CN114195755B - A kind of preparation method of glycolide - Google Patents

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

A kind of preparation method of glycolide

Technical field

The invention belongs to the field of chemical synthesis, and specifically relates to a preparation method of glycolide.

Background technique

Currently, there are two main process routes for preparing biodegradable material polyglycolic acid (PGA for short): one is direct dehydration polymerization of glycolic acid, and the other is glycolide ring-opening polymerization. Although the direct dehydration polymerization process of glycolic acid has a simple route, it cannot obtain a sufficiently high molecular weight, which also greatly limits the application range of polyglycolic acid prepared by this route. Although the process route of glycolide ring-opening polymerization is relatively complicated, polyglycolic acid products with sufficiently high molecular weight can be obtained, and the polymerization degree of polyglycolic acid can be controlled to meet the needs of different uses. Therefore, glycolide ring-opening polymerization has now become the mainstream process route for the preparation of polyglycolic acid.

As an important monomer required for the preparation of polyglycolic acid, the synthesis route of glycolide is mainly divided into two types. One is to prepare glycolide ( Referred to as the "two-step" process), the other is directly cyclized by glycolic acid or glycolate esters under the action of a catalyst (referred to as the "one-step" process). However, the above-mentioned first synthesis route usually requires reaction under the conditions of high temperature, high vacuum and the presence of high boiling point solvent (boiling point is usually ≥280°C). The reaction conditions are relatively harsh, energy consumption is large, and the materials in the kettle are prone to coking. Cleaning is troublesome and can easily lead to reduced product yields and pipeline blockage, which will undoubtedly seriously affect the normal production of glycolide. In addition, due to the use of a large amount of high-boiling point solvents, it will have a greater impact on product purity.

Different from the first synthesis path mentioned above, the second synthesis path can often avoid coking problems and the process flow is relatively short. Therefore, many researchers are currently working hard to explore the feasibility of the "one-step" process. As a typical "one-step" process, the gas-phase direct cyclization method is a process for directly synthesizing glycolide from glycolic acid or glycolate ester. For example, Rik De Clercq et al. (De Clercq et al. ChemCatChem. 2018, Vol. 10 (No. 24): 5649-5655) used inert gases such as nitrogen as a carrier to entrain vaporized methyl glycolate to the reactor. , glycolide and methanol are generated under the action of TiO ₂ /SiO ₂ catalyst. Methanol steam is extracted from the upper part, and glycolide is extracted from the lower part of the reactor in liquid phase. The invention patent with publication number CN112010834 discloses that the glycolate ester vaporized at 150-600°C is passed into a reactor equipped with a tin-containing molecular sieve catalyst, and a cyclization reaction is performed at 240-320°C to obtain glycolide. The invention patent with publication number CN112794839A discloses that glycolic acid ester vaporized at 150-600°C is subjected to a cyclization reaction at 240-320°C under conditions catalyzed by titanium-containing molecular sieves to obtain glycolide. However, the gas-phase direct cyclization method still has the following technical problems: the catalyst preparation process is complex, easy to deactivate quickly, low processing capacity, and high energy consumption. It is still a long way from industrialization.

Therefore, there is an urgent need to develop a glycolide preparation method based on a "one-step" process that is easy to achieve industrial scale-up production, has low energy consumption and is highly efficient.

Contents of the invention

The purpose of the present invention is to provide a preparation method of glycolide in order to solve the above problems.

The object of the present invention is achieved through the following technical solutions:

A method for preparing glycolide. In a reactor, glycolic acid or glycolate ester, a catalyst and a polar solvent are mixed, and then reacted for a period of time at a temperature higher than the boiling point of the polar solvent. After stopping the reaction, The mixed products in the reactor are separated and purified to obtain the glycolide product.

