Refining method of glycolide and glycolide obtained by refining method

Abstract

The invention provides a refining method of glycolide and glycolide obtained by the refining method. The glycolide refining method comprises a step of forming a glycolide material flow into a particle mixture, and a step of removing particles with a diameter less than or equal to 100 microns, and / or removing particles with a diameter greater than or equal to 600 microns, preferably, the method comprises the step of removing particles with the diameter smaller than or equal to 90 micrometers and / or removing particles with the diameter larger than or equal to 700 micrometers. According to the method, oligomer impurities in the glycolide can be quickly and efficiently removed, the purified oligomer impurities are low in content, the purity of the glycolide is high, the operation is simple, and the method has a relatively high industrial application value.

Description

Technical Field

[0001] The present invention relates to the technical field of glycolide, and further relates to a method for refining glycolide and the obtained glycolide. Background Art

[0002] Polyglycolic acid is formed by ring-opening polymerization of cyclic ester monomer glycolide under the action of a catalyst. It has good biocompatibility and biodegradability, and can be prepared into materials of different shapes, such as fibers, membranes, microspheres, sponges, etc. PGA used for medical sutures, scaffolds, dressings, and fracturing balls needs to use polymerization-grade glycolide for polymerization. Glycolide needs to have high purity and low terminal carboxyl content to meet the requirements of preparing spinning-grade or injection-molding-grade PGA after polymerization. Usually, the terminal carboxyl content should be at least less than 10 μmol / g.

[0003] As a polymerization monomer, the particle size uniformity of glycolide is an extremely important factor, which directly affects the quality, performance, and controllability of the polymerization product. Polymerization monomers with uneven particle sizes may cause the following problems: First, uneven particle distribution may affect the physical and chemical properties of the product, thereby reducing the consistency and stability of the product, which will have an irreversible impact on the final performance and quality of the product, especially in the production of highly refined polymerization monomers; Second, the non-uniformity of the polymerization monomer may also affect production efficiency. Over-sized or under-sized particles may cause equipment blockage or uneven reactions, thereby increasing maintenance costs and reducing production efficiency; Most importantly, when there are abnormal-shaped particles in the polymerization monomer, these abnormal-shaped particles may contain more impurities, which will have an adverse impact on the application of the polymerization monomer. For example, the impurities may interfere with the polymerization process, resulting in incomplete polymerization or reduced product performance.

[0004] Therefore, paying attention to the particle size uniformity of the polymerization monomer is crucial for ensuring product quality, production efficiency, and safety. Taking appropriate means to remove abnormal-shaped particles, especially over-sized or under-sized particles, is crucial for producing high-quality and high-performance polymerization monomers. This not only helps to improve product quality, but also helps to reduce production costs, improve the safety and maintainability of the factory.

[0005] The prior art usually only performs solid-liquid separation on the solid-liquid mixture of glycolide and organic solvent, and still needs to study the physical properties such as the particle size distribution of the particles in the solid-liquid mixture, and develop more processing methods suitable for the solid-liquid mixture in this field to further improve the purity of the recovered solid phase. In addition, the prior art usually regards all the solid-phase glycolide recovered by solid-liquid separation as the product, and uses the dried solid phase for ring-opening polymerization without distinction. It is still necessary to study the formation mechanism, physical and chemical properties, etc. of the abnormal-shaped particles in the glycolide product, and develop more particle processing methods to further improve the purity of glycolide. Summary of the Invention

[0006] To solve the technical problems existing in the prior art, the present invention provides a method for refining glycolide and the obtained glycolide.

[0007] The present invention provides a novel method for removing oligomer impurities from polymer monomers, which is simple to operate and has great industrial application value.

[0008] Through experimental analysis, the present invention has a new understanding of the composition of glycolide particles, that is, glycolide particles are composed of particles with different particle sizes, and the particles with smaller particle sizes contain more oligomer impurities and lower purity. Therefore, by utilizing the particle size difference of glycolide particles, when performing solid-liquid separation on the glycolide-solvent mixture, the glycolide particles are selectively collected, and the particles with smaller particle sizes are removed, thereby improving the purity of glycolide.

[0009] In addition, through experimental analysis, the present invention also realizes that if the small particles in the glycolide-organic solvent solid-liquid mixture are allowed to mix into the recovered solid phase after solid-liquid separation, after the recovered solid phase is dried, the above small particles are extremely easy to adhere and agglomerate into larger particles, for example, particles with a diameter greater than or equal to 600 microns or 700 microns.

[0010] Regarding the formation mechanism of small particles in the glycolide-organic solvent solid-liquid mixture and the mechanism of their transformation into large particles during drying, the inventors have the following inferences: (1) Crude glycolide comes from the upstream ring-forming unit. During the purification process, phase change means are often used to obtain glycolide in a particulate state. During the growth of glycolide particles, the phenomenon that the above oligomer impurities interfere with crystal growth is widespread; (2) The small particles in the solid-liquid mixture are essentially a combination of glycolide microcrystals and oligomer impurities, and, from a chemical composition perspective, glycolide is the main component; (3) During the process of free glycolide molecules combining and arranging with each other to form crystal particles, oligomer impurities will be inserted into the glycolide crystals, causing the impurities to be wrapped in the crystals and affecting the purity of the crystals; (4) Oligomer impurities are also enriched on the surface of the formed glycolide microcrystals, acting as a surfactant between the organic solvent and the microcrystals, fully occupying the surface sites where free glycolide molecules bind to the microcrystals, resulting in the inability of glycolide microcrystals to further grow, usually having a diameter of no more than 100 microns or 90 microns; (5) The oligomer molecules occupying the surface of the glycolide microcrystals change the surface properties of the particles, endowing the small particles with stickiness; when the small particles are in the flow field generated by the stirrer, the small particles can be dispersed by the organic solvent, but when the organic solvent is basically completely removed during the solid-liquid separation and drying processes, the small particles agglomerate to form large particles, usually having a diameter exceeding 600 microns or 700 microns.

