A crystallizer and treatment method for use in the hydrolytic synthesis of methionine hydroxy analogs process and in the isolation stage

Abstract

The application discloses a crystallizer and treatment method for cyanohydrin hydrolysis synthesis methionine hydroxy analogue neutralization and separation stage. The crystallizer is based on the DTB crystallizer, the baffle is arranged in the structure of upper end sealing and lower end suspension, the MHA oil phase is separated in situ by the density difference of the baffle, and the precise extraction is realized by the circumferential multi-point oil outlet and the densimeter; the multi-layer alternating nozzle of ammonia gas and hydrolysis liquid is arranged at the lower part of the crystallizer, and the neutralization reaction can be directly completed; the online cleaning system is formed by the outer circulation heating, the lower part hot water jacket cooperative heating, the annular flushing pipe and the pipeline flushing port. The application integrates the neutralization reaction, the evaporation crystallization and the oil phase separation, cancels the independent layered equipment, can reduce the MHA entrainment amount in the ammonium sulfate product to below 0.04%, increases the total MHA yield by more than 1.5%, solves the problems of easy caking and scabbing at the bottom of the traditional crystallizer and short operation cycle, and is suitable for large-scale continuous MHA production device.

Description

Technical Field

[0001] This invention relates to the field of chemical separation and crystallization technology, specifically to a crystallizer and processing method for the neutralization and separation stage in the process of hydrolyzing cyanohydrin to synthesize methionine hydroxy analogues (MHA). The crystallizer can separate the entrained MHA oil phase in situ while evaporating and crystallizing the byproduct ammonium sulfate solution. Background Technology

[0002] MHA is an important feed additive that has a growth-promoting effect similar to methionine in poultry farming and is widely used in animal feed. Currently, the mainstream production method for MHA is the cyanohydrin hydrolysis method: methylthiopropionaldehyde reacts with hydrogen cyanide to produce 2-hydroxy-4-methylthiobutyronitrile (cyanohydrin), which is then hydrolyzed in excess sulfuric acid. Finally, the excess sulfuric acid is neutralized with ammonia water, yielding MHA product while producing a large amount of ammonium sulfate as a byproduct. According to the existing process, after the neutralization reaction, the oil phase of MHA and the ammonium sulfate aqueous solution naturally separate due to their density difference. The aqueous phase rich in ammonium sulfate is then sent to a crystallizer for evaporation and crystallization to produce fertilizer-grade ammonium sulfate.

[0003] The DTB (Device-Baffle) type crystallizer is recognized in the industry as a high-performance internal circulation crystallizer. It features an internal guide tube that forms a circulation channel. This ensures excellent slurry mixing conditions, rapidly eliminating supersaturation at the boiling interface and maintaining a consistently low level of supersaturation, making it particularly suitable for processing products with steep solubility curves. Practical experience has proven that the DTB type crystallizer offers high production intensity, produces large crystal particles, and is less prone to internal scaling, making it the mainstream form of continuous crystallizer suitable for various operating conditions such as vacuum cooling crystallization, evaporation crystallization, and reactive crystallization.

[0004] Several patents have been published regarding improvements to DTB-type crystallizers. For example, CN202155067U removes the reducer and agitator, replaces the guide tube with a structure featuring a cooling jacket, and adds a vortex device and a circulating pump to reduce vibration, minimize leakage, and prevent oil contamination. However, this solution primarily addresses the power structure and cooling efficiency issues, without addressing the separation of organic impurities. Regarding oil-water separation, CN204522386U discloses a device for separating light oil from the acid vapor condensate in a DTB crystallizer. This device utilizes gravity settling through vertical and horizontal baffles, but it is located outside the crystallizer and cannot achieve in-situ internal separation.

[0005] Regarding MHA production and byproduct treatment, Chinese patent CN114349671B discloses a novel reaction pathway that uses a specific compound as an intermediate, allowing nitrogen to be recycled during the preparation process and avoiding the generation of large amounts of ammonium sulfate waste. Chinese patent CN114223789B discloses a raw material composition and a method for preparing MHA without separating byproduct salts, reducing byproduct salt generation by replacing some sulfuric acid with phosphoric acid. However, none of the above patents address the optimized design of the crystallizer's internal structure, particularly failing to solve the problem of trace amounts of MHA oil phase entrained in the ammonium sulfate crystal slurry during the evaporation crystallization process.