In the present invention, glycolic acid or glycolate ester, a catalyst and a polar solvent are mixed. In the reaction system, the polar solvent provides a liquid phase reaction situation and is used to assist dispersion and heat transfer. It does not participate in the reaction itself, and the reaction can be carried out in a certain amount of time. Under 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 glycolic acid oligomers with higher viscosity can be avoided. During the reaction process , the viscosity of the system can be basically maintained at a low level, which is not only conducive to improving the heat transfer efficiency of the reaction system and reducing heat loss, but also effectively avoiding the uneven heating of the material due to the rapid increase in system viscosity, resulting in solidification and/or coking. , thereby achieving continuous, stable and efficient production of glycolide.

As a preferred embodiment, the reaction is carried out at a temperature 10-60°C higher than the boiling point of the polar solvent. The control of the reaction temperature has an important impact on finally obtaining high-quality glycolide. If the temperature is too low, such as below When the boiling point of the polar solvent is 10°C, the reaction will be incomplete and insufficient, affecting the final yield of the product; and if the temperature is too high, such as 60°C higher than the boiling point of the polar solvent, coking problems will occur and it is easy to form in the mixed product. Dark brown or black coked lumps appear, and the free acid content of the product is too high. When the temperature is controlled to be 10-60°C higher than the boiling point of the polar solvent, a more ideal product can be obtained. Based on the selected polar solvent, the reaction temperature in the method of the present invention can be selected from 90 to 310°C, preferably from 110 to 240°C.

As a preferred embodiment, timing starts when gas is generated. The reaction time is controlled until the mass of the distilled by-products reaches 70-90% of the theoretical total mass of the distilled by-products. The reaction termination time is controlled to obtain a high Another factor influencing the quality of glycolide. If the reaction is stopped too early, the reaction will be incomplete and the yield will be too low. If the reaction time is too long, there will also be negative effects. On the one hand, it will be difficult to continue to increase the yield, and on the other hand, it will increase. Large energy consumption is not conducive to energy saving and consumption reduction. The reaction time in the method of the present invention can generally be selected from 0.5 to 16 hours.

It should be noted here that when the raw material is glycolic acid, the by-product is water; when the raw material is glycolate ester, the by-product is the corresponding alcohol. For example, when the raw material is methyl glycolate, the by-product is water. The by-product is methanol.

As an embodiment, the catalyst can 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, tin lactate, etc. Antimony oxide, diethyl zinc, zinc acetate dihydrate, sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, cesium carbonate, or rubidium sulfate, etc.

As an embodiment, the added amount of the catalyst is 0.1-15% of the mass of glycolic acid or glycolate ester.

As an embodiment, the polar solvent is 0.5-20 times the mass of glycolic acid or glycolate ester, and the reaction materials in the reactor are always kept in the liquid phase during the reaction process. In the reaction system, the main function of the polar solvent is to assist dispersion and heat transfer, and it does not participate in the reaction.

As an embodiment, the polar solvent is selected from aromatic hydrocarbon solvents or ketone solvents with a boiling point of 80-250°C, preferably 100-180°C.

Preferably, the aromatic hydrocarbon solvent can be selected from, for example, but not limited to, toluene, p-xylene, etc.; the ketone solvent can be selected from, for example, but not limited to, cyclohexanone, 4-methylcyclohexanone. , methyl isobutyl ketone, etc.

As an embodiment, the polar solvent may contain water, and the mass percentage of water is ≤5%.

As an embodiment, the separation and purification is to mix the mixed product and the organic solvent in the reactor at 5-75°C, stir, and filter to obtain a pretreatment liquid, and then evaporate and concentrate the pretreatment liquid to obtain a concentrated liquid. , and then the concentrated liquid is cooled to precipitate glycolide crystals. After suction filtration, the solid is retained, and then vacuum dried to obtain the glycolide product.

As an embodiment, the organic solvent may be selected from, for example, but not limited to, methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate, methanol, ethanol, n-propanol, isopropyl alcohol, butyl acetate. One or more of alcohol, acetone or acetonitrile.