[0011] In the prior art, when performing solid-liquid separation on a glycolide-organic solvent solid-liquid mixture, oligomer impurities are mixed into the recovered solid phase, thereby reducing the purification effect of glycolide. In the present invention, the solid-liquid mixture formed by processes such as recrystallization and solvent washing is fully mixed and then dynamically filtered. After removing particles with small particle sizes, the solid phase is recovered through solid-liquid separation, which can quickly and efficiently remove oligomer impurities in glycolide, and has the advantages of low oligomer impurity content and high glycolide purity after purification.

[0012] In the prior art, the solid phase recovered from a glycolide-organic solvent solid-liquid mixture through solid-liquid separation is mixed with particles having a relatively high oligomer content. After the recovered solid phase is dried, the above-mentioned impurity-containing particles continue to be mixed into the dried glycolide product, reducing the ring-opening polymerization effect of glycolide. In the present invention, the dried glycolide particles are screened, pneumatically classified, or vibrationally classified to remove particles with large particle sizes, which can quickly and efficiently remove oligomer impurities in glycolide, and also has the advantages of low oligomer impurity content and high glycolide purity after purification.

[0013] One of the objectives of the present invention is to provide a method for refining glycolide, including the step of forming a particle mixture from a glycolide stream, and the step of removing particles with a diameter less than or equal to 100 microns, and / or removing particles with a diameter greater than or equal to 600 microns; preferably, including the step of removing particles with a diameter less than or equal to 90 microns, and / or removing particles with a diameter greater than or equal to 700 microns.

[0014] The raw material of the glycolide stream can be crude glycolide or refined glycolide. The refined glycolide can further improve its purity by removing a small part of the particles therein.

[0015] The method of removing small-sized particles in the particle mixture and then collecting the remaining solid phase, removing large-sized particles in the particle mixture and then collecting the remaining solid phase, or first removing small-sized particles in the particle mixture and then removing large-sized particles in the particle mixture and then collecting the remaining solid phase can all obtain refined glycolide with a low content of glycolic acid oligomer impurities.

[0016] In a preferred embodiment of the present invention,

[0017] The particle mixture is a solid-liquid mixture or a dried particle mixture; preferably,

[0018] Remove particles with a diameter less than or equal to 100 microns in the solid-liquid mixture, and more preferably remove particles with a diameter less than or equal to 90 microns;

[0019] Remove particles with a diameter greater than or equal to 600 microns in the dried particle mixture, and more preferably remove particles with a diameter greater than or equal to 700 microns;

[0020] After removing the said particles, the remaining solid-phase particles are collected to obtain purified glycolide.

[0021] In a preferred embodiment of the present invention,

[0022] The proportion of the removed particles in the total solid weight of the particle mixture is less than or equal to 10% by weight, preferably 1-10% by weight;

[0023] The content of oligomer impurities in the removed particles is greater than or equal to 1% by weight, preferably greater than or equal to 2% by weight.

[0024] The removed particles include at least one of the following particles: particles with a diameter less than or equal to 100 μm or 90 μm, particles with a diameter greater than or equal to 600 μm or 700 μm; it is also possible to include both types of particles at the same time.

[0025] In a preferred embodiment of the present invention,

[0026] The solid-liquid mixture contains a solid phase and a liquid phase; preferably,

[0027] The mass fraction of the solid phase is less than or equal to 50%, preferably less than or equal to 40%, more preferably 5-40%, and most preferably 10-40%; the purpose of the mass fraction of the solid phase being less than or equal to 50% is to increase the average distance between particles in the mixture, making it easier for the solid-liquid mixture to be mixed, slurried and made uniform under the action of methods such as stirring, oscillation, gas fluidization, and rotating barrels;

[0028] The median diameter of the solid phase is less than or equal to 600 μm, preferably less than or equal to 500 μm; the purpose of the median diameter of the solid phase being less than or equal to 600 μm is that the particles are easy to suspend and not easy to settle under the action of the flow field, and are easy to move frequently to the surface of the filter medium during dynamic filtration, which is beneficial for small particles to pass through the filter medium and separate from the remaining solid phase;

[0029] The liquid phase is a saturated organic solvent solution of glycolide;

[0030] The solid phase is solid particles containing glycolide;

[0031] The density deviation between any parts of the solid-liquid mixture does not exceed 30%, preferably does not exceed 20%, and more preferably does not exceed 15%; the density deviation is obtained by sampling and testing the density of any part of the solid-liquid mixture and calculating the deviation between the densities.

[0032] In a preferred embodiment of the present invention,

[0033] The solid-liquid mixture is obtained by adding molten glycolide stream to an organic solvent in at least one of the ways of dropping, injecting, spraying, showering, and atomizing; preferably, the molten glycolide stream is an unpurified molten glycolide stream and / or a purified molten glycolide stream from a glycolide synthesis unit; and / or, the mass content of glycolide in the molten glycolide stream is 85.0-99.9%; in the above sources, the gaseous crude glycolide generated by the depolymerization reaction becomes liquid after heat exchange and condensation, stays for a period of time or is immediately added to the organic solvent in at least one of the ways of dropping, injecting, spraying, showering, and atomizing. The liquid crude glycolide quickly solidifies into solid-phase particles when cooled, and combines with the organic solvent to form a solid-liquid mixture. The purified solid-phase glycolide can also be melted to form a molten state after heating, or the liquid glycolide generated by processes such as melt crystallization is added to the organic solvent in at least one of the above ways, and a solid-liquid mixture can also be generated.

