Glycolide, method for preparing glycolide and glycolide obtained

Abstract

The present invention discloses glycolide, a preparation method of glycolide and the obtained glycolide, wherein the glycolide has an acid value of less than 5 mol / t, a linear dimer content of less than 200 ppm, and a total cyclic polymer content of less than 400 ppm; the method comprises: (1) reacting an aqueous glycolic acid solution in the presence of a catalyst to obtain glycolic acid oligomers, wherein the aqueous glycolic acid solution contains at least one of an aldehyde compound, a ketone compound, and an ether compound; (2) washing the glycolic acid oligomers to obtain purified glycolic acid oligomers; (3) depolymerizing the purified glycolic acid oligomers to obtain a crude glycolide product; and (4) refining the crude glycolide product to obtain glycolide. The method of the present invention has a high glycolide yield, and the obtained glycolide product has the advantages of low acid value and low content of linear dimers and cyclic polymers (tetramer to octamer).

Description

Technical Field

[0001] The invention belongs to the field of glycolide preparation, and in particular relates to glycolide, a method for preparing glycolide and the obtained glycolide. Background Art

[0002] As an aliphatic polyester, polyglycolide has high biodegradability and good biocompatibility. It can be hydrolyzed in the body and metabolized by microorganisms in the natural environment, and finally decomposed into water and carbon dioxide. In addition, polyglycolide has good mechanical properties such as heat resistance and tensile strength, and good gas barrier properties when used as a film sheet. Therefore, polyglycolide is expected to replace general biodegradable polymers in medical polymer materials, agricultural resource materials, and various packaging or container materials. Polyglycolide has been used in surgical sutures, artificial skin and blood vessels, bone fixation and repair, drug controlled release, tissue engineering and other fields.

[0003] There are two methods for preparing polyglycolide. One is to obtain it by direct dehydration and polycondensation of glycolic acid. The molecular weight of the polyglycolide obtained by this method is not high, and it is difficult to be used for processing and molding materials. The other method is to heat and decompose the glycolic acid polycondensation polymer to obtain cyclic glycolide, and then use glycolide ring-opening polymerization to obtain polyglycolide with a molecular weight of tens of thousands to hundreds of thousands, which can meet the needs of post-processing.

[0004] Glycolide is a compound with a cyclic dimer structure formed by removing two molecules of water from two molecules of glycolic acid. Glycolide is not only a monomer for synthesizing polyglycolide, but it can also be ring-opened copolymerized with other cyclic monomers to obtain random copolymers or block copolymers. Generally, the synthesis of glycolide monomer is divided into two steps: first, a low molecular weight polymer called glycolic acid oligomer is synthesized through condensation polymerization of glycolic acid; second, the glycolic acid oligomer is depolymerized by high-temperature distillation, and the gaseous product glycolide crude product is extracted from the reaction system.

[0005]

[0006] The crude glycolide product obtained by the above reaction usually contains various impurities such as water, glycolic acid, glycolic acid oligomers, etc. The very small amount of active hydrogen contained in these impurities will have a great impact on the molecular weight of the polymer during the ring-opening polymerization of glycolide, and cannot meet the requirements of the intrinsic viscosity of polyglycolic acid not less than 1 and the mass average molecular weight not less than 100,000 required for applications such as surgical sutures. Therefore, the crude glycolide product obtained by depolymerization needs to be purified by recrystallization, distillation, extraction, etc. to obtain a refined glycolide product with high purity, low impurity content, and meeting the requirements of medical-grade PGA products.

[0007] In addition, the composition of the glycolic acid raw material also has a great influence on the quality of the glycolide product. CN1496359A introduces that when an industrial-grade glycolic acid aqueous solution is used for depolymerization to synthesize glycolic acid oligomers, the trace alkali metal ions contained in the glycolic acid oligomers will make the depolymerization reaction system unstable in a relatively short time, the depolymerization reaction system will turn black in a relatively short time, and the glycolide crude product will be contaminated by black impurities. By reducing the alkali metal ion content to 0.001% or lower to carry out the depolymerization reaction of synthesizing glycolic acid oligomers, the depolymerization reaction can remain stable for a long time. If sulfates and / or organic acid salts in the form of divalent or multivalent cations are added thereto, it can be ensured that the depolymerization reaction remains stable for a long time even in the presence of alkali metal cations. Alternatively, by using glycolic acid oligomers whose alkali metal ion content is controlled at 0.001% or lower and containing at least one sulfate and / or organic acid salt in the form of divalent or multivalent cations as a stabilizer, the long-term stability of the depolymerization can be further improved. However, sulfates and / or organic acid salts introduced in the form of divalent or multivalent cations are not easy to remove during the glycolide refining process, which is not conducive to improving the purity of glycolide.