[0006] Furthermore, Chinese patent CN116375618B discloses a method for recovering methionine hydroxy analogues from ammonium sulfate byproducts. This method involves reacting the ammonium sulfate byproducts with calcium oxide or calcium hydroxide to convert the entrained MHA into calcium salts of methionine hydroxy analogues. This technical solution is a post-processing step after crystallization, increasing the process steps and processing costs, and fails to achieve in-situ separation within the crystallization equipment.

[0007] Systematic analysis revealed the following shortcomings in existing technologies: First, in current processes, the neutralization reaction typically takes place in a separate neutralization reactor. After ammonia neutralization, the MHA oil phase and the ammonium sulfate aqueous phase separate into layers, requiring further separation by a separate preliminary separation device before the aqueous phase can be fed into the crystallizer. This stepwise process of "neutralization → stratification → crystallization" involves large investments, requires a large footprint, has a long process time, and consumes significant energy for material transport. Second, even after preliminary stratification, the ammonium sulfate aqueous phase entering the crystallizer inevitably contains trace amounts of dispersed MHA oil droplets (typically 0.1%~1.0%). Third, traditional DTB crystallizers rely on a single heat source, primarily using jackets or internal heat exchangers, resulting in limited heat exchange area and uneven temperature distribution. While some improved solutions add cooling jackets for cooling crystallization, they lack specific design for supplying the heat required for evaporation crystallization. Fourth, existing patented technologies involving MHA recovery from ammonium sulfate byproducts are all post-processing steps after crystallization, increasing process complexity and processing costs, and failing to achieve in-situ separation within the crystallization equipment.

[0008] Furthermore, while existing technologies disclose single-equipment structures such as gravity settling in the DTB settling zone and external circulation heating, no technical solution integrates ammonia neutralization reaction, ammonium sulfate evaporation and crystallization, and in-situ recovery of micro-emulsified MHA oil phase into the same DTB crystallizer. Existing MHA production processes require separate neutralization kettles and oil-water pre-separation tanks, resulting in numerous pieces of equipment, long processes, and the inability to recover dispersed micro-oil droplets during the crystallization stage online, which can only be recovered by calcium salt conversion after crystallization, increasing the amount of auxiliary materials and energy consumption. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a crystallizer and processing method for the neutralization and separation stage of methionine hydroxy analogue synthesis by hydrolysis of cyanohydrin, which realizes the integration of neutralization reaction, evaporation crystallization and in-situ separation of oil phase, with short process flow, simplified equipment and high production efficiency.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a crystallizer for the neutralization and separation stage of methionine hydroxy analogue synthesis by cyanohydrin hydrolysis, comprising a crystallizer body 1, an external circulation heating system, and a lower hot water jacket. Inside the crystallizer body 1, a guide cylinder 2, a stirring shaft 3, and a stirring impeller 4 are coaxially arranged to form a stirrer. A baffle 5 is provided on the outside of the guide cylinder 2, forming a baffle zone 16 between the baffle 5 and the crystallizer body 1, and a settling zone 15 between the guide cylinder 2 and the baffle 5. The upper end of the baffle 5 is sealed to the inner wall of the crystallizer body 1, and the lower end is suspended, allowing the MHA oil phase in the settling zone 15 to float upwards and enter the baffle zone 16 through the suspended area at the lower end of the baffle 5, where it accumulates to form an oil layer on the upper part of the baffle zone 16. The crystallizer also includes an oil phase trapping and separation structure, which is included in the baffle zone 16. At least one oil phase outlet 17 and an oil phase discharge pump 18 connected to the oil phase outlet 17 are provided on the upper side wall; the lower part of the crystallizer body 1 is provided with a multi-layer nozzle feeding structure, and the bottom of the crystallizer body (1) is provided with a crystallization outlet 6.

