CN114195755B - Preparation method of glycolide - Google Patents
Preparation method of glycolide Download PDFInfo
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- CN114195755B CN114195755B CN202111417971.2A CN202111417971A CN114195755B CN 114195755 B CN114195755 B CN 114195755B CN 202111417971 A CN202111417971 A CN 202111417971A CN 114195755 B CN114195755 B CN 114195755B
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Abstract
The invention relates to a preparation method of glycolide, which comprises the steps of mixing glycolic acid or glycolate, a catalyst and a polar solvent in a reactor, then reacting for a period of time at a temperature higher than the boiling point of the polar solvent, and separating and purifying the mixed product in the reactor after stopping the reaction, thus obtaining the glycolide product. The process for preparing glycolide provided by the invention effectively shortens the reaction flow, basically does not generate glycolic acid oligomer with higher viscosity in the reaction process, is beneficial to improving the heat transfer efficiency of a reaction system, reduces the heat loss, can effectively avoid the phenomenon of solidification and/or coking caused by uneven heating of materials due to rapid increase of the viscosity of the system, can realize continuous and stable efficient production of glycolide, avoids unnecessary material loss, is beneficial to saving production equipment investment, reduces the production cost and energy consumption, realizes low-carbonization production, and is convenient for industrialized expansion production.
Description
Technical Field
The invention belongs to the field of chemical synthesis, and particularly relates to a preparation method of glycolide.
Background
Currently, there are two main routes for preparing polyglycolic acid (PGA) as a biodegradable material: one is the direct dehydration polymerization of glycolic acid, and the other is the ring-opening polymerization of glycolide. Although the direct dehydration polymerization process of glycolic acid is simple in route, a sufficiently high molecular weight cannot be obtained, which also greatly limits the application range of the route for preparing polyglycolic acid. However, although the process route of glycolide ring-opening polymerization is complex, polyglycolic acid products with high enough molecular weight can be obtained, and different application requirements can be met by controlling the polymerization degree of polyglycolic acid. Thus, glycolide ring-opening polymerization has now become the dominant process route for the preparation of polyglycolic acid.
As important monomers required for preparing polyglycolic acid, the synthetic route of glycolide is mainly divided into two types, one is to prepare glycolide by polycondensation-cleavage into rings by taking glycolic acid or glycolate ester substances as raw materials (abbreviated as a two-step process), and the other is to directly cyclize glycolic acid or glycolate ester substances under the action of a catalyst (abbreviated as a one-step process). However, the first synthetic route generally needs to be carried out under the conditions of high temperature, high vacuum degree and high boiling point solvent (the boiling point is usually more than or equal to 280 ℃), the reaction conditions are more severe, the energy consumption is high, the materials in the kettle are easy to coke and are troublesome to clean, the product yield is easy to be reduced, the pipeline is easy to be blocked, the normal production of glycolide is definitely affected, and in addition, the purity of the product is greatly affected due to the use of a large amount of high boiling point solvent.
Unlike the first synthetic route described above, the second synthetic route tends to avoid coking problems and the process flow is relatively short, and thus, there are also some researchers currently struggling to find the feasibility of a "one-step" process. As is typical of the "one-step" process, the gas phase direct cyclization process is a process for the direct synthesis of glycolide from glycolic acid or glycolic esters. For example, rik De Clercq et al (De Clercq et al ChemCatChem.2018, vol.10 (No. 24): 5649-5655) entrain vaporized methyl glycolate into a reactor with an inert gas such as nitrogen, and then carry out the reaction in TiO 2 /SiO 2 Under the action of the catalyst, glycolide and methanol are generated, methanol steam is extracted from the upper part, and glycolide is extracted from the lower part of the reactor in a liquid phase mode. The invention patent publication No. CN112010834 discloses that glycolide is obtained by introducing glycollate vaporized at 150-600deg.C into a reactor containing a tin-containing molecular sieve catalyst, and performing cyclization at 240-320 deg.C. The invention patent with publication number CN112794839A discloses that glycollic acid ester vaporized at 150-600 ℃ is cyclized under the catalysis of titanium-containing molecular sieve at 240-320 ℃ to obtain glycolide. However, the following technical difficulties remain in the gas phase direct cyclization process: the catalyst has the advantages of complex preparation process, easy and quick deactivation, low treatment capacity, high energy consumption and the like, and has a long path from industrialization.
