Method and system for drying glycolide

Abstract

The application provides a drying method and drying system for glycolide, and belongs to the field of organic drying. The drying method comprises the following steps: (a) separating a solid-liquid mixture of glycolide into small-particle wet glycolide and large-particle wet glycolide; the particle size of the small-particle wet glycolide is 0.1-60 microns; the particle size of the large-particle wet glycolide is 40-1000 microns; (b) feeding the small-particle wet glycolide into a fluidized dryer, introducing hot nitrogen into the fluidized dryer to dry the small-particle wet glycolide, and discharging the dried glycolide from the bottom of the fluidized dryer; and (c) feeding the large-particle wet glycolide into a vacuum belt dryer, wherein the vacuum belt dryer comprises one or more drying belts, and the dried glycolide is discharged through the last drying belt. The method has good drying effect and high product purity.

Description

Technical Field

[0001] This invention belongs to the field of organic drying, and specifically relates to a drying method and system for glycolide. Background Technology

[0002] Polyglycolic acid (PGA), also known as polyglycolic acid, is a biodegradable aliphatic polymer. It can be hydrolyzed in organisms (such as microorganisms) under the catalysis of enzymes, acids, or bases, ultimately forming carbon dioxide and water. It is a biodegradable material with great development potential. Glycolic acid is a cyclic dimer of glycolic acid. Ring-opening polymerization of glycolide is a relatively mature method for preparing PGA, which can yield PGA with a high relative molecular mass. In the synthesis of PGA, the purity of the raw material glycolide has a significant impact; therefore, optimizing processes such as purification and drying of crude glycolide is crucial.

[0003] The production of glycolide involves using glycolic acid or glycolate compounds as reactants. Glycolic acid oligomers are prepared through polycondensation, and then these oligomers are cleaved into rings to produce glycolide. The crude glycolide produced from the cyclization reactor contains impurities such as water, glycolic acid, and glycolic acid oligomers in addition to glycolide. It requires purification before use, and drying is a crucial step in the glycolide purification process.

[0004] For example, after purifying impure glycolide through recrystallization, the glycolide needs to be dried to obtain high-purity glycolide. Similarly, glycolide can be washed with a polar solvent and then dried to obtain high-purity glycolide. Glycolide drying typically employs airflow drying. Due to the heat sensitivity of glycolide, the drying process requires a large airflow and a relatively low upper temperature limit, necessitating a long drying time to meet product requirements. This results in a long drying process or low efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a drying method and system for glycolide that has good drying effect and high product purity.

[0006] In a first aspect, the present invention provides a method for drying glycolide, the drying method comprising:

[0007] (a) Separating the glycolide solid-liquid mixture into small-particle glycolide wet material and large-particle glycolide wet material; wherein the particle size of glycolide in the small-particle glycolide wet material ranges from 0.1 to 60 μm; and the particle size of glycolide in the large-particle glycolide wet material ranges from 40 to 1000 μm;

[0008] (b) The small particle wet glycolide material is fed into a fluidized bed dryer, and hot nitrogen is introduced into the fluidized bed dryer to dry the small particle wet glycolide material. The dried glycolide flows out from the bottom of the fluidized bed dryer.

[0009] (c) The large-particle wet glycolide material is fed into a vacuum belt dryer, which includes one or more drying belts, and the dried glycolide is sent out through the final drying belt.

[0010] In one or more embodiments, the glycolide solid-liquid mixture is a solid-liquid mixture obtained by glycolide crystallization or recrystallization.

[0011] In one or more embodiments, the average particle size of the small-particle wet glycolide material is 10-20 μm, and the total moisture content is ≥20%.

[0012] In one or more embodiments, the average particle size of the large-particle wet glycolide material is 150–300 μm, and the total moisture content is ≥10%.

[0013] In one or more embodiments, step (b) has one or more of the following characteristics:

[0014] The operating temperature of the fluidized dryer is 50–70°C.

[0015] The operating pressure of the fluidized bed dryer is 0.10–0.30 MPa.

[0016] The residence time of the material in the fluidized bed dryer is 0.05 to 3.0 hours.

[0017] In one or more embodiments, step (b) further includes:

[0018] The gas-solid mixture formed by water-containing nitrogen and entrained glycolide flows out from the top outlet of the fluidized dryer and enters the gas-solid separator;

[0019] Water-containing nitrogen flows out from the top outlet of the gas-solid separator, and after drying and pressurization and heating by a heater, it returns to the fluidized dryer. The outlet temperature of the heater is 60-90°C, and the operating pressure is 0.15-0.35 MPaA.

[0020] The glycolide flows out from the bottom outlet of the gas-solid separator and returns to the fluidized dryer for drying.

[0021] In one or more embodiments, step (c) has one or more of the following characteristics:

[0022] The operating temperature of the vacuum belt dryer is 20–80°C;

[0023] The operating pressure of the vacuum belt dryer is ≤5.0 kPaA;

[0024] The residence time of the material in the vacuum belt dryer is 0.2 to 2.0 hours;

[0025] The fabric thickness of the large-particle glycolide wet material is 5-40 mm.

[0026] In one or more embodiments, the vacuum belt dryer includes at least two drying belts, wherein in at least the last two drying belts, the conveying speed of the next drying belt is 1.1 to 1.5 times that of the previous drying belt.