[0011] Furthermore, the baffle zone 16 is equipped with a density meter 19 for real-time monitoring of the density of the oil phase in the upper part of the baffle zone 16; 4 to 8 oil phase discharge outlets 17 are evenly arranged along the circumference of the baffle zone 16. The external circulation heating system includes an external circulation pipeline 7, a circulation pump 8 and a heater 9 installed on the external circulation pipeline. The external circulation pipeline 7 connects the liquid outlet 10 at the top of the crystallizer body 1 and the liquid return port 11 at the bottom. 2 to 4 liquid return ports 11 are evenly arranged along the lower circumference of the crystallizer body 1; a circulation pipeline flushing water inlet 27 is provided on the external circulation pipeline 7, located upstream of the heater 9. The outlet pipeline of the circulation pump 8 is equipped with a circulation pump outlet sight glass 26, and the outlet pipeline of the oil phase discharge pump 18 is equipped with an oil phase discharge pump outlet sight glass 28. The crystallizer body (1) has an annular flushing pipe 20 at the top. Several small flushing holes 21 are provided on both the upper and lower sides of the annular flushing pipe 20 for flushing the baffle 5 and the scale on the inner wall of the crystallizer body 1. The lower hot water jacket 12 is located on the lower outer wall of the crystallizer body 1. The lower hot water jacket 12 has a hot water inlet 13 at the bottom and a hot water outlet 14 at the top. The multi-layer nozzle feeding structure includes, from bottom to top, a first ammonia nozzle layer 22, a first hydrolysate nozzle layer 23, a second ammonia nozzle layer 24, and a second hydrolysate nozzle layer 25, for introducing ammonia gas to neutralize the acidic hydrolysate containing MHA. Each nozzle layer has 4-6 nozzles.

[0012] The present invention also provides a method for treating a solution of ammonium sulfate, a byproduct of the hydrolysis of cyanohydrin to synthesize MHA, in the crystallizer, comprising the following steps: A. The acidic hydrolysate containing MHA and ammonia gas are continuously fed into the crystallizer body 1 through a multi-layer nozzle feeding structure, and the neutralization reaction is carried out by alternating contact during the rising process; B. Turn on the external circulation heating system, drive the crystal slurry circulation through the circulation pump 8, and provide the heat required for evaporation and crystallization through the heater 9; at the same time, turn on the lower hot water jacket 12 to provide auxiliary heating to the lower area of ​​the crystallizer; C. The crystal slurry flows out from the top of the guide tube 2 and enters the settling zone 15. The ammonium sulfate crystals settle downward and return to the circulation zone through the lower end of the baffle 5. The MHA oil phase floats upward and enters the baffle zone 16 through the lower end of the baffle 5, where it accumulates to form an oil layer in the upper part of the baffle zone 16. D. The density of the oil phase in the upper part of the baffle zone 16 is monitored in real time by the densitometer 19. When the density reaches the set value, the oil phase discharge pump 18 is started to continuously extract the accumulated oil layer. E. The crystal slurry discharged from the crystallization outlet 6 at the bottom of the crystallizer is separated into solid and liquid components to obtain ammonium sulfate crystal products.

[0013] Furthermore, the oil flow rate of the oil phase discharge pump 18 is 20~40m³. 3 / h; the ratio of circulating slurry flow rate to feed flow rate in the external circulation heating system is 8:1 to 80:1. The hot water temperature in the lower hot water jacket 12 is 70 to 90°C; when it is necessary to clean the inside of the crystallizer, the flushing liquid is sprayed onto the baffle 5 and the inner wall of the crystallizer body 1 through the annular flushing pipe 20, while the liquid level in the crystallizer is lowered to flush away the scale; when it is necessary to clean the circulation pipeline and heater 9, flushing water is introduced through the flushing water inlet 27 of the circulation pipeline for online flushing.

[0014] The beneficial effects that this invention can achieve are: 1. High process integration, significantly simplifying the process. The ammonia neutralization reaction, ammonium sulfate evaporation and crystallization, and MHA oil phase in-situ separation are integrated into the same DTB crystallizer, eliminating the need for separate neutralization reactors and pre-separation equipment, reducing equipment investment and floor space, shortening the process flow, and reducing energy consumption for material transportation.