[0034] The solid-liquid mixture is obtained by adding a solid-phase glycolide stream to an organic solvent; preferably, the solid-phase glycolide stream is obtained by condensing and solidifying a molten glycolide stream; in the above sources, the gaseous crude glycolide generated by the depolymerization reaction becomes solid after heat exchange and condensation, and is added to the organic solvent after being processed by means of controlling the particle size such as crushing and grinding, and is mixed with the organic solvent to form a solid-liquid mixture.

[0035] The solid-liquid mixture is obtained by mixing any material stream containing solid-phase glycolide with an organic solvent; preferably, the solid-phase glycolide is a wet filter cake or purified glycolide after drying; in the above sources, the solid phase is recovered after the solid-liquid separation operation of the glycolide-organic solvent solid-liquid mixture generated in any previous process, and more organic solvent is added to the recovered solid phase to form a new solid-liquid mixture. The previous processes include but are not limited to washing, extraction, and crystallization, and a certain amount of the organic solvent from the previous process usually remains in the solid phase recovered after the solid-liquid separation operation. The proportion of the organic solvent in the recovered solid phase (including the solvent) usually does not exceed 50% by weight. The above recovered solid phase can also be dried to any extent, and a trace amount of the organic solvent from the previous process still remains in the dried glycolide, usually greater than or equal to 20 ppm.

[0036] The solid-liquid mixture is obtained after the glycolide solution phase undergoes cooling crystallization or evaporation crystallization operations; preferably, the glycolide solution phase is a solution formed by dissolving a molten or solid-phase glycolide stream in an organic solvent; in the above sources, a saturated or unsaturated glycolide solution is formed by dissolving molten or solid-phase crude glycolide in an organic solvent. Optionally, the solution is filtered to remove insoluble substances with any filtration accuracy, and then the solution is crystallized by at least one of the ways of cooling, evaporation, and adding an anti-solvent. The precipitated particles and the solution form a solid-liquid mixture.

[0037] In a preferred embodiment of the present invention,

[0038] The liquid phase of the solid-liquid mixture is a saturated organic solvent solution of glycolide, that is, a part of glycolide is dissolved in the organic solvent; the organic solvent is at least one of acetone, ethyl acetate, ethylene glycol dimethyl ether, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, n-hexane, cyclohexane, pentane, petroleum ether.

[0039] In a preferred embodiment of the present invention,

[0040] The dry granular mixture is obtained by solid-liquid separation of the solid-liquid mixture and drying the recovered solid phase; preferably,

[0041] The organic solvent in the dry granular mixture is the residual organic solvent after drying, usually with a low content. The mass fraction of the organic solvent in the dry granular mixture is less than or equal to 0.5%, preferably less than or equal to 0.2%, and more preferably less than or equal to 0.1%;

[0042] The median diameter of the solid phase of the dry granular mixture is less than or equal to 600 microns, preferably less than or equal to 500 microns;

[0043] The solid-liquid separation is carried out by centrifugation or filtration.

[0044] In a preferred embodiment of the present invention,

[0045] The method for removing particles with a diameter less than or equal to 100 microns or 90 microns is dynamic filtration;

[0046] During dynamic filtration, usually smaller particles can pass through the pores of the filter medium, while larger particles are retained on the filter medium due to the pore size limitation. A filter medium with an appropriate pore size is usually selected to ensure that small particles can pass through. For example, a filter medium with a pore size in the range of 50-100 microns is selected to separate all or part of the particles with a diameter of 100 microns or less than 90 microns. The equipment used for dynamic filtration is a dynamic filter driven by pressure, vacuum or centrifugal force, and pressure, vacuum or centrifugal force can all increase the rate of small particles passing through the filter medium.

[0047] The method for collecting the remaining solid phase particles is centrifugation or filtration; then, the recovered solid phase is dried by a method of the prior art. Convective drying under a thermally inert gas or heat conduction drying under vacuum can be used again, such as vacuum drying at 40-80 °C for 2-10 hours.

[0048] The method for removing particles with a diameter greater than or equal to 600 microns or 700 microns is at least one of screening, air classification, and vibration classification.

[0049] In actual production, it is very difficult for the shape of the glycolide obtained to reach the standard sphere, and it is usually an irregular non-sphere. For example, the diameter measured along a certain direction is significantly higher than that in other directions. When using a laser particle size analyzer (based on Mie scattering theory) for testing, the particles are equivalent to standard spheres with the same volume, and the diameter of the standard sphere is fed back as the test result. For the particles removed in the present invention, the D10 particle size (the volume content of particles smaller than this particle size accounts for 10% of all particles) and the D90 particle size (the volume content of particles smaller than this particle size accounts for 90% of all particles) are measured using a laser particle size analyzer. Among them, D90 is applicable to the case of removing small particle size particles. D90 is less than or equal to 90 microns, indicating that at least 90% of the volume of the removed particles has an equivalent diameter not exceeding 90 microns; it is allowed that some particles have an equivalent diameter exceeding 90 microns due to irregular shapes and other reasons. Similarly, D10 is applicable to the case of removing large particle size particles. D10 is greater than or equal to 700 microns, indicating that at least 90% of the volume of the removed particles has an equivalent diameter exceeding 700 microns.

[0050] For the removal of small and large particle size particles (collectively referred to as irregular particles), there is actually a problem of separation accuracy. The separation method provided in this case does not pursue 100% separation accuracy, which is very difficult to achieve. As long as the vast majority of the removed particles meet the expectations, it is sufficient to ensure good invention effects.

