CN113336739B - Method for preparing high-purity glycolide - Google Patents
Method for preparing high-purity glycolide Download PDFInfo
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Abstract
The invention belongs to the technical field of organic synthesis, and particularly discloses a method for preparing high-purity glycolide. The method comprises the following steps: heating and dehydrating glycolic acid or glycolate under the action of a catalyst or dealcoholizing to obtain a glycolic acid oligomer, and then heating and decompressing to crack in a depolymerization kettle to obtain crude glycolide; recrystallizing the crude glycolide with a solvent under the protection of protective gas, and separating the crystal by melt crystallization after vacuum drying to obtain the polymer grade glycolide with the purity of more than or equal to 99.9 percent. The invention uses the method of coupling recrystallization and melt crystallization to purify the crude glycolide, can realize the recycling of materials, does not produce waste, and simultaneously prepares the glycolide product with high purity (more than or equal to 99.9%) with high yield. The invention is a high-efficiency, environment-friendly and high-purity glycolide synthesis method, and is suitable for industrial production.
Description
Technical Field
The invention relates to the field of organic synthesis, in particular to a method for preparing high-purity glycolide.
Background
The problem of environmental pollution (white pollution) caused by uncontrolled production and use of disposable/disposable petroleum-based plastics (e.g., packaging materials, agricultural films, edible preservative films, disposable cutlery boxes, etc.) has attracted serious attention worldwide. Biodegradable polymers based on renewable resources, such as: polylactic acid (PLA), polyglycolic acid (PGA), polylactic acid-glycolic acid (PLGA) have been recognized by students at home and abroad as the most promising alternative to petroleum-based plastics. Polyglycolic acid (PGA) is an absorbable polymer material for medical use, and has important applications in clinical and medical fields due to its excellent biodegradability and biocompatibility. Polyglycolic acid was synthesized by corother in the early 30 s of the last century, but the resulting polymer was poor in mechanical properties due to its low molecular weight and not highly practical as a strength material. From the 70 s, a large amount of polyglycolic acid was used in the preparation of absorbable sutures. In 1962, the Cyanamid company of the united states developed the first commercial surgical suture under the trade name "Dexon". In 1975, the commercial name of the absorbable suture prepared by copolymerizing glycolic acid and lactic acid in a molar ratio of 90:10 is Vicryl, and the degradation rate of the polymer is obviously improved due to the addition of the lactic acid. After that, the synthesis of medical biodegradable materials has been studied more widely, and various glycolic acid copolymers have been used in absorbable suture materials, tissue repair materials, genetic engineering, orthopedic fixation and drug controlled release systems. Currently, there are two main synthetic methods for polyglycolic acid: direct polycondensation and ring-opening polymerization processes. The ring-opening polymerization method is also called a two-step method, namely, glycolide is prepared by dehydration and depolymerization of glycolic acid, and then the glycolide is subjected to ring-opening polymerization reaction under the action of a catalyst to prepare polyglycolic acid. Compared with the direct polycondensation method, the ring-opening polymerization method has the advantages of mild reaction conditions and short reaction time, can be used for controllably synthesizing polyglycolic acid products with molecular weight reaching hundreds of thousands, and is a main preparation method of commercial polyglycolic acid. However, the purity and quality requirements for the monomeric glycolide are extremely high.
Glycolide is prepared by forming an oligomer of glycolic acid as a reaction raw material under the condition of autocatalysis. The oligomer is depolymerized under the action of a catalyst to form crude glycolide. The crude glycolide is purified by adopting methods such as a recrystallization method, a rectification method, a melt crystallization method, a water washing method and the like to obtain the polymer grade glycolide.
(1) Recrystallization method
The recrystallization method is a method for separation and purification by utilizing the difference of solubility of different substances in the same solvent at different temperatures. For example, kang et al (Kang Lin, newark Del, glycolide purificatin process, U.S. Pat. No. 3, 5223630) mixed glycolide with a solvent such as acetone and then recrystallized in ethyl acetate at low temperature to yield 85% or more of refined glycolide. Mountain roots, mountain lines and the like (mountain roots, mountain lines, chuan allied, yuan xing, preparation method of cyclic esters and refining method, CN 100441575C) are dissolved in a mixed solution composed of lower esters or lower alcohols and lower ketones, and one or more low boiling point solvents such as methanol, diethyl ether, methylene dichloride and the like are added to promote formation of glycolide crystal nuclei in supersaturated solutions. Zhang Xianzheng (Zhang Xianzheng, li Shiying, feng Jun, a process for producing glycolide, CN 103242287B) and the like, crude glycolide is dissolved in one or more solutions of lower esters or lower alcohols, and the mixture is subjected to reflux dissolution, cooling crystallization, filtration of the crystals, repeated recrystallization and purification. Such methods generally employ organic solvents and are difficult to implement in continuous operation, and thus are difficult to apply in commercial glycolide production.
