A synthetic L-menthol crystallization purification system and a purification method thereof

Abstract

The application discloses a kind of synthetic L-menthol crystallization purification systems, including menthol crystallizer, menthol tank, acetone mother liquor tank, drying kettle, menthol tank and acetone mother liquor tank with the feed end communication of menthol crystallizer, cooling liquid is equipped in menthol crystallizer, and the discharge end of menthol crystallizer is communicated with drying kettle by pipeline, and the acetone output end of drying kettle is communicated with acetone mother liquor tank by pipeline.L-menthol and acetone are carried out solvent crystallization in tube type crystallizer, L-menthol is precipitated in acicular crystal form by cooling, impurities are discharged after mother liquor, and acicular crystal is melted to obtain high-purity L-menthol with content of 99.9%, crystallization period is within 24 hours, and single crystallization yield is more than 40%.With acetone as solvent crystallization, impurities in L-menthol crude product are more thoroughly dissolved, and acetone is volatile and easy to remove.The application overcomes the shortcomings of prior art, and has high social use value and application prospect.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a synthesis and crystallization purification system and method for L-menthol. Background Technology

[0002] L-menthol synthesized from thymol can generally only be obtained with a purity of 99% after deesterification and distillation. Manufacturers typically require a purity of 99.5% or higher for synthesized menthol, which can be achieved through distillation, but the purification cost is high, significantly increasing production costs for industrial applications.

[0003] Currently, menthol crystallization is generally used for the crystallization of natural menthol, which has the problem of a long crystallization cycle. The inventors tried to use traditional batch static crystallization and dynamic solvent crystallization methods. Static crystallization involves mixing L-menthol and acetone in a 10:1 ratio and cooling the mixture in a crystallizer. The crystals are small, and the crystallization cycle is about 48 hours, which is a long time. Dynamic solvent crystallization involves mixing L-menthol and acetone in a 10:1 ratio in a crystallizer and cooling the mixture with stirring. The crystallized product is small and needle-like, and the material needs to be transferred to a plate centrifuge for separation. The operation is more cumbersome and the crystallization yield is lower.

[0004] Therefore, based on the inventor's extensive experience in design, development, and practical manufacturing in the relevant industry over many years, the inventor has researched and improved the existing structure and its shortcomings, and provided a method for synthesizing and purifying L-menthol crystals, in order to achieve a more practical purpose. Summary of the Invention

[0005] To address the issue mentioned in the background section that the L-menthol synthesized from thymol typically yields only 99% purity L-menthol after deesterification and distillation, while L-menthol users generally require a purity of 99.5% or higher, which can be achieved through distillation but is costly and would significantly increase production costs for industrial applications, this invention provides a synthetic L-menthol crystallization purification system and method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A synthetic L-menthol crystallization and purification system includes a menthol crystallizer, a menthol tank, an acetone mother liquor tank, and a drying kettle. The discharge ends of the menthol tank and the acetone mother liquor tank are connected to the feed end of the menthol crystallizer via pipelines. The menthol crystallizer is equipped with a cooling liquid for cooling the material, and the discharge end of the menthol crystallizer is connected to the drying kettle via a pipeline. The acetone output end of the drying kettle is connected to the acetone mother liquor tank via a pipeline.

[0008] Preferably, the system also includes a circulation tank and a crystallization heat exchanger. The circulation tank stores coolant, and its outlet is connected to the inlet heating end of the crystallization heat exchanger via a pipe. The crystallization heat exchanger contains hot water for heat exchange and heating of the coolant, and its outlet is connected to the heat exchange inlet of the menthol crystallizer via a pipe. The heat exchange outlet of the menthol crystallizer is connected to the inlet of the circulation tank via a pipe.

[0009] Preferably, it also includes a cooling water supply pipe, a cooling water return pipe, a hot water supply pipe, and a hot water return pipe. The cooling water supply pipe is connected to the inlet of the circulating tank, the outlet of the circulating tank is connected to the cooling water return pipe through a pipe, the hot water supply pipe is connected to the hot water inlet of the crystallizer heat exchanger, and the hot water return pipe is connected to the hot water outlet of the crystallizer heat exchanger.

[0010] Preferably, the circulating tank includes a tank body, an inlet pipe is provided at the water inlet end on one side of the tank body, a drain pipe is provided at the drain outlet end at the bottom of the tank body, a spraying mechanism is provided inside the tank body that is connected to the water inlet pipe and is used for uniform spraying of coolant, and a water-absorbing cotton layer is provided inside the tank body for gas-liquid separation of rising hot airflow, and a compression mesh plate that can move up and down and is used to squeeze the water-absorbing cotton layer is provided on the water-absorbing cotton layer.

