Drying method and system for glycolide

Abstract

The present invention relates to the field of organic matter drying, and provides a drying method and system for glycolide. The drying method comprises: (a) separating a glycolide solid-liquid mixture into a small-particle glycolide wet material and a 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; (b) feeding the small-particle glycolide wet material into a fluidized dryer, passing hot nitrogen into the fluidized dryer to dry the small-particle glycolide wet material, and the dried glycolide flowing out from the bottom of the fluidized dryer; and (c) feeding the large-particle glycolide wet material into a vacuum belt dryer comprising one or more stages of drying belts, and discharging the dried glycolide through a final-stage drying belt. The method of the present invention has a good drying effect and high product purity.

Description

Glycolide drying method and drying system Technical Field

[0001] The invention belongs to the field of organic matter drying, and particularly relates to a glycolide drying method and a drying system. Background Art

[0002] Polyglycolic acid, also known as polyglycolic acid (PGA), is a biodegradable aliphatic polymer that can be hydrolyzed in organisms (such as microorganisms) under the catalysis of enzymes, acids, or bases to ultimately form carbon dioxide and water. It is a biodegradable material with great development potential. Glycolide is a cyclic dimer of glycolic acid. Ring-opening polymerization of glycolide is a relatively mature method for preparing polyglycolic acid, which can produce polyglycolic acid with a higher relative molecular weight. In the process of synthesizing polyglycolic acid, the purity of the raw glycolide cannot be ignored. Optimization of the purification and drying processes of crude glycolide is extremely important.

[0003] The production of glycolide involves polycondensation of glycolic acid or glycolate esters to produce glycolic acid oligomers. These oligomers are then cleaved into rings to form glycolide. The crude glycolide produced in the ring-forming reactor contains impurities such as water, glycolic acid, and glycolic acid oligomers, in addition to glycolide. Purification and refining are essential steps in this process, with drying being a crucial step.

[0004] For example, after purifying impure glycolide through recrystallization, the glycolide must be dried to obtain high-purity glycolide. Another example is washing glycolide with a polar solvent and finally drying it to obtain high-purity glycolide. Glycolide is typically dried using airflow drying. Because glycolide is heat-sensitive, the drying process requires high airflow and a low upper temperature limit. This results in a long drying time to achieve product requirements, leading to lengthy drying processes and low efficiency. Summary of the Invention

[0005] The object of the present invention is to provide a method and system for drying glycolide with good drying effect and high product purity.

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

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

[0008] (b) feeding the small-particle glycolide wet material into a fluidized bed dryer, introducing hot nitrogen into the fluidized bed dryer to dry the small-particle glycolide wet material, and the dried glycolide flowing out from the bottom of the fluidized bed dryer;

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

[0010] In one or more embodiments, the glycolide solid-liquid mixture is a solid-liquid mixture of glycolide crystallized or recrystallized.

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

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

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

[0014] The operating temperature of the fluidized bed dryer is 50-70°C;

[0015] The operating pressure of the fluidized bed dryer is 0.10-0.30 MPaA;

[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 comprises:

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

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

[0020] Glycolide flows out from the bottom outlet of the gas-solid separator and returns to the fluidized bed 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 ≤5.0kPaA;

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

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

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

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

[0028] (1) sedimenting the glycolide solid-liquid mixture to separate into a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles;

[0029] (2) performing solid-liquid separation on the solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles, respectively, to obtain the small-particle glycolide wet material and the large-particle glycolide wet material.

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

[0031] (1) filtering and intercepting the glycolide solid-liquid mixture to obtain the large-particle glycolide wet material and the small-particle solid-liquid mixture;

[0032] (2) further performing solid-liquid separation on the solid-liquid mixture containing small particles to obtain the small particle glycolide wet material.

[0033] In a second aspect of the present invention, a glycolide drying system is provided for implementing the method described in the first aspect of the present invention, wherein the drying system comprises a separation assembly device, a fluidized bed dryer, and a vacuum belt dryer;

[0034] The separation 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 equipment includes a sedimentation equipment, a first solid-liquid separation equipment and a second solid-liquid separation equipment, wherein the first solid-liquid separation equipment is respectively connected to the upper outlet of the sedimentation equipment and the fluidized bed dryer, and the second solid-liquid separation equipment is respectively connected to the bottom outlet of the sedimentation equipment and the vacuum belt dryer.