As an embodiment, the mass ratio of the mixed product to the organic solvent is 1:1-5.

As an embodiment, the conditions for evaporation and concentration are: evaporation and concentration are carried out at an absolute pressure of 1-10kPa and 40-85°C until the mass of the remaining liquid reaches 5-80% of the mass of the pretreatment liquid, and the evaporation and concentration are stopped.

As an embodiment, the temperature of the freezing treatment is -30~-5°C.

As an embodiment, the vacuum drying conditions are: drying at an absolute pressure ≤ 2 kPa and a temperature of 40-70°C for 1-2 hours.

The purity of glycolide in the glycolide product prepared by the method of the invention can reach more than 99.5%, the free acid content is ≤0.03wt%, and the water content is ≤0.01wt%.

In the present invention, the content of glycolide is measured using a gas chromatography analysis method known in the art, the content of water is measured using a Karl Fischer moisture analyzer, and the content of free acid is measured using a potentiometric titration method known in the art. (for example, measured using an automatic potentiometric titrator).

Compared with the prior art, the present invention has the following beneficial effects:

The present invention provides a "one-step" process for preparing glycolide. Compared with the existing "two-step" process, the reaction process can be effectively shortened. Since the reaction is carried out in a polar solvent, there will be no Producing high-viscosity glycolic acid oligomers allows the viscosity of the reaction system to be at a lower level, which is not only beneficial to improving the heat transfer efficiency of the reaction system and reducing heat loss, but also effectively overcomes the problem of generating high-viscosity ethanol in the existing technology. Acid oligomers can easily lead to technical problems such as solidification and/or coking of materials in the reactor. It can achieve continuous, stable and efficient production of glycolide, and can effectively avoid unnecessary material loss, which is beneficial to saving investment in production equipment. , reduce production costs, and have low energy consumption, can achieve low-carbon production, and facilitate industrial expansion of production.

Experimental results show that the purity of glycolide products produced by the process of the present invention can reach more than 99.5%, and the yield of glycolide can reach more than 80%. The product quality is good and can be used in the production of high-quality polyglycolic acid. preparation.

Description of drawings

Figure 1 is a GC-MS chart of the glycolide product prepared in Example 1-1.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1-1

Add about 7.6kg of glycolic acid, about 8.0kg of toluene, and about 0.3kg of stannous octoate into the reactor, stir and mix evenly, heat to about 120°C under normal pressure, and start timing when steam is generated. The by-product water generated in the reaction system will distill out along with the toluene. During the reaction process, an appropriate amount of toluene can be added to the reactor according to the actual situation to keep the liquid level of the reaction materials in the reactor stable. At the same time, each Record the mass of the discharged liquid phase at intervals of about 30 minutes, and use a Karl Fischer moisture analyzer to measure the water content in the liquid phase until the mass of distilled water reaches about 1.28kg (when 7.6kg of glycolic acid is completely reacted, the theoretical value of the distilled water The total mass is about 1.8kg), stop the reaction, retain the mixed product in the reactor, and then mix the mixed product and ethyl acetate at a mass ratio of 1:1 at about 10°C. After stirring, use a Buchner funnel. Perform suction filtration to obtain the pretreatment liquid, and then perform evaporation and concentration under the conditions of an absolute pressure of 1kPa and a temperature of 40°C until the mass of the remaining liquid is approximately 25% of the mass of the pretreatment liquid. Stop evaporation and concentration to obtain the concentrated liquid. , and then place the concentrated liquid at about -18°C for cooling and crystallization to precipitate glycolide crystals, and then use a Buchner funnel for suction filtration to retain the solid, and then dry it at an absolute pressure of 1kPa and a temperature of about 56°C In about 2 hours, about 4.72kg of glycolide product is obtained. Since the theoretical mass of glycolide generated by the complete reaction of 7.6kg of glycolic acid is 5.8kg, the yield of glycolide in this embodiment is about 81.4%. Figure 1 is a GC-MS diagram of the glycolide product prepared in this example.