[0011] Preferably, the tank body is provided with a fixedly connected support mesh plate, the support mesh plate is fixedly connected to one end of the corresponding absorbent cotton layer, the extrusion mesh plate is disposed at the other end of the absorbent cotton layer and can move up and down, the tank body is provided with a rotatable adjustment shaft, the adjustment shaft passes through the extrusion mesh plate, and the adjustment shaft and the extrusion mesh plate are connected by a reciprocating thread.

[0012] Preferably, the spraying mechanism includes a spraying disc and spraying pipes. The spraying disc is rotatably disposed inside the tank, and the spraying pipes are evenly disposed on the outside of the spraying disc, with spraying holes provided on the lower side of the same side of the spraying pipes.

[0013] Preferably, the bottom of the adjusting shaft is fixedly connected to the spray plate, and an annular and rotatably connected adjusting frame is provided on the outside of the adjusting shaft. The adjusting shaft is provided with multiple communicating holes that communicate with the inside of the adjusting frame. One side of the adjusting frame is connected to a corresponding water inlet pipe. The spray plate located above the spray pipe is provided with multiple evenly distributed and fan-shaped fan blades. The rotation of the fan blades can generate an upward airflow, which drives the hot airflow to move automatically upward.

[0014] Preferably, the tank body is further provided with a first mesh plate for gas-liquid separation, and the first mesh plate is provided with water-absorbing balls.

[0015] A method for synthesizing and purifying L-menthol by crystallization includes the following steps:

[0016] (1) Ingredients: Prepare a solution by mixing crude L-menthol raw material with acetone at a ratio of 10:1;

[0017] (2) Crystallizer feeding: The well-stirred and prepared solution is pumped into the menthol crystallizer and filled to the brim;

[0018] (3) Cooling and crystallization: After the feeding is completed, observe the temperature of the menthol crystallizer, open the menthol crystallizer water pump and water valve, so that the coolant in the circulating tank enters the menthol crystallizer at the set temperature after passing through the crystallization heat exchanger and heating up. At the same time, adjust the valve to set the temperature > crystallization point + 3℃ for rapid cooling.

[0019] (4) Discharge of mother liquor: After cooling is completed, open the bottom valve of the menthol crystallizer to the valve of the mother liquor tank, open the steam-cooling pipe of the lower end of the menthol crystallizer, and discharge the end material and mother liquor into the acetone mother liquor tank;

[0020] (5) Feeding: After observing through the sight glass that no obvious material is discharged, close the chilled water regulating valve and allow the internal temperature of the menthol crystallizer to rise at full speed to 50-55℃. Open the steam valve of the lower end of the menthol crystallizer, open the bottom valve and shut-off valve of the crystallizer to feed the material into the drying kettle. After feeding, close the bottom valve and shut-off valve to prepare for the next batch of feeding. The cycle should be controlled within 24 hours.

[0021] (6) Acetone removal: After the material enters the drying kettle, the drying kettle is stirred and the internal material is heated to discharge the acetone in the form of gas and transport it to the acetone mother liquor tank to achieve acetone removal.

[0022] Preferably, in step (2), after the temperature drops to the crystallization point +3℃, the cooling rate is set to 1℃ / hour. After reaching the crystallization point, the temperature begins to rebound. After maintaining the rebound for 1 hour, the temperature begins to drop. The temperature drops at a rate of 1℃ for the first 4 hours, at a rate of 1.5℃ for the middle 4 hours, and after dropping by 10℃, the temperature drops at a rate of 3℃ per hour until it drops to 15℃ below the crystallization point.

[0023] Preferably, in step (6), the acetone removal method includes the following steps:

[0024] (1) After the material enters the drying kettle, turn on the stirring inside the drying kettle, turn on the vacuum pump to all valves in the drying kettle, and at the same time turn on the liquid pipe of the condenser to condense the gaseous acetone into liquid, so that the liquid flows into the acetone mother liquor tank.

[0025] (2) After the vacuum is turned on, the acetone will vaporize and enter the condenser. Adjust the vacuum level. The initial vacuum level adjustment valve is set to -20KPa. As the amount of acetone decreases, the vacuum level is gradually increased. When the vacuum level reaches the maximum value of the pump (the adjustment valve is closed), the hot water jacket of the drying kettle can be turned on.

[0026] (3) Open the hot water inlet and outlet valves of the jacketed tracing pipe and adjust the temperature to gradually rise to 60℃;

[0027] (4) After the temperature reaches 60℃ and the vacuum reaches -90KPa or above, observe that there is no acetone in the sight glass of the lower liquid pipe of the condenser. Then turn on the feeding pump of the drying kettle and start self-circulation sampling. When the acetone content is ≤10ppm, it means that the drying is qualified. Then the valve of the gas phase pipe from the drying kettle to the condenser can be closed.