[0051] Due to the irregular characteristics of the glycolide particles, a certain floating range can be allowed for the set pore size during dynamic filtration or screening. Taking the pore size of the dynamic filtration medium as 50 - 100 microns as an example, when the pore size is set to be relatively small, such as 50 - 90 microns, the D90 particle size of the small particle size particles is obviously less than or equal to 90 microns; when the pore size is set to be relatively large, such as 100 microns, although a small number of particles with a size of 90 - 100 microns and extremely few particles with a size above 100 microns are removed by dynamic filtration, it can still meet the requirement that the D90 particle size is less than or equal to 90 microns.

[0052] The screening mentioned above refers to a method of separating particles of different sizes through a filter screen or sieve. The large particles are left on the sieve, while the small particles fall through the sieve holes and are collected; usually, a sieve with an appropriate pore size is selected. For example, a sieve with a pore size in the range of 600 - 1000 microns is selected, so that all or part of the particles with a diameter of 600 microns or 700 microns or more are separated.

[0053] The air classification mentioned above refers to separating the particles in a particle mixture according to their sizes through air flow. In the classifier, the air flow will carry away the smaller particles and recover them through further gas-solid separation, while the larger particles cannot be carried away, thus achieving separation.

[0054] The vibration classification refers to placing a mixture of particles on a vibrating platform or device, and using the differences in particle size and density to enable smaller particles to move faster during vibration, thereby being separated and collected.

[0055] In a preferred embodiment of the present invention,

[0056] The device used for the dynamic filtration is a dynamic filter driven by pressure, vacuum or centrifugal force;

[0057] The dynamic filter used for the dynamic filtration contains a filtering medium with pore sizes in the range of 50 to 100 microns, preferably a filtering medium with pore sizes in the range of 70 to 90 microns;

[0058] In the dynamic filtration, the particles passing through the filtering medium are removed, and the particles not passing through the filtering medium are retained and collected after purification. Within the said pore size range, the pore size distribution of the filtering medium is preferably a narrow distribution. For example, all the pore sizes of the filtering medium are 75 microns; the pore sizes can also be a wide distribution. For example, the pore size range is 70 to 90 microns.

[0059] The device used for the screening is at least one of a vibrating screen, a rotary screen, and a circular screen;

[0060] The screening device contains a filtering medium with pore sizes in the range of 600 to 1000 microns, preferably a filtering medium with pore sizes in the range of 700 to 850 microns;

[0061] In the screening, the particles passing through the filtering medium are retained and collected after purification, and the particles not passing through the filtering medium are removed. Within the said pore size range, the pore size distribution of the filtering medium is preferably a narrow distribution. For example, all the pore sizes of the filtering medium are 800 microns; the pore sizes can also be a wide distribution. For example, the pore size range is 700 to 850 microns.

[0062] The device used for the air classification is an air classifier;

[0063] The device used for the vibration classification is a vibration classifier.

[0064] The preferred specific technical solution of the present invention is:

[0065] It includes subjecting the solid-liquid mixture formed by the glycolide stream to dynamic filtration to remove particles with diameters less than or equal to 100 microns or 90 microns in the solid-liquid mixture; collecting the remaining solid-phase particles by centrifugation or filtration to obtain purified glycolide; or,

[0066] It includes solid-liquid separation of the solid-liquid mixture formed from the glycolide feed stream, drying the recovered solid phase, and then removing particles with a diameter greater than or equal to 600 microns or 700 microns in the dried particle mixture by at least one of screening, air classification, and vibration classification to obtain purified glycolide; or,

[0067] It includes subjecting the solid-liquid mixture formed from the glycolide feed stream to dynamic filtration to remove particles with a diameter less than or equal to 100 microns or 90 microns in the solid-liquid mixture; collecting the remaining solid phase particles by centrifugation or filtration, and then removing particles with a diameter greater than or equal to 600 microns or 700 microns in the dried particle mixture by at least one of screening, air classification, and vibration classification to obtain purified glycolide.

[0068] The second object of the present invention is to provide a glycolide obtained by the above method.

[0069] Compared with the prior art, the beneficial effects of the present invention are:

[0070] In the present invention, the glycolide particles in the solid-liquid mixture are composed of particles with different particle sizes, and the particles with smaller particle sizes contain more oligomer impurities and lower purity. Therefore, by utilizing the particle size difference of the glycolide particles, during the solid-liquid separation operation of the glycolide-solvent mixture, the glycolide particles are selectively collected, and the particles with smaller particle sizes are removed, thereby improving the purity of glycolide. By fully mixing the solid-liquid mixture formed by processes such as recrystallization and solvent washing and then performing dynamic filtration, removing the particles with smaller particle sizes and then recovering the solid phase through solid-liquid separation, the oligomer impurities in glycolide can be removed quickly and efficiently.

[0071] In the present invention, the small particles in the glycolide-organic solvent solid-liquid mixture are allowed to mix into the recovered solid phase after solid-liquid separation. After the recovered solid phase is dried, the above small particles are extremely easy to adhere and agglomerate into particles with larger particle sizes. By removing particles with a diameter greater than or equal to 600 microns or 700 microns, the purity of glycolide can also be improved. By screening, air classifying, or vibration classifying the dried glycolide particles to remove the particles with larger particle sizes, the oligomer impurities in glycolide can be removed quickly and efficiently.

[0072] The present invention provides a novel method for removing oligomer impurities in polymerization monomers. After purification, the glycolide has a low content of oligomer impurities and a high purity of glycolide, with simple operation and great industrial application value. Detailed embodiments

[0073] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0074] The raw materials used in the embodiments are all conventional commercially available raw materials.

[0075] The method for testing the average particle size of glycolide crystals in the present invention is as follows:

[0076] Use a Malvern Mastersizer 3000 laser particle size analyzer to measure the average particle size (median diameter, i.e., the particle size at which the cumulative volume distribution of particles is 50%), D10 particle size (the particle volume content less than this particle size accounts for 10% of all particles), and D90 particle size (the particle volume content less than this particle size accounts for 90% of all particles) of glycolide. Isopropanol is used as the dispersion medium.