[0027] In one or more embodiments, step (a) includes the following steps:

[0028] (1) The glycolide solid-liquid mixture is subjected to sedimentation to separate a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles;

[0029] (2) The solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles are subjected to solid-liquid separation to obtain the wet material of small particle glycolide and the wet material of large particle glycolide.

[0030] In one or more embodiments, step (a) includes the following steps:

[0031] (1) The glycolide solid-liquid mixture is filtered and intercepted to obtain the large-particle glycolide wet material and the solid-liquid mixture containing small particles;

[0032] (2) Further solid-liquid separation is performed on the solid-liquid mixture containing small particles to obtain the wet material of small particle glycolide.

[0033] A second aspect of the present invention provides a drying system for glycolide, for implementing the method described in the first aspect of the present invention, the drying system comprising a separation combination device, a fluidized dryer, and a vacuum belt dryer;

[0034] The separation and combination equipment is used to separate the glycolide solid-liquid mixture into small-particle glycolide wet material and large-particle glycolide wet material. The fluidized bed dryer is used to dry the small-particle glycolide wet material, and the vacuum belt dryer is used to dry the large-particle glycolide wet material.

[0035] In one or more embodiments, the separation combination device includes a sedimentation device, a first solid-liquid separation device, and a second solid-liquid separation device, wherein the first solid-liquid separation device is connected to the upper outlet of the sedimentation device and the fluidized dryer, and the second solid-liquid separation device is connected to the bottom outlet of the sedimentation device and the vacuum belt dryer.

[0036] In one or more embodiments, the separation combination device includes a filtration device and a solid-liquid separation device, wherein the solid outlet of the filtration device is connected to the vacuum belt dryer, the liquid outlet of the filtration device is connected to the solid-liquid separation device, and the solid-liquid separation device is connected to the fluidized dryer.

[0037] The beneficial effects of this invention include:

[0038] This invention processes a solid-liquid mixture containing glycolide into small-particle and large-particle wet glycolide materials. The small-particle wet glycolide material is dried using a fluidized bed dryer, ensuring uniform heating within the dryer. The large-particle wet glycolide material is dried using a vacuum belt dryer, preventing excessively high temperatures on the outer layer. By employing different drying methods, this invention achieves excellent drying results and high product purity. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the drying system for glycolide provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the settling equipment;

[0041] Figure 3 This is a schematic diagram of a drying system for glycolide provided in another embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the structure of a vacuum belt dryer in some embodiments of the present invention.

[0043] Among them, 1-inlet; 2-drying chamber; 3-drying conveyor belt; 4-outlet; 5-vacuum device; 6-heat exchange device; 7-liquid storage device; 8-vacuum belt dryer; 10-sedimentation device; 11-hollow conveying pipe; 12-upper outlet of sedimentation device; 13-bottom outlet of sedimentation device; 14-filtration device; 15-solid outlet of filtration device; 16-liquid outlet of filtration device; 21-first solid-liquid separation device; 21B-solid-liquid separation device; 22-second solid-liquid separation device; 30-fluidized dryer; 31-top outlet of fluidized dryer; 40-gas-solid separator; 41-top outlet of gas-solid separator; 42-bottom outlet of gas-solid separator; 50-drying pressurization device; 60-heater. Detailed Implementation

[0044] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as embodiments) can be combined with each other to form preferred technical solutions.

[0045] In the process of developing this invention, the inventors discovered that using fluidized bed drying to dry small-particle wet lactide (LPD) materials results in good drying performance because the small particle size and similar particle size distribution of LPD ensure uniform heating within the fluidized bed dryer. Conversely, using a vacuum belt dryer to dry large-particle wet LPD materials allows for relatively lower operating temperatures under vacuum conditions, preventing excessively high temperatures on the outer layer of the large LPD particles and thus avoiding LPD denaturation. Therefore, combining fluidized bed drying and vacuum belt drying to dry LPD materials with different particle size ranges effectively improves drying efficiency and ensures product quality.

[0046] If all wet glycolide is dried using fluidized bed drying, the particle size difference between glycolide particles is significant. Larger glycolide particles are prone to localized overheating or incomplete drying, affecting the quality of the final product. Smaller glycolide particles are easily carried out of the fluidized bed by the higher flow rate. If all wet glycolide is dried using vacuum belt drying, smaller glycolide particles dry faster than larger particles (especially under vacuum conditions). This makes smaller glycolide particles more susceptible to being carried away by solvent vapor and generating dust during vacuum belt drying, which can affect the continuous operation of the equipment and requires regular cleaning.

[0047] This invention provides a method for drying glycolide, the method comprising:

[0048] (a) Separate the glycolide solid-liquid mixture into small-particle glycolide wet material and large-particle glycolide wet material; the particle size range of glycolide in the small-particle glycolide wet material is 0.1 to 60 μm; the particle size range of glycolide in the large-particle glycolide wet material is 40 to 1000 μm;

[0049] (b) The small particle wet glycolide material is fed into a fluidized bed dryer, and hot nitrogen is introduced into the fluidized bed dryer to dry the small particle wet glycolide material. The dried glycolide flows out from the bottom of the fluidized bed dryer.

[0050] (c) The large-particle wet glycolide material is fed into a vacuum belt dryer, which includes one or more drying belts. The dried glycolide is then sent out via the final drying belt.