Therefore, there is a need to develop a glycolide preparation method based on a one-step process, which is easy to realize industrial scale-up production, low in energy consumption and high in efficiency.
Disclosure of Invention
The invention aims to solve the problems and provide a preparation method of glycolide.
The aim of the invention is achieved by the following technical scheme:
a process for preparing glycolide includes such steps as mixing glycolic acid or its ester, catalyst and polar solvent, reacting at temp higher than boiling point of polar solvent for a certain period of time, and separating and purifying.
According to the invention, glycolic acid or glycollate, a catalyst and a polar solvent are mixed, in a reaction system, the polar solvent provides a liquid-phase reaction occasion for assisting dispersion and heat transfer, the polar solvent does not participate in the reaction, the reaction can be carried out under a certain pressure (preferably normal pressure) and at a temperature higher than the boiling point of the polar solvent under the corresponding pressure, glycolide can be continuously generated, and the production of glycolic acid oligomer with higher viscosity can be avoided, in the reaction process, the viscosity of the system can be basically maintained at a lower level, thereby being beneficial to improving the heat transfer efficiency of the reaction system, reducing the heat loss, and effectively avoiding the coagulation and/or coking phenomena caused by uneven heating of materials due to rapid increase of the viscosity of the system, so that the continuous, stable and high-efficiency production of glycolide is realized.
As a preferred embodiment, the reaction is carried out at a temperature 10-60 ℃ higher than the boiling point of the polar solvent, and the control of the reaction temperature has an important effect on the final obtaining of high-quality glycolide, and if the temperature is too low, such as 10 ℃ lower than the boiling point of the polar solvent, incomplete and insufficient reaction is caused to affect the final yield of the product; if the temperature is too high, such as 60 ℃ higher than the boiling point of the polar solvent, coking problems can occur, dark brown or black coking blocky bodies are easy to appear in the mixed product, the content of free acid in the product is too high, and when the temperature is controlled to be 10-60 ℃ higher than the boiling point of the polar solvent, a more ideal product can be obtained. The reaction temperature in the process of the invention may be selected from 90 to 310℃and preferably from 110 to 240℃based on the polar solvent selected.
As a preferred embodiment, the reaction time is controlled so as to be from the time when the gas is generated until the mass of the distillate by-product reaches 70 to 90% of the theoretical total mass of the distillate by-product, and the control of the reaction termination time is another influencing factor for obtaining high-quality glycolide. If the reaction is stopped too soon, the problem of incomplete reaction exists, the problem of too low yield can be caused, and if the reaction time is too long, negative effects can exist, on the one hand, the yield is difficult to continuously increase, on the other hand, the energy consumption can be increased, and the energy conservation and consumption reduction are not facilitated. The reaction time in the process of the invention can generally be selected from 0.5 to 16 hours.
Here, when the raw material is glycolic acid, the by-product is water, and when the raw material is glycolic acid ester, the by-product is a corresponding alcohol, for example, when the raw material is methyl glycolate, the by-product is methanol.
As an embodiment, the catalyst may be selected from at least one of tin compounds, antimony compounds, zinc compounds, or alkali metal salts, such as, but not limited to, stannous octoate, stannous chloride, tin lactate, antimony trioxide, diethyl zinc, zinc acetate dihydrate, sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, cesium carbonate, or rubidium sulfate, and the like.
As one embodiment, the catalyst is added in an amount of 0.1 to 15% by mass of glycolic acid or glycolate.
As one embodiment, the polar solvent is 0.5 to 20 times the mass of the glycolic acid or glycolate and maintains the reaction mass in the liquid phase throughout the reaction. In the reaction system, the main function of the polar solvent is to assist dispersion and heat transfer, and the polar solvent does not participate in the reaction.
In one embodiment, the polar solvent is selected from aromatic hydrocarbon solvents or ketone solvents having a boiling point of 80-250 ℃, preferably 100-180 ℃.