[0036] In one or more embodiments, the separation combination equipment includes a filtering device and a solid-liquid separation device, the solid discharge port of the filtering device is connected to the vacuum belt dryer, the liquid discharge port of the filtering device is connected to the solid-liquid separation device, and the solid-liquid separation device is connected to the fluidized bed dryer.

[0037] The beneficial effects of the present invention include:

[0038] The solid-liquid mixture containing glycolide is processed into small-particle glycolide wet material and large-particle glycolide wet material, and the small-particle glycolide wet material is dried by fluidized bed drying. The small-particle glycolide wet material is evenly heated inside the fluidized bed dryer, and the large-particle glycolide wet material is dried by vacuum belt drying, thereby avoiding the outer layer of the large-particle glycolide wet material from being easily overheated. The present invention uses different drying methods to dry the obtained wet materials, so the drying effect is good and the product purity is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a schematic diagram of a glycolide drying system provided in an embodiment of the present invention;

[0040] FIG2 is a schematic structural diagram of a sedimentation device;

[0041] FIG3 is a schematic diagram of a glycolide drying system provided by another embodiment of the present invention;

[0042] FIG4 is a schematic structural diagram of a vacuum belt dryer according to some embodiments of the present invention.

[0043] Among them, 1-feed port; 2-drying chamber; 3-drying crawler; 4-discharge port; 5-vacuum extraction device; 6-heat exchange device; 7-liquid storage device; 8-vacuum belt dryer; 10-sedimentation equipment; 11-hollow conveying pipe; 12-upper outlet of the sedimentation equipment; 13-bottom outlet of the sedimentation equipment; 14-filtering equipment; 15-solid discharge port of the filter equipment; 16-liquid discharge port of the filter equipment; 21-first solid-liquid separation equipment; 21B-solid-liquid separation equipment; 22-second solid-liquid separation equipment; 30-fluidized bed dryer; 31-top outlet of the fluidized bed dryer; 40-gas-solid separator; 41-top outlet of the gas-solid separator; 42-bottom outlet of the gas-solid separator; 50-drying booster equipment; 60-heater. DETAILED DESCRIPTION

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

[0045] During the process of implementing the present invention, the inventors discovered that using fluidized drying to dry small-particle glycolide wet materials resulted in uniform heating within the fluidized dryer, resulting in a better drying effect, due to the small particle size and similar particle size differences between the particles. Using vacuum belt drying to dry large-particle glycolide wet materials, the operating temperature can be relatively low under a vacuum environment, and the outer temperature of the large-particle glycolide will not be too high, thus avoiding glycolide denaturation. Therefore, using a combined fluidized drying and vacuum belt drying method to dry glycolide wet materials of varying particle size ranges can effectively improve glycolide drying efficiency and ensure product quality.

[0046] If the entire wet glycolide material is dried using fluidized bed drying, the particle sizes of the glycolide particles vary significantly, and large glycolide particles are prone to local overheating or incomplete drying, affecting the quality of the final product. Small glycolide particles are easily carried out of the fluidized bed by the higher flow rate. If the entire wet glycolide material is dried using vacuum belt drying, small glycolide particles dry faster than large particles (especially under vacuum conditions). This makes small glycolide particles easily entrained by solvent vapor during the vacuum belt drying process, generating dust. This can affect the continuous operation of the equipment and require regular equipment cleaning.

[0047] The present invention provides a method for drying glycolide, which comprises:

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

[0049] (b) feeding the small-particle glycolide wet material into a fluidized bed dryer, introducing hot nitrogen into the fluidized bed dryer to dry the small-particle glycolide wet material, and the dried glycolide flowing out from the bottom of the fluidized bed dryer;

[0050] (c) The large-particle glycolide wet material is sent to a vacuum belt dryer, which includes one or more drying tracks. The dried glycolide is sent out through the final drying track.