[0077] The method for measuring the acid content of crude glycolide and glycolide in the present invention is as follows:

[0078] Use an acid-base titration method to measure the acid content in crude glycolide. The specific operation is as follows: Dissolve the crude glycolide sample in about 30 mL of dry dimethyl sulfoxide. After it is dissolved, add a few drops of bromophenol blue indicator solution, and the solution turns yellow. Titrate it with a dilute solution of sodium hydroxide in benzyl alcohol with a known concentration. The end point is when the solution color changes from yellow to green. Calculate the content of terminal carboxyl groups (unit: μmol) in glycolide by calculating the volume of sodium hydroxide solution used at the end point of the titration, and divide it by the mass of the crude glycolide sample to obtain the acid content of crude glycolide (unit: μmol / g).

[0079] The method for measuring the purity of glycolide in the present invention is as follows:

[0080] The purity of glycolide is determined by gas chromatography (GC). Dissolve 200 mg of the glycolide sample to be measured and 40 mg of p-chlorobenzophenone as the internal standard substance in 10 ml of acetone. Inject 2 μl of the dissolved solution into the gas chromatograph to measure the amount of glycolide; use a standard calibration curve prepared in advance with glycolide standard samples (at least 5 points between 160 and 200 mg) and the internal standard substance (40 mg), that is, p-chlorobenzophenone, to obtain the purity of glycolide. The measuring device is Agilent 7890B, the chromatographic column is a capillary column HP-5 (30 m × 0.32 mm, 0.25 μm), the column temperature is 280 °C, the injection port temperature is 150 °C, and the detector is FID.

[0081] The method for measuring the content of glycolic acid oligomers in crude glycolide and glycolide in the present invention is as follows:

[0082] Dissolve 5 g of crude glycolide or purified glycolide sample in 50 g of dry ethyl acetate at a dissolution temperature of 25°C. After the glycolide is completely dissolved, centrifuge the solution at a high speed (centrifugation speed: 10,000 rpm, centrifugation duration: 10 min) to allow the insoluble matter in the solution to fully deposit. After discarding the upper clear liquid after centrifugation, add 20 g of dry ethyl acetate to the sediment and mix well at a mixing temperature of 25°C to dissolve the remaining glycolide. Centrifuge at a high speed again and discard the upper clear liquid after centrifugation. Weigh the sediment after vacuum drying (at 40°C for 4 hours), and divide it by the mass of the crude glycolide or glycolide sample to obtain the content of glycolic acid oligomers.

[0083]

Example 1

[0084] Preparation of solid-liquid mixture:

[0085] Add 400.0 g of glycolide (commercially available, white powder, residual ethyl acetate content: 167 ppm) and 800.0 g of anhydrous isopropanol (dehydrated with 4A molecular sieve to a water content of 10 ppm) to a 2 L glass reactor to prepare a solid-liquid mixture with a solid mass fraction of 33.0%. The median diameter of the solid phase in the solid-liquid mixture is 460 microns. Transfer the solid-liquid mixture to a 4 L flat-plate two-in-one filter (stainless steel filter mesh, pore size: 90 microns).

[0086] Dynamic filtration under pressure:

[0087] Control the internal temperature at 25°C through the jacket water. Start the stirring paddle, and stir at a speed of 90 rpm to suspend the particle mixture. Take samples from near the liquid surface and the bottom of the filter respectively to test the density of the solid-liquid mixture, and the density deviation is 11.5%. Fill the inside of the filter with nitrogen to an absolute pressure of 250 kPa. Open the filtrate valve at the bottom of the filter, and collect the filtrate (including the passing-through particles) for 15 min while maintaining the stirring state. The D90 diameter of the solid phase in the suspension (fine particle diameter particles to be removed and solution passing through the filter medium) is 81 microns, and the proportion of the solid phase particles in the suspension in all the solid phases in the solid-liquid mixture is 4.16 wt%.

[0088] Solid-liquid separation and drying:

[0089] Stop the stirring paddle, and continue to filter the remaining solid-liquid mixture in the filter to collect the wet filter cake; collect the solid phase of the particles in the filtrate by suction filtration, and then place them in a vacuum dryer at 50°C for 4 hours respectively to obtain purified glycolide and glycolide separated by dynamic filtration.

[0090] The test results are shown in Table 1.

[0091] Table 1

[0092]

[0093]

Example 2

[0094] Preparation of solid-liquid mixture:

[0095] Add 400.0 g of glycolide (commercially available, white powder, residual ethyl acetate content 167 ppm) and 800.0 g of anhydrous isopropanol (dehydrated with 4A molecular sieve to 10 ppm of water) into a 2 L glass reactor to prepare a solid-liquid mixture with a solid phase mass fraction of 33.0%. The median diameter of the solid phase in the solid-liquid mixture is 460 microns. Transfer the solid-liquid mixture to a 4 L plate-type two-in-one filter (stainless steel filter screen, pore size 70 microns).

[0096] Dynamic filtration under pressure:

[0097] Control the internal temperature at 25 °C through the jacket water. Turn on the stirring paddle, and stir at a speed of 90 rpm to suspend the particle mixture. Take samples from near the liquid surface and the bottom of the filter respectively to test the density of the solid-liquid mixture, and the density deviation is 11.5%. Fill the inside of the filter with nitrogen to an absolute pressure of 250 kPa, open the filtrate valve at the bottom of the filter, and collect the filtrate (including the particles passing through the filter) for 15 min while maintaining the stirring state. The D90 diameter of the solid phase in the suspension is 63 microns, and the proportion of the particles with a slow settling rate in all the solid phases in the solid-liquid mixture is 3.19% by weight.