(2) Rectification method
The rectification method is a technological method for separating and purifying by utilizing the boiling point difference of each component in the crude product. For example, mountain roots and lines, etc. (mountain roots and lines, star wisdom, known as cyclic ester refining method, CN 101616907B) a mixture of glycolide and a polyalkylene glycol ether having a boiling point of 230 to 450 ℃ and a molecular weight of 150 to 450 is heated under normal pressure or reduced pressure to form a substantially homogeneous phase in solution, whereby the glycolide fraction is collected at a suitable temperature.
The rectification method is one of the methods commonly used in the current commercial glycolide production, but the method has the problems of complex process and high energy consumption. In addition, because crude glycolide generally contains acidic impurities, the polymerization of glycolide can occur during the rectification and purification process, and polymer residues can also be formed.
(3) Melt crystallization method
The melt crystallization method is a method for separating and purifying by utilizing the difference of melting points of components in a crude product. Because the melting point of glycolide is 84-86 ℃, the reaction can be carried out at normal pressure and low temperature, and the operation is simple and safe. Compared with the recrystallization method using the solvent, the method does not need to use extra solvent, reduces cost and environmental pollution, and has the energy consumption of only 1/3 of that of rectification. However, the acidic impurities (glycolic acid, oligomers) contained in the crude glycolide have high requirements on equipment materials, and the crystallization efficiency is reduced.
(4) Water washing method
The water washing method is a method for separating and purifying by utilizing the solubility difference of each substance in the crude product in water. The glycolide crude product contains a small amount of glycolic acid, glycolic acid oligomer and water, and the solubility of the acid substances in water is greatly higher than that of the glycolide, so that the glycolide can be well separated. The presence of moisture in glycolide also causes its polymerization or degradation, so timely drying is critical for the purification of glycolide by water washing. The washing method does not need to use an organic solvent, meanwhile, the equipment condition requirement is low, the method is relatively more energy-saving and environment-friendly, but the washing conditions of glycolide with different qualities are different, the subsequent drying process also has strict requirements, and the method has few successful application in scientific research and industry at present.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention aims to provide a method for preparing high-purity glycolide, which is used for solving the problems of high cost, low production efficiency, high energy consumption, large amount of three wastes, inconvenient industrialization and the like of glycolide synthesis in the prior art.
To achieve the above and other related objects, the present invention provides a method for preparing high purity glycolide, comprising the steps of: heating and dehydrating glycolic acid or glycolate under the action of a catalyst or dealcoholizing to obtain a glycolic acid oligomer, and then heating and decompressing to crack in a depolymerization kettle to obtain crude glycolide; recrystallizing the crude glycolide with a solvent under the protection of protective gas, and separating the crystal by melt crystallization after vacuum drying to obtain the polymer grade glycolide with the purity of more than or equal to 99.9 percent.
Further, the glycolate is at least one selected from the group consisting of methyl glycolate, ethyl glycolate, propyl glycolate, and butyl glycolate.
Further, the catalyst is at least one selected from tin compounds, antimony oxide and zinc compounds.
Optionally, the tin compound is at least one selected from stannous chloride, stannous octoate, stannous chloride dihydrate, stannic lactate and stannous benzoate, and the zinc compound is at least one selected from zinc chloride, zinc oxide, diethyl zinc, zinc acetate dihydrate and zinc lactate.
Further, the catalyst is used in an amount of 0.005 to 0.1% by weight of glycolic acid or glycolate.
Further, the temperature of the dehydration or dealcoholization reaction is between normal temperature and 200 ℃, and the reaction pressure is between 1 and 5KPa.