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

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

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

[0054] (1) sedimenting the glycolide solid-liquid mixture to separate into a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles;

[0055] (2) performing solid-liquid separation on the solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles, respectively, to obtain a small-particle glycolide wet material and a large-particle glycolide wet material.

[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 by a solid-liquid separation method commonly used in the art, such as centrifugation, suction filtration, or filter pressing. 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 separation of the solid-liquid mixture containing small particles can be carried out by filter pressing to obtain a small-particle glycolide wet material, and the solid-liquid separation of the solid-liquid mixture containing large particles can be carried out by centrifugation to obtain a large-particle glycolide wet material.

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

[0058] (1) filtering and intercepting the glycolide solid-liquid mixture to obtain a glycolide wet material containing large particles and a solid-liquid mixture containing small particles;

[0059] (2) further performing solid-liquid separation on the solid-liquid mixture containing small particles to obtain a wet material of small-particle glycolide.

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

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

[0062] Furthermore, the gas-solid mixture formed by the hydrous nitrogen and the 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 hydrous 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 drying. The operating temperature of the gas-solid separator may be 50 to 70°C, for example, 55°C, 60°C, 65°C. The operating pressure of the gas-solid separator may be 0.10 to 0.30 MPaA, for example, 0.15 MPaA, 0.20 MPaA, 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 may 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 flowing out from the top outlet of the gas-solid separator is dried and pressurized and heated by the heater, then flows out of the heater and is mixed with fresh nitrogen and enters the fluidized bed dryer together to achieve gas recycling. The drying and pressurization treatment can be carried out by conventional methods in the art. For example, the water-containing nitrogen can be dried by passing through a drying tower, and then the dried nitrogen can be pressurized by passing through a gas booster pump. For another example, a booster dryer can be used to dry and pressurize the water-containing nitrogen. The outlet temperature of the heater can be 60 to 90°C, for example, 65°C, 70°C, 75°C, 80°C, or 85°C. The operating pressure of the heater can be 0.15 to 0.35 MPaA, for example, 0.20 MPaA, 0.25 MPaA, 0.30 MPaA, or 0.32 MPaA. As a preferred solution, the outlet temperature of the heater is 5-15° C. higher than the operating temperature of the fluidized bed dryer, and the operating pressure of the heater is 0.03-0.1 MPa higher than the operating pressure of the fluidized bed dryer.

[0064] In step (c), the operating temperature of the vacuum belt dryer may 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 may 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 may be 0.2-2.0 hours, for example, 0.5 hours, 1.0 hours, 1.5 hours, or 1.8 hours. The thickness of the large-particle glycolide wet material may be 5-40 mm, for example, 10 mm, 15 mm, 25 mm, 30 mm, or 35 mm. Preferably, the thickness of the large-particle glycolide wet material is 8-20 mm.

[0065] Furthermore, the vacuum belt dryer has at least two stages of drying tracks, such as three, four, five, or six stages of drying tracks. As a preferred solution, the vacuum belt dryer has at least two stages of drying tracks, and the lengths of the drying tracks at each stage are the same.

[0066] As a preferred embodiment, in at least the last two drying tracks, the conveying speed of the subsequent drying tracks is greater than that of the previous drying tracks. In the early stages of the drying process, the volume of the wet glycolide material gradually decreases as the drying process progresses. Given the same conveying speed on each drying track, the thickness of the wet glycolide material also gradually decreases. In the later stages of the drying process, the total moisture content of the wet glycolide material is already low, and as the drying process continues, the volume of the wet glycolide material changes little. By setting the conveying speed of the subsequent drying tracks to be greater than that of the previous drying tracks in at least the last two drying tracks, the thickness of the wet glycolide material in the final drying tracks decreases step by step, thereby improving the drying effect. Optionally, in at least the last two drying tracks, the conveying speed of the subsequent drying tracks can be 1.1 to 1.5 times, for example, 1.2, 1.3, or 1.4 times, of the conveying speed of the previous drying tracks.