[0008] JP2008101030A proposes that after washing and treating glycolic acid oligomers in (alkaline) water at 20-90°C to remove impurities, it is beneficial to obtain PGA with a weight average molecular weight of more than 30,000, stable production and light color after subsequent solid phase polycondensation. JP2008101031A further studies that after washing and treating glycolic acid oligomers in (alkaline) water at 20-90°C to remove impurities, adding a polyol with at least three hydroxyl groups and a polyacid with at least two carboxyl groups as a chain extender, a PGA polymer with a weight average molecular weight of 130,000 can be obtained. However, glycolic acid oligomers will undergo hydrolysis reaction in (alkaline) water at a certain temperature, and the high alkali metal ion content will cause the depolymerization reaction system to turn black in a relatively short time, and the crude glycolide product is easily contaminated by black impurities, which affects the quality of the refined glycolide product.

[0009] In our research on the preparation of glycolide from industrial-grade glycolic acid aqueous solution, we found that after coal is used as raw material to produce synthesis gas, in the process of producing ethylene glycol by direct synthesis or indirect synthesis, methyl glycolate is obtained as a byproduct, and methyl glycolate is hydrolyzed to obtain glycolic acid aqueous solution. However, the crude glycolide product prepared by prepolymerization and depolymerization reaction of this raw material has a high acid value in the purified glycolide after purification, and the content of linear dimers and cyclic polymers (tetramers to octamers) is high [discovered by chromatographic detection], which affects the quality of the glycolide product. The existing technology does not involve the control of the yield and quality of glycolide products prepared by the industrial-grade glycolic acid aqueous solution obtained from the coal-to-ethylene glycol route. Summary of the invention

[0010] In order to overcome the problems existing in the prior art, the present invention provides a kind of glycolide, a method for preparing glycolide and the obtained glycolide, wherein the preparation method uses an aqueous glycolic acid solution containing aldehydes, ketones and ethers as raw materials, thereby solving the problems that the glycolide prepared by such aqueous glycolic acid solution has a high acid value and a high content of linear dimers and cyclic polymers (tetramers to octamers).

[0011] One of the objects of the present invention is to provide a glycolide, wherein the acid value of the glycolide is <5 mol / t, and / or the linear dimer content in the glycolide is <200 ppm, and / or the total cyclic polymer content in the glycolide is <400 ppm.

[0012] The second object of the present invention is to provide a method for preparing glycolide, preferably for preparing the glycolide described in one of the objects of the present invention, the preparation method comprising:

[0013] (1) reacting an aqueous glycolic acid solution in the presence of a catalyst to obtain glycolic acid oligomers, wherein the aqueous glycolic acid solution contains at least one of an aldehyde compound, a ketone compound, and an ether compound;

[0014] (2) washing the glycolic acid oligomers to obtain purified glycolic acid oligomers;

[0015] (3) depolymerizing the purified glycolic acid oligomers to obtain a crude glycolide product; and optionally:

[0016] (4) purifying the crude glycolide product to obtain glycolide.

[0017] In the present invention, step (4) can be performed optionally.

[0018] In a preferred embodiment, in step (1), the aqueous glycolic acid solution is an industrial-grade aqueous glycolic acid solution obtained from a coal-to-ethylene glycol route, which contains at least one of aldehyde compounds, ketone compounds, and ether compounds (impurities).

[0019] In a further preferred embodiment, the aldehyde compound is selected from at least one of formaldehyde, acetaldehyde, butyraldehyde, glyoxal, hydroxyacetaldehyde, etc., the ketone substance is selected from at least one of acetone, butanone, etc., and the ether compound is selected from at least one of hydroxyacetaldehyde glycol ether (HOCCH2OCH2CH2OH), hydroxyacetaldehyde diethylene glycol ether (HOCCH2OCH2CH2OCH2CH2OH), etc.