Preferably, the aromatic hydrocarbon solvent may be selected from, for example, but not limited to, toluene, para-xylene, and the like; the ketone solvent may be selected from, for example, but not limited to, cyclohexanone, 4-methylcyclohexanone, methyl isobutyl ketone, and the like.
As one embodiment, the polar solvent may contain water, and the mass percentage of water is less than or equal to 5%.
As one implementation scheme, the separation and purification are that the mixed product in a reactor and an organic solvent are mixed at 5-75 ℃, stirred and filtered to obtain a pretreatment liquid, then the pretreatment liquid is evaporated and concentrated to obtain a concentrated liquid, the concentrated liquid is cooled to separate out glycolide crystals, and the glycolide crystals are subjected to suction filtration, remain solids and are subjected to vacuum drying to obtain glycolide products.
As an embodiment, the organic solvent may be selected from, for example, but not limited to, one or more of methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, or acetonitrile.
As one embodiment, the mass ratio of the mixed product to the organic solvent is 1:1-5.
As one embodiment, the conditions of the evaporation concentration are: evaporating and concentrating at absolute pressure of 1-10kPa and at 40-85deg.C until the mass of the rest liquid is 5-80% of that of the pretreatment liquid, and stopping evaporating and concentrating.
As one embodiment, the temperature of the freezing treatment is-30 to-5 ℃.
As one embodiment, the conditions of the vacuum drying are: drying at 40-70deg.C for 1-2 hr under absolute pressure less than or equal to 2 kPa.
The glycolide product prepared by the method has the glycolide purity of more than 99.5 percent, the free acid content of less than or equal to 0.03 weight percent and the water content of less than or equal to 0.01 weight percent.
The glycolide content of the present invention is measured by gas chromatography as known in the art, the water content is measured by karl fischer moisture meter, and the free acid content is measured by potentiometric titration as known in the art (e.g., by automatic potentiometric titration).
Compared with the prior art, the invention has the following beneficial effects:
compared with the existing two-step process, the process for preparing glycolide by the one-step method can effectively shorten the reaction flow, can not generate high-viscosity glycolic acid oligomer in the whole reaction process due to the reaction in a polar solvent, so that the viscosity of a reaction system can be at a lower level, thereby being beneficial to improving the heat transfer efficiency of the reaction system, reducing the heat loss, effectively overcoming the technical problems of easy solidification and/or coking phenomena of materials in a reactor and the like caused by the generation of the high-viscosity glycolic acid oligomer in the prior art, realizing continuous, stable and high-efficiency production of glycolide, effectively avoiding unnecessary material loss, being beneficial to saving production equipment investment, reducing the production cost, realizing low-carbonization production and facilitating industrialized expansion production.
Experimental results show that the purity of the glycolide product prepared by the process method can reach more than 99.5%, the yield of glycolide can reach more than 80%, and the product quality is good, so that the glycolide can be applied to the production and preparation of high-quality polyglycolic acid.
Drawings
FIG. 1 is a GC-MS diagram of the glycolide product obtained in example 1-1.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
Example 1-1
Adding about 7.6kg of glycolic acid, about 8.0kg of toluene and about 0.3kg of stannous octoate into a reactor, stirring and mixing uniformly, heating to about 120 ℃ under normal pressure, starting timing from the moment of steam generation, distilling off by-product water generated in a reaction system along with toluene, adding a proper amount of toluene into the reactor according to actual conditions in the reaction process, so that the liquid level of a reaction material in the reactor is kept stable, recording and discharging the mass of the liquid phase every 30min, measuring the water content in the liquid phase by using a Karl Fischer water analyzer until the distilled water mass reaches about 1.28kg (7.6 kg of the total mass of distilled water is about 1.8kg in theory when the complete reaction of the glycolic acid is carried out), stopping the reaction, retaining a mixed product in the reactor, then mixing the mixed product and ethyl acetate at a mass ratio of 1:1 at about 10 ℃, carrying out suction filtration by using a Buchner funnel, obtaining a pretreatment liquid, evaporating the pretreatment liquid at a temperature of 40 ℃ under a pressure of 1kPa until the mass of the absolute pressure is about 25 kg of the total mass of the total distilled water, concentrating the distilled water until the total mass of the distilled water is about 1.8kg of the total distilled water, concentrating the total mass of the distilled water at about 25.6 kg of the total distilled water, concentrating the total distilled water until the total mass of the total distilled water is about 25.6 kg of the total distilled water, concentrating the total distilled water at about 25.5 kg of the total distilled water, concentrating the total distilled water, and cooling the total distilled water, concentrating the residual ethyl glycolide, and concentrating the total crystalline, and concentrating the residual ethyl glycolide, and concentrating the ethyl acetate under the total mass, and cooling to obtain the product, and cooling and the product, and the product. FIG. 1 is a GC-MS diagram of the glycolide product prepared in this example.