[0051] In step (a), the particle size range of lactide in the small-particle wet lactide mix is ​​0.1–60 μm, for example, 0.5–50 μm, 1–60 μm, 10–50 μm, and 5–40 μm; the particle size range of lactide in the large-particle wet lactide mix is ​​40–1000 μm, for example, 45–700 μm, 60–800 μm, 50–600 μm, and 40–480 μm. It is understood that the particle size ranges of lactide in the small-particle and large-particle wet lactide mixes are mainly influenced by the particle size range of lactide in the lactide solid-liquid mixture and the separation method.

[0052] In some embodiments, the glycolide solid-liquid mixture may be a crystalline liquid obtained from glycolide crystallization or recrystallization, and the average particle size of glycolide in the separated small-particle wet glycolide material is 10-20 μm; further, the total moisture content of the small-particle wet glycolide material is ≥20%, for example, 24%, 27%, 35%, or 40%. The average particle size of glycolide in the separated large-particle wet glycolide material is 150-300 μm; further, the total moisture content of the large-particle wet glycolide material may be ≥10%, for example, 11%, 16%, 25%, 35%, or 40%.

[0053] In some implementations, step (a) may specifically include the following steps:

[0054] (1) The solid-liquid mixture of glycolide was settled to separate the solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles;

[0055] (2) Solid-liquid separation was performed on the solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles to obtain wet material of small particles of glycolide and wet material of large particles of glycolide.

[0056] In step (2), the solid-liquid separation of the solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles can be carried out using commonly used solid-liquid separation methods in the art, such as centrifugation, vacuum filtration, or pressure filtration. Preferably, a suitable solid-liquid separation method can be selected according to the particle size of the solid-liquid mixture to be processed. For example, the solid-liquid mixture containing small particles can be separated by pressure filtration to obtain wet material containing small particles of glycolide, and the solid-liquid mixture containing large particles can be separated by centrifugation to obtain wet material containing large particles of glycolide.

[0057] In some other implementations, step (a) may specifically include the following steps:

[0058] (1) The glycolide solid-liquid mixture is filtered and intercepted to obtain large-particle glycolide wet material and a solid-liquid mixture containing small particles;

[0059] (2) Further solid-liquid separation is performed on the solid-liquid mixture containing small particles to obtain wet material of small particles of glycolide.

[0060] In step (1), a filter element can be used to filter and intercept the glycolide solid-liquid mixture. Large particles cannot pass through the filter element and are intercepted and accumulated on the surface of the filter element to form large particle glycolide wet material. The solid-liquid mixture containing small particles passes through the filter element and is further separated into solid and liquid in step (2) to obtain small particle glycolide wet material.

[0061] In step (b), the operating temperature of the fluidized bed dryer can be 50–70°C, for example, 55°C, 60°C, 65°C, or 68°C. The operating pressure can be 0.10–0.30 MPaA, for example, 0.15 MPaA, 0.20 MPaA, 0.25 MPaA, or 0.27 MPaA. The residence time can be 0.05–3.0 hours, for example, 0.1 hours, 0.5 hours, 0.8 hours, 1 hour, 1.5 hours, or 2.5 hours.

[0062] Further, the gas-solid mixture formed by the water-containing nitrogen and entrained glycolide flows out from the top outlet of the fluidized bed dryer and enters the gas-solid separator. After gas-solid separation in the gas-solid separator, the water-containing nitrogen flows out from the top outlet of the gas-solid separator, and the glycolide flows out from the bottom outlet of the gas-solid separator and returns to the fluidized bed dryer for further drying. The operating temperature of the gas-solid separator can be 50–70°C, for example, 55°C, 60°C, or 65°C. The operating pressure of the gas-solid separator can be 0.10–0.30 MPaA, for example, 0.15 MPaA, 0.20 MPaA, or 0.25 MPaA. The operating temperature of the gas-solid separator is the same as or higher than the operating temperature of the fluidized bed dryer, and the operating pressure of the gas-solid separator can be less than or equal to the operating pressure of the fluidized bed dryer. In some embodiments, the operating temperature of the gas-solid separator is equal to the operating temperature of the fluidized bed dryer, and the operating pressure of the gas-solid separator is equal to the operating pressure of the fluidized bed dryer.

[0063] In some embodiments, the water-containing nitrogen gas flowing from the top outlet of the gas-solid separator is dried, pressurized, and heated by a heater before flowing out from the heater and mixing with fresh nitrogen gas to enter a fluidized bed dryer, thus achieving gas recycling. The drying and pressurization process can employ conventional methods in the art. For example, the water-containing nitrogen gas can be first dried in a drying tower, and then pressurized by a gas booster pump; alternatively, a pressurized dryer can be used directly to dry and pressurize the water-containing nitrogen gas. The heater outlet temperature can be 60–90°C, for example, 65°C, 70°C, 75°C, 80°C, or 85°C. The heater operating pressure can be 0.15–0.35 MPaA, for example, 0.20 MPaA, 0.25 MPaA, 0.30 MPaA, or 0.32 MPaA. As a preferred embodiment, the outlet temperature of the heater is 5 to 15°C higher than the operating temperature of the fluidized bed dryer, and the operating pressure of the heater is 0.03 to 0.1 MPa higher than the operating pressure of the fluidized bed dryer.