[0020] Among them, the inventors found through a large number of experiments and studies that compared with glycolic acid prepared by the chloroacetic acid method or the cyanide method, the industrial-grade glycolic acid aqueous solution obtained by the coal-to-ethylene glycol route contains not only impurities such as methoxyacetic acid, diglycolic acid, oxalic acid, and sodium chloride, but also contains impurities such as aldehyde compounds (such as glyoxylic acid, formaldehyde, acetaldehyde, butyraldehyde, glyoxal, hydroxyacetaldehyde), ketone compounds (such as acetone, butanone), and ether compounds (such as hydroxyacetaldehyde ethylene glycol ether, hydroxyacetaldehyde diethylene glycol ether).

[0021] In a further preferred embodiment, in the (industrial grade) glycolic acid aqueous solution, the content of aldehyde compounds is greater than 2000 ppm, and / or the content of ketone compounds is greater than 700 ppm, and the content of ether compounds is greater than 400 ppm.

[0022] Among them, as long as any one of the above three impurities exceeds the specified value, it will affect the yield of the glycolide product as well as the acid value, dimer content and cyclic polymer content of the glycolide product.

[0023] Specifically, after a large number of experimental studies, the inventors found that aldehydes, ketones, and ether compounds in the ethanolic acid aqueous solution raw material will enter the crude glycolide during the prepolymerization reaction and the depolymerization reaction, resulting in a decrease in the yield of the crude glycolide; among them, aldehyde compounds will be oxidized to generate acids in an acidic environment, which will increase the acid value of the crude glycolide. If the acid value is too high, it will be difficult to reduce it in the subsequent refining process, which will ultimately lead to a high acid value of the refined glycolide product, which cannot meet the requirements of glycolide polymerization, and on the other hand, it will also increase the synthesis of dimers and polymers; ketones and ether compounds are not easily removed in the refining process, resulting in a decrease in the purity of the refined glycolide, which cannot meet the requirements of glycolide polymerization.

[0024] Preferably, in the industrial-grade glycolic acid aqueous solution, the content of aldehyde compounds is 2000-4000 ppm, the content of ketone compounds is 500-1000 ppm (eg, 700-800 ppm), and the content of ether compounds is 300-800 ppm (eg, 400-800 ppm).

[0025] In a preferred embodiment, in step (1), the catalyst is selected from at least one of stannous octoate, stannous chloride, antimony trioxide, zinc oxide, and zinc acetylacetonate.

[0026] In a further preferred embodiment, in step (1), the ratio of the catalyst to glycolic acid is 0.05-1 wt%, preferably 0.1-0.5 wt%.

[0027] For example, the catalyst is used in an amount ratio of 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%.

[0028] In a preferred embodiment, the reaction in step (1) is carried out as follows: the temperature is raised to 160-260° C. for preliminary reaction, and then (while maintaining the system temperature) the vacuum degree of the reaction system is controlled to 0.05-10 kPa to continue the reaction for 0.5-10 h.

[0029] In a further preferred embodiment, the reaction in step (1) is carried out as follows: the temperature is raised to 190-240° C. for preliminary reaction, and then (while maintaining the system temperature) the vacuum degree of the reaction system is controlled to 0.1-5 kPa to continue the reaction for 2-5 hours.

[0030] For example, the reaction in step (1) is carried out as follows: first, the temperature is raised from room temperature to 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or 260°C for pre-reaction, and then (while maintaining the system temperature) the vacuum degree of the reaction system is controlled to 0.05 kPa, 0.1 kPa, 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa or 10 kPa and the reaction is continued for 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0031] Preferably, after the pre-reaction, the vacuum degree of the reaction system is controlled to 1-5 kPa for 2-5 hours, and then the vacuum degree is reduced to 0.1-1 kPa for 2-5 hours.

[0032] In a preferred embodiment, in step (2), washing is performed using a polar organic solvent.

[0033] In a further preferred embodiment, the polar organic solvent is selected from at least one of alcohol solvents, ketone solvents or a combination of two of them and ethyl acetate. Preferably, based on the total volume of the polar organic solvent as 100%, the volume fraction of ethyl acetate does not exceed 50%.