[0015] 2. Excellent oil-phase separation, improving yield and purity. Through a flow channel design of "sealed upper baffle + suspended lower baffle," the inherent baffle zone of the DTB crystallizer is utilized to achieve the enrichment and separation of trace amounts of dispersed oil droplets. Combined with precise monitoring by a density meter and multi-point oil discharge, the MHA entrainment in the ammonium sulfate product can be reduced to below 0.04%, the ammonium sulfate purity reaches over 99.2%, and the total MHA yield is increased by approximately 1.6%.

[0016] 3. Coordinated heating and anti-scaling design ensure strong operational stability. The external circulation heating and the lower hot water jacket work together to ensure a uniform temperature field in the crystallizer and prevent crystal agglomeration at the bottom; the matching annular flushing pipe and pipeline flushing water inlet can realize online cleaning of equipment and pipelines, significantly extending the continuous operation cycle and reducing shutdown maintenance costs.

[0017] 4. High operational flexibility, suitable for industrial production. The equipment can operate stably within a wide range of feed loads and cycle ratios, and is suitable for MHA production lines of different scales. It can be directly used for new plants or the renovation of existing crystallization systems. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the overall structure of the crystallizer described in this invention.

[0019] In the diagram: 1 - Crystallizer body, 2 - Guide tube, 3 - Stirring shaft, 4 - Stirring impeller, 5 - Baffle, 6 - Crystallization outlet, 7 - External circulation pipeline, 8 - Circulation pump, 9 - Heater, 10 - Liquid outlet, 11 - Liquid return port, 12 - Lower hot water jacket, 13 - Hot water inlet, 14 - Hot water outlet, 15 - Settling zone, 16 - Baffle zone, 17 - Oil phase outlet, 18 - Oil phase discharge pump, 19 - Density meter, 20 - Annular flushing pipe, 21 - Flushing orifice, 22 - First ammonia nozzle layer, 23 - First hydrolysate nozzle layer, 24 - Second ammonia nozzle layer, 25 - Second hydrolysate nozzle layer, 26 - Circulation pump outlet sight glass, 27 - Flushing water inlet, 28 - Oil phase discharge pump outlet sight glass. Detailed Implementation

[0020] 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that: in the embodiments of this invention, the directional indicators (such as "up", "down", "forward", "backward") are only used to explain the relative positional relationship of each component under a specific posture (as shown in the attached figure). If the posture changes, the directional indicators will be adjusted accordingly; the terms "connection" and "fixed" are understood in the conventional understanding of the mechanical field, and can refer to fixed connection, detachable connection or integral integration, depending on the specific assembly requirements; the component numbers in all attached figures are consistent with the instruction manual to ensure clear correspondence.

[0022] As shown in Figure 1, this crystallizer mainly consists of four parts: the crystallizer body 1, the external circulation heating system, the lower hot water jacket 12, and the oil phase collection and separation structure.

[0023] The crystallizer body 1 is a vertical cylindrical pressure-bearing structure with a conical bottom section. A crystallization outlet 6 is located at the center of the bottom of the conical section for continuously discharging ammonium sulfate slurry. A guide cylinder 2 is coaxially arranged inside the crystallizer body 1. The guide cylinder 2 is an open-top and bottom cylindrical structure, fixed to the inner wall of the body by radial supports, forming an upward channel for the internal circulation of the ammonium sulfate slurry. A stirring shaft 3 is arranged along the central axis of the crystallizer body 1, with one end extending out of the crystallizer body 1 and connected to an external drive mechanism. An impeller 4 is installed at the other end of the stirring shaft 3, located in the lower inner cavity of the guide cylinder 2. During operation, the impeller 4 drives the ammonium sulfate slurry to flow upwards along the guide cylinder 2, overflowing from the top of the guide cylinder 2 and spreading outwards, then returning downwards to the bottom along the settling zone 15, forming a stable internal circulation flow field.