[0098] Solid-liquid separation and drying:

[0099] Stop the stirring paddle, continue to filter the remaining solid-liquid mixture in the filter, and collect the wet filter cake; collect the solid phase of the particles in the filtrate by suction filtration, and then place them in a vacuum dryer at 50 °C for 4 hours respectively to obtain the purified glycolide and the glycolide separated by dynamic filtration.

[0100] The test results are shown in Table 2.

[0101] Table 2

[0102]

[0103]

Example 3

[0104] Preparation of particle mixture:

[0105] 400.0 g of glycolide (commercially available, white powder, residual ethyl acetate content 167 ppm), the median particle diameter is 476 microns.

[0106] Screening:

[0107] The above-mentioned commercially available glycolide particles were treated with a 24-mesh (aperture 700 μm) stainless steel sieve (round sieve) at 25 °C for 5 min. The particles that passed through the sieve and those that could not pass through the sieve were collected separately to obtain purified glycolide and sieve-separated glycolide, respectively. The D10 diameter of the latter was 795 μm.

[0108] The test results are shown in Table 3.

[0109] Table 3

[0110]

[0111]

Example 4

[0112] Preparation of molten glycolide stream:

[0113] After adding 1200 g of glycolic acid crystals and 16 g of stannous octoate catalyst to the reactor, the temperature was raised from room temperature to 90 °C. After the solid was completely dissolved, the temperature was raised to 120 °C for atmospheric pressure prepolymerization. After 2 h of prepolymerization, the temperature was raised to 210 °C. After no water was distilled out, the system maintained the temperature and started to evacuate. The vacuum degree was controlled at 2 kPa during this process. After no water was distilled out, 945 g of glycolic acid oligomer was obtained.

[0114] The oligomer was fed to a depolymerization reactor. The depolymerization system was reacted at a reaction temperature of 285 °C, a vacuum degree of 1 kPa, and a stirring speed of 120 rpm to prepare crude glycolide. The crude glycolide vapor produced by the depolymerization reactor was condensed using a spherical condenser with a jacket water temperature of 85 °C to obtain molten crude glycolide. After 2 hours of reaction, the reaction was stopped, and 796 g of crude glycolide was obtained.

[0115] Preparation of solid-liquid mixture:

[0116] 480.0 g of the above-mentioned molten glycolide stream (pale yellow liquid) was kept warm in jacketed reactor A at 90 °C. 720 g of ethyl acetate was added to jacketed reactor B, and it was stirred at 120 rpm and kept warm at 10 °C. The melt in reactor A was fed to reactor B at a rate of 70 wt% of the solvent mass per hour. During this period, the stirring rate was 600 rpm, and the internal temperature was maintained at 10 °C by controlling the jacket water. After completion, a solid-liquid mixture with a solid mass fraction of 34.8 wt% was obtained. The median diameter of the solid phase in the solid-liquid mixture was 305 μm. The solid-liquid mixture was transferred to a 4 L flat plate two-in-one filter (stainless steel filter mesh, aperture 90 μm).

[0117] Dynamic filtration under vacuum push:

[0118] Control the internal temperature at 10°C through the jacket water. Turn on the filter agitator paddle, and stir at a speed of 90 rpm to suspend the particle mixture. Take samples from near the liquid surface and the bottom of the filter respectively to test the density of the solid-liquid mixture, with a density deviation of 12.6%. Connect the filter filtrate outlet to the receiving tank and the vacuum unit in sequence. Start the vacuum unit to reduce the pressure in the receiving tank to an absolute pressure of 3 kPa and maintain it. Open the filtrate valve at the bottom of the filter, and collect the filtrate (including the filtered-through particles) for 10 minutes while maintaining the stirring state. The D90 diameter of the solid phase in the suspension is 84 microns, and the proportion of the solid phase in the suspension in all the solid phases in the solid-liquid mixture is 8.62% by weight.

[0119] Solid-liquid separation and drying:

[0120] Stop the agitator paddle, and continue to filter the remaining solid-liquid mixture in the filter under vacuum to collect the wet filter cake; collect the solid phase of the particles in the filtrate by suction filtration, and then place them in a vacuum dryer at 50°C for 4 hours respectively to obtain purified glycolide and glycolide separated by dynamic filtration.

[0121] The test results are shown in Table 4.

[0122] Table 4

[0123]

[0124]

Example 5

[0125] Preparation of solid glycolide stream:

[0126] The steps to obtain the glycolide stream are the same as those in Example 4. The difference from Example 4 is that a spherical condenser with a jacket water temperature of 7°C is used to condense the crude glycolide steam produced by the depolymerization reactor to obtain 800 g of solid glycolide stream.

[0127] Preparation of solid-liquid mixture:

[0128] Put 480.0 g of the above solid glycolide stream (pale yellow solid) and 720 g of the mixed solvent (80% by mass of cyclohexane and 20% by mass of ethyl acetate) into the jacketed reaction kettle B, stir at 1200 rpm, and keep warm at 20°C. After 1 hour, a solid-liquid mixture with a solid mass fraction of 38.3 wt% is obtained. The median diameter of the solid phase in the solid-liquid mixture is 192 microns, and transfer the solid-liquid mixture to a 4L flat plate two-in-one filter (stainless steel filter mesh, pore size 70 microns).

[0129] Dynamic filtration under vacuum:

[0130] Control the internal temperature at 20°C through the jacket water. Start the stirring paddle with a stirring speed of 120 rpm to suspend the particulate mixture. Take samples from near the liquid surface and the bottom of the filter respectively to test the density of the solid-liquid mixture, with a density deviation of 7.1%. Connect the filtrate outlet of the filter to the receiving tank and the vacuum unit in sequence. Start the vacuum unit to reduce the pressure in the receiving tank to an absolute pressure of 5 kPa and maintain it. Open the filtrate valve at the bottom of the filter and collect the filtrate (including the filtered-through particles) for 10 minutes while maintaining the stirring state. The D90 diameter of the solid phase in the suspension is 64 microns, and the proportion of the solid phase in the suspension in all the solid phases in the solid-liquid mixture is 7.94% by weight.