[0034] Preferably, the polar organic solvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, cyclohexanone, acetone and a combination of two thereof and ethyl acetate, such as a combination of isopropanol and ethyl acetate.

[0035] In a further preferred embodiment, the weight ratio of the glycolic acid oligomer to the polar organic solvent is 1:(0.5-1.5), preferably 1:(0.8-1.2).

[0036] For example, based on the total volume of the polar organic solvent as 100%, the volume fraction of ethyl acetate is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 48%.

[0037] In a preferred embodiment, in step (2), the washing is carried out at 40-100°C, preferably 50-80°C.

[0038] For example, the washing is carried out at 40°C, 50°C, 60°C, 70°C, 80°C or 90°C.

[0039] In a further preferred embodiment, in step (2), the temperature is lowered to room temperature for filtration after washing.

[0040] In a preferred embodiment, in step (3), the depolymerization is carried out as follows: the temperature is raised to 210-300° C., the vacuum degree is increased to 0.05-10 kPa, the reaction is carried out for 0.5-10 hours to decompose the glycolic acid oligomers, and the glycolide is distilled under reduced pressure to obtain a crude glycolide product.

[0041] In a further preferred embodiment, in step (3), the depolymerization is carried out as follows: the temperature is raised to 230-290° C., the vacuum degree is increased to 0.1-5 kPa, the reaction is carried out for 2-5 hours to decompose the glycolic acid oligomers, and the glycolide is distilled under reduced pressure to obtain a crude glycolide product.

[0042] For example, in step (3), the depolymerization is carried out as follows: the temperature is raised to 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C or 300°C, the vacuum degree is increased to 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 kPa, the reaction is carried out for 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 hours to decompose the glycolic acid oligomers, and distill under reduced pressure to obtain a crude glycolide product.

[0043] Preferably, in step (3), the depolymerization is carried out as follows: gradually raising the temperature from room temperature to 210-250°C, increasing the vacuum degree to 0.1-5 kPa, and reacting for 2-5 hours. During the reaction, the temperature is gradually raised to 270-300°C to decompose the glycolic acid oligomers, and distilling under reduced pressure is performed to obtain a crude glycolide product.

[0044] In a preferred embodiment, in step (4), the purification includes one or more recrystallizations and drying.

[0045] In a further preferred embodiment, the recrystallization is carried out as follows: the crude glycolide product is added to a solvent, heated (preferably to 50-90° C., for example 60-80° C.) and stirred, then cooled to crystallize, and finally filtered to remove the solvent; preferably, the solvent is selected from a polar organic solvent, preferably at least one of ethyl acetate, isopropanol, ethanol, and acetone.

[0046] During recrystallization, the temperature is raised to 50°C, 60°C, 70°C, 80°C or 90°C and stirred for 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min or 80 min.

[0047] In a further preferred embodiment, the drying temperature is 40-90°C, preferably 50-70°C, the drying pressure is 10-100 Pa, preferably 30-100 Pa (absolute pressure), and the drying time is not less than 8 hours, preferably not less than 10 hours.

[0048] For example, the drying temperature is 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, the drying pressure is 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 Pa, and the drying time is 10, 12, 14, 16, 18 or 20 hours.

[0049] In the method of the present invention, the industrial-grade glycolic acid aqueous solution obtained by the coal-to-ethylene glycol route is used as a raw material, the glycolic acid aqueous solution is mixed with a catalyst and then subjected to a prepolymerization reaction to obtain glycolic acid oligomers, the glycolic acid oligomers are washed with a polar organic solvent, and then the glycolic acid oligomers are formed into a homogeneous melt, and a glycolide crude product is obtained by reduced pressure distillation. The glycolide crude product is purified to obtain refined glycolide, the acid value of the refined glycolide is less than 5 mol / t, the linear dimer content is less than 200 ppm, and the total content of cyclic polymers (tetramer to octamer) is less than 400 ppm, and a good technical effect is achieved.

[0050] In the invention, the linear dimer refers to HOCH2COOCH2COOH, with a molecular weight of 134, and the cyclic polymer includes tetramer to octamer, with a molecular weight of 232 to 464, while the content of cyclic polymers with a higher degree of polymerization is basically negligible.