Examples 1 to 2
The procedure of this example was essentially the same as that of example 1-1, except that the reactor was heated to about 140℃in this example, and the reaction was stopped when the distilled water mass reached about 1.52kg, and the remainder was the same as that of example 1-1.
The glycolide product finally obtained in this example was about 5.09kg, corresponding to a yield of about 87.7%.
Examples 1 to 3
The procedure of this example was essentially the same as that of example 1-1, except that the reactor was heated to about 170℃in this example, and the reaction was stopped when the distilled water mass reached about 1.48kg, and the remainder was the same as that of example 1-1.
The glycolide product finally obtained in this example was about 4.94kg, corresponding to a yield of about 85.2%.
Comparative examples 1 to 1
The procedure of this comparative example was essentially the same as in example 1-1 except that the reactor was heated to about 112℃and the reaction was stopped when the distilled water mass reached about 1.0kg, and the remainder was the same as in example 1-1.
The glycolide product finally obtained in this comparative example was about 3.05kg, and the corresponding yield was about 52.6%, which was too low as compared to the above-mentioned example 1-1, probably due to the fact that the reaction temperature was low and the reaction was stopped with less by-product distilled off, so that the reaction was insufficient.
Comparative examples 1 to 2
The procedure of this comparative example was essentially the same as in example 1-1 except that the reactor was heated to about 195℃and the reaction was stopped when the distilled water mass reached about 1.45kg, and the remainder was the same as in example 1-1.
The glycolide product finally obtained in this example was about 4.81kg, corresponding to a yield of about 82.9%, which is a decrease in the yield of this comparative example compared to example 1-1 described above, probably due to the excessive reaction temperature, and the purity was only 98.8% (less than 99%) as seen in table 1.
Comparative examples 1 to 3
The procedure of this comparative example was essentially the same as in example 1-1, except that the reactor was heated to about 240℃and the reaction was stopped when the distilled water mass reached about 1.31kg, and dark brown or black coke cake appeared in the mixed product in the reactor, and the remainder was the same as in example 1-1.
The glycolide product finally obtained in this example was about 3.52kg, corresponding to a yield of about 60.7%. Compared with the example 1-1, the comparative example has the advantages that dark brown or black coking blocky bodies appear in the product due to the excessively high reaction temperature, the yield is further reduced, the purity is only 98.1 percent, and the free acid content is 0.44 percent, which is far greater than that of the example 1-1.
Example 2
Adding about 7.6kg of glycolic acid, about 40kg of toluene and about 0.8kg of tin lactate and about 0.34kg of antimony trioxide into a reactor, stirring and mixing uniformly, heating to about 156 ℃ under normal pressure, starting timing when steam is generated, distilling off by-product water generated in the reaction system along with toluene, adding a proper amount of toluene into the reactor according to actual conditions in the reaction process, so that the liquid level of the reaction material in the reactor is kept stable, recording the mass of a discharged liquid phase every 30min, measuring the water content in the liquid phase by using a Karl Fischer moisture meter until the distilled water mass reaches about 1.42kg (7.6 kg of the total mass of theoretical distilled water is about 1.8kg when the complete reaction is carried out), stopping the reaction, then mixing the mixed product and methyl acetate according to a mass ratio of 1:4 at about 5 ℃, carrying out suction filtration by using a Buchner funnel, obtaining a pretreatment liquid, then evaporating the pretreatment liquid at a temperature of 3kPa, concentrating the liquid until the mass of the liquid is about 48% under the absolute temperature of about 5 ℃ at about 5 ℃ and the absolute temperature of about 5, concentrating the rest of the glycolide, concentrating the liquid until the mass is about 17.5.8 kg of the total mass of the glycolide, concentrating the glycolide, and concentrating until the mass of the rest is about 17.5.5% of the glycolide, concentrating, and concentrating the glycolide, and concentrating until the glycolide at about 17.3.8% by the theoretical mass, and concentrating the mass of the glycolide, and concentrating the product, and the ethyl acetate, thus obtaining the product.
