduced into the ultrasonic processor through the pipeline for fine crystal crushing and then returned to the corresponding crystallization kettle through the pipeline. The particle size distribution of the crystallized product is detected in real time at the outlet of the third-stage crystallization kettle and the particle size data is fed back to the DCS control unit. The DCS control unit automatically adjusts the crystallization temperature and ultrasonic crushing power of each stage crystallization kettle according to the particle size distribution feedback signal to control the product particle size. (2) The crystal slurry that has been crystallized from the multi-stage crystallization unit is processed by the post-processing unit to obtain the ammonium acetate crystals.

[0018] The ammonium acetate crystal preparation process of this invention differs from traditional crystallization processes, where parameters such as crystallization temperature and stirring speed are set empirically and operate in an open-loop manner. This invention organically combines three-stage gradient cooling crystallization, ultrasonic fine-crystal circulation crushing, and real-time online particle size detection to form a closed-loop control circuit of "detection-feedback-adjustment." The DCS control unit dynamically adjusts the crystallization temperature and ultrasonic crushing power of each stage of the crystallizer based on the real-time particle size distribution data fed back by the online particle size analyzer at the discharge end, ensuring that the crystallization system always operates within the optimal supersaturation range. This intelligent control method, with product particle size as the direct control target, is pioneering in the field of ammonium acetate crystallization.

[0019] As a preferred embodiment of the present invention, the temperature of the ammonium acetate solution is 60-80°C, wherein the temperature can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, or 80°C, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass concentration is 70-80%, wherein the mass concentration can be 70%, 72%, 74%, 76%, 78%, or 80%, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The temperature of the primary crystallization vessel is 35-45°C, wherein the temperature can be 35°C, 36°C, 37°C, 38°C, etc. The temperatures of the secondary crystallizer are 9℃, 40℃, 41℃, 42℃, 43℃, 44℃, or 45℃, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable. The temperature of the secondary crystallizer is 20~30℃, where the temperature can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable. The temperature of the tertiary crystallizer is 5~10℃, where the temperature can be 5℃, 6℃, 7℃, 8℃, 9℃, or 10℃, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Based on the solubility-temperature characteristics of ammonium acetate, this invention sets up a three-stage gradient cooling mode with a primary crystallizer at 35-45℃ (controllable nucleation and growth under high supersaturation), a secondary crystallizer at 20-30℃ (main growth stage), and a tertiary crystallizer at 5-10℃ (deep precipitation stage). Combined with the synergistic effects of stirring and ultrasonic waves at each stage, this invention achieves segmented and precise control of the entire process from nucleation and growth to final precipitation, significantly improving the uniformity of crystal size compared to traditional single-stage or two-stage cooling methods.

[0021] As a preferred technical solution of the present invention, in step (1), during the crystallization process, the crystal slurry in the primary crystallization vessel is continuously introduced into the ultrasonic processor through the pipeline for fine crystal crushing and then returned to the primary crystallization vessel through the pipeline; during the fine crystal crushing process, the fine crystals with a particle size of less than 10 μm are subjected to ultrasonic treatment, wherein the particle size can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or 9 μm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] This invention connects an ultrasonic processor to the circulation pipeline of the primary crystallizer to selectively break down fine crystals with a particle size of less than 10 μm in the crystal slurry using ultrasonic waves. The resulting tiny crystals are directly returned to the primary crystallizer. These broken crystals serve as "secondary seed crystals" in the subsequent tertiary gradient cooling crystallization process. This eliminates the adverse effects of fine crystals on the product's particle size distribution and filtration performance, while avoiding the operational complexity and contamination risks associated with adding additional seed crystals. This creates a novel continuous crystallization process of "online fine crystal elimination—in-situ seed crystal generation—continuous crystal growth."

[0023] The DCS control unit mentioned in step (1) also receives temperature, liquid level and flow signals, and automatically adjusts the cooling medium flow rate, stirring speed, circulating pump flow rate and the opening degree of each regulating valve.

[0024] As a preferred embodiment of the present invention, the crystallization vessel further includes a mother liquor circulation unit, which includes a nanofiltration membrane.

[0025] The crystal slurry flowing out of the multi-stage crystallization unit is processed by the post-processing unit to obtain ammonium acetate crystals and waste liquid. The waste liquid is introduced into the mother liquor recycling unit and treated by the nanofiltration membrane to separate it into permeate and concentrate.