[0064] In step (c), the operating temperature of the vacuum belt dryer can be 20–80°C, for example, 30°C, 35°C, 45°C, 50°C, 55°C, 60°C, or 70°C; preferably, the operating temperature is 40–65°C. The operating pressure can be ≤5.0 kPaA, for example, 0.1 kPaA, 0.5 kPaA, 0.8 kPaA, 1.0 kPaA, 2.0 kPaA, or 4.0 kPaA. The residence time can be 0.2–2.0 hours, for example, 0.5 hours, 1.0 hours, 1.5 hours, or 1.8 hours. The fabric thickness of the large-particle wet glycolide material can be 5–40 mm, for example, 10 mm, 15 mm, 25 mm, 30 mm, or 35 mm. Preferably, the fabric thickness of the large-particle wet glycolide material is 8–20 mm.

[0065] Furthermore, the vacuum belt dryer has at least two stages of drying belts, such as three, four, five, or six stages. Preferably, the vacuum belt dryer has at least two stages of drying belts, and each stage of the drying belts is of the same length.

[0066] As a preferred embodiment, in at least the last two stages of the drying conveyor belts, the conveying speed of the next stage is greater than that of the previous stage. In the early stages of the drying process, as the drying process progresses, the volume of the wet lactide material gradually decreases, and with the same conveying speed at each stage, the thickness of the wet lactide material also gradually decreases. In the later stages of the drying process, the total moisture content of the wet lactide material is already low, and the volume change of the wet lactide material is minimal as the drying process continues. By setting the conveying speed of the next stage of the drying conveyor belt to be greater than that of the previous stage in at least the last two stages, the thickness of the wet lactide material in the last stage decreases progressively, which is beneficial for improving the drying effect. Optionally, in at least the last two stages of the drying conveyor belts, the conveying speed of the next stage can be 1.1 to 1.5 times that of the previous stage, for example, 1.2, 1.3, or 1.4 times.

[0067] In some embodiments, when the drying belt contains at least three stages, the conveying speed of the next stage of the drying belt is greater than the conveying speed of the previous stage in at least the last two stages, and the conveying speeds of at least the first two stages are equal. That is, at least the first two stages form a constant speed zone, and at least the last two stages form a progressively increasing speed zone. For example, when the vacuum belt dryer has three stages of drying belts, the conveying speeds of the first and second stages are equal, and the conveying speed of the third stage is greater than that of the second stage. When the vacuum belt dryer has four stages of drying belts, the conveying speeds of the first and second stages are equal, and the conveying speeds of the second, third, and fourth stages increase progressively. When the vacuum belt dryer has five stages of drying belts, the conveying speeds of the first, second, and third stages are equal, and the conveying speeds of the third, fourth, and fifth stages increase progressively.

[0068] Furthermore, step (c) also includes: mechanically crushing the dried glycolide conveyed by the final drying conveyor. During the vacuum drying process of large-particle wet glycolide, the solvent gradually evaporates, and the glycolide dissolved in the solvent precipitates out after evaporation, causing the glycolide particles to easily adhere and clump together. By mechanically crushing the dried glycolide, a product with a more uniform particle size can be obtained. It should be noted that the crushing process here is a gentle crushing, which only disrupts the adhesion between crystals without destroying the crystal structure; for example, a blade-type crushing method or a pendulum-type crushing method can be used to mechanically crush the dried glycolide.

[0069] The dried glycolide obtained in step (b) and the dried glycolide obtained in step (c) are mixed to obtain the glycolide product. The residual organic solvent content of the glycolide product is ≤0.1%, for example, ≤0.09%, ≤0.05%, ≤0.03%, or ≤0.01%. Preferably, the residual organic solvent content of the glycolide product is ≤0.037%. The residual moisture content of the glycolide product is ≤0.01%, for example, ≤0.007%, ≤0.004%, or ≤0.001%. Preferably, the residual moisture content of the glycolide product is ≤0.009%. The glycolide purity of the glycolide product is ≥99.85%, for example, ≥99.88%, ≥99.92%, or ≥99.95%. Preferably, the glycolide purity of the glycolide product is ≥99.90%.

[0070] This invention also provides a drying system for glycolide, which is used to implement the drying method of this invention. The drying system includes a separation unit, a fluidized bed dryer, and a vacuum belt dryer. The separation unit separates the glycolide solid-liquid mixture into small-particle and large-particle wet glycolide materials. The fluidized bed dryer dries the small-particle wet glycolide materials, and the vacuum belt dryer dries the large-particle wet glycolide materials.

[0071] In some embodiments, the drying system for glycolide provided by the present invention is as follows: Figure 1 As shown. The separation unit includes a settling device 10, a first solid-liquid separation device 21, and a second solid-liquid separation device 22. The first solid-liquid separation device 21 is connected to the upper outlet 12 of the settling device and the fluidized bed dryer 30, respectively. The second solid-liquid separation device 22 is connected to the bottom outlet 13 of the settling device and the vacuum belt dryer 8, respectively. The settling device 10 is used to separate the glycolide solid-liquid mixture into a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles. The first solid-liquid separation device 21 is used to perform solid-liquid separation treatment on the solid-liquid mixture containing small particles to obtain small particle glycolide wet material. The second solid-liquid separation device 22 is used to perform solid-liquid separation treatment on the solid-liquid mixture containing large particles to obtain large particle glycolide wet material.