Optionally, after glycolic acid or glycolate is added into the reaction kettle, the temperature is gradually increased to 200 ℃ from normal temperature, and dehydration or dealcoholization reaction is carried out.
Preferably, the glycolic acid is taken as a raw material, firstly, the glycolic acid crystal is added into a reaction kettle, firstly, the temperature is gradually increased to 90 ℃ from normal temperature under normal pressure, the glycolic acid crystal is melted, then a catalyst is added, and then the reaction kettle is vacuumized to reduce the pressure to 1-5 KPa, and the temperature is gradually increased to 200 ℃ for dehydration or dealcoholization reaction; and/or adding the glycolate serving as a raw material into a reaction kettle, heating the glycolate liquid and the catalyst to 180 ℃ from normal temperature in a gradient way under normal pressure, vacuumizing to reduce the pressure of the reaction kettle to 1-5 KPa, heating the reaction kettle to 200 ℃ in a gradient way, and carrying out dehydration or dealcoholization reaction.
Further, after completely anhydrous or alcohol-free distillation, dehydration or dealcoholization reaction is completed to obtain glycolic acid oligomer.
Further, the dehydration or dealcoholization reaction is performed under the protection of a protective gas.
Further, the reaction temperature in the depolymerization kettle is 200-260 ℃ and the reaction pressure is 500-1000 Pa.
Further, the solvent is at least one selected from ethyl acetate, acetone, methanol, ethanol, n-propanol and isopropanol.
Further, the solvent is used in an amount of 0.5 to 0.8 times the mass of the crude glycolide.
Further, the temperature of solid-liquid separation after recrystallization is 5-10 ℃.
Further, the crude glycolide is solid, the crude glycolide is mixed with a solvent, heated, kept for 30-60min after the crude glycolide is completely dissolved, cooled and crystallized (i.e. a recrystallization process), and suction-filtered at 5-10 ℃, and the obtained solid is a crystal.
Further, the vacuum drying temperature is 50-60 ℃, and the vacuum drying time is not less than 4 hours.
Further, the melting crystallization operation comprises film formation, cooling crystallization, heating to sweat, collecting product and discharging mother liquor, heating glycolide to 85-90 ℃ for melting, cooling crystallization at 0.1-0.5 ℃/min, and controlling the temperature difference between 15-30 ℃; heating at 0.1-0.5 deg.C/min for sweating, controlling temperature difference at 5-20deg.C, and removing sweat; and finally, heating, melting and collecting glycolide products.
Further, the residue of the depolymerization kettle is used for the next cracking reaction.
Further, the mother liquor of recrystallization and melt crystallization is used in the next dehydration or dealcoholization reaction.
In the present invention, the shielding gas is at least one of shielding gases commonly used in the art, such as nitrogen, argon, helium, etc.
As described above, the method for preparing high-purity glycolide according to the present invention has the following advantageous effects:
the invention uses the method of coupling recrystallization and melt crystallization to purify the crude glycolide, can realize the recycling of materials through mother liquor, does not produce waste, and simultaneously prepares the glycolide product with high purity (more than or equal to 99.9%) with high yield. The invention is a high-efficiency, environment-friendly and high-purity glycolide synthesis method, and is suitable for industrial production.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.
The invention provides a method for preparing high-purity glycolide, which comprises the following steps:
heating and dehydrating glycolic acid or glycolate under the action of a catalyst or dealcoholizing to obtain a glycolic acid oligomer, and then heating and decompressing to crack in a depolymerization kettle to obtain crude glycolide; recrystallizing the crude glycolide with a solvent under the protection of protective gas, and separating the crystal by melt crystallization after vacuum drying to obtain the polymer grade glycolide with the purity of more than or equal to 99.9 percent.
Further, the glycolate is at least one selected from the group consisting of methyl glycolate, ethyl glycolate, propyl glycolate, and butyl glycolate.
Further, the catalyst is at least one selected from tin compounds, antimony oxide and zinc compounds. Optionally, the tin compound is at least one selected from stannous chloride, stannous octoate, stannous chloride dihydrate, stannic lactate and stannous benzoate, and the zinc compound is at least one selected from zinc chloride, diethyl zinc, zinc acetate dihydrate and zinc lactate.
Further, the catalyst is used in an amount of 0.005 to 0.1% by weight of glycolic acid or glycolate.