[0026] The nanofiltration membrane has a molecular weight cutoff of 50-300 Da, which can be 50 Da, 100 Da, 150 Da, 200 Da, 250 Da, or 300 Da, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. Preferably, it is 50-100 Da.

[0027] The operating pressure for separation is 1.0~2.0 MPa, wherein the pressure can be 1.0 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa or 2.0 MPa, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] The operating temperature is 30~40℃, where the temperature can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] The permeate contains ammonium acetate and water and is returned to the primary crystallizer, while the concentrate is returned to the ammonium acetate solution preparation unit.

[0030] This invention introduces a nanofiltration membrane separation unit into the post-crystallization treatment process of ammonium acetate. It selectively separates the waste liquid after crystallization (molecular weight cutoff 50-300 Da), and the permeate (containing ammonium acetate and water) is directly returned to the primary crystallizer to participate in the next batch of crystallization. The concentrate is returned to the ammonium acetate solution preparation unit for concentration adjustment. This method tightly couples mother liquor recovery with the crystallization process, achieving efficient recycling of ammonium acetate without introducing new impurities, representing an innovative design for material recycling processes. By controlling the membrane-side pressure, flow rate, and temperature, the nanofiltration system is ensured to operate steadily within the safe supersaturation range of ammonium acetate, preventing heterogeneous nucleation of solutes on the membrane surface and in the flow channels from the source. The membrane module only performs the function of concentration and enrichment and does not produce crystals.

[0031] As a preferred technical solution of the present invention, the crystal slurry after crystallization in step (2) is successively thickened, separated and dried to obtain the ammonium acetate crystals.

[0032] When the slurry is thick, the solid content is increased to 35-40%, where the solid content can be 35%, 36%, 37%, 38%, 39%, or 40%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The separation is performed by centrifugation at a speed of 800-1500 rpm. This speed can be 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, or 1500 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The drying temperature is 50-70℃, and this temperature can be 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, or 70℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, resulting in the ammonium acetate crystals.

[0033] This invention provides a specific and complementary combination of process parameters for the post-processing steps of the crystal slurry after crystallization: first, thickening to a solid content of 35-40%, then centrifugation at 800-1500 rpm, and finally drying at 50-70°C. This parameter combination matches the characteristics of the crystal slurry produced by the three-stage gradient crystallization process, effectively reducing the amount of mother liquor adhering to the crystal surface, minimizing impurity entrainment, and obtaining a high-purity, low-water-content ammonium acetate crystal product.

[0034] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a three-stage continuous gradient cooling crystallization, combined with the stirring of the propeller and turbine propeller and the inner wall baffle with turbulence holes, to precisely control the supersaturation of each crystallization stage, effectively avoid explosive nucleation, significantly improve the uniformity of crystal particle size distribution, greatly reduce the content of fine crystals, and the resulting ammonium acetate crystals have high purity, high bulk density and good batch stability.

[0035] (2) This invention uses an online particle size analyzer to detect the particle size distribution at the discharge end in real time and feeds it back to the DCS control unit. It automatically adjusts the crystallization temperature and ultrasonic crushing power of each crystallizer, and constructs a closed-loop intelligent control system of "detection-feedback-adjustment". This realizes multi-parameter coordinated automated control of the crystallization process, reduces manual intervention, and is suitable for large-scale continuous production.

[0036] (3) The present invention selectively crushes fine crystals with a particle size of less than 10 μm using an ultrasonic processor. After crushing, the crystals are returned to the primary crystallization kettle as seed crystals to promote secondary crystal growth. At the same time, the waste liquid is separated into permeate and concentrate by nanofiltration membrane and returned to the multi-stage crystallization unit and ammonium acetate solution preparation unit respectively. This realizes the in-situ reuse of fine crystals and the closed-loop recycling of mother liquor, which significantly improves the utilization rate of raw materials and reduces waste liquid discharge. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the reaction vessel apparatus used in the present invention for preparing ammonium acetate crystals.