[0024] A baffle 5 is arranged around the outer side of the guide tube 2. The baffle 5 is annular, with its upper end sealed and welded to the inner wall of the crystallizer body 1, and its lower end extending downwards into the lower circulation zone of the crystallizer body. Thus, the annular space between the outer wall of the guide tube 2 and the inner wall of the baffle 5 forms a settling zone 15, and the annular space between the outer wall of the baffle 5 and the inner wall of the crystallizer body 1 forms a baffle zone 16. The settling zone 15 and the baffle zone 16 are connected only through the suspended area at the lower end of the baffle 5, preventing the low-density MHA oil phase in the settling zone 15 from overflowing directly from the upper end of the annular baffle 5. It must flow downwards to the lower end of the baffle 5 before floating into the baffle zone 16 and accumulating in the upper part. This flow channel design effectively extends the residence time of oil droplets, ensuring the full coalescence of tiny oil droplets.

[0025] The lower part of the crystallizer body 1 is equipped with a multi-layer nozzle feeding structure. This structure consists of four horizontally arranged annular nozzle groups, from bottom to top: the first ammonia nozzle layer 22, the first hydrolysate nozzle layer 23, the second ammonia nozzle layer 24, and the second hydrolysate nozzle layer 25. Each layer of nozzles has 4-6 nozzles evenly arranged circumferentially. Ammonia and acidic hydrolysate are fed alternately in layers, making multiple contacts and fully dispersing them during the upward process, thus efficiently completing the neutralization reaction without the need for an additional independent neutralization reactor.

[0026] The external circulation heating system includes an external circulation pipeline 7, a circulation pump 8, and a heater 9. An outlet 10 is located on the upper side wall of the crystallizer body 1, and a return outlet 11 is located on the lower side wall. The external circulation pipeline 7 connects the outlet 10 and the return outlet 11, with the circulation pump 8 and heater 9 connected in series on the pipeline. A flushing water inlet 27 is located on the upstream side pipeline of heater 9, allowing flushing water to be introduced during equipment operation to flush away scale buildup on the inner wall of the pipeline and within the heater tubes, preventing a decrease in heat exchange efficiency and pipeline blockage. A sight glass 26 is located on the outlet pipeline of circulation pump 8 for direct observation of the state of the circulating slurry and the entrainment of the oil phase. Two to four return outlets 11 are evenly distributed along the lower circumference of the crystallizer body 1 to ensure uniform distribution of the returned slurry within the tower, avoiding localized uneven concentration and temperature.

[0027] The lower hot water jacket 12 is wrapped around the lower conical section and the lower outer wall of the straight section of the crystallizer body 1. A hot water inlet 13 is provided at the bottom of the jacket and a hot water outlet 14 is provided at the top. Hot water is continuously introduced to assist in heating the bottom area of ​​the crystallizer, increase the temperature of the mother liquor at the bottom, prevent the low-temperature deposition and agglomeration of ammonium sulfate crystals, and ensure continuous and smooth discharge from the crystallization outlet 6.

[0028] The oil phase capture and separation structure includes an oil phase outlet 17, an oil phase discharge pump 18, and a density meter 19. On the sidewall of the upper oil layer accumulation area of ​​the crystallizer body 1 corresponding to the baffle zone 16, 4-8 oil phase outlets 17 are evenly distributed circumferentially. Each outlet is connected to the oil phase discharge pump 18 via an external manifold for continuous extraction of the enriched MHA oil phase. An oil phase discharge pump outlet sight glass 28 is installed on the outlet pipeline of the oil phase discharge pump 18 to observe the state of the extracted oil phase and adjust the pumping flow rate accordingly. A density meter 19 is installed on the upper part of the baffle zone 16, with its detection end extending into the oil layer area to monitor changes in oil phase density in real time, accurately determine the oil layer thickness, and achieve quantitative and continuous extraction of the oil phase.

[0029] An annular flushing pipe 20 is installed inside the crystallizer body 1 above the annular baffle 5. Several flushing holes 21 are opened on both the upper and lower sides of the annular flushing pipe 20. When the equipment is maintained by lowering the liquid level, flushing liquid can be sprayed out through the flushing pipe to spray and clean the scale on the baffle 5 and the inner wall of the crystallizer body 1 in an all-round way, thus extending the continuous operation cycle of the equipment.