[0028] (5) After closing the gas phase valve, the vacuum system can be shut down, and nitrogen gas can be introduced into the drying kettle through the nitrogen pipeline to break the vacuum.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. A tubular crystallizer is adopted, which has a porous structure with each single hole having a diameter of DN80. The inner layer contains the crystallizing material, while the outer layer is filled with circulating cooling water. The crystals form needle-like crystals on the inner wall through heat exchange. As the number of seed crystals increases, they accumulate and support each other, facilitating the formation of needle-like crystals. When discharging the mother liquor, the mother liquor flows out from inside the tube, and the crystals do not collapse, achieving smooth crystallization separation and minimizing crystal loss due to collapse. The use of a tubular crystallizer makes temperature rise and fall easier to control, and the adjustment and replacement are beneficial for controlling the crystallization temperature rise and fall curve, and can greatly shorten the crystallization cycle. Compared with the traditional batch crystallizer, the tubular crystallizer contains multiple tubes, and the inner surface of each tube is in contact with the crystallizing material, while the outer surface is in contact with the cooling circulating water. The heat exchange area is increased, and the heat transfer effect is better. During the temperature control process, the difference between the water temperature and the material temperature is smaller, which is beneficial for controlling the crystallization temperature rise and fall curve. Furthermore, due to the good heat exchange effect, the temperature rises slightly to reach the crystallization point of L-menthol, the mother liquor is discharged, and the crystals fall off by gravity. The crystallization cycle is short and the efficiency is high.

[0031] 2. The design of the circulating tank and crystallization heat exchanger: The crystallization heat exchanger can regulate the coolant temperature in a timely manner through heat exchange, controlling the temperature of the coolant entering the menthol crystallizer. This allows for precise control of the temperature required for crystallization within the menthol crystallizer. The circulating tank design allows for the recycling of coolant, effectively reducing the need for additional coolant and lowering costs. The design of the absorbent cotton layer utilizes its strong adsorption capacity to absorb moisture from the airflow, achieving gas-liquid separation and reducing coolant loss. The support mesh effectively fixes the absorbent cotton layer, while the up-and-down movement of the squeezing mesh, by moving closer to and further away from the support mesh, achieves intermittent squeezing of the absorbent cotton layer. This ensures that the liquid adsorbed by the absorbent cotton layer is promptly squeezed and separated, maintaining a good adsorption state and ensuring efficient adsorption of liquid in the airflow. This continuously maintains efficient gas-liquid separation of the passing airflow, improves coolant recovery rate, reduces losses, and saves costs.

[0032] 3. L-menthol and acetone are subjected to solvent crystallization in a tubular crystallizer. By cooling, L-menthol is precipitated in the form of needle-shaped crystals. After the impurities are discharged with the mother liquor, the needle-shaped crystals are melted to obtain high-purity L-menthol with a content of 99.9%. The crystallization cycle is within 24 hours, and the yield of a single crystallization is over 40%.

[0033] 4. Using acetone as a solvent for crystallization allows for a more thorough dissolution of impurities in crude L-menthol, and acetone is volatile and easy to remove. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a plan view of the equipment piping of the present invention.

[0036] Figure 2 This is a three-dimensional structural diagram of the circulating tank of the present invention.

[0037] Figure 3 This is a schematic diagram of the three-dimensional connection structure of the absorbent cotton layer and absorbent ball of the present invention.

[0038] Figure 4 This is a schematic diagram of the internal structure of the absorbent cotton layer and absorbent ball of the present invention.

[0039] Figure 5 This is a schematic diagram of the three-dimensional connection structure between the water-absorbing ball and the first mesh plate of the present invention.