[0038] In the diagram: 1-Ammonium acetate solution preparation unit; 2-Multi-stage crystallization unit; 2-1-Primary crystallization kettle; 2-2-Secondary crystallization kettle; 2-3-Tertiary crystallization kettle; 2-4-Ultrasonic processor; 2-5-Online particle size analyzer; 3-Post-processing unit; 4-DCS control unit; 5-Mother liquor circulation unit; 6-Crystal finished product. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Example 1: This embodiment provides a method such as Figure 1 The reactor apparatus shown is used to prepare ammonium acetate crystals. The reactor apparatus includes a DCS control unit 4 and an ammonium acetate solution preparation unit 1, a multi-stage crystallization unit 2 and a post-processing unit 3 connected in sequence. The multi-stage crystallization unit 2 includes an ultrasonic processor 2-4, an online particle size analyzer 2-5, and a primary crystallization vessel 2-1, a secondary crystallization vessel 2-2, and a tertiary crystallization vessel 2-3 connected in sequence. The DCS control unit 4 is signal-connected to each crystallization vessel of the multi-stage crystallization unit 2, as well as the ultrasonic processor 2-4 and the online particle size analyzer 2-5. The ultrasonic processor 2-4 is connected to either the primary crystallization vessel 2-1 or the tertiary crystallization vessel 2-3 in the multi-stage crystallization unit 2 via a circulation pipeline. The online particle size analyzer 2-5 is located at the discharge end of the multi-stage crystallization unit 2 and is used to detect the particle size distribution of the ammonium acetate crystallized product discharged from the discharge end in real time and output a feedback signal. The DCS control unit 4 receives the feedback signal and automatically adjusts the crystallization temperature of each crystallization vessel of the multi-stage crystallization unit 2 and the ultrasonic power of the ultrasonic processor according to the particle size distribution.

[0041] In this embodiment, the ammonium acetate solution preparation unit 1 is used to prepare an ammonium acetate solution; the inlet of the multi-stage crystallization unit 2 is connected to the outlet of the ammonium acetate solution preparation unit 1, and is used to crystallize the ammonium acetate reaction solution to obtain a crystal slurry; the ultrasonic processor is used to selectively crush fine crystals with a particle size of less than 10 μm; the post-processing unit is used to separate the crystal slurry into ammonium acetate crystal product and waste liquid.

[0042] In this embodiment, the reactor device further includes a mother liquor circulation unit 5, which includes a nanofiltration membrane. The crystal slurry flowing out of the multi-stage crystallization unit 2 after crystallization is completed is processed by the post-processing unit 3 to obtain ammonium acetate crystal product and waste liquid. The waste liquid is introduced into the mother liquor circulation unit 5 and treated by the nanofiltration membrane to separate it into permeate and concentrate. The permeate and concentrate are then returned to the multi-stage crystallization unit 2 and the ammonium acetate solution preparation unit 1, respectively.

[0043] In this embodiment, a combined agitator is provided in the primary crystallizer 2-1, the secondary crystallizer 2-2, and the tertiary crystallizer 2-3. The blades of the combined agitator include a propeller and a turbine, and the inner wall is provided with an inner wall baffle with turbulence holes.

[0044] In this embodiment, the DCS control unit receives the crystallization temperature, liquid level and flow rate signals of each crystallizer of the multi-stage crystallization unit 2, and automatically adjusts the heat exchange medium flow rate of each crystallizer, the stirring speed of each crystallizer, the flow rate of the circulating pump and the opening degree of each regulating valve.

[0045] In this embodiment, the DCS control unit is also signal-connected to the ammonium acetate solution preparation unit 1.

[0046] Example 2: This embodiment provides a method for continuously preparing ammonium acetate crystals using the reactor apparatus described in Embodiment 1, wherein the ultrasonic processor is connected to the primary crystallization reactor 2-1 via a circulation pipeline, and the method specifically includes the following steps: (1) Preparation of ammonium acetate solution Ammonium acetate dihydrate (purity ≥99.5%) and deionized water were added to the mixing vessel of ammonium acetate solution preparation unit 1. The combined propeller and turbine agitator was turned on, and the speed was controlled at 120 rpm. The mixture was heated to 80 ℃ and stirred for 30 min to completely dissolve the ammonium acetate, resulting in a clear ammonium acetate solution with a mass concentration of approximately 75%. During the dissolution process, the opening of the heating steam valve was automatically adjusted by the DCS control unit 4 to control the temperature fluctuation ≤±1 ℃.

[0047] (2) Three-stage continuous gradient cooling crystallization The ammonium acetate solution obtained in step (1) is continuously fed into the primary crystallizer 2-1, the secondary crystallizer 2-2, and the tertiary crystallizer 2-3, with the feed flow rate controlled at 200 L / h. The effective volume of each crystallizer is 1.5 m³, and the liquid level is controlled at 75% of the tank volume. Continuous discharge is achieved through a combination of a level gauge and a discharge valve.