Further, the temperature of the dehydration or dealcoholization reaction is between normal temperature and 200 ℃, and the reaction pressure is between 1 and 5KPa.
Optionally, after glycolic acid or glycolate is added into the reaction kettle, the temperature is gradually increased to 200 ℃ from normal temperature, and dehydration or dealcoholization reaction is carried out. Preferably, the glycolic acid is taken as a raw material, firstly, the glycolic acid crystal is added into a reaction kettle, firstly, the temperature is gradually increased to 90 ℃ from normal temperature under normal pressure, the glycolic acid crystal is melted, then a catalyst is added, and then the reaction kettle is vacuumized to reduce the pressure to 1-5 KPa, and the temperature is gradually increased to 200 ℃ for dehydration or dealcoholization reaction; the adopted raw material glycolate is liquid, the glycolate liquid and the catalyst are added into a reaction kettle, the temperature is gradually increased to 180 ℃ from normal temperature under normal pressure, then the reaction kettle is vacuumized to reduce the pressure to 1-5 KPa, and the temperature is gradually increased to 200 ℃ for dehydration or dealcoholization reaction.
Further, after complete anhydrous or alcohol-free distillation, dehydration or dealcoholization reaction is completed to obtain glycolic acid oligomer.
Further, the dehydration or dealcoholization reaction is performed under the protection of a protective gas.
Further, the reaction temperature in the depolymerization kettle is 200-260 ℃ and the reaction pressure is 500-1000 Pa.
Further, the solvent is at least one selected from ethyl acetate, acetone, methanol, ethanol, n-propanol and isopropanol.
Further, the solvent is used in an amount of 0.5 to 0.8 times the mass of the crude glycolide.
Further, the temperature of solid-liquid separation after recrystallization is 5-10 ℃. Specifically, the crude glycolide is solid, the crude glycolide is mixed with a solvent, heated, kept for 30-60min after the crude glycolide is completely dissolved, cooled and crystallized, and suction filtration is carried out at 5-10 ℃, and the obtained solid is a crystal.
Further, the vacuum drying temperature is 50-60 ℃, and the vacuum drying time is not less than 4 hours.
Further, the melting crystallization operation comprises film formation, cooling crystallization, heating for sweating, collecting products and discharging mother liquor, and the steps are as follows: heating glycolide to 85-90 ℃ for melting, cooling and crystallizing at 0.1-0.5 ℃/min, and controlling the temperature difference between 15-30 ℃; heating at 0.1-0.5 deg.C/min for sweating, controlling temperature difference at 5-20deg.C, and removing sweat; and finally, heating, melting and collecting glycolide products.
Further, the depolymerization kettle residue is used for the next cracking reaction.
Further, the mother liquor of recrystallization and melt crystallization is used in the next dehydration or dealcoholization reaction.
The shielding gas of the present invention is at least one of shielding gases commonly used in the art, such as nitrogen, argon, helium, etc.
The invention is further illustrated by the following specific examples.
Example 1
The method for preparing high-purity glycolide in this example comprises the following steps:
305g of glycolic acid crystal is added into a four-neck flask, the temperature is raised to 90 ℃ under the protection of nitrogen, 0.03g of stannous chloride is added after the solid is completely melted, then the vacuum pumping is started to reduce the system pressure to 3KPa, the gradient temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after complete anhydrous distillation. Regulating the pressure of the system to 800Pa, performing cracking reaction at 200-260 ℃, continuously evaporating light yellow liquid, and cooling to obtain light yellow solid, thus obtaining crude glycolide with the yield of 92%.
Heating and dissolving crude glycolide (214 g) and 150g of ethyl acetate, preserving heat for 30min after complete dissolution, cooling and crystallizing, carrying out suction filtration at 10 ℃, carrying out vacuum drying on the solid to obtain a white product, and applying the white product to the next batch of experiments after the solvent of the mother liquor is removed. Purifying the recrystallized product by a melt crystallizer, wherein the main operation comprises film hanging, cooling crystallization, heating and sweating, collecting the product, discharging mother liquor and the like, and the specific process comprises the following steps: firstly, heating glycolide to 90 ℃ for melting, secondly, cooling and crystallizing at 0.2 ℃/min, and controlling the cooling temperature difference to be 20 ℃; heating at 0.2 deg.c/min to produce sweat, controlling the temperature difference to 20 deg.c and eliminating sweat; and finally, heating, melting and collecting glycolide products, and applying the mother liquor to the next batch of reaction. After two purifications, 171.2g of white glycolide product is obtained, the purity is 99.91%, the purification yield is 80%, and the total yield is 73.6%.