[0040] In the diagram: 1. Menthol crystallizer; 2. Nitrogen pipeline; 3. Circulation tank; 30. Spray plate; 301. Spray pipe; 302. Spray hole; 31. Cooling water supply pipeline; 32. Cooling water return pipeline; 33. Drain pipe; 34. Inlet pipe; 35. Drive motor; 36. Exhaust pipe; 37. Adjusting shaft; 371. Connecting hole; 372. Adjusting frame; 373. Connecting ring plate; 374. Reciprocating thread; 38. Water-absorbing ball; 381. First mesh plate; 382. Torsion spring; 383. First rod; 384. Rotating rod; 385. Second rod; 39. Water-absorbing cotton layer; 391. Support mesh plate; 392. Extrusion mesh plate; 4. Crystallization heat exchanger; 41. Hot water return pipeline; 42. Hot water supply pipeline; 5. Acetone mother liquor tank; 6. Menthol tank; 7. Drying kettle. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] Reference Figure 1 A synthetic L-menthol crystallization and purification system includes a menthol crystallizer 1, a menthol tank 6, an acetone mother liquor tank 5, and a drying kettle 7. The discharge ends of the menthol tank 6 and the acetone mother liquor tank 5 are connected to the feed end of the menthol crystallizer 1 via pipes. The menthol crystallizer 1 is equipped with a cooling liquid for cooling the material, and the discharge end of the menthol crystallizer 1 is connected to the drying kettle 7 via a pipe. The acetone output end of the drying kettle 7 is connected to the acetone mother liquor tank 5 via a pipe. In this embodiment, the menthol crystallizer 1 is a tubular crystallizer. The tubular design allows the material to be evenly distributed on the inner wall of the tubes, thus ensuring uniform heating, more precise temperature control, and better crystallization. The crystals form needle-like crystals on the inner wall through heat exchange. As the number of seed crystals increases, they accumulate and support each other, facilitating the formation of needle-like crystals. When discharging the mother liquor, the mother liquor flows out from inside the tubes, preventing the crystals from collapsing, thus achieving smooth crystallization separation and minimizing crystal loss due to collapse.

[0044] As one possible implementation, refer to Figure 1 The system also includes a circulation tank 3 and a crystallization heat exchanger 4. The circulation tank 3 stores coolant, and its outlet is connected to the inlet heating end of the crystallization heat exchanger 4 via a pipe. The crystallization heat exchanger 4 contains hot water for heat exchange and heating of the coolant, and its outlet is connected to the inlet heating end of the menthol crystallizer 1 via a pipe. The outlet heating end of the menthol crystallizer 1 is connected to the inlet heating end of the circulation tank 3 via a pipe. The design of the circulation tank 3 and the crystallization heat exchanger 4 allows the crystallization heat exchanger 4 to regulate the coolant temperature in a timely manner through heat exchange, controlling the temperature of the coolant entering the menthol crystallizer 1. This enables precise control of the temperature required for crystallization within the menthol crystallizer 1. The circulation tank 3 design allows for the recycling of the coolant, effectively reducing the need for additional coolant and lowering costs.

[0045] In this embodiment, it also includes a cooling water supply pipe 31, a cooling water return pipe 32, a hot water supply pipe 42, and a hot water return pipe 41. The cooling water supply pipe 31 is connected to the inlet end of the circulation tank 3, and the outlet end of the circulation tank 3 is connected to the cooling water return pipe 32 through a pipe. The hot water supply pipe 42 is connected to the hot water inlet end of the crystallizer heat exchanger 4, and the hot water return pipe 41 is connected to the hot water outlet end of the crystallizer heat exchanger 4. It also includes a nitrogen inlet pipe, which is connected to the menthol crystallizer 1.

[0046] As one possible implementation, refer to Figure 2-4 The circulating tank 3 includes a tank body, an inlet pipe 34 at one side of the tank body, a drain pipe 33 at the bottom of the tank body, and an exhaust pipe 36 at the top of the tank body for discharging hot air. The tank body contains a spray mechanism connected to the inlet pipe 34 for uniformly spraying coolant. It also contains an absorbent cotton layer 39 for gas-liquid separation of the rising hot air. An extrusion mesh plate 392, movable up and down, is provided on the absorbent cotton layer 39 for squeezing the absorbent cotton layer 39. A fixedly connected support mesh plate 391 is provided inside the tank body, and each support mesh plate 391 is fixedly connected to one end of a corresponding absorbent cotton layer 39. The extrusion mesh plate 392 is movable up and down at the other end of the absorbent cotton layer 39. A rotatable adjusting shaft 37 is provided inside the tank body, passing through the extrusion mesh plate 392, and connected to the extrusion mesh plate 392 by a reciprocating thread 374.

[0047] The spray mechanism is designed to evenly distribute coolant at a certain temperature through spraying. This allows the hot airflow inside the coolant to rise and separate in a timely manner, thus achieving a certain degree of cooling and enabling the coolant to recover its initial temperature, improving coolant circulation. The absorbent cotton layer 39 utilizes its strong adsorption capacity to absorb moisture from the airflow, achieving gas-liquid separation and reducing coolant loss. The supporting mesh plate 391 effectively fixes the absorbent cotton layer 39. The up-and-down movement of the extrusion mesh plate 392, by moving closer to and further away from the support mesh plate 391, achieves intermittent extrusion of the absorbent cotton layer 39. This allows the liquid adsorbed by the absorbent cotton layer 39 to be extruded and separated in a timely manner, ensuring that the absorbent cotton layer 39 maintains a good adsorption state and thus guaranteeing the adsorption efficiency of liquid in the airflow and continuously maintaining the gas-liquid separation efficiency of the passing airflow. At the same time, the design of the adjusting shaft 37 and the reciprocating thread 374 allows the extrusion mesh plate 392 to achieve periodic up-and-down movement by combining the continuous rotation of the adjusting shaft 37 with the reciprocating thread 374.