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

[0068] Furthermore, step (c) also includes: mechanically crushing the dried glycolide sent out by the final drying crawler. During the vacuum drying process of the large-particle glycolide wet material, the solvent gradually evaporates. After evaporation, the glycolide dissolved in the solvent precipitates, causing the glycolide particles to easily stick together and form lumps. By mechanically crushing the dried glycolide, a product with a relatively uniform particle size can be obtained. It should be noted that the crushing treatment here is gentle crushing, which only destroys the adhesion between the crystals without destroying the crystal structure; illustratively, the dried glycolide can be mechanically crushed by a blade-type crushing method or a pendulum-type crushing method.

[0069] The dried glycolide obtained in step (b) and the dried glycolide obtained in step (c) are mixed to obtain a glycolide product. The residual organic solvent rate of the glycolide product may be ≤0.1%, for example, ≤0.09%, ≤0.05%, ≤0.03%, or ≤0.01%. Preferably, the residual organic solvent rate of the glycolide product is ≤0.037%. The residual moisture rate of the glycolide product may be ≤0.01%, for example, ≤0.007%, ≤0.004%, or ≤0.001%. Preferably, the residual moisture rate 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] The present invention also provides a glycolide drying system for implementing the drying method of the present invention. The drying system comprises a separation assembly, a fluidized bed dryer, and a vacuum belt dryer. The separation assembly 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.

[0071] In some embodiments, the drying system of glycolide provided by the present invention is shown in Figure 1. The separation combination equipment includes a sedimentation 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 sedimentation device and the fluidized bed dryer 30, respectively, and the second solid-liquid separation device 22 is connected to the bottom outlet 13 of the sedimentation device and the vacuum belt dryer 8, respectively. The sedimentation 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 a 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 a large-particle glycolide wet material.

[0072] The glycolide solid-liquid mixture can be separated by sedimentation in a sedimentation device 10 to obtain a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles. In some embodiments, the structural schematic diagram of the sedimentation device 10 is shown in Figure 2. The sedimentation device 10 includes a bottom outlet 13 located at its bottom and an upper outlet 12 located at its side. It also includes a hollow conveying pipe 11. The hollow conveying pipe 11 and the feed pipe are located on opposite sides of the sedimentation device 10; one end of the hollow conveying pipe 11 extends into the bottom of the sedimentation device 10, and the other end extends from the upper outlet. The upper outlet 12 of the sedimentation device is connected to the first solid-liquid separation device 21 through the hollow conveying pipe 11 to output the solid-liquid mixture containing small particles to the first solid-liquid separation device 21. The bottom outlet 13 of the sedimentation device is connected to the second solid-liquid separation device 22 to output the solid-liquid mixture containing large particles to the second solid-liquid separation device 22. Large particles settle quickly, and the solid-liquid mixture containing them flows out of the bottom outlet 13 of the settling device. Small particles settle slowly, and the solid-liquid mixture containing them flows out of the upper outlet 12 of the settling device through the hollow conveying tube 11. In practical applications, the particle size of the settled large particles can be controlled by adjusting the flow rate of the glycolide solid-liquid mixture and / or the diameter of the hollow conveying tube 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, suction filtration, or filter pressing. Considering the varying 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 decanter centrifuge, a suction filter, or a filter press.

[0074] In other embodiments, the glycolide drying system provided by the present invention is shown in Figure 3. The separation assembly device includes a filter device 14 and a solid-liquid separation device 21B. The solid discharge port 15 of the filter device is connected to the vacuum belt dryer 8, and the liquid discharge port 16 of the filter device is connected to the solid-liquid separation device 21B. The solid-liquid separation device 21B is connected to the fluidized bed dryer 30. The filter device 14 can separate the glycolide solid-liquid mixture into a large-particle glycolide wet material and a solid-liquid mixture containing small particles. The large-particle glycolide wet material is discharged from the solid discharge port 15 and enters the vacuum belt dryer 8 for drying. The solid-liquid mixture containing small particles is discharged from the liquid discharge port 16 and passes through the solid-liquid separation device 21B for further solid-liquid separation before entering the fluidized bed dryer 30 for drying.