Example 1-2

The operating steps of this example are basically the same as those of Example 1-1. The difference is that in this example, the reactor is heated to about 140°C, and this example stops when the mass of distilled water reaches about 1.52kg. The rest of the reaction was the same as in Example 1-1.

The glycolide product finally obtained in this example is about 5.09kg, and the corresponding yield is about 87.7%.

Example 1-3

The operating steps of this example are basically the same as those of Example 1-1. The difference is that in this example, the reactor is heated to about 170°C, and this example stops when the mass of distilled water reaches about 1.48kg. The rest of the reaction was the same as in Example 1-1.

The glycolide product finally obtained in this example is about 4.94kg, and the corresponding yield is about 85.2%.

Comparative example 1-1

The operating steps of this comparative example are basically the same as those of Example 1-1. The difference is that in this comparative example, the reactor is heated to about 112°C, and this comparative example stops when the mass of distilled water reaches about 1.0kg. The rest of the reaction was the same as in Example 1-1.

The final glycolide product obtained in this comparative example is about 3.05kg, and the corresponding yield is about 52.6%. Compared with the above embodiment 1-1, the yield of this comparative example is too low, which may be due to the reaction temperature It is lower and the reaction stops when less by-products are distilled, resulting in insufficient reaction.

Comparative Example 1-2

The operating steps of this comparative example are basically the same as those of Example 1-1. The difference is that in this comparative example, the reactor is heated to about 195°C, and this comparative example stops when the mass of distilled water reaches about 1.45kg. The rest of the reaction was the same as in Example 1-1.

The glycolide product finally obtained in this example is about 4.81kg, and the corresponding yield is about 82.9%. Compared with the above-mentioned Example 1-1, the yield of this comparative example has decreased, which may be due to the reaction Caused by excessive temperature, it can be seen from Table 1 that its purity is only 98.8% (less than 99%).

Comparative Example 1-3

The operating steps of this comparative example are basically the same as those of Example 1-1. The difference is that in this comparative example, the reactor is heated to about 240°C, and this comparative example stops when the mass of distilled water reaches about 1.31kg. After the reaction, dark brown or black coked lumps appeared in the mixed product in the reactor, and the rest was the same as in Example 1-1.

The glycolide product finally obtained in this example is about 3.52kg, and the corresponding yield is about 60.7%. Compared with the above-mentioned Example 1-1, in this comparative example, due to the reaction temperature being too high, dark brown or black coked lumps appeared in the product, the yield was further reduced, the purity was only 98.1%, and the free acid content was 0.44%, which was far greater. In Example 1-1.

Example 2

Add about 7.6kg of glycolic acid, about 40kg of toluene, about 0.8kg of tin lactate and about 0.34kg of antimony trioxide into the reactor, stir and mix evenly, and heat to about 156°C under normal pressure. Start timing when steam is generated. The by-product water generated in the reaction system will distill out along with the toluene. During the reaction process, an appropriate amount of toluene can be added to the reactor according to the actual situation to ensure that the liquid level of the reaction materials in the reactor is Maintain stability, and at the same time, record the mass of the discharged liquid phase every 30 minutes, and use a Karl Fischer moisture analyzer to measure the water content in the liquid phase until the mass of distilled water reaches approximately 1.42kg (when 7.6kg glycolic acid is completely reacted) (theoretically the total mass of distilled water is about 1.8kg), stop the reaction, retain the mixed product in the reactor, and then mix the mixed product and methyl acetate at a mass ratio of 1:4 at about 5°C. After stirring , use a Buchner funnel to perform suction filtration to obtain the pretreatment liquid, and then perform evaporation and concentration under the conditions of an absolute pressure of 3kPa and a temperature of 48°C until the mass of the remaining liquid is approximately 10% of the mass of the pretreatment liquid, and stop evaporation Concentrate to obtain a concentrated liquid, and then place the concentrated liquid at about -23°C for cooling and crystallization to precipitate glycolide crystals, and then use a Buchner funnel for suction filtration to retain the solid, and then filter it under an absolute pressure of 0.5kPa, Dry at a temperature of about 60°C for about 2 hours to obtain about 5.17kg of glycolide product. Since the theoretical mass of glycolide generated by the complete reaction of 7.6kg of glycolic acid is 5.8kg, therefore, in this embodiment, the glycolide product The yield of lactide was approximately 89.1%.