[0048] In this embodiment, refer to Figure 4The absorbent cotton layers 39 are multiple, and each pair of absorbent cotton layers 39 forms a group. Support mesh plates are respectively set at the upper and lower ends of each group of absorbent cotton layers 39. There are two extrusion mesh plates 392, which are set between each pair of absorbent cotton layers 39 and are fixedly connected to the corresponding absorbent cotton layers 39. A connecting ring plate 373 is provided between two adjacent extrusion mesh plates 392. The connecting ring plate 373 is sleeved on the outside of the adjusting shaft 37, and the upper and lower ends of the connecting ring plate 373 are fixedly connected to the corresponding extrusion mesh plate 392. The adjusting shaft 37 is provided with a reciprocating thread 374, and the inner side of the connecting ring plate 373 is engaged with the reciprocating thread 374. Multiple limiting slide rods are provided between the upper and lower support mesh plates 391 to restrict the extrusion mesh plate 392 to move only up and down. The limiting slide rods move through the extrusion mesh plate 392. The absorbent cotton layers 39 are arranged in pairs, with the support mesh plates 391 positioned on the upper and lower sides and the squeezing mesh plate 392 positioned in the middle. This design ensures that when the adjusting shaft 37 rotates, causing the squeezing mesh plates 392 to move up and down, within each pair, while one squeezing mesh plate 392 moves upward to squeeze the absorbent cotton layer 39, the other squeezing mesh plate 392 moves upward simultaneously. This ensures that at least one absorbent cotton layer 39 in each pair is always adsorbing moisture, thus guaranteeing the efficiency of the absorbent cotton layers 39 in separating gas and liquid in the airflow. Simultaneously, it can also squeeze another absorbent cotton layer 39 that has already absorbed moisture, separating the moisture. Thus, with the periodic up and down movement of the squeezing mesh plate 392, one absorbent cotton layer 39 is always squeezed and separated, while the other absorbent cotton layer 39 remains in an adsorbed state.

[0049] In this embodiment, a drive motor 35 is provided at the upper end of the tank body, and the output end of the drive motor 35 is connected to the adjustment shaft 37.

[0050] As one possible implementation, refer to Figure 3-4 The spraying mechanism includes a spray plate 30 and spray pipes 301. The spray plate 30 is rotatably mounted inside the tank. The spray pipes 301 are evenly distributed on the outer side of the spray plate 30, and each spray pipe 301 has a spray hole 302 on the lower side of the same side. The design of the spray plate 30 and spray pipes 301 allows the spray plate 30 to rotate, causing the spray holes 302 on the spray pipes 301 to spray the coolant evenly, enabling rapid separation of hot and cold air.

[0051] As a feasible embodiment, the bottom of the adjusting shaft 37 is fixedly connected to the spray plate 30, and an adjusting frame 372 in a ring shape and rotatably connected is provided on the outside of the adjusting shaft 37. The adjusting shaft 37 is provided with a plurality of communicating holes 371 communicating with the inside of the adjusting frame 372. One side of the adjusting frame 372 is connected to the corresponding water inlet pipe 34. The spray plate 30 located above the spray pipe 301 is provided with a plurality of evenly distributed fan-shaped blades. The rotation of the fan blades can generate an upward airflow, which drives the hot airflow to move automatically upward. The fixed connection between the adjusting shaft 37 and the spray plate 30 allows the spray pipe 301 to rotate synchronously when the adjusting shaft 37 rotates. The design of the adjusting frame 372 and the connecting hole 371 enables the spray plate 30 to connect with the water inlet pipe 34 without affecting the rotation of the adjusting shaft 37. The fan blade design allows the spray pipe 301 to rotate simultaneously with the spray plate 30, creating an upward airflow that more quickly separates the hot air from the coolant, thus cooling the coolant more effectively and rapidly. In this embodiment, multiple one-way air inlets can be provided on the tank sidewall below the spray pipe 301 for airflow entry. The one-way air inlet design allows for faster cooling of the coolant by allowing cold air to enter. Additionally, multiple electronic cooling tubes can be installed at the bottom of the tank to help the coolant return to its initial temperature.