Example 2
The method for preparing high-purity glycolide in this example comprises the following steps:
305g of glycolic acid crystal is added into a four-neck flask, the temperature is raised to 90 ℃ under the protection of nitrogen, 0.03g of stannous chloride is added after the solid is completely melted, then the vacuum pumping is started to reduce the system pressure to 1KPa, the gradient temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after complete anhydrous distillation. The pressure of the system is regulated to 500Pa, the cracking reaction is carried out at the temperature of 200-260 ℃, the light yellow liquid is continuously distilled out, and the light yellow solid is obtained after cooling, thus obtaining the crude glycolide with the yield of 94%.
Heating and dissolving crude glycolide (219 g) and 153g of ethyl acetate, preserving heat for 30min after complete dissolution, cooling and crystallizing, carrying out suction filtration at 5 ℃, carrying out vacuum drying on the solid to obtain a white product, and applying the white product to the next batch of experiments after the solvent of the mother liquor is removed; purifying the recrystallized product by a melt crystallizer, wherein the main operation comprises film hanging, cooling crystallization, heating and sweating, collecting the product, discharging mother liquor and the like, and the specific process comprises the following steps: firstly, heating glycolide to 85 ℃ for melting, secondly, cooling and crystallizing at 0.3 ℃/min, and controlling the cooling temperature difference to 25 ℃; then heating and sweating at 0.4 ℃/min, controlling the temperature difference to be 10 ℃, and removing the sweating; and finally, heating, melting and collecting glycolide products, and applying the mother liquor to the next batch of reaction. After two purifications, 179.6g of white glycolide product is obtained, the purity is 99.93%, the purification yield is 82%, and the total yield is 77.08%.
Example 3
The method for preparing high-purity glycolide in this example comprises the following steps:
305g of glycolic acid crystal is added into a four-neck flask, the temperature is raised to 90 ℃ under the protection of nitrogen, 0.03g of stannous chloride is added after the solid is completely melted, then the vacuum pumping is started to be reduced to 2KPa, the gradient temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after the complete anhydrous distillation. The pressure of the system is regulated to 600Pa, the cracking reaction is carried out at the temperature of 200-260 ℃, the light yellow liquid is continuously distilled out, and the light yellow solid is obtained after cooling, thus obtaining the crude glycolide with the yield of 94%.
Heating and dissolving crude glycolide (219 g) and 131g of ethyl acetate, preserving heat for 30min after complete dissolution, cooling and crystallizing, carrying out suction filtration at 6 ℃, carrying out vacuum drying on the solid to obtain a white product, and applying the white product to the next batch of experiments after the solvent of the mother liquor is removed; purifying the recrystallized product by a melt crystallizer, wherein the main operation comprises film hanging, cooling crystallization, heating and sweating, collecting the product, discharging mother liquor and the like, and the specific process comprises the following steps: firstly, heating glycolide to 88 ℃ for melting, secondly, cooling and crystallizing at 0.4 ℃/min, and controlling the cooling temperature difference to be 20 ℃; heating at 0.4 deg.c/min to produce sweat and controlling the temperature difference to 15 deg.c to eliminate sweat; and finally, heating, melting and collecting glycolide products, and applying the mother liquor to the next batch of reaction. After two purifications, 188.3g of white glycolide product is obtained, the purity is 99.92%, the purification yield is 86%, and the total yield is 80.8%.
Example 4
The method for preparing high-purity glycolide in this example comprises the following steps:
305g of glycolic acid crystal is added into a four-neck flask, the temperature is raised to 90 ℃ under the protection of nitrogen, 0.03g of stannous octoate is added after the solid is completely melted, then the vacuum pumping is started to reduce the system pressure to 5KPa, the gradient temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after complete anhydrous distillation. The pressure of the system is regulated to 1000Pa, the cracking reaction is carried out at the temperature of 200-260 ℃, the light yellow liquid is continuously distilled out, and the light yellow solid is obtained after cooling, thus obtaining the crude glycolide with the yield of 94.5%.