Example 3
Adding about 7.6kg of glycolic acid, about 76kg of paraxylene and about 0.1kg of cesium hydroxide into a reactor, stirring and mixing uniformly, heating to about 170 ℃ under normal pressure, starting from the time when steam is generated, distilling off by-product water generated in a reaction system along with paraxylene, feeding a proper amount of paraxylene into the reactor according to actual conditions in the reaction process so as to keep the liquid level of reaction materials in the reactor stable, recording the mass of a discharged liquid phase every 30min, measuring the water content in the liquid phase by using a Karl Fischer moisture meter until the distilled water mass reaches about 1.53kg (when 7.6kg of glycolic acid is completely reacted, the total mass of distilled water is about 1.8kg theoretically), stopping the reaction, and retaining the mixed products in the reactor, mixing the mixed product and isopropyl acetate according to the mass ratio of 1:1 at about 75 ℃, stirring, carrying out suction filtration by using a Buchner funnel to obtain a pretreatment liquid, then carrying out evaporation concentration under the conditions of absolute pressure of 2kPa and temperature of 85 ℃, stopping evaporation concentration until the mass of the residual liquid is about 5% of the mass of the pretreatment liquid to obtain a concentrated solution, cooling and crystallizing the concentrated solution at about-30 ℃ to separate out glycolide crystals, carrying out suction filtration by using the Buchner funnel, retaining solids, and drying at the absolute pressure of 1.2kPa and temperature of about 70 ℃ for about 1 hour to obtain about 5.01kg of glycolide product, wherein the theoretical mass of glycolide generated by the complete reaction of 7.6kg of glycolic acid is 5.8kg, and thus the yield of glycolide in the embodiment is about 86.4%.
Example 4
About 9.0kg of methyl glycolate, about 180kg of cyclohexanone (the mass of water contained therein is about 2.1 kg), and about 0.9kg of diethyl zinc and about 0.45kg of cesium carbonate are added into a reactor, stirred and mixed uniformly, heated to about 170 ℃ under normal pressure, and the by-product methanol generated in the reaction system is distilled off along with the cyclohexanone from the time when steam is generated, a proper amount of cyclohexanone can be fed into the reactor according to actual conditions in the reaction process so as to keep the liquid level of the reaction material in the reactor stable, the mass of the discharged liquid phase is recorded every about 30min, a gas chromatograph is used for measuring the content of methanol in the liquid phase until the distilled methanol mass reaches about 2.86kg (the total mass of theoretically distilled methanol is about 3.2kg when 9.0kg of methyl glycolate is completely reacted), the reaction is stopped, the mixed product in the reactor is reserved, the mixed product and n-butyl acetate are mixed according to the mass ratio of 1:2 at the temperature of about 65 ℃, after stirring, suction filtration is carried out by adopting a Buchner funnel, thus obtaining pretreatment liquid, then evaporation concentration is carried out under the condition of absolute pressure of 10kPa and temperature of 60 ℃, the evaporation concentration is stopped until the mass of the residual liquid is about 50% of the mass of the pretreatment liquid, thus obtaining concentrated liquid, the concentrated liquid is placed at the temperature of about-10 ℃ for cooling crystallization so as to separate glycolide crystals, suction filtration is carried out by adopting the Buchner funnel, solids are reserved, and drying is carried out for about 1 hour at the absolute pressure of 2kPa and the temperature of about 62 ℃, thus obtaining about 4.95kg of glycolide product, and the theoretical mass of glycolide produced by the complete reaction of 9.0kg of methyl glycolate is 5.8kg, so that the yield of glycolide in the embodiment is about 85.3%.