Example 3

Add about 7.6kg of glycolic acid, about 76kg of paraxylene, and about 0.1kg of cesium hydroxide into the reactor, stir and mix evenly, heat to about 170°C under normal pressure, and start timing when steam is generated. , the by-product water generated in the reaction system will distill out along with the paraxylene. During the reaction process, an appropriate amount of paraxylene can be added to the reactor according to the actual situation to maintain the liquid level of the reaction materials in the reactor. Stable, at the same time, record the mass of the discharged liquid phase every 30 minutes, and use a Karl Fischer moisture analyzer to measure the water content in the liquid phase until the mass of distilled water reaches about 1.53kg (when 7.6kg of glycolic acid is completely reacted, Theoretically the total mass of distilled water is about 1.8kg), stop the reaction, retain the mixed product in the reactor, and then mix the mixed product and isopropyl acetate at a mass ratio of 1:1 at about 75°C, after stirring , use a Buchner funnel to perform suction filtration to obtain the pretreatment liquid, and then perform evaporation and concentration under the conditions of an absolute pressure of 2kPa and a temperature of 85°C until the mass of the remaining liquid is approximately 5% of the mass of the pretreatment liquid, and stop evaporation Concentrate to obtain a concentrated liquid, and then place the concentrated liquid at about -30°C for cooling and crystallization to precipitate glycolide crystals, and then use a Buchner funnel to perform suction filtration to retain the solid, and then filter under an absolute pressure of 1.2kPa, After drying for about 1 hour at a temperature of about 70°C, about 5.01kg of glycolide product is obtained. Since the theoretical mass of glycolide produced by the complete reaction of 7.6kg of glycolic acid is 5.8kg, therefore, in this embodiment, the glycolide product is The yield of lactide was approximately 86.4%.

Example 4

Add about 9.0kg of methyl glycolate, about 180kg of cyclohexanone (the mass of water contained in it is about 2.1kg), about 0.9kg of diethyl zinc and about 0.45kg of cesium carbonate into the reactor, and stir Mix evenly, and heat to about 170°C under normal pressure. Start timing when steam is generated. The by-product methanol generated in the reaction system will distill out along with the cyclohexanone. During the reaction, the reaction can be directed to the reactor according to the actual situation. Add an appropriate amount of cyclohexanone into the reactor to keep the liquid level of the reaction materials in the reactor stable. At the same time, record the mass of the discharged liquid phase every 30 minutes, and use a gas chromatograph to measure the methanol content in the liquid phase. Until the mass of methanol distilled reaches about 2.86kg (when 9.0kg methyl glycolate is completely reacted, the total mass of methanol distilled is theoretically about 3.2kg), the reaction is stopped, the mixed product in the reactor is retained, and then at about 65 The mixed product and n-butyl acetate are mixed at a mass ratio of 1:2 at ℃. After stirring, the Buchner funnel is used for suction filtration to obtain the pretreatment liquid, and then the pretreatment liquid is obtained under the conditions of an absolute pressure of 10kPa and a temperature of 60℃. Carry out evaporation and concentration until the mass of the remaining liquid is about 50% of the mass of the pretreatment liquid. Stop evaporation and concentration to obtain a concentrated liquid. The concentrated liquid is then placed at about -10°C for cooling and crystallization to precipitate glycolide. The crystals are then suction filtered using a Buchner funnel to retain the solid, and then dried at an absolute pressure of 2kPa and a temperature of about 62°C for about 1 hour to obtain about 4.95kg of glycolide product. Since 9.0kg of glycolic acid methyl The theoretical mass of glycolide produced by the complete reaction of the ester is 5.8 kg. Therefore, the yield of glycolide in this embodiment is about 85.3%.