[0030] Example 1 A 2800mm diameter DTB-type crystallizer is used to process the MHA-containing acidic material in the cyanohydrin hydrolysis section. The crystallizer body 1 has a diameter of 2800mm, a straight section height of 3800mm, and a lower conical section height of 900mm. The guide tube 2 has a diameter of 1600mm and a height of 2200mm. The agitator uses an axial flow impeller with a rotation speed of 70-100rpm. The upper end of the baffle 5 is sealed to the inner wall of the crystallizer body 1, while the lower end is suspended. The settling zone 15 is 400mm wide, and the baffle zone 16 is 200mm wide. Six oil phase discharge outlets 17 (with an adjacent angle of 60°) are evenly arranged circumferentially on the upper part of the baffle zone 16. A density meter is installed inside the baffle zone 16. An annular flushing pipe is installed above the baffle 5, with flushing holes of 5mm diameter and 100mm spacing on both the upper and lower sides. The external circulation heating system is configured with a flow rate of 1000m³. 3 A circulating pump with a heat exchange area of ​​180m² / h 2 The heater has a sight glass 26 at the outlet of the circulating pump 8, and a flushing water inlet 27 upstream of the heater; three return ports are evenly distributed circumferentially. The lower hot water jacket is 1200mm high and operates at 75-85℃. The multi-layer nozzle feeding structure consists of four layers from bottom to top: an ammonia layer, a hydrolysate layer, another ammonia layer, and another hydrolysate layer.

[0031] Operating conditions: Acidic hydrolysate (MHA content 36-40wt%), feed flow rate 25m³ / h 3 The system operates at atmospheric pressure and a temperature of 70-85℃, with a neutralization reaction achieved by alternately injecting ammonia gas and hydrolysate through multiple nozzles at a rate of 1000 m³ / h. The external circulation slurry flow rate is 1000 m³ / h. 3 / h, circulation ratio 40:1; heater outlet temperature 85-90℃, hot water jacket temperature 80℃; stirring speed 85rpm; effective crystallizer volume approximately 18.7m³. 3 The nominal stay is approximately 45 minutes.

[0032] After the oil phase in the MHA (Medium-Hydrogen Acid) zone floats to the surface, it enters the baffle zone through the lower end of the baffle and accumulates in the upper part to form an oil layer. The density of the oil phase is monitored in real time using a densitometer at 30m³. 3 The oil layer was continuously extracted at a flow rate of / h through 6 outlets. The oil discharge status was confirmed by the sight glass at the outlet of the discharge pump, and the crystal slurry was confirmed to have no obvious oil phase entrainment by the sight glass at the outlet of the circulation pump.

[0033] Operating results: The unit operated continuously and stably for 30 days (720 hours), with the amount of MHA entrained in the ammonium sulfate crystals remaining stable below 0.04%, and the product purity reaching over 99.2%; the average MHA content in the recovered oil phase was 92.5%, and the total MHA yield was 1.6% higher than that of the traditional process; there was no clumping at the bottom during operation, the discharge was smooth, and there was no need to stop for cleaning due to scaling.

[0034] Example 2 Based on Example 1, the feed rate was increased to 35m³. 3 / h, external circulation crystal slurry flow rate maintained at 1000m³ / h 3 With the flow rate unchanged, the circulation ratio decreased to 28.6:1, and the heater outlet temperature increased to 92~97℃. The operational flexibility under high evaporation intensity was investigated. Results: MHA oil phase precipitation was approximately 14m³. 3 / h, maintain an oil pumping flow rate of 30m³ / h. 3 The device can operate continuously and stably at a rate of [per hour]; the upward flow velocity in the settling zone is approximately 0.0024 m / s, far below the settling threshold. The amount of MHA entrained in the ammonium sulfate crystals increases slightly to 0.06%-0.08%, the product purity is approximately 98.8%-99.0%, and the total MHA yield increases by approximately 1.3%, still meeting the requirements for industrial production.