[0048] Primary crystallizer: The temperature is controlled at 40±1 ℃, the stirring speed is 100 rpm, and a combination of propeller and turbine propeller is used for stirring. The diameter of the baffle holes on the inner wall is Φ8 mm. The crystal slurry is pumped out by a circulating pump at a flow rate of 1.2 m³ / h and sent to an ultrasonic processor 2-4 (frequency 20 kHz, initial power setting of 150 W) for fine crystal crushing. After crushing, the crystal slurry is returned to the primary crystallizer. The residence time in the primary crystallizer is 5.6 h.

[0049] Secondary crystallization reactor: temperature controlled at 25±1 ℃, stirring speed at 80 rpm, residence time at 5.6 h.

[0050] Three-stage crystallizer: temperature controlled at 8±1 ℃, stirring speed at 60 rpm, residence time at approximately 5.6 h.

[0051] During the crystallization process, an online particle size analyzer 2-5 (FBRM type focused beam reflectance measuring instrument) installed on the discharge pipe of the three-stage crystallizer detects the particle size distribution of the crystallized product every 30 seconds and feeds back the particle size data (with a focus on monitoring the proportion of D50, D90, and <10 μm fine crystals) to the DCS control unit 4 in real time. The DCS control unit 4 has a built-in PID control algorithm and executes the following linkage adjustment strategy based on the feedback signal: When the product particle size D50 is detected to be lower than the target value (target D50 = 180~220 μm) or the proportion of fine crystals (<10 μm) exceeds 8%, the flow rate of the heat exchange medium in each crystallizer is automatically adjusted (to make the cooling rate 0.5~1.0 ℃ / h), and the ultrasonic power is gradually increased from 150 W to 200~250 W to enhance the crushing of fine crystals. When the particle size D50 is detected to be higher than the upper limit of the target value (>220 μm), the temperature of each crystallizer is automatically increased (heating rate 0.3 ℃ / h), and the ultrasonic power is reduced to 100W to avoid excessive crushing. When the particle size and fine crystal index return to the target range, the power should be gradually reduced back to the initial setting of 150W, and the temperature of each crystallizer should be stopped.

[0052] When the particle size D50 is within the target range and the proportion of fine crystals is ≤5%, maintain the current parameters.

[0053] DCS control unit 4 receives real-time signals from temperature sensors, level gauges, and flow meters in each stage of the crystallizer, and automatically adjusts the total flow rate of the heat exchange medium (adjustment range 5~15 m³). 3 / h), wherein the circulating pump is installed on the external circulation pipeline between the bottom outlet of the primary crystallizer 2-1 and the inlet of the ultrasonic processor 2-4.

[0054] (3) Post-treatment of crystal slurry The crystal slurry (32% solid content) flowing out of the outlet of the three-stage crystallizer 2-3 is introduced into the post-processing unit 3. It first enters the thickener for thickening treatment until the solid content reaches 38±1% (controlled by the linkage between the bottom discharge flow rate and the overflow clear liquid return flow rate). The thickened slurry is then fed into a horizontal screw centrifuge at a flow rate of 150 L / h and centrifuged at 1200 rpm to obtain wet crystals and waste liquid. The wet crystals are then fed into a fluidized bed dryer and dried under hot air conditions at 60±2 ℃ until the moisture content is ≤0.5%, yielding ammonium acetate crystal product 6. Testing shows that the product purity is ≥99.6%, particle size D50=198 μm, particle size distribution span ((D90-D10) / D50)≤1.2, and fine crystal (<10 μm) content ≤3%.

[0055] (4) Mother liquor nanofiltration membrane circulation treatment Step (3) The waste liquid generated by centrifugation is introduced into the mother liquor circulation unit 5, collected into the waste liquid storage tank, and pumped into the nanofiltration membrane unit. The nanofiltration membrane has a molecular weight cutoff of approximately 100 Da and a membrane area of ​​40 m². 2 The nanofiltration membrane is controlled at an operating pressure of 1.5 MPa, an operating temperature of 35 ± 2 ℃, and a feed flow rate of 1.0 m³ / s. 3 / h. The waste liquid is separated into permeate and concentrate by nanofiltration membrane. The permeate is returned to the primary crystallizer 2-1 for solvent reuse; the concentrate is returned to the mixing tank of ammonium acetate solution preparation unit 1, where it is mixed with fresh ammonium acetate dihydrate raw material to prepare ammonium acetate solution again, realizing a closed-loop circulation of mother liquor. During the operation of the nanofiltration membrane, when the permeate flux drops to 80% of the initial value, the online cleaning program is automatically started (rinsing with 30 ℃ deionized water for 20 min, followed by circulating cleaning with 1% citric acid solution for 30 min). After cleaning, the flux recovers to more than 95% of the initial value.