[0072] The glycolide solid-liquid mixture can be separated into a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles by sedimentation within sedimentation device 10. In some embodiments, a schematic diagram of the sedimentation device 10 is shown below. Figure 2 As shown, the settling device 10 includes a bottom outlet 13 at its bottom and an upper outlet 12 on its side, and also includes a hollow conveying pipe 11. The hollow conveying pipe 11 and the feed pipe are located on opposite sides of the settling device 10. One end of the hollow conveying pipe 11 extends into the bottom of the settling device 10, and the other end extends out from the upper outlet. The upper outlet 12 of the settling device is connected to a first solid-liquid separation device 21 through the hollow conveying pipe 11 to output a solid-liquid mixture containing small particles to the first solid-liquid separation device 21. The bottom outlet 13 of the settling device is connected to a second solid-liquid separation device 22 to output a solid-liquid mixture containing large particles to the second solid-liquid separation device 22. Large particles settle quickly, and the solid-liquid mixture containing large particles flows out from the bottom outlet 13 of the settling device. Small particles settle slowly, and the solid-liquid mixture containing small particles flows out from the upper outlet 12 of the settling device through the hollow conveying pipe 11. In practical applications, the particle size of large particles settling down can be controlled by adjusting the flow rate of the glycolide solid-liquid mixture and / or the diameter of the hollow conveying pipe 11.

[0073] Both the first solid-liquid separation device 21 and the second solid-liquid separation device 22 can perform solid-liquid separation by centrifugation, vacuum filtration, or pressure filtration. Considering the different particle sizes of the solid phase in the solid-liquid mixture, the first solid-liquid separation device 21 is preferably a rotary drum filter press, more preferably a rotary drum filter press with a scraper. The second solid-liquid separation device 22 can be selected from a belt centrifuge, a horizontal screw centrifuge, a vacuum filter, or a filter press.

[0074] In other embodiments, the drying system for glycolide provided by the present invention is as follows: Figure 3 As shown, the separation unit includes a filtration device 14 and a solid-liquid separation device 21B. The solid outlet 15 of the filtration device is connected to a vacuum belt dryer 8, and the liquid outlet 16 of the filtration device is connected to the solid-liquid separation device 21B. The solid-liquid separation device 21B is connected to a fluidized bed dryer 30. The filtration device 14 can separate the glycolide solid-liquid mixture into large-particle glycolide wet material and a solid-liquid mixture containing small particles. The large-particle glycolide wet material is discharged from the solid outlet 15 and enters the vacuum belt dryer 8 for drying. The solid-liquid mixture containing small particles is discharged from the liquid outlet 16 and, after further solid-liquid separation by the solid-liquid separation device 21B, enters the fluidized bed dryer 30 for drying.

[0075] Specifically, the filtration device 14 includes a filter element. Large particles cannot pass through the filter element of the filtration device 14 and are therefore intercepted on the surface of the filter element, accumulating to form large particles of wet glycolide, which are discharged from the solid outlet 15 of the filtration device 14. The solid-liquid mixture containing small particles passes through the filter element and is discharged from the liquid outlet 16 of the filtration device 14 into the solid-liquid separation device 21B. After further solid-liquid separation by the solid-liquid separation device 21B, small particles of wet glycolide are obtained.

[0076] It is understood that the specific positions of the solid outlet 15 and the liquid outlet 16 on the filter device 14 can be set according to the filter element and the filtration method. For example, when the filter element is installed vertically inside the filter device 14, the solid outlet 15 is located at the bottom of the filter device 14, and the liquid outlet 16 is located on the side of the filter device 14; when the filter element is installed horizontally inside the filter device 14, the solid outlet 15 is located on the side of the filter device 14, and the liquid outlet 16 is located at the bottom of the filter device 14. For example, the filter device 14 can be a scraper filter, with the filter element installed vertically inside the scraper filter. Large particles of wet glycolide are intercepted on the surface of the filter element and scraped off by a scraper, collected at the bottom. The solid-liquid mixture containing small particles passes through the filter element and flows out from the side of the scraper filter.

[0077] The solid-liquid separation device 21B can perform solid-liquid separation by centrifugation, vacuum filtration, or pressure filtration. In some embodiments, the solid-liquid separation device 21B is the first solid-liquid separation device 21.

[0078] In some embodiments, the fluidized dryer 30 of this application is a fluidized bed dryer.

[0079] exist Figure 1 and Figure 3 Furthermore, the drying system also includes a gas-solid separator 40 for separating the gas-solid mixture containing water-containing nitrogen and entrained glycolide. The inlet of the gas-solid separator is connected to the top outlet 31 of the fluidized bed dryer 30, so that the gas-solid mixture containing water-containing nitrogen and entrained glycolide flows from the fluidized bed dryer 30 into the gas-solid separator 40. The bottom outlet 42 of the gas-solid separator is connected to the fluidized bed dryer 30, allowing the separated glycolide to be returned to the fluidized bed dryer 30 for drying, while the water-containing nitrogen is discharged from the top outlet 41 of the gas-solid separator. Exemplary gas-solid separators 40 include, but are not limited to, cyclone separators and bag filters.

[0080] Optionally, the drying system also includes a drying pressurization device 50. In practical applications, the drying pressurization device 50 may include independent drying equipment and pressurization equipment, or it may be a drying pressurization device that integrates drying and pressurization functions. Exemplary drying equipment includes, but is not limited to, a drying tower for drying moisture in water-containing nitrogen gas; exemplary pressurization equipment includes, but is not limited to, a gas booster pump.