[0075] Specifically, the filter device 14 includes a filter element. Large particles of material cannot pass through the filter element of the filter device 14 and are therefore intercepted on the surface of the filter element, accumulating to form large-particle glycolide wet material, which is discharged from the solid discharge port 15 of the filter device 14; the solid-liquid mixture containing small particles passes through the filter element and is discharged from the liquid discharge port 16 of the filter device 14 into the solid-liquid separation device 21B, where small-particle glycolide wet material is obtained after further solid-liquid separation in the solid-liquid separation device 21B.

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

[0077] The solid-liquid separation device 21B can perform solid-liquid separation by centrifugation, suction filtration or filter pressing. 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 the present application is a fluidized bed dryer.

[0079] In Figures 1 and 3, the drying system further includes a gas-solid separator 40 for separating the gas-solid mixture containing water 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 nitrogen and entrained glycolide flows out of the fluidized bed dryer 30 and enters the gas-solid separator 40. The bottom outlet 42 of the gas-solid separator is connected to the fluidized bed dryer 30, and the separated glycolide can be returned to the fluidized bed dryer 30 for drying, and 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 and pressurizing device 50. In practical applications, the drying and pressurizing device 50 may include independent drying and pressurizing devices, or it may be a drying and pressurizing device that integrates drying and pressurizing functions. Exemplary drying devices include, but are not limited to, drying towers for drying water from hydrous nitrogen; exemplary pressurizing devices include, but are not limited to, gas booster pumps.

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

[0082] In some embodiments, the portion of the drying system for drying the small-particle glycolide wet material includes a fluidized dryer 30 , a gas-solid separator 40 , a drying pressurizing device 50 , and a heater 60 , which are connected in sequence.

[0083] In some embodiments, the structure of a vacuum belt dryer 8 for drying large-particle glycolide wet material in a drying system is shown in FIG4 . The vacuum belt dryer 8 includes a drying chamber 2, a feed port 1 located at one end of the top of the drying chamber 2, a discharge port 4 located at one end of the bottom of the drying chamber 2, and one or more drying belts 3 arranged inside the drying chamber 2. A heating device for heating the drying belt 3 is provided below each drying belt 3 (not shown in FIG4 ). In some embodiments, the vacuum belt dryer 8 includes at least two drying belts 3, for example, the vacuum belt dryer 8 includes a three-stage drying belt, a four-stage drying belt, a five-stage drying belt, a six-stage drying belt, or a seven-stage drying belt. The conveying directions of the adjacent two-stage drying belts 3 are opposite, and the starting end of the next-stage drying belt 3 is located below the end of the previous-stage drying belt 3; the feed port 1 is toward the starting end of the first-stage drying belt, and the discharge port 4 is toward the end of the last-stage drying belt.

[0084] The drying chamber 2 is connected to the vacuum pump 5 and the liquid storage device 7 via a heat exchanger 6. Solvent vapor generated by the large-particle glycolide wet material heated in a vacuum environment is discharged from the drying chamber 2 and then enters the heat exchanger 6 for heat exchange. The liquid obtained by condensation of 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, an operating pressure of ≤5 kPaA during drying.

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

[0086] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

[0087] Measurement method

[0088] Determination of the total moisture content of glycolide wet material: Accurately weigh M0 of glycolide wet material, spread it flat, and place it in a 40°C oven under vacuum to dry. Dry the glycolide wet material under an absolute pressure of less than 1 kPaA for one hour. Then, remove it from the oven and place it in a desiccator. After cooling, weigh it and calculate it 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 rate and purity of glycolide after drying were determined by gas chromatography, and the residual water rate was determined by Karl Fischer moisture analyzer.

[0091] Example 1

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

[0093] The small-particle glycolide wet material enters the fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 55°C, the operating pressure is 0.10 MPaA, and the residence time is 0.5 hour. The operating temperature of the gas-solid separator is 55°C, the operating pressure is 0.10 MPaA. The nitrogen flowing out of the gas-solid separator enters the nitrogen heater after drying and pressurization treatment. The outlet temperature of the nitrogen heater is 65°C, and the operating pressure is 0.15 MPaA.

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

[0095] After mixing the dried glycolide flowing out from the bottom of the fluidized bed dryer and the dried glycolide sent out through the vacuum belt dryer, the resulting glycolide product has an organic solvent residual rate of 0.037wt%, a moisture residual rate of 0.006wt%, and a glycolide purity of 99.93%.