[0056] The entire process ran continuously for 72 hours, with stable system operation and no blockage or scaling. The total yield of ammonium acetate reached 96.8%, which is a significant improvement over the traditional batch process (yield of 89%), and the wastewater discharge was reduced by about 65%.

[0057] Example 3 In this embodiment, the crystallization temperature of the primary crystallizer 2-1 is replaced with 50°C, the crystallization temperature of the secondary crystallizer 2-2 is replaced with 35°C, and the crystallization temperature of the tertiary crystallizer 2-3 is replaced with 15°C. All other conditions are the same as in Example 2.

[0058] Example 4 In this embodiment, the crystallization temperature of the primary crystallizer 2-1 is replaced with 30°C, the crystallization temperature of the secondary crystallizer 2-2 is replaced with 15°C, and the crystallization temperature of the tertiary crystallizer 2-3 is replaced with 3°C. All other conditions are the same as in Example 2.

[0059] Example 5 In this embodiment, except that the ultrasonic processor 2-4 is connected to the three-stage crystallizer 2-3 through a circulation pipeline to crush the crystal slurry before it is discharged from the three-stage crystallizer 2-3, all other conditions are the same as in embodiment 2.

[0060] Comparative Example 1 Except for the fact that the crystallization vessels in this comparative example are not connected to ultrasonic processors 2-4 (i.e., there is no fine crystal crushing stage), all other conditions are the same as in Example 2.

[0061] The particle size D50, fine crystal ratio, particle size distribution range, product purity, total yield, and scaling of the crystallization vessel were tested for Examples 2-5 and Comparative Example 1. The test results are shown in Table 1.

[0062] Table 1 As shown in Table 1, using a gradient combination of 35~45 ℃ / 20~30 ℃ / 5~10 ℃, combined with DCS dynamic adjustment of ultrasonic power, can produce a product with the largest particle size, narrowest distribution, fewest fine crystals, and highest yield. As shown in Example 3, if the crystallization temperature is too high, the initial supersaturation will be insufficient, nucleation will be delayed, and nucleation will occur explosively in the secondary reactor, resulting in a large number of fine crystals. As shown in Example 4, if the crystallization temperature in the tertiary crystallizer is too low, the solution viscosity will increase, mass transfer will be limited, crystal growth will be hindered, and the yield will decrease.

[0063] As can be seen from Examples 2, 5 and Comparative Example 1, placing ultrasonic fine crystal crushing on the circulation pipeline of the primary crystallizer, so that the crushed crystals participate in the three-stage gradient growth as "in-situ seed crystals" throughout the process, is the optimal layout for obtaining large, uniform crystals.

[0064] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A reaction vessel apparatus for preparing ammonium acetate crystals, characterized in that, The reactor device includes a DCS control unit and an ammonium acetate solution preparation unit, a multi-stage crystallization unit, and a post-processing unit connected in sequence. The multi-stage crystallization unit includes an ultrasonic processor, an online particle size analyzer, and a primary crystallization vessel, a secondary crystallization vessel, and a tertiary crystallization vessel connected in sequence. The DCS control unit is signal-connected to each crystallization vessel of the multi-stage crystallization unit, as well as the ultrasonic processor and the online particle size analyzer. The ultrasonic processor is connected to either the primary or tertiary crystallization vessel in the multi-stage crystallization unit via a circulation pipeline. The online particle size analyzer is located at the discharge end of the multi-stage crystallization unit and is used to detect the particle size distribution of the ammonium acetate crystallized product discharged from the discharge end in real time and output a feedback signal. The DCS control unit receives the feedback signal and automatically adjusts the crystallization temperature of each crystallization vessel of the multi-stage crystallization unit and the ultrasonic power of the ultrasonic processor according to the particle size distribution.

2. The reactor apparatus for preparing ammonium acetate crystals according to claim 1, characterized in that, The ammonium acetate solution preparation unit is used to prepare an ammonium acetate solution; the inlet of the multi-stage crystallization unit is connected to the outlet of the ammonium acetate solution preparation unit, and is used to crystallize the ammonium acetate reaction solution to obtain a crystal slurry; the ultrasonic processor is used to selectively crush fine crystals with a particle size of less than 10 μm; the post-processing unit is used to separate the crystal slurry into ammonium acetate crystal product and waste liquid.