[0081] Optionally, the drying system also includes a heater 60. The inlet of the heater 60 is connected to the drying pressurization device 50, and the outlet of the heater 60 is connected to the fluidized dryer 30. In a specific implementation, the hot nitrogen flowing out of the heater 60 is mixed with fresh nitrogen and then returned to the fluidized dryer 30 for drying.

[0082] In some embodiments, the portion of the drying system used for drying small particles of wet glycolide includes a fluidized bed dryer 30, a gas-solid separator 40, a drying pressurizer 50, and a heater 60 connected in sequence.

[0083] In some embodiments, the structure of the vacuum belt dryer 8 in the drying system for drying large-particle wet glycolide material is as follows: Figure 4 As shown. The vacuum belt dryer 8 includes a drying chamber 2, a feed inlet 1 located at one top end of the drying chamber 2, a discharge outlet 4 located at one bottom end of the drying chamber 2, and one or more stages of drying belts 3 disposed inside the drying chamber 2. Each stage of drying belt 3 is provided with a heating device for heating the drying belt 3. Figure 4(Not shown in the image). In some embodiments, the vacuum belt dryer 8 includes at least two drying belts 3, for example, the vacuum belt dryer 8 includes three, four, five, six, or seven drying belts. The conveying directions of adjacent drying belts 3 are opposite, and the starting end of the next drying belt 3 is located below the end of the previous drying belt 3; the feed inlet 1 faces the starting end of the first drying belt, and the discharge outlet 4 faces the end of the last drying belt.

[0084] The drying chamber 2 is connected to the vacuum pumping device 5 and the liquid storage device 7 via a heat exchanger 6. Solvent vapor generated by the large-particle wet glycolide material under vacuum is discharged from the drying chamber 2 and enters the heat exchanger 6 for heat exchange. The condensed liquid from the solvent vapor flows into the liquid storage device 7 for solvent recovery and reuse. The vacuum belt dryer 8 operates under negative pressure; for example, the operating pressure during drying is ≤5 kPaA.

[0085] In some implementations, the drying system further includes a crushing unit. The crushing unit is located at or connected to the discharge port 4 of the vacuum belt dryer 8; the crushing unit includes, but is not limited to, a blade crushing mechanism and a pendulum crushing mechanism.

[0086] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Percentages and parts are by weight unless otherwise stated.

[0087] Measurement method

[0088] Determination of total moisture content of wet glycolide stock: Accurately weigh a mass of M0 of wet glycolide stock, spread it out and place it in a 40℃ oven for vacuum drying. Dry the wet glycolide stock under an absolute pressure vacuum of less than 1 kPaA for 1 hour, then remove it and place it in a desiccator. After cooling, weigh it and record the weight as M1. Total moisture content = (M0 - M1) / M0.

[0089] The particle size range and average particle size of glycolide in the wet material were determined using a laser particle size analyzer.

[0090] The residual organic solvent content and purity of the dried glycolide were determined by gas chromatography, and the residual moisture content was determined by Karl Fischer moisture analyzer.

[0091] Example 1

[0092] The solid-phase glycolide mass fraction in the crystallization solution after recrystallization from ethyl acetate is approximately 20%. After separation by a sedimentation device, a solid-liquid mixture of small-particle glycolide and a solid-liquid mixture of large-particle glycolide are obtained. The small-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a rotary filter press with a scraper to obtain a wet small-particle glycolide material. The particle size range of the wet small-particle glycolide material is 1–55 μm, the average particle size is 10 μm, and the total moisture content is 22%. The large-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a horizontal screw centrifuge to obtain a wet large-particle glycolide material. The particle size range of the wet large-particle glycolide material is 40–400 μm, the average particle size is 165 μm, and the total moisture content is 13%.

[0093] Small-particle wet glycolide material is fed into a fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 55℃, the operating pressure is 0.10 MPaA, and the residence time is 0.5 hours. The operating temperature of the gas-solid separator is 55℃, and the operating pressure is 0.10 MPaA. The nitrogen gas flowing out of the gas-solid separator is dried and pressurized before entering the nitrogen heater. The outlet temperature of the nitrogen heater is 65℃, and the operating pressure is 0.15 MPaA.

[0094] Large-particle wet glycolide material enters a vacuum belt dryer for drying. The vacuum belt dryer has four drying belts, each 10m long. The operating temperature of the vacuum belt dryer is 60℃, the operating pressure is 2.0kPaA, the fabric thickness of the large-particle wet glycolide material is 8mm, the conveying speed of each drying belt is the same, and the total residence time is 0.5 hours.

[0095] The dried glycolide flowing from the bottom of the fluidized bed dryer and the dried glycolide sent from the vacuum belt dryer were mixed to obtain a glycolide product with an organic solvent residue of 0.037 wt%, a moisture residue of 0.006 wt%, and a glycolide purity of 99.93%.

[0096] Example 2

[0097] The solid-phase glycolide mass fraction in the crystallization solution after recrystallization from ethyl acetate is approximately 30%. After separation by a sedimentation device, a solid-liquid mixture of small-particle glycolide and a solid-liquid mixture of large-particle glycolide are obtained. The small-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a rotary filter press with a scraper to obtain a wet small-particle glycolide material. The particle size range of the wet small-particle glycolide material is 0.5–50 μm, the average particle size is 13 μm, and the total moisture content is 26%. The large-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a horizontal screw centrifuge to obtain a wet large-particle glycolide material. The particle size range of the wet large-particle glycolide material is 40–480 μm, the average particle size is 210 μm, and the total moisture content is 16%.