[0051] The third object of the present invention is to provide glycolide obtained by the preparation method described in one of the objects of the present invention.

[0052] Preferably, the acid value of the glycolide is <5 mol / t, and / or the linear dimer content in the glycolide is <200 ppm, and / or the total content of cyclic polymers (tetramer to octamer) in the glycolide is <400 ppm.

[0053] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be regarded as specifically disclosed in this article.

[0054] Compared with the prior art, the present invention has the following beneficial effects: the glycolide yield of the method of the present invention is high, and the obtained glycolide product has the advantages of low acid value and low content of linear dimers and cyclic polymers (tetramers to octamers). DETAILED DESCRIPTION

[0055] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0056] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0057] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0058] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0059] The raw materials used in the specific implementation manner of the present invention are commercially available.

[0060] The analysis and determination method of the glycolide product in the present invention is:

[0061] (1) Determination of impurity content in aqueous glycolic acid solution

[0062] Prepare 1000mg / L acetonitrile solution (containing 1% phosphoric acid), take 20 microliters of glycolic acid aqueous solution sample or mix with 1 ml of the above acetonitrile solution, heat in a water bath for 30 minutes and then inject and analyze. Use ultra-high performance liquid chromatography for analysis, column C18, injection speed 0.4mL / min, mobile phase 0min (5% ACN) -> 6min (95% ACN), UV detection at 365nm.

[0063] (2) Determination of glycolide acid value

[0064] The acid value of the crude glycolide product was determined by acid-base titration. The sample was dissolved in 20 mL of dry dimethyl sulfoxide, and after it was dissolved, a few drops of bromophenol blue indicator solution were added, and the solution was yellow. It was titrated with a standard concentration of sodium hydroxide in benzyl alcohol, and the end point was when the solution color changed from yellow to green. The acid value of the sample was calculated by calculating the volume of the sodium hydroxide solution used when the titration end point was reached.

[0065] (3) Determination of glycolide linear dimer (molecular weight 134) and cyclic polymer (tetramer to octamer, molecular weight 232 to 464)

[0066] High performance liquid chromatography-diode array detector-charged aerosol detector (HPLC-DAD-CAD) was used for analysis. 0.1 g of glycolide was dissolved in acetonitrile to prepare a 10% acetonitrile solution. The chromatographic column was C18, the injection speed was 1.0 mL / min, and the mobile phase was 0.05 TFA. The content of the oligomer relative to glycolide was estimated based on the peak area of ​​the retention time of different oligomers.

[0067] [Example 1]

[0068] Using glycolic acid aqueous solution A as raw material, its impurity content was tested, and the aldehyde impurity content was 2180 ppm, the ketone impurity content was 890 ppm, and the ether impurity content was 510 ppm.

[0069] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt%, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 5 kPa by vacuum, and the reaction was continued for 2 h, and then the system pressure was reduced to 1 kPa, and the reaction was continued for 3 h to obtain glycolic acid oligomers, which were crushed after cooling.

[0070] 400 g of glycolic acid oligomer and 400 g of a combined solvent of ethyl acetate and isopropanol were placed in a three-necked flask and mixed, with the volume ratio of ethyl acetate to isopropanol being 45:55, and the mixture was heated to 80°C and stirred for 50 minutes. The mixture was cooled to 25°C and filtered to remove the solvent.

[0071] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 5kPa. React under this pressure for 5h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 289.2g crude glycolide with a yield of 96.4%. Mix 250g crude glycolide and 250g ethyl acetate in a three-necked flask, heat the mixture to 75°C, stir for 60min, cool to 25°C to precipitate glycolide crystals, and filter to remove the solvent. Dry the solid filter cake at 70°C and 30Pa (absolute pressure) in vacuum for 10h to obtain refined glycolide. The acid value of the refined glycolide was measured to be 1.79mol / t, and the linear dimer content was 142ppm by liquid chromatography analysis, and the total content of cyclic polymers (tetramers to octamers) was 280ppm.

[0072] [Example 2]

[0073] Using glycolic acid aqueous solution B as raw material, its impurity content was tested, and the aldehyde impurity content was 3340 ppm, the ketone impurity content was 920 ppm, and the ether impurity content was 690 ppm.