Heating and dissolving crude glycolide (220 g) and 131g of ethyl acetate, preserving heat for 30min after complete dissolution, cooling and crystallizing, carrying out suction filtration at 8 ℃, carrying out vacuum drying on the solid to obtain a white product, and applying the white product to the next batch of experiments after the solvent of the mother liquor is removed; purifying the recrystallized product by a melt crystallizer, wherein the main operation comprises film hanging, cooling crystallization, heating and sweating, collecting the product, discharging mother liquor and the like, and the specific process comprises the following steps: firstly, heating glycolide to 87 ℃ for melting, secondly, cooling and crystallizing at 0.5 ℃/min, and controlling the cooling temperature difference at 30 ℃; heating at 0.5 deg.c/min to produce sweat and controlling the temperature difference to 20 deg.c to eliminate sweat; and finally, heating, melting and collecting glycolide products, and applying the mother liquor to the next batch of reaction. After two purifications, 188.1g of white glycolide product is obtained, the purity is 99.94%, the purification yield is 85.5%, and the total yield is 80.7%.
Example 5
The method for preparing high-purity glycolide in this example comprises the following steps:
360g of methyl glycolate and 0.4g of stannous octoate are added into a four-neck flask, the mixture is stirred and reacted under normal pressure to heat up to 180 ℃, then the vacuum pumping is started to reduce the pressure of the system to 3KPa, the temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after no fraction (namely methanol) is completely distilled out. The pressure of the system is regulated to 500Pa, the cracking reaction is carried out at the temperature of 200-260 ℃, the light yellow liquid is continuously distilled out, and the light yellow solid is obtained after cooling, thus obtaining the crude glycolide with the yield of 92.5 percent.
Heating and dissolving crude glycolide (215 g) and 129g of ethyl acetate, preserving heat for 30min after complete dissolution, cooling and crystallizing, carrying out suction filtration at 10 ℃, carrying out vacuum drying on the solid to obtain a white product, and applying the white product to the next batch of experiments after the solvent of the mother liquor is removed; purifying the recrystallized product by a melt crystallizer, wherein the main operation comprises film hanging, cooling crystallization, heating and sweating, collecting the product, discharging mother liquor and the like, and the specific process comprises the following steps: firstly, heating glycolide to 90 ℃ for melting, secondly, cooling and crystallizing at 0.1 ℃/min, and controlling the temperature difference of cooling at 15 ℃; heating at 0.1 deg.c/min to produce sweat and controlling the temperature difference to 5 deg.c to eliminate sweat; and finally, heating, melting and collecting glycolide products, and applying the mother liquor to the next batch of reaction. After two purifications, 178.5g of white product is obtained, the purity is 99.94%, the purification yield is 83%, and the total yield is 76.8%.
Comparative example 1
The procedure for preparing high purity glycolide in this comparative example is as follows:
305g of glycolic acid crystal is added into a four-neck flask, the temperature is raised to 90 ℃ under the protection of nitrogen, 0.03g of stannous chloride is added after the solid is completely melted, then the vacuum pumping is started to reduce the system pressure to 3KPa, the gradient temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after complete anhydrous distillation. The pressure of the system is regulated to 800Pa, the cracking reaction is carried out at the temperature of 200-260 ℃, the light yellow liquid is continuously distilled out, and the light yellow solid is obtained after cooling, thus obtaining the crude glycolide with the yield of 93 percent.
Heating and dissolving crude glycolide (216 g) and 130g of ethyl acetate, preserving heat for 30min after complete dissolution, cooling and crystallizing, carrying out suction filtration at 10 ℃, carrying out vacuum drying on the solid to obtain a white product, and applying the white product to the next batch of experiments after the solvent of the mother liquor is removed; after purification, 186.2g of white glycolide product was obtained, with a purity of 98.5%, a purification yield of 86% and a total yield of 80.0%.