Example 5
About 9.0kg of methyl glycolate, about 20kg of 4-methylcyclohexanone (the mass of water contained therein is about 0.38 kg), and about 0.01kg of stannous chloride are added into the reactor, stirred and mixed uniformly, heated to about 195 ℃ under normal pressure, the by-product methanol generated in the reaction system is distilled off along with the 4-methylcyclohexanone when starting to generate steam, an appropriate amount of 4-methylcyclohexanone can be fed into the reactor according to actual conditions in the reaction process so as to keep the liquid level of the reaction material in the reactor stable, the mass of the discharged liquid phase is recorded every about 30min, a gas chromatograph is adopted to measure the content of the methanol in the liquid phase until the distilled methanol mass reaches about 2.46kg (the total mass of the distilled methanol is about 3.2kg theoretically when 9.0kg of methyl glycolate is completely reacted), the reaction is stopped, the mixed product in the reactor is reserved, the mixed product and ethyl acetate are mixed according to the mass ratio of 1:5 at about 40 ℃, after stirring, suction filtration is carried out by adopting a Buchner funnel, thus obtaining pretreatment liquid, then evaporation concentration is carried out under the condition of absolute pressure of 4kPa and temperature of 56 ℃, the evaporation concentration is stopped until the mass of the residual liquid is about 80% of the mass of the pretreatment liquid, thus obtaining concentrated liquid, the concentrated liquid is placed at about-5 ℃ for cooling crystallization to separate glycolide crystals, suction filtration is carried out by adopting the Buchner funnel, solids are reserved, and drying is carried out for about 2 hours at the absolute pressure of 0.1kPa and the temperature of about 40 ℃, thus obtaining about 5.09kg of glycolide product, and the theoretical mass of glycolide generated by the complete reaction of 9.0kg of methyl glycolate is 5.8kg, thus the yield of glycolide in the embodiment is about 87.8%.
Example 6
About 9.0kg of methyl glycolate, about 10kg of 4-methylcyclohexanone (the mass of water contained therein is about 0.03 kg), and about 0.1kg of stannous octoate and about 0.06kg of cesium hydroxide are added into the reactor, and stirred and mixed uniformly, heated to about 195 ℃ under normal pressure, and the by-product methanol generated in the reaction system is distilled off along with the 4-methylcyclohexanone from the time when steam is generated, an appropriate amount of 4-methylcyclohexanone can be fed into the reactor according to actual conditions during the reaction so that the liquid level of the reaction material in the reactor is kept stable, the mass of the discharged liquid phase is recorded every 30min, and a gas chromatograph is used to measure the content of methanol in the liquid phase until the distilled methanol mass reaches about 2.80kg (the total mass of distilled methanol is about 3.2kg in theory when 9.0kg of methyl glycolate is completely reacted), stopping the reaction, keeping the mixed product in the reactor, mixing the mixed product and ethyl acetate according to the mass ratio of 1:4 at about 25 ℃, stirring, carrying out suction filtration by using a Buchner funnel to obtain a pretreatment liquid, then carrying out evaporation concentration under the conditions of absolute pressure of 1kPa and temperature of 50 ℃ until the mass of the residual liquid is about 20% of the mass of the pretreatment liquid, stopping evaporation concentration to obtain a concentrated solution, then placing the concentrated solution at about-20 ℃ for cooling crystallization to separate glycolide crystals, carrying out suction filtration by using the Buchner funnel, keeping the solid, and drying at the absolute pressure of 0.1kPa and the temperature of about 40 ℃ for about 2 hours to obtain about 5.24kg of glycolide product, wherein the theoretical mass of glycolide generated by the complete reaction of 9.0kg of methyl glycolate is 5.8kg, the glycolide yield in this example was about 90.3%.