[0098] Small-particle wet glycolide material is fed into a fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 65℃, the operating pressure is 0.25MPaA, and the residence time is 0.05 hours. The operating temperature of the gas-solid separator is 65℃, and the operating pressure is 0.25MPaA. The nitrogen gas flowing out of the gas-solid separator is dried and pressurized before entering the nitrogen heater. The outlet temperature of the nitrogen heater is 75℃, and the operating pressure is 0.30MPaA.

[0099] Large-particle wet glycolide material enters a vacuum belt dryer for drying. The vacuum belt dryer has four drying belts, each 10m long. The operating temperature of the vacuum belt dryer is 60℃, the operating pressure is 0.10kPaA, the fabric thickness of the large-particle wet glycolide material is 10mm, the conveying speed of each drying belt is the same, and the total residence time is 1.0 hour.

[0100] The dried glycolide flowing from the bottom of the fluidized bed dryer and the dried glycolide sent from the vacuum belt dryer were mixed to obtain a glycolide product with an organic solvent residue of 0.028 wt%, a moisture residue of 0.009 wt%, and a glycolide purity of 99.92%.

[0101] Example 3

[0102] The solid-phase glycolide mass fraction in the crystallization solution after recrystallization from ethyl acetate is approximately 15%. After separation by a sedimentation device, a solid-liquid mixture of small-particle glycolide and a solid-liquid mixture of large-particle glycolide are obtained. The small-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a rotary filter press with a scraper to obtain a wet small-particle glycolide material. The particle size range of the wet small-particle glycolide material is 0.5–60 μm, the average particle size is 20 μm, and the total moisture content is 30%. The large-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a horizontal screw centrifuge to obtain a wet large-particle glycolide material. The particle size range of the wet large-particle glycolide material is 45–700 μm, the average particle size is 280 μm, and the total moisture content is 11%.

[0103] Small-particle wet glycolide material is fed into a fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 62℃, the operating pressure is 0.27MPaA, and the residence time is 1.0 hour. The operating temperature of the gas-solid separator is 62℃, and the operating pressure is 0.27MPaA. The nitrogen gas flowing out of the gas-solid separator is dried and pressurized before entering the nitrogen heater. The outlet temperature of the nitrogen heater is 72℃, and the operating pressure is 0.32MPaA.

[0104] Large-particle wet glycolide material enters a vacuum belt dryer for drying. The vacuum belt dryer has four drying belts, each 10m long. The operating temperature of the vacuum belt dryer is 50℃, the operating pressure is 0.10kPaA, the fabric thickness of the large-particle wet glycolide material is 15mm, the conveying speed of the first three drying belts is the same, the conveying speed of the fourth drying belt is 1.5 times that of the first three drying belts, and the total residence time is 1.1 hours.

[0105] The dried glycolide flowing from the bottom of the fluidized bed dryer and the dried glycolide sent from the vacuum belt dryer were mixed to obtain a glycolide product with an organic solvent residue of 0.020 wt%, a moisture residue of 0.006 wt%, and a glycolide purity of 99.93%.

[0106] Example 4

[0107] The solid-phase glycolide mass fraction in the crystallization solution after recrystallization from ethyl acetate is approximately 30%. After separation by a sedimentation device, a solid-liquid mixture of small-particle glycolide and a solid-liquid mixture of large-particle glycolide are obtained. The small-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a rotary filter press with a scraper to obtain a wet small-particle glycolide material. The particle size range of the wet small-particle glycolide material is 1–60 μm, the average particle size is 15 μm, and the total moisture content is 27%. The large-particle glycolide solid-liquid mixture is subjected to solid-liquid separation using a horizontal screw centrifuge to obtain a wet large-particle glycolide material. The particle size range of the wet large-particle glycolide material is 55–800 μm, the average particle size is 300 μm, and the total moisture content is 20%.

[0108] Small-particle wet glycolide material is fed into a fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 60℃, the operating pressure is 0.20MPaA, and the residence time is 2.0 hours. The operating temperature of the gas-solid separator is 60℃, and the operating pressure is 0.20MPaA. The nitrogen gas flowing out of the gas-solid separator is dried and pressurized before entering the nitrogen heater. The outlet temperature of the nitrogen heater is 70℃, and the operating pressure is 0.25MPaA.

[0109] Large-particle wet glycolide material enters a vacuum belt dryer for drying. The vacuum belt dryer has four drying belts, each 10m long. The operating temperature of the vacuum belt dryer is 55℃, the operating pressure is 0.50kPaA, the fabric thickness of the large-particle wet glycolide material is 20mm, the conveying speed of each drying belt is the same, and the total residence time is 1.5 hours.

[0110] The dried glycolide flowing from the bottom of the fluidized bed dryer and the dried glycolide sent from the vacuum belt dryer were mixed to obtain a glycolide product with an organic solvent residue of 0.023 wt%, a moisture residue of 0.007 wt%, and a glycolide purity of 99.90%.

[0111] Comparative Example 1

[0112] The mass fraction of solid-phase glycolide in the crystallization solution after recrystallization from ethyl acetate is approximately 20%. Solid-liquid separation is performed using a horizontal screw centrifuge to obtain wet glycolide material. The particle size range of the wet glycolide material is 1–400 μm, the average particle size is 145 μm, and the total moisture content is 13%.