[0074] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt %, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 5 kPa by vacuum pumping, and the reaction was continued for 2 h, and then the system pressure was reduced to 0.1 kPa, and the reaction was continued for 1.5 h to obtain glycolic acid oligomers, which were crushed after cooling.

[0075] 400 g of glycolic acid oligomer and 400 g of a combined solvent of ethyl acetate and acetone were placed in a three-necked flask and mixed, with the volume ratio of ethyl acetate to acetone being 35:65, and the mixture was heated to 70°C and stirred for 50 minutes. The mixture was cooled to 25°C and filtered to remove the solvent.

[0076] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 0.1kPa. React at this pressure for 2h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 290.4g crude glycolide with a yield of 96.8%. 250g crude glycolide and 250g ethyl acetate are placed in a three-necked flask and mixed. The mixture is heated to 75°C, stirred for 60min, cooled to 25°C to precipitate glycolide crystals, and filtered to remove the solvent. The solid filter cake is vacuum dried at 65°C and 50Pa (absolute pressure) for 14h to obtain refined glycolide. The acid value content of the refined glycolide is measured to be 2.05mol / t. The linear dimer content of liquid chromatography analysis is 168ppm, and the total content of cyclic polymers (tetramers to octamers) is 310ppm.

[0077] [Example 3]

[0078] Using glycolic acid aqueous solution C as raw material, its impurity content was tested, and the aldehyde impurity content was 3960 ppm, the ketone impurity content was 560 ppm, and the ether impurity content was 380 ppm.

[0079] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt%, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 1 kPa by vacuum, and the reaction was continued for 2 h to obtain glycolic acid oligomers, which were then crushed after cooling.

[0080] 400 g of glycolic acid oligomer and 400 g of a combined solvent of ethyl acetate and n-butanol were placed in a three-necked flask and mixed, with the volume ratio of ethyl acetate to n-butanol being 50:50, and the mixture was heated to 60°C and stirred for 50 minutes. The mixture was cooled to 25°C and filtered to remove the solvent.

[0081] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 3kPa. React at this pressure for 4.5h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 285.3g crude glycolide with a yield of 95.1%. Mix 250g crude glycolide and 250g ethyl acetate in a three-necked flask, heat the mixture to 75°C, stir for 60min, cool to 25°C to precipitate glycolide crystals, and filter to remove the solvent. Dry the solid filter cake at 50°C and 40Pa (absolute pressure) in vacuum for 18h to obtain refined glycolide. The acid value of the refined glycolide was measured to be 2.89mol / t, and the linear dimer content was 188ppm by liquid chromatography analysis, and the total content of cyclic polymers (tetramers to octamers) was 364ppm.

[0082] [Example 4]

[0083] Using glycolic acid aqueous solution D as raw material, its impurity content was tested, and the aldehyde impurity content was 2830 ppm, the ketone impurity content was 680 ppm, and the ether impurity content was 304 ppm.

[0084] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt %, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 3 kPa by vacuum pumping, and the reaction was continued for 2 h, and then the system pressure was reduced to 0.5 kPa, and the reaction was continued for 2 h to obtain glycolic acid oligomers, which were then crushed after cooling.

[0085] 400 g of glycolic acid oligomer and 400 g of a combined solvent of ethyl acetate and cyclohexanone were placed in a three-necked flask and mixed, with the volume ratio of ethyl acetate to cyclohexanone being 40:60, and the mixture was heated to 70°C and stirred for 50 minutes. The mixture was cooled to 25°C and filtered to remove the solvent.

[0086] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 2kPa. React at this pressure for 3.5h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 288.3g crude glycolide with a yield of 96.1%. Mix 250g crude glycolide and 250g ethyl acetate in a three-necked flask, heat the mixture to 75°C, stir for 60min, cool to 25°C to precipitate glycolide crystals, and filter to remove the solvent. Dry the solid filter cake at 70°C and 100Pa (absolute pressure) for 16h to obtain refined glycolide. The acid value of the refined glycolide was measured to be 3.14mol / t, and the linear dimer content was 174ppm by liquid chromatography analysis, and the total content of cyclic polymers (tetramers to octamers) was 283ppm.