[0035] Example 3 Based on Example 1, the external circulation crystal slurry flow rate was adjusted to 200 m³ / s. 3 The cycle ratio was reduced to 8:1, and the heater outlet temperature was increased to 95-100℃ to compensate for the heat supply. Performance under low cycle ratio conditions was investigated. Results: The device could operate continuously, but the axial temperature difference of the crystallizer was approximately 3-4℃, and the viscosity of MHA increased in the local low-temperature zone. The MHA entrainment in the ammonium sulfate crystals was 0.09%-0.13%, and the product purity was approximately 98.5%-98.7%, which, although inferior to Example 1, was still significantly better than the traditional DTB crystallizer (0.3%-0.5%). The results indicate that the device can still operate when the cycle ratio is close to the lower limit of 8:1, and a cycle ratio ≥15:1 is preferred for better separation.

[0036] Example 4 Based on Example 1, the external circulation crystal slurry flow rate was adjusted to 2000 m³ / s. 3 The circulation ratio was increased to 80:1, and the heater outlet temperature dropped to 82-85℃. Performance under high circulation ratio conditions was investigated. Results: The external circulation velocity in the settling zone increased to 0.13 m / s, and some tiny MHA droplets with a particle size ≤80 μm were carried back to the circulation zone by the crystal slurry; the MHA entrainment in the ammonium sulfate crystals was 0.05%-0.08%, the product purity was approximately 98.9%-99.1%, and the total MHA yield increased by approximately 1.4%. High circulation ratios significantly increased pump power consumption and reduced economic efficiency; therefore, a circulation ratio ≤40:1 is preferred.

[0037] Comparative Example This conventional DTB crystallizer employs an oil-free phase trapping structure and an external circulation heating system. The equipment cylinder dimensions are identical to those in Example 1. It relies solely on the cylinder's steam jacket for heating, and lacks features such as baffled oil discharge, online density monitoring, and a multi-layer nozzle feeding structure. The acidic hydrolysate feed flow rate is 25 m³ / h. 3 The ammonia neutralization conditions inside the reactor were maintained as in Example 1. After 180 hours of operation, a large amount of ammonium sulfate crystals deposited and agglomerated at the bottom of the reactor, causing intermittent blockage at the crystal slurry outlet. After 280 hours of operation, large-area scaling occurred on the jacket heat exchange surface, resulting in a significant decrease in heat exchange efficiency, necessitating shutdown and cleaning. Full-cycle data showed that the MHA entrainment in the ammonium sulfate crystals was 0.30%-0.50%, and the purity of the by-product ammonium sulfate was only 96.0%-96.5%. The MHA oil phase was discharged with the crystal slurry and could not be recovered, resulting in a significantly lower overall yield than in this invention.

[0038] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions or improvements made within the technical principles and concepts of the present invention should be included within the scope of protection of the present invention.

Claims

1. A crystallizer for the neutralization and separation stage of methionine hydroxy analogue synthesis via cyanohydrin hydrolysis, comprising a crystallizer body (1), an external circulation heating system, and a lower hot water jacket. The crystallizer body (1) is coaxially equipped with a guide tube (2), a stirring shaft (3), and a stirring impeller (4) forming a stirrer. A baffle (5) is provided on the outside of the guide tube (2), forming a flow deflection zone (16) between the baffle (5) and the crystallizer body (1), and a settling zone (15) between the guide tube (2) and the baffle (5). The crystallizer body (1) is characterized by: The upper end of the baffle (5) is sealed to the inner wall of the crystallizer body (1), and the lower end is suspended, so that the MHA oil phase in the settling zone (15) floats upward and enters the baffle zone (16) through the suspended area at the lower end of the baffle (5), and accumulates in the upper part of the baffle zone (16) to form an oil layer; The crystallizer also includes an oil phase trapping and separation structure, which includes at least one oil phase outlet (17) provided on the side wall of the upper part of the baffle zone (16) and an oil phase discharge pump (18) connected to the oil phase outlet (17); The lower part of the crystallizer body (1) is provided with a multi-layer nozzle feeding structure, and the bottom of the crystallizer body (1) is provided with a crystallization outlet (6).