Comparative example 2
The procedure for preparing high purity glycolide in this comparative example is as follows:
305g of glycolic acid crystal is added into a four-neck flask, the temperature is raised to 90 ℃ under the protection of nitrogen, 0.03g of stannous chloride is added after the solid is completely melted, then the vacuum pumping is started to reduce the system pressure to 3KPa, the gradient temperature is raised to 200 ℃, and the glycolic acid oligomer is obtained after complete anhydrous distillation. The pressure of the system is regulated to 800Pa, the cracking reaction is carried out at the temperature of 200-260 ℃, the light yellow liquid is continuously distilled out, and the light yellow solid is obtained after cooling, thus obtaining the crude glycolide with the yield of 93.5 percent.
Purifying the crude glycolide by a melt crystallizer, wherein the main operations comprise film formation, cooling crystallization, heating and sweating, collecting products, discharging mother liquor and the like; the crystallization temperature difference is controlled to be 15-30 ℃, the sweating temperature is controlled to be 5-20 ℃, and the mother liquor is applied to the next batch of reaction. After two purifications, 189.3g of white glycolide product with the purity of 99.05%, the purification yield of 86.8% and the total yield of 81.2% are obtained.
As is clear from the above, the purity of glycolide products of examples 1-5 is greater than or equal to 99.9%, which is higher than that of comparative examples 1-2. The above results show that the use of a coupled rectification and melt crystallization method to purify crude glycolide can further enhance the quality of the product as compared to a single process of recrystallization or melt crystallization purified product.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (4)
1. A process for preparing high purity glycolide comprising the steps of: heating and dehydrating glycolic acid or glycollate under the action of a catalyst or dealcoholizing to obtain glycolic acid oligomer, and then heating and decompressing to crack in a depolymerization kettle to obtain crude glycolide, wherein the reaction temperature in the depolymerization kettle is 200-260 ℃ and the reaction pressure is 500-1000 Pa;
the adopted raw material glycolic acid is glycolic acid crystal, firstly, the glycolic acid crystal is added into a reaction kettle, firstly, the temperature is gradually increased to 90 ℃ from normal temperature under normal pressure, the glycolic acid crystal is melted, then a catalyst is added, the reaction kettle is vacuumized to reduce the pressure to 1-5 KPa, the temperature is gradually increased to 200 ℃, and dehydration or dealcoholization reaction is carried out; and/or, adding the glycolate liquid and the catalyst into a reaction kettle, heating the mixture to 180 ℃ from normal temperature in a gradient way under normal pressure, vacuumizing to reduce the pressure of the reaction kettle to 1-5 KPa, heating the mixture to 200 ℃ in a gradient way, and carrying out dehydration or dealcoholization reaction;
the crude glycolide is recrystallized by a solvent under the protection of protective gas, and the recrystallization process is as follows: mixing crude glycolide with solvent, heating, maintaining the temperature for 30-60min after the crude glycolide is completely dissolved, cooling for crystallization, performing suction filtration at 5-10deg.C, and vacuum drying at 50-60deg.C for at least 4 hr to obtain solid crystal;
finally, melting crystallization is used for separating to obtain polymer grade glycolide with purity more than or equal to 99.9%, the melting crystallization operation comprises film forming, cooling crystallization, heating up to sweat, collecting products and discharging mother liquor, heating the glycolide to 85-90 ℃ for melting, cooling crystallization at 0.1-0.5 ℃/min, and controlling the temperature difference between 15 ℃ and 30 ℃; heating at 0.1-0.5 deg.C/min for sweating, controlling temperature difference at 5-20deg.C, and removing sweat; finally, heating, melting and collecting glycolide products;
the glycollate is at least one selected from methyl glycolate, ethyl glycolate, propyl glycolate and butyl glycolate; the catalyst is selected from tin compounds, wherein the tin compounds are at least one of stannous chloride, stannous octoate, stannous chloride dihydrate, stannous lactate and stannous benzoate, and the dosage of the catalyst is 0.005-0.1% of the weight of glycolic acid or glycolate; the solvent is selected from ethyl acetate, and the dosage of the solvent is 0.5-0.8 times of the mass of the crude glycolide.
2. The method for producing high-purity glycolide according to claim 1, wherein: the shielding gas is at least one selected from nitrogen, argon and helium.
3. The method for producing high-purity glycolide according to claim 1, wherein: and (3) applying the residue of the depolymerization kettle to the next cracking reaction.
4. The method for producing high-purity glycolide according to claim 1, wherein: the mother liquor of recrystallization and melt crystallization is used in the next dehydration or dealcoholization reaction.
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