[0113] The wet glycolide material is dried in a fluidized bed dryer. The operating temperature of the fluidized bed dryer is 55℃, the operating pressure is 0.10MPaA, and the residence time is 2.0 hours. The operating temperature of the gas-solid separator is 55℃, and the operating pressure is 0.10MPaA. The outlet operating temperature of the nitrogen heater is 65℃, and the operating pressure is 0.15MPaA.

[0114] The dried glycolide product flowing out from the bottom of the fluidized bed dryer has an organic solvent residue of 0.13 wt%, a moisture residue of 0.04 wt%, and a glycolide purity of 99.81%.

[0115] This invention has been described through the specific embodiments described above. Those skilled in the art should understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Parts not described in detail in this specification are well-known to those skilled in the art. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from its scope; therefore, this invention is not limited to the specific embodiments disclosed.

Claims

1. A method for drying glycolide, characterized in that, The drying method includes: (a) Separating the glycolide solid-liquid mixture into small-particle glycolide wet material and large-particle glycolide wet material, wherein the total moisture content of the small-particle glycolide wet material is ≥20%, and the total moisture content of the large-particle glycolide wet material is ≥10%; the particle size range of glycolide in the small-particle glycolide wet material is 0.1–60 μm; and the particle size range of glycolide in the large-particle glycolide wet material is 40–1000 μm. (b) The small particle wet glycolide material is fed into a fluidized bed dryer, and hot nitrogen is introduced into the fluidized bed dryer to dry the small particle wet glycolide material. The dried glycolide flows out from the bottom of the fluidized bed dryer. (c) The large-particle wet glycolide material is fed into a vacuum belt dryer, which includes one or more drying belts, and the dried glycolide is sent out through the final drying belt. Step (a) includes the following steps: (1) The glycolide solid-liquid mixture is subjected to sedimentation to separate a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles; (2) The solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles are subjected to solid-liquid separation to obtain the wet material of small-particle glycolide and the wet material of large-particle glycolide. Alternatively, step (a) may include the following steps: (1) The glycolide solid-liquid mixture is filtered and intercepted to obtain the large-particle glycolide wet material and the solid-liquid mixture containing small particles; (2) Further solid-liquid separation is performed on the solid-liquid mixture containing small particles to obtain the wet material of small particle glycolide.

2. The drying method for glycolide as described in claim 1, characterized in that: The glycolide solid-liquid mixture is a solid-liquid mixture obtained by crystallization or recrystallization of glycolide; and / or, The average particle size of the small-particle wet glycolide material is 10–20 μm; and / or, The average particle size of the large-particle wet glycolide material is 150–300 μm.

3. The drying method for glycolide as described in claim 1, characterized in that, Step (b) has one or more of the following characteristics: The operating temperature of the fluidized dryer is 50–70°C. The operating pressure of the fluidized bed dryer is 0.10–0.30 MPa. The residence time of the material in the fluidized bed dryer is 0.05 to 3.0 hours.

4. The drying method for glycolide as described in claim 3, characterized in that, Step (b) also includes: The gas-solid mixture formed by water-containing nitrogen and entrained glycolide flows out from the top outlet of the fluidized dryer and enters the gas-solid separator; Water-containing nitrogen flows out from the top outlet of the gas-solid separator, and after drying and pressurization and heating by a heater, it returns to the fluidized dryer. The outlet temperature of the heater is 60-90°C, and the operating pressure is 0.15-0.35 MPaA. The glycolide flows out from the bottom outlet of the gas-solid separator and returns to the fluidized dryer for drying.

5. The drying method for glycolide as described in claim 1, characterized in that, Step (c) has one or more of the following characteristics: The operating temperature of the vacuum belt dryer is 20–80°C; The operating pressure of the vacuum belt dryer is ≤5.0 kPaA; The residence time of the material in the vacuum belt dryer is 0.2 to 2.0 hours; The fabric thickness of the large-particle glycolide wet material is 5-40 mm.

6. The drying method for glycolide as described in claim 5, characterized in that, The vacuum belt dryer includes at least two drying belts, and in at least the last two drying belts, the conveying speed of the next drying belt is 1.1 to 1.5 times that of the previous drying belt.

7. A drying system for glycolide, characterized in that, For implementing the method as described in claim 1, the drying system includes a separation combination device, a fluidized dryer, and a vacuum belt dryer; The separation and combination equipment is used to separate the glycolide solid-liquid mixture into small-particle glycolide wet material and large-particle glycolide wet material. The fluidized bed dryer is used to dry the small-particle glycolide wet material, and the vacuum belt dryer is used to dry the large-particle glycolide wet material.

8. The drying system for glycolide as described in claim 7, characterized in that, The separation combination equipment includes a sedimentation device, a first solid-liquid separation device, and a second solid-liquid separation device. The first solid-liquid separation device is connected to the upper outlet of the sedimentation device and the fluidized dryer, respectively. The second solid-liquid separation device is connected to the bottom outlet of the sedimentation device and the vacuum belt dryer, respectively. Alternatively, the separation combination device includes a filtration device and a solid-liquid separation device, wherein the solid outlet of the filtration device is connected to the vacuum belt dryer, the liquid outlet of the filtration device is connected to the solid-liquid separation device, and the solid-liquid separation device is connected to the fluidized dryer.

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