2. The crystallizer according to claim 1, characterized in that, The baffle zone (16) is equipped with a density meter (19) for real-time monitoring of the density of the oil phase in the upper part of the baffle zone (16); the oil phase outlet (17) is uniformly arranged in 4 to 8 locations along the circumference of the baffle zone (16).

3. The crystallizer according to claim 1, characterized in that, The external circulation heating system includes an external circulation pipeline (7), a circulation pump (8) and a heater (9) installed on the external circulation pipeline. The external circulation pipeline (7) connects the liquid outlet (10) at the top of the crystallizer body (1) and the liquid return port (11) at the bottom. There are 2 to 4 liquid return ports (11) evenly arranged along the lower circumference of the crystallizer body (1). A circulation pipeline flushing water inlet (27) is provided on the external circulation pipeline (7) upstream of the heater (9).

4. The crystallizer according to claim 3, characterized in that, The outlet pipeline of the circulating pump (8) is provided with a circulating pump outlet sight glass (26), and the outlet pipeline of the oil phase discharge pump (18) is provided with an oil phase discharge pump outlet sight glass (28).

5. The crystallizer according to claim 1, characterized in that, The crystallizer body (1) has an annular flushing pipe (20) at the top. The annular flushing pipe (20) has several flushing holes (21) on both the upper and lower sides for flushing the baffle (5) and the scale on the inner wall of the crystallizer body (1).

6. The crystallizer according to claim 1, characterized in that, The lower hot water jacket (12) is disposed on the lower outer wall of the crystallizer body (1). The bottom of the lower hot water jacket (12) is provided with a hot water inlet (13) and the upper part is provided with a hot water outlet (14).

7. The crystallizer according to claim 1, characterized in that, The multi-layer nozzle feeding structure includes, from bottom to top, a first ammonia nozzle layer (22), a first hydrolysate nozzle layer (23), a second ammonia nozzle layer (24), and a second hydrolysate nozzle layer (25), which are used to introduce ammonia gas to neutralize the acidic hydrolysate containing MHA. Each nozzle layer is provided with 4 to 6 nozzles.

8. A method for treating a solution of ammonium sulfate, a byproduct of the hydrolysis of cyanohydrin to synthesize MHA, using the crystallizer described in any one of claims 1 to 7, characterized in that, Includes the following steps: A. The acidic hydrolysate containing MHA and ammonia gas are continuously fed into the crystallizer body (1) through a multi-layer nozzle feeding structure, and neutralization reaction is carried out by alternating contact during the rising process; B. Turn on the external circulation heating system, drive the crystal slurry circulation through the circulation pump (8), and provide the heat required for evaporation and crystallization through the heater (9); at the same time, turn on the lower hot water jacket (12) to provide auxiliary heating to the lower area of ​​the crystallizer; C. The crystal slurry flows out from the top of the guide tube (2) and enters the settling zone (15). The ammonium sulfate crystals settle downward and return to the circulation zone through the lower end of the baffle (5). The MHA oil phase floats upward and enters the baffle zone (16) through the lower end of the baffle (5). It accumulates in the upper part of the baffle zone (16) to form an oil layer. D. The density of the oil phase above the baffle zone (16) is monitored in real time by a densitometer (19). When the density reaches the set value, the oil phase discharge pump (18) is started to continuously extract the accumulated oil layer. E. The crystal slurry discharged from the crystallization outlet (6) at the bottom of the crystallizer is separated into solid and liquid to obtain ammonium sulfate crystal products.

9. The method according to claim 8, characterized in that, The oil discharge pump (18) has a pumping flow rate of 20~40m³ / h. 3 / h; the ratio of circulating slurry flow rate to feed flow rate in the external circulation heating system is 8:1 to 80:

1.

10. The method according to claim 8, characterized in that, The hot water temperature of the lower hot water jacket (12) is 70~90℃; When it is necessary to clean the inside of the crystallizer, the flushing liquid is sprayed onto the baffle (5) and the inner wall of the crystallizer body (1) through the annular flushing pipe (20), while the liquid level inside the crystallizer is lowered to flush away the scale. When it is necessary to clean the circulation pipeline and heater (9), flushing water is introduced through the flushing water inlet (27) of the circulation pipeline for online flushing.

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