[0052] As one possible implementation, refer to Figure 2-4 The tank body is also equipped with a first mesh plate 381 for gas-liquid separation, and the first mesh plate 381 is equipped with water-absorbing balls 38. The design of the first mesh plate 381 and the water-absorbing balls 38 can further separate the gas and liquid in the airflow, further improve the gas-liquid separation efficiency, reduce coolant loss, and reduce costs.

[0053] In this embodiment, refer to Figure 2-4The adjusting shaft 37 rotatably passes through the first mesh plate 381. The bottom of the first mesh plate 381 is provided with multiple evenly distributed striking mechanisms for driving the water-absorbing balls 38 to jump up and down. The striking mechanism includes a first rod 383, a second rod 385, and a torsion spring 382. The torsion spring 382 is fixedly installed at the bottom of the first mesh plate 381. The first rod 383 is located at one end of the torsion spring 382, ​​and the second rod 385 is located at the other end of the torsion spring 382. At the same time, the ends of the first rod 383 and the second rod 385 located inside the torsion spring 382 are connected. At this time, by moving the second rod 385, the first rod 383 can be separated from the bottom of the first mesh plate 381, and the torsion spring 382 can store energy. The adjusting shaft 37 is provided with multiple rotating rods 384 that are fixedly connected and used to move the second rod 385. This design allows the adjusting shaft 37 to rotate, enabling the rotating rod 384 to rotate periodically. When the rotating rod 384 moves to the side of the second rod 385, it causes the second rod 385 to rotate, separating the first rod 383 from the bottom of the first mesh plate 381 and storing energy in the torsion spring 382. After the rotating rod 384 separates from the second rod 385, the stored energy in the torsion spring 382 can drive the first rod 383 to strike the first mesh plate 381, causing the multiple water-absorbing balls 38 on the first mesh plate 381 to bounce up and down. This effectively increases the contact area between the water-absorbing balls 38 and the airflow, improving the efficiency of water vapor separation in the airflow. In this embodiment, the first mesh plate 381 is disposed above the absorbent cotton layer 39, or it can be disposed below the absorbent cotton layer 39. In this way, the rising airflow can better drive the absorbent balls 38 up and down, allowing the absorbent balls 38 to bounce more fully, further improving the separation efficiency, thereby reducing the loss of coolant and reducing costs.

[0054] Example 2

[0055] Please see Figure 1 A method for synthesizing and purifying L-menthol by crystallization includes the following steps:

[0056] (1) Ingredients: Prepare a solution by mixing crude L-menthol raw material with acetone at a ratio of 10:1;

[0057] (2) Crystallizer feeding: The well-stirred and prepared solution is pumped into menthol crystallizer 1 and filled to the brim;

[0058] (3) Cooling and crystallization: After the feeding is completed, observe the temperature of menthol crystallizer 1, turn on the water pump and water valve of menthol crystallizer 1, so that the coolant in the circulating tank 3 enters menthol crystallizer 1 at the set temperature after passing through the crystallization heat exchanger 4 and heating up. At the same time, adjust the valve to set the temperature > crystallization point + 3℃ for rapid cooling.

[0059] (4) Discharge of mother liquor: After cooling is completed, open the bottom valve of menthol crystallizer 1 to the valve of mother liquor tank, open the outer coil of the lower end of menthol crystallizer 1 to steam the material, and discharge the material of the end and mother liquor into acetone mother liquor tank 5;

[0060] (5) Feeding: After observing through the sight glass that no obvious material is discharged, close the chilled water regulating valve and make the internal temperature of the menthol crystallizer 1 rise to 50-55℃ at full speed. Open the steam valve of the lower end of the menthol crystallizer 1, open the bottom valve and the shut-off valve of the crystallizer 1 to feed the material into the drying kettle 7. After feeding, close the bottom valve and the shut-off valve to prepare for the next batch of feeding. The cycle is controlled within 24 hours.

[0061] (6) Acetone removal: After the material enters the drying kettle 7, the drying kettle 7 is turned on to stir and the internal material is heated to discharge the acetone in the form of gas and transport it to the acetone mother liquor tank 5 to achieve acetone removal.

[0062] Furthermore, in step (2), after the temperature drops to the crystallization point +3°C, the cooling rate is set to 1°C / hour. After reaching the crystallization point, the temperature begins to rebound. After maintaining the rebound for 1 hour, the temperature begins to drop. For the first 4 hours, the temperature drops at a rate of 1°C, and for the next 4 hours, it drops at a rate of 1.5°C. After dropping by 10°C, the temperature drops at a rate of 3°C / hour until it reaches 15°C below the crystallization point. When the crystallization point is reached, the supersaturated liquid transforms into a solid, undergoing a phase transition. The release of energy as the substance becomes more stable leads to a temperature rise. To ensure that the crystals are large and regular, and to maintain the cooling water temperature, it is necessary to maintain the rebound temperature for 1 hour before starting to cool down.