[0131] Solid-liquid separation and drying:

[0132] Stop the stirring paddle and continue to filter the remaining solid-liquid mixture in the filter under vacuum to collect the wet filter cake; collect the solid phase from the particles in the filtrate by suction filtration, and then place them in a vacuum dryer at 50°C for 4 hours respectively to obtain purified glycolide and glycolide separated by dynamic filtration.

[0133] The test results are shown in Table 5.

[0134] Table 5

[0135]

[0136]

Example 6

[0137] Preparation of solid-liquid mixture:

[0138] Take 314.4 g of the purified glycolide feed stream (wet filter cake, containing 4.6% by weight of ethyl acetate) from Example 4 and 600 g of n-propanol and put them into the jacketed reaction kettle B. Stir at 600 rpm and keep warm at 30°C. After 1 hour, a solid-liquid mixture with a solid mass fraction of 32.5 wt% is obtained. The median diameter of the solid phase in the solid-liquid mixture is 329 microns. Transfer the solid-liquid mixture to a 4L filter equipped with a three-blade centrifugal stirring paddle (the wall is set with a stainless steel filter mesh with a pore diameter of 75 microns).

[0139] Dynamic filtration under centrifugal drive:

[0140] Control the internal temperature at 30°C through the jacket water. Start the stirring paddle with a stirring speed of 400 pm to suspend the particulate mixture. Take samples from near the liquid surface and the bottom of the filter respectively to test the density of the solid-liquid mixture, with a density deviation of 13.0%. Open the filtrate valve at the bottom of the filter and collect the filtrate (including the filtered-through particles) for 2 minutes while maintaining the stirring state. The D90 diameter of the solid phase in the suspension is 60 microns, and the proportion of the solid phase in the suspension in all the solid phases in the solid-liquid mixture is 5.61% by weight.

[0141] Solid-liquid separation and drying:

[0142] Stop the stirring paddle, and continue to filter the remaining solid-liquid mixture under centrifugal force in the filter to collect the wet filter cake; collect the solid phase of the particles in the filtrate by suction filtration, and then place them in a vacuum dryer at 50 °C for 4 hours respectively to obtain purified glycolide and glycolide separated by dynamic filtration.

[0143] The test results are shown in Table 6.

[0144] Table 6

[0145]

[0146]

Example 7

[0147] Preparation of solid-liquid mixture:

[0148] Put 300.0 g of the dried and purified glycolide stream (containing 86 ppm of cyclohexane and 170 ppm of ethyl acetate) obtained in Example 5 and 2400 g of a mixed solvent (75% by mass of isopropanol and 25% by mass of ethylene glycol dimethyl ether) into the jacketed reactor B, stir at 350 rpm, and keep warm at 55 °C. After 1 hour, a glycolide solution is obtained. Control the temperature of the jacket water to cool the solution at a cooling rate of 15 °C / h to 5 °C, so that the glycolide crystals recrystallize and precipitate. Keep warm at 5 °C for another 30 min to obtain a solid-liquid mixture with a solid phase mass fraction of 10.2 wt%. The median diameter of the solid phase in the solid-liquid mixture is 445 microns. Transfer the solid-liquid mixture to a 4 L filter equipped with a three-blade centrifugal stirring paddle (a stainless steel filter screen with a pore diameter of 75 microns is set on the wall).

[0149] Dynamic filtration under centrifugal force:

[0150] Control the internal temperature at 5 °C through the jacket water. Start the stirring paddle, and stir at a speed of 400 pm to suspend the particle mixture. Sample and test the density of the solid-liquid mixture from near the liquid surface and the bottom of the filter respectively, and the density deviation is 10.4%. Open the filtrate valve at the bottom of the filter, and collect the filtrate (including the particles passing through the filter) for 2 min while maintaining the stirring state. The D90 diameter of the solid phase in the suspension is 69 microns, and the proportion of the solid phase in the suspension in all the solid phases in the solid-liquid mixture is 2.63 wt%.

[0151] Solid-liquid separation and drying:

[0152] Stop the stirring paddle, and continue to filter the remaining solid-liquid mixture under centrifugal force in the filter to collect the wet filter cake; collect the solid phase of the particles in the filtrate by suction filtration, and then place them in a vacuum dryer at 50 °C for 4 hours respectively to obtain purified glycolide and glycolide separated by dynamic filtration.

[0153] The test results are shown in Table 7.

[0154] Table 7

[0155]

[0156]

Example 8

[0157] Preparation of the particle mixture:

[0158] 300.0 g of glycolide (the glycolide obtained after drying and purification in Example 7, with a residual isopropanol content of 181 ppm and a residual ethylene glycol dimethyl ether content of 206 ppm), and the median particle diameter is 491 microns.

[0159] Screening:

[0160] The above-mentioned glycolide particles were treated with a 20-mesh (aperture 830 microns) stainless steel sieve (circular sieve) at 25°C for 5 minutes. The particles passing through the sieve and those unable to pass through the sieve were collected separately to obtain purified glycolide and glycolide separated by screening, and the D10 diameter of the latter was 1050 microns.

[0161] The test results are shown in Table 8.

[0162] Table 8

[0163]

[0164]

Example 9

[0165] Preparation of the particle mixture:

[0166] 300.0 g of glycolide (the glycolide obtained after drying and purification in Example 7, with a residual isopropanol content of 181 ppm and a residual ethylene glycol dimethyl ether content of 206 ppm), and the median particle diameter is 491 microns.