Product testing
Glycolide products prepared in examples 1-1 to 1-3, comparative examples 1-1 to 1-3, and examples 2-6 above, wherein the glycolide content was measured using a gas chromatography method well known in the art, the water content was measured using a karl fischer moisture meter, and the free acid content was measured using a potentiometric titration method well known in the art (e.g., using an automatic potentiometric titration apparatus), the measurement results are shown in table 1 below.
Table 1 test results
| Project | Purity of | Free acid content | Water content |
| Example 1-1 | 99.6％ | 0.010％ | 0.0066％ |
| Examples 1 to 2 | 99.8％ | 0.012％ | 0.0059％ |
| Examples 1 to 3 | 99.5％ | 0.018％ | 0.0047％ |
| Comparative examples 1 to 1 | 99.5％ | 0.029％ | 0.0074％ |
| Comparative examples 1 to 2 | 98.8％ | 0.023％ | 0.0077％ |
| Comparative examples 1 to 3 | 98.1％ | 0.44％ | 0.0086％ |
| Example 2 | 99.8％ | 0.014％ | 0.0055％ |
| Example 3 | 99.7％ | 0.008％ | 0.0069％ |
| Example 4 | 99.6％ | 0.020％ | 0.0070％ |
| Example 5 | 99.7％ | 0.009％ | 0.0051％ |
| Example 6 | 99.9％ | 0.010％ | 0.0063％ |
As shown in the test results of the table 1, the glycolide product prepared by the method has the purity of more than or equal to 99.5%, the free acid content of less than or equal to 0.03wt% and the water content of less than or equal to 0.01wt%, and belongs to high-quality glycolide.
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.
Claims (7)
1. A preparation method of glycolide is characterized in that glycolic acid or glycolate and a catalyst are mixed with an aromatic hydrocarbon solvent or ketone solvent with the boiling point of 100-180 ℃ in a reactor, then the mixture is reacted for a period of time at the temperature 10-60 ℃ higher than the boiling point of the aromatic hydrocarbon solvent or ketone solvent, and after stopping the reaction, the mixed product in the reactor is separated and purified to obtain a glycolide product;
wherein the catalyst is at least one of tin compounds, antimony compounds, zinc compounds or alkali metal salts;
the aromatic hydrocarbon solvent is toluene or paraxylene, and the ketone solvent is cyclohexanone, 4-methylcyclohexanone or methyl isobutyl ketone;
starting from the time when gas is generated, the reaction time is controlled to be 70-90% of the total mass of the distillation byproducts.
2. The method for producing glycolide according to claim 1, wherein the catalyst is added in an amount of 0.1 to 15% by mass of the glycolic acid or the glycolate.
3. The method for producing glycolide according to claim 1, wherein the polar solvent is 0.5 to 20 times by mass of glycolic acid or glycolate, and the reaction mass in the reactor is maintained in the liquid phase all the time during the reaction.
4. The method for preparing glycolide according to claim 1, wherein the separation and purification are to mix the mixed product in the reactor with an organic solvent at 5-75 ℃, stir and filter the mixture to obtain a pretreatment liquid, then evaporate and concentrate the pretreatment liquid to obtain a concentrate, then cool the concentrate to separate out glycolide crystals, suction-filter the concentrate, retain solids, and then vacuum-dry the concentrate to obtain the glycolide product.
5. The method for preparing glycolide according to claim 4, wherein the organic solvent is one or more selected from methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate, methanol, ethanol, n-propanol, isopropanol, butanol, acetone and acetonitrile, and the mass ratio of the mixed product to the organic solvent is 1:1-5.
6. The method for preparing glycolide according to claim 4, wherein the evaporating and concentrating conditions are as follows: evaporating and concentrating at absolute pressure of 1-10kPa and at 40-85deg.C until the mass of the rest liquid is 5-80% of that of the pretreatment liquid, and stopping evaporating and concentrating.
7. The method for preparing glycolide according to claim 4, wherein the cooling treatment is freezing treatment, and the temperature is-30 to-5 ℃;
the conditions of the vacuum drying are as follows: drying at 40-70deg.C for 1-2 hr under absolute pressure less than or equal to 2 kPa.
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