Example 5

Add about 9.0kg of methyl glycolate, about 20kg of 4-methylcyclohexanone (the mass of water contained in it is about 0.38kg), and about 0.01kg of stannous chloride into the reactor, stir and mix evenly , under normal pressure, heat to about 195°C. Start timing when steam is generated. The by-product methanol generated in the reaction system will distill out along with 4-methylcyclohexanone. During the reaction process, the reaction can be adjusted according to the actual situation. Add an appropriate amount of 4-methylcyclohexanone to the reactor to keep the liquid level of the reaction materials in the reactor stable. At the same time, record the mass of the discharged liquid phase every 30 minutes and use a gas chromatograph to measure the liquid level. The content of methanol in the phase until the mass of methanol distilled reaches about 2.46kg (when 9.0kg methyl glycolate is completely reacted, the total mass of methanol distilled is theoretically about 3.2kg), the reaction is stopped and the mixing in the reactor is retained. product, and then mix the mixed product and ethyl acetate at a mass ratio of 1:5 at about 40°C. After stirring, use a Buchner funnel for suction filtration to obtain the pretreatment liquid, and then filter it at an absolute pressure of 4kPa and a temperature of Carry out evaporation and concentration under the conditions of 56°C until the mass of the remaining liquid is about 80% of the mass of the pretreatment solution. Stop the evaporation and concentration to obtain a concentrated solution. The concentrated solution is then placed at about -5°C for cooling and crystallization. Glycolide crystals are precipitated, and then filtered using a Buchner funnel to retain the solid, and then dried at an absolute pressure of 0.1kPa and a temperature of about 40°C for about 2 hours to obtain about 5.09kg of glycolide product. The theoretical mass of glycolide produced by the complete reaction of 9.0 kg of methyl glycolate is 5.8 kg. Therefore, the yield of glycolide in this embodiment is about 87.8%.

Example 6

About 9.0kg of methyl glycolate, about 10kg of 4-methylcyclohexanone (the mass of water contained in it is about 0.03kg), about 0.1kg of stannous octoate and about 0.06kg of hydrogen were added to the reactor. Cesium oxide, stir and mix evenly, and heat to about 195°C under normal pressure. Start timing when steam is generated. The by-product methanol generated in the reaction system will distill out along with 4-methylcyclohexanone. During the reaction During the process, an appropriate amount of 4-methylcyclohexanone can be added to the reactor according to the actual situation to keep the liquid level of the reaction materials in the reactor stable. At the same time, the quality of the discharged liquid phase is recorded every 30 minutes and used Use a gas chromatograph to measure the methanol content in the liquid phase until the mass of distilled methanol reaches about 2.80kg (when 9.0kg of methyl glycolate is completely reacted, the theoretical total mass of distilled methanol is about 3.2kg), stop the reaction, Retain the mixed product in the reactor, and then mix the mixed product and ethyl acetate at a mass ratio of 1:4 at about 25°C. After stirring, use a Buchner funnel for suction filtration to obtain a pretreatment liquid, which is then Carry out evaporation and concentration under the conditions of absolute pressure of 1kPa and temperature of 50°C until the mass of the remaining liquid is about 20% of the mass of the pretreatment liquid. Stop evaporation and concentration to obtain a concentrated liquid, and then place the concentrated liquid at about -20°C. Cool and crystallize at a low temperature to precipitate glycolide crystals, and then use a Buchner funnel to perform suction filtration to retain the solid, and then dry it at an absolute pressure of 0.1kPa and a temperature of about 40°C for about 2 hours, to obtain about 5.24kg of For glycolide products, since the theoretical mass of glycolide produced by the complete reaction of 9.0 kg of methyl glycolate is 5.8 kg, the yield of glycolide in this embodiment is about 90.3%.