[0167] Vibrating classification:

[0168] The above-mentioned glycolide particles were treated with a linear vibrating sieve equipped with two discharge ports (coarse and fine particles) and internally equipped with a stainless steel sieve (24 mesh, aperture 700 microns) at 25°C. The glycolide material flows discharged from the fine particle and coarse particle outlets were collected separately to obtain purified glycolide and glycolide separated by vibrating classification, and the D10 diameter of the latter was 812 microns.

[0169] The test results are shown in Table 9.

[0170] Table 9

[0171]

[0172] By removing the particles with a diameter less than or equal to 90 microns and the particles with a diameter greater than or equal to 700 microns in the particle mixture in Examples 1-9, the oligomer impurities in glycolide can be removed quickly and efficiently. The purified glycolide has a low impurity content and a high glycolide purity, and the operation is simple, having great industrial application value.

Claims

1. A method for refining glycolide, comprising the step of forming a particulate mixture of a glycolide stream, and the step of removing particles having a diameter less than or equal to 100 microns, and / or removing particles having a diameter greater than or equal to 600 microns; preferably, the step of removing particles having a diameter less than or equal to 90 microns, and / or removing particles having a diameter greater than or equal to 700 microns.

2. The method for refining glycolide according to claim 1, wherein: The particulate mixture is a solid-liquid mixture or a dry particulate mixture; preferably, removing particles having a diameter less than or equal to 100 microns in the solid-liquid mixture, more preferably removing particles having a diameter less than or equal to 90 microns; and / or, removing particles having a diameter greater than or equal to 600 microns in the dry particulate mixture, more preferably removing particles having a diameter greater than or equal to 700 microns; and / or, collecting the remaining solid-phase particles after removing the particles to obtain purified glycolide.

3. The method for refining glycolide according to claim 1 or 2, wherein: The proportion of the removed particles in the total solid phase weight of the particulate mixture is less than or equal to 10% by weight, preferably 1-10% by weight; and / or, The content of oligomer impurities in the removed particles is greater than or equal to 1% by weight, preferably greater than or equal to 2% by weight.

4. The method for refining glycolide according to claim 2, wherein: The solid-liquid mixture comprises a solid phase and a liquid phase; preferably, the mass fraction of the solid phase is less than or equal to 50%, preferably less than or equal to 40%, more preferably 5-40%, most preferably 10-40%; and / or, the median diameter of the solid phase is less than or equal to 600 microns, preferably less than or equal to 500 microns; and / or, the liquid phase is a saturated organic solvent solution of glycolide; and / or, the solid phase is solid particles containing glycolide; and / or, the density deviation between any parts of the solid-liquid mixture does not exceed 30%, preferably does not exceed 20%, more preferably does not exceed 15%.

5. The method for refining glycolide according to claim 2, wherein: The solid-liquid mixture is obtained by adding a molten glycolide stream to an organic solvent by at least one of dropping, injecting, spraying, showering, and spraying methods; preferably, the molten glycolide stream is an unpurified molten glycolide stream and / or a purified molten glycolide stream from a glycolide synthesis unit; and / or, the mass content of glycolide in the molten glycolide stream is 85.0-99.9%; and / or, The solid-liquid mixture is obtained by adding a solid-phase glycolide stream to an organic solvent; preferably, the solid-phase glycolide stream is obtained by condensing and solidifying a molten glycolide stream; and / or, The solid-liquid mixture is obtained by mixing any stream containing a glycolide solid phase with an organic solvent; preferably, the glycolide solid phase is a wet filter cake or purified glycolide after drying treatment; and / or, The solid-liquid mixture is obtained by cooling crystallization or evaporation crystallization of a glycolide solution phase; preferably, the glycolide solution phase is a solution formed by dissolving a molten or solid glycolide stream in an organic solvent.

6. The method for purifying glycolide according to claim 5, wherein: The organic solvent is at least one of acetone, ethyl acetate, ethylene glycol dimethyl ether, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, n-hexane, cyclohexane, pentane, and petroleum ether.

7. The method for purifying glycolide according to claim 2, wherein: The dry particle mixture is obtained by solid-liquid separation of the solid-liquid mixture and drying the recovered solid phase; preferably, The mass fraction of the organic solvent in the dry particle mixture is less than or equal to 0.5%, preferably less than or equal to 0.2%, more preferably less than or equal to 0.1%; and / or, The median diameter of the solid phase in the dry particle mixture is less than or equal to 600 microns, preferably less than or equal to 500 microns; and / or, The solid-liquid separation is carried out by centrifugation or filtration.

8. The method for purifying glycolide according to claim 1 or 2, wherein: The method for removing particles with a diameter less than or equal to 100 microns or 90 microns is dynamic filtration; and / or, The method for collecting the remaining solid phase particles is centrifugation or filtration; and / or, The method for removing particles with a diameter greater than or equal to 600 microns or 700 microns is at least one of screening, air classification, and vibration classification.

9. The method for purifying glycolide according to claim 8, wherein: The device used for dynamic filtration is a dynamic filter driven by pressure, vacuum, or centrifugal force; and / or, The dynamic filter used for dynamic filtration contains a filter medium with a pore size in the range of 50-100 microns, preferably contains a filter medium with a pore size in the range of 70-90 microns; and / or, The device used for screening is at least one of a vibrating screen, a rotary screen, and a circular screen; and / or, The screening device contains a filter medium with a pore size in the range of 600-1000 microns, preferably contains a filter medium with a pore size in the range of 700-850 microns; and / or, The device used for air classification is an air classifier; and / or, The device used for vibration classification is a vibration classifier.

10. A glycolide prepared by the purification method according to any one of claims 1-9.

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