3. The reactor apparatus for preparing ammonium acetate crystals according to claim 1, characterized in that, The reactor apparatus further includes a mother liquor circulation unit, which includes a nanofiltration membrane. The crystal slurry flowing out of the multi-stage crystallization unit after crystallization is processed by the post-processing unit to obtain ammonium acetate crystal product and waste liquid. The waste liquid is introduced into the mother liquor recycling unit and treated by the nanofiltration membrane to separate it into permeate and concentrate. The permeate and concentrate are returned to the multi-stage crystallization unit and the ammonium acetate solution preparation unit, respectively. The primary, secondary, and tertiary crystallization reactors are all equipped with a combined agitator. The blades of the combined agitator include a propeller and a turbine, and the inner wall is provided with an inner wall baffle with turbulence holes.

4. The reactor apparatus for preparing ammonium acetate crystals according to claim 1, characterized in that, The DCS control unit receives crystallization temperature, liquid level, and flow rate signals from each crystallizer of the multi-stage crystallization unit, and automatically adjusts the heat exchange medium flow rate, stirring speed, circulating pump flow rate, and opening degree of each regulating valve in each crystallizer.

5. The reactor apparatus for preparing ammonium acetate crystals according to claim 1, characterized in that, The ultrasonic processor is connected to the primary crystallizer via a circulation pipeline.

6. A method for preparing ammonium acetate crystals, characterized in that, The preparation method uses the reactor apparatus as described in any one of claims 1-5, and the preparation method includes the following steps: (1) The ammonium acetate solution prepared by the ammonium acetate solution preparation unit enters the multi-stage crystallization unit and is sequentially fed into the first-stage crystallization kettle, the second-stage crystallization kettle and the third-stage crystallization kettle for three-stage continuous gradient cooling crystallization. During the crystallization process, the crystal slurry in the first-stage crystallization kettle or the third-stage crystallization kettle is continuously introduced into the ultrasonic processor through the pipeline for fine crystal crushing and then returned to the corresponding crystallization kettle through the pipeline. At the discharge end of the third-stage crystallization kettle, the particle size distribution of the crystallized product is detected in real time by an online particle size analyzer and the particle size data is fed back to the DCS control unit. The DCS control unit automatically adjusts the crystallization temperature of each stage of the multi-stage crystallization unit and the ultrasonic power of the ultrasonic processor according to the particle size distribution feedback signal in order to control the product particle size. (2) The crystal slurry that has completed crystallization flows out of the multi-stage crystallization unit is processed by the post-processing unit to obtain the ammonium acetate crystals.

7. The preparation method according to claim 6, characterized in that, In step (1), the temperature of the ammonium acetate solution is 60~80℃ and the mass concentration is 70~80%; the temperature of the primary crystallization vessel is 35~45℃, the temperature of the secondary crystallization vessel is 20~30℃, and the temperature of the tertiary crystallization vessel is 5~10℃.

8. The preparation method according to claim 6, characterized in that, In step (1), during the crystallization process, the crystal slurry in the primary crystallizer is continuously introduced into the ultrasonic processor through the pipeline for fine crystal crushing and then returned to the primary crystallizer through the pipeline. During the fine grain crushing process, fine grains with a particle size of less than 10 μm are subjected to ultrasonic crushing treatment.

9. The preparation method according to claim 6, characterized in that, The reactor apparatus further includes a mother liquor circulation unit, which includes a nanofiltration membrane. The crystal slurry flowing out of the multi-stage crystallization unit is processed by the post-processing unit to obtain ammonium acetate crystals and waste liquid. The waste liquid is introduced into the mother liquor recycling unit and treated by the nanofiltration membrane to separate it into permeate and concentrate. The nanofiltration membrane has a molecular weight cutoff of 50~300 Da, a separation operating pressure of 1.0~2.0 MPa, and an operating temperature of 30~40℃. The permeate is returned to the primary crystallizer, and the concentrate is returned to the ammonium acetate solution preparation unit.

10. The preparation method according to claim 6, characterized in that, The crystal slurry after crystallization in step (2) is successively thickened, separated and dried to obtain the ammonium acetate crystals; When the slurry is thickened, the solid content is increased to 35-40%. The separation is carried out by centrifugation at a speed of 800-1500 rpm, and the drying temperature is 50-70°C.

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