[0063] Furthermore, in step (6), the method for removing acetone includes the following steps:

[0064] (1) After the material enters the drying kettle 7, turn on the stirring inside the drying kettle 7, turn on the vacuum pump to all valves in the drying kettle 7, and at the same time turn on the liquid pipe of the condenser to condense the gaseous acetone into liquid, so that the liquid flows into the acetone mother liquor tank 5.

[0065] (2) After the vacuum is turned on, the acetone will vaporize and enter the condenser. Adjust the vacuum degree. The initial vacuum degree adjustment valve is adjusted to -20KPa. As the amount of acetone decreases, the vacuum degree is gradually increased. When the vacuum degree reaches the maximum value of the pump (the adjustment valve is closed), the hot water jacket of the drying kettle 7 can be turned on.

[0066] (3) Open the hot water inlet and outlet valves of the jacketed tracing pipe and adjust the temperature to gradually rise to 60℃;

[0067] (4) After the temperature reaches 60℃ and the vacuum reaches -90KPa or above, observe that there is no acetone in the sight glass of the liquid pipe of the condenser. Then turn on the feeding pump of the drying kettle 7 and start self-circulation sampling. When the acetone content is ≤10ppm, it means that the drying is qualified. Then close the valve of the gas phase pipe from the drying kettle 7 to the condenser.

[0068] (5) After closing the gas phase valve, the vacuum system can be shut off, and nitrogen gas can be introduced into the drying kettle 7 through the nitrogen pipeline 2 to break the vacuum.

[0069] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0070] In this invention, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," "link," and "fix" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0071] The control method of this invention is automatic control through a controller. The control circuit of the controller can be implemented by simple programming by those skilled in the art. The power supply is also common knowledge in the art. Furthermore, since this invention is mainly used to protect mechanical devices, the control method and circuit connection will not be explained in detail here.

[0072] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A system for synthesizing and purifying L-menthol through crystallization, characterized in that: The equipment includes a menthol crystallizer (1), a menthol tank (6), an acetone mother liquor tank (5), and a drying kettle (7). The discharge ends of the menthol tank (6) and the acetone mother liquor tank (5) are connected to the feed end of the menthol crystallizer (1) through pipes. The menthol crystallizer (1) is equipped with a cooling liquid for cooling the material, and the discharge end of the menthol crystallizer (1) is connected to the drying kettle (7) through pipes. The acetone output end of the drying kettle (7) is connected to the acetone mother liquor tank (5) through pipes. It also includes a circulating tank (3) and a crystallizer heat exchanger (4); the circulating tank (3) stores coolant, and the outlet of the circulating tank (3) is connected to the inlet heating end of the crystallizer heat exchanger (4) through a pipe. The crystallizer heat exchanger (4) is provided with hot water for heat exchange and heating of the coolant, and the outlet of the crystallizer heat exchanger (4) is connected to the inlet of the menthol crystallizer (1) through a pipe. The outlet of the menthol crystallizer (1) is connected to the inlet of the circulating tank (3) through a pipe. The circulating tank (3) includes a tank body, an inlet pipe (34) is provided at the water inlet end on one side of the tank body, a drain pipe (33) is provided at the drain end at the bottom of the tank body, a spraying mechanism is provided inside the tank body that is connected to the inlet pipe (34) and is used for uniform spraying of coolant, and a water-absorbing cotton layer (39) is provided inside the tank body for gas-liquid separation of rising hot airflow, and a squeezing mesh plate (392) that can move up and down and is used to squeeze the water-absorbing cotton layer (39) is provided on the water-absorbing cotton layer (39). The spraying mechanism includes a spraying disc (30) and a spraying pipe (301). The spraying disc (30) is rotatably disposed inside the tank. The spraying pipe (301) is evenly disposed on the outside of the spraying disc (30), and spraying holes (302) are provided on the lower side of the same side of the spraying pipe (301).

2. The L-menthol synthesis crystallization and purification system according to claim 1, characterized in that: It also includes a cooling water supply pipe (31), a cooling water return pipe (32), a hot water supply pipe (42), and a hot water return pipe (41). The cooling water supply pipe (31) is connected to the inlet of the circulating tank (3). The outlet of the circulating tank (3) is connected to the cooling water return pipe (32) through a pipe. The hot water supply pipe (42) is connected to the hot water inlet of the crystallizer heat exchanger (4). The hot water return pipe (41) is connected to the hot water outlet of the crystallizer heat exchanger (4).