product testing

For the glycolide products prepared in the above-mentioned Examples 1-1 to 1-3, Comparative Examples 1-1 to 1-3, and Example 2-6, the content of glycolide is analyzed by gas chromatography well-known in the art. To measure, the water content is measured using a Karl Fischer moisture analyzer, and the free acid content is measured using a potentiometric titration method known in the art (for example, using an automatic potentiometric titrator). The measurement results are shown in Table 1 below.

Table 1 test results

project purity free acid content water content Example 1-1 99.6% 0.010% 0.0066% Example 1-2 99.8% 0.012% 0.0059% Example 1-3 99.5% 0.018% 0.0047% Comparative example 1-1 99.5% 0.029% 0.0074% Comparative Example 1-2 98.8% 0.023% 0.0077% Comparative Example 1-3 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%

From the test results in Table 1 above, it can be seen that the glycolide product produced based on this method has a purity of ≥99.5%, a free acid content of ≤0.03wt%, and a water content of ≤0.01wt%, and is a high-quality glycolide.

The above description of the embodiments is to facilitate those of ordinary skill in the technical field to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without inventive efforts. Therefore, the present invention is not limited to the above embodiments. Based on the disclosure of the present invention, improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims (7)

1. A preparation method of glycolide, characterized in that, in a reactor, glycolic acid or glycolic acid ester, a catalyst and an aromatic hydrocarbon solvent or ketone solvent with a boiling point of 100-180°C are mixed, and then the mixture is heated at high temperature. React for a period of time at a temperature of the aromatic hydrocarbon solvent or ketone solvent with a boiling point of 10-60°C. After stopping the reaction, separate and purify the mixed product in the reactor to obtain the 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 p-xylene, and the ketone solvent is cyclohexanone, 4-methylcyclohexanone or methyl isobutyl ketone; Timing begins when gas is generated, and the reaction time is controlled until the mass of the distilled by-products reaches 70-90% of the theoretical total mass of the distilled by-products. 2. The preparation method of glycolide according to claim 1, characterized in that the added amount of the catalyst is 0.1-15% of the mass of the glycolic acid or glycolate ester. 3. The preparation method of glycolide according to claim 1, characterized in that the polar solvent is 0.5-20 times the quality of glycolic acid or glycolate ester, and the reactor is always maintained during the reaction process. The reaction material is in the liquid phase. 4. The preparation method of glycolide according to claim 1, characterized in that the separation and purification is to mix the mixed product in the reactor and the organic solvent at 5-75°C, stir, and filter to obtain The pretreatment liquid is then evaporated and concentrated to obtain a concentrated liquid. The concentrated liquid is then cooled to precipitate glycolide crystals. After suction filtration, the solid is retained, and then vacuum dried to obtain the glycolide product. . 5. a kind of preparation method of glycolide according to claim 4, is characterized in that, described organic solvent is selected from methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate, methanol, ethanol, One or more of n-propanol, isopropanol, butanol, acetone or acetonitrile, the mass ratio of the mixed product to the organic solvent is 1:1-5. 6. The preparation method of glycolide according to claim 4, characterized in that the conditions for evaporation and concentration are: evaporation and concentration at an absolute pressure of 1-10kPa and 40-85°C until the remaining liquid is The quality is 5-80% of the quality of the pretreatment liquid. Stop evaporation and concentration. 7. The preparation method of glycolide according to claim 4, characterized in that the cooling treatment is freezing treatment, and the temperature is -30~-5°C; The conditions for vacuum drying are: drying at an absolute pressure of ≤2kPa and a temperature of 40-70°C for 1-2 hours.