[0096] Example 2

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

[0098] The small-particle glycolide wet material enters the fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 65°C, the operating pressure is 0.25 MPaA, and the residence time is 0.05 hour. The operating temperature of the gas-solid separator is 65°C, and the operating pressure is 0.25 MPaA. The nitrogen flowing out of the gas-solid separator enters the nitrogen heater after drying and pressurization treatment. The outlet temperature of the nitrogen heater is 75°C, and the operating pressure is 0.30 MPaA.

[0099] The large-particle glycolide wet material enters the vacuum belt dryer for drying. The vacuum belt dryer is equipped with four levels of drying crawlers, and the length of each drying crawler is 10m. The operating temperature of the vacuum belt dryer is 60℃, the operating pressure is 0.10kPaA, the cloth thickness of the large-particle glycolide wet material is 10mm, the conveying speed of each level of drying crawlers is the same, and the total residence time is 1.0 hour.

[0100] After mixing the dried glycolide flowing out from the bottom of the fluidized bed dryer and the dried glycolide sent out through the vacuum belt dryer, the resulting glycolide product has an organic solvent residual rate of 0.028wt%, a moisture residual rate of 0.009wt%, and a glycolide purity of 99.92%.

[0101] Example 3

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

[0103] The small-particle glycolide wet material enters the fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 62°C, the operating pressure is 0.27 MPaA, and the residence time is 1.0 hour. The operating temperature of the gas-solid separator is 62°C, the operating pressure is 0.27 MPaA. The nitrogen flowing out of the gas-solid separator enters the nitrogen heater after drying and pressurization treatment. The outlet temperature of the nitrogen heater is 72°C, and the operating pressure is 0.32 MPaA.

[0104] The large-particle glycolide wet material enters the vacuum belt dryer for drying. The vacuum belt dryer is equipped with four stages of drying crawlers, and the length of each drying crawler is 10m. The operating temperature of the vacuum belt dryer is 50℃, the operating pressure is 0.10kPaA, the cloth thickness of the large-particle glycolide wet material is 15mm, the conveying speed of the first three stages of drying crawlers is the same, the conveying speed of the fourth stage of drying crawlers is 1.5 times that of the first three stages of drying crawlers, and the total residence time is 1.1 hours.

[0105] After mixing the dried glycolide flowing out from the bottom of the fluidized bed dryer and the dried glycolide sent out through the vacuum belt dryer, the resulting glycolide product has an organic solvent residual rate of 0.020wt%, a moisture residual rate of 0.006wt%, and a glycolide purity of 99.93%.

[0106] Example 4

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

[0108] The small-particle glycolide wet material enters the fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 60°C, the operating pressure is 0.20 MPaA, and the residence time is 2.0 hours. The operating temperature of the gas-solid separator is 60°C, the operating pressure is 0.20 MPaA. The nitrogen flowing out of the gas-solid separator enters the nitrogen heater after drying and pressurization treatment. The outlet temperature of the nitrogen heater is 70°C, and the operating pressure is 0.25 MPaA.

[0109] The large-particle glycolide wet material enters the vacuum belt dryer for drying. The vacuum belt dryer is equipped with four levels of drying crawlers, and the length of each drying crawler is 10m. The operating temperature of the vacuum belt dryer is 55℃, the operating pressure is 0.50kPaA, the cloth thickness of the large-particle glycolide wet material is 20mm, the conveying speed of each level of drying crawlers is the same, and the total residence time is 1.5 hours.

[0110] After mixing the dried glycolide flowing out from the bottom of the fluidized bed dryer and the dried glycolide sent out through the vacuum belt dryer, the resulting glycolide product has an organic solvent residual rate of 0.023wt%, a moisture residual rate of 0.007wt%, and a glycolide purity of 99.90%.

[0111] Comparative Example 1

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

[0113] The glycolide wet material enters the fluidized bed dryer for drying. The operating temperature of the fluidized bed dryer is 55°C, the operating pressure is 0.10 MPaA, and the residence time is 2.0 hours; the operating temperature of the gas-solid separator is 55°C, the operating pressure is 0.10 MPaA; the outlet operating temperature of the nitrogen heater is 65°C, and the operating pressure is 0.15 MPaA.