3. The synthetic L-menthol crystallization and purification system according to claim 1, characterized in that: The tank is provided with a fixedly connected support mesh plate (391), which is fixedly connected to one end of the corresponding absorbent cotton layer (39). The extrusion mesh plate (392) is disposed at the other end of the absorbent cotton layer (39) and can move up and down. The tank is provided with a rotatable adjustment shaft (37), which passes through the extrusion mesh plate (392) and is connected to the extrusion mesh plate (392) by a reciprocating thread (374).

4. The L-menthol synthesis crystallization and purification system according to claim 1, characterized in that: The tank is also provided with a first mesh plate (381) for gas-liquid separation, and the first mesh plate (381) is provided with water-absorbing balls (38).

5. A purification method for the synthetic L-menthol crystallization purification system according to any one of claims 1-4, characterized in that, Includes the following steps: 1) Ingredients: Prepare a solution by mixing crude L-menthol with acetone at a ratio of 10:1; 2) Feeding the crystallizer: The well-stirred and prepared solution is fed into the menthol crystallizer (1) and filled to the brim; 3) Cooling and crystallization: After the feeding is completed, observe the temperature of the menthol crystallizer (1), turn on the water pump and water valve of the menthol crystallizer (1), so that the coolant in the circulating tank (3) enters the menthol crystallizer (1) at the set temperature after passing through the crystallization heat exchanger (4) and heating up. At the same time, adjust the valve to set the temperature > crystallization point + 3℃ for rapid cooling. 4) Discharge mother liquor: After cooling is completed, open the bottom valve of the menthol crystallizer (1) to the mother liquor tank valve, open the outer coil of the lower end of the menthol crystallizer (1) to steam the material, and discharge the end material and mother liquor into the acetone mother liquor tank (5). 5) Discharge: After observing through the sight glass that no obvious material is discharged, close the chilled water regulating valve and raise the internal temperature of the menthol crystallizer (1) to 50-55℃ at full speed. Open the steam valve of the lower end of the menthol crystallizer (1), open the bottom valve and the shut-off valve of the crystallizer (1) to discharge the material into the drying kettle (7). After discharging the material, close the bottom valve and the shut-off valve and prepare for the next batch of material to be fed. The cycle is controlled within 24 hours. 6) Acetone removal: After the material enters the drying kettle (7), the drying kettle (7) is turned on for stirring and the internal material is heated to discharge the acetone in the form of gas and transport it to the acetone mother liquor tank (5) to achieve acetone removal.

6. The purification method according to claim 5, characterized in that: In step 3), after the temperature drops to the crystallization point +3℃, the cooling rate is set to 1℃ / hour. After reaching the crystallization point, the temperature begins to rebound. After maintaining the rebound for 1 hour, the temperature begins to drop. For the first 4 hours, the temperature drops at a rate of 1℃, and for the next 4 hours, it drops at a rate of 1.5℃. After the temperature drops by 10℃, it drops at a rate of 3℃ per hour until it reaches 15℃ below the crystallization point.

7. The purification method according to claim 5, characterized in that: In step 6), the method for removing acetone includes the following steps: 1) After the material enters the drying kettle (7), turn on the stirring inside the drying kettle (7), turn on the vacuum pump to all valves of the drying kettle (7), and at the same time turn on the liquid pipe of the condenser to condense the gaseous acetone into liquid, so that the liquid flows into the acetone mother liquor tank (5). 2) After the vacuum is turned on, the acetone will vaporize and enter the condenser. Adjust the vacuum degree. The initial vacuum degree adjustment valve is adjusted to -20KPa. As the amount of acetone decreases, the vacuum degree is gradually increased. When the vacuum degree reaches the maximum value of the pump, the drying kettle (7) jacketed hot water can be turned on. 3) Open the hot water inlet and outlet valves of the jacketed tracing pipe and gradually raise the temperature to 60℃; 4) After the temperature reaches 60℃ and the vacuum reaches -90KPa or above, observe that there is no acetone in the sight glass of the liquid pipe of the condenser. Then turn on the feeding pump of the drying kettle (7) and start self-circulation sampling. When the acetone content is ≤10ppm, it means that the drying is qualified. Then close the valve of the gas phase pipe from the drying kettle (7) to the condenser. 5) After closing the gas phase valve, the vacuum system can be shut off. Nitrogen gas is then introduced into the drying kettle (7) through the nitrogen pipeline (2) to break the vacuum.

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