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

[0115] The present invention is described by the above-mentioned specific embodiments. It should be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the present invention without departing from the scope of the present invention. Parts not described in detail in the present specification are well known to those skilled in the art. In addition, various modifications may be made to the present invention for specific situations or circumstances without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

Claims

1. A method for drying glycolide, characterized in that: The drying method comprises: (a) separating the glycolide solid-liquid mixture into small-particle glycolide wet material and large-particle glycolide wet material; the glycolide particle size range of the small-particle glycolide wet material is 0.1 to 60 μm; the glycolide particle size range of the large-particle glycolide wet material is 40 to 1000 μm; (b) feeding the small-particle glycolide wet material into a fluidized dryer, introducing hot nitrogen into the fluidized dryer to dry the small-particle glycolide wet material, and the dried glycolide flows out from the bottom of the fluidized dryer; (c) sending the large-particle glycolide wet material into a vacuum belt dryer, wherein the vacuum belt dryer includes one or more drying tracks, and the dried glycolide is sent out through the final drying track.

2. The method for drying glycolide according to claim 1, characterized in that: The glycolide solid-liquid mixture is a solid-liquid mixture of glycolide crystallized or recrystallized; The average particle size of the small-particle glycolide wet material is 10-20 μm, and the total moisture content is ≥20%; and / or the average particle size of the large-particle glycolide wet material is 150-300 μm, and the total moisture content is ≥10%.

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

4. The method for drying glycolide according to claim 3, characterized in that: Step (b) further comprises: The gas-solid mixture formed by the water-containing nitrogen and the entrained glycolide flows out from the top outlet of the fluidized dryer and enters the gas-solid separator; The water-containing nitrogen flows out from the top outlet of the gas-solid separator, and returns to the fluidized dryer after being dried, pressurized and heated by a heater. The outlet temperature of the heater is 60-90° C., and the operating pressure is 0.15-0.35 MPaA. Glycolide flows out from the bottom outlet of the gas-solid separator and returns to the fluidized dryer for drying.

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

6. The method for drying glycolide according to claim 5, characterized in that: The vacuum belt dryer comprises at least two stages of drying tracks, and at least in the last two stages of drying tracks, the conveying speed of the next stage of drying tracks is 1.1 to 1.5 times the conveying speed of the previous stage of drying tracks.

7. The method for drying glycolide according to any one of claims 1 to 6, characterized in that: Step (a) comprises the following steps: (1) sedimenting the glycolide solid-liquid mixture to separate into a solid-liquid mixture containing small particles and a solid-liquid mixture containing large particles; (2) performing solid-liquid separation on the solid-liquid mixture containing small particles and the solid-liquid mixture containing large particles respectively to obtain the small particle glycolide wet material and the large particle glycolide wet material.

8. The method for drying glycolide according to any one of claims 1 to 6, characterized in that: Step (a) comprises the following steps: (1) filtering and intercepting the glycolide solid-liquid mixture to obtain the large-particle glycolide wet material and the small-particle solid-liquid mixture; (2) further subjecting the solid-liquid mixture containing small particles to solid-liquid separation to obtain the small particle glycolide wet material.

9. A drying system for glycolide, characterized in that: For implementing the method according to claim 1, the drying system comprises a separation assembly device, a fluidized bed dryer and a vacuum belt dryer; The separation 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.

10. The glycolide drying system according to claim 9, characterized in that: The separation assembly device comprises a sedimentation device, a first solid-liquid separation device and a second solid-liquid separation device, wherein the first solid-liquid separation device is respectively connected to the upper outlet of the sedimentation device and the fluidized dryer, and the second solid-liquid separation device is respectively connected to the bottom outlet of the sedimentation device and the vacuum belt dryer; Alternatively, the separation combination equipment includes a filtering device and a solid-liquid separation device, the solid discharge port of the filtering device is connected to the vacuum belt dryer, the liquid discharge port of the filtering device is connected to the solid-liquid separation device, and the solid-liquid separation device is connected to the fluidized bed dryer.

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