[0087] [Example 5]

[0088] Using glycolic acid aqueous solution E as raw material, its impurity content was tested, and the aldehyde impurity content was 2490 ppm, the ketone impurity content was 710 ppm, and the ether impurity content was 440 ppm.

[0089] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt %, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 3 kPa by vacuum pumping, and the reaction was continued for 1 hour, and then the system pressure was reduced to 1 kPa, and the reaction was continued for 2 hours to obtain glycolic acid oligomers, which were crushed after cooling.

[0090] 400 g of glycolic acid oligomer and 400 g of a combined solvent of ethyl acetate, cyclohexanone and isopropanol were placed in a three-necked flask and mixed, the volume ratio of ethyl acetate to cyclohexanone and isopropanol being 35:30:35, the mixture was heated to 75°C and stirred for 50 min, cooled to 25°C, and the solvent was removed by filtration.

[0091] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 2kPa. React under this pressure for 5h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 288.9g crude glycolide with a yield of 96.3%. Mix 250g crude glycolide and 250g ethyl acetate in a three-necked flask, heat the mixture to 75°C, stir for 60min, cool to 25°C to precipitate glycolide crystals, and filter to remove the solvent. Dry the solid filter cake at 65°C and 30Pa (absolute pressure) in vacuum for 12h to obtain refined glycolide. The acid value of the refined glycolide was measured to be 2.38mol / t, and the linear dimer content was 159ppm by liquid chromatography analysis, and the total content of cyclic polymers (tetramers to octamers) was 302ppm.

[0092] [Example 6]

[0093] Using glycolic acid aqueous solution F as raw material, its impurity content was tested, and the aldehyde impurity content was 3530 ppm, the ketone impurity content was 966 ppm, and the ether impurity content was 579 ppm.

[0094] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt %, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 4 kPa by vacuum pumping, and the reaction was continued for 1 hour, and then the system pressure was reduced to 1 kPa, and the reaction was continued for 4 hours to obtain glycolic acid oligomers, which were then crushed after cooling.

[0095] 400 g of glycolic acid oligomer and 400 g of a combined solvent of ethyl acetate and ethanol were placed in a three-necked flask and mixed, with the volume ratio of ethyl acetate to ethanol being 50:50, and the mixture was heated to 50°C and stirred for 50 minutes. The mixture was cooled to 25°C and filtered to remove the solvent.

[0096] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 2.5kPa. React at this pressure for 4h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 286.8g crude glycolide with a yield of 95.6%. Mix 250g crude glycolide and 250g ethyl acetate in a three-necked flask, heat the mixture to 75°C, stir for 60min, cool to 25°C to precipitate glycolide crystals, and filter to remove the solvent. Dry the solid filter cake at 60°C and 30Pa (absolute pressure) in vacuum for 14h to obtain refined glycolide. The acid value of the refined glycolide was measured to be 3.23mol / t, and the linear dimer content was 192ppm by liquid chromatography analysis, and the total content of cyclic polymers (tetramers to octamers) was 377ppm.

[0097] [Comparative Example 1]

[0098] Using glycolic acid aqueous solution A as raw material, its impurity content was tested, and the aldehyde impurity content was 2180 ppm, the ketone impurity content was 890 ppm, and the ether impurity content was 510 ppm.

[0099] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt%, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 5 kPa by vacuum, and the reaction was continued for 2 h, and then the system pressure was reduced to 1 kPa, and the reaction was continued for 3 h to obtain glycolic acid oligomers, which were crushed after cooling.

[0100] Add 300g glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 5kPa. React under this pressure for 5h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 252.9g crude glycolide with a yield of 84.3%. Mix 250g crude glycolide and 250g ethyl acetate in a three-necked flask, heat the mixture to 75°C, stir for 60min, cool to 25°C to precipitate glycolide crystals, and filter to remove the solvent. Dry the solid filter cake at 70°C and 30Pa (absolute pressure) in vacuum for 10h to obtain refined glycolide. The acid value of the refined glycolide was measured to be 25.83mol / t, and the linear dimer content of liquid chromatography analysis was 569ppm, and the total content of cyclic polymers (tetramers to octamers) was 647ppm.

[0101] [Comparative Example 2]

[0102] Using glycolic acid aqueous solution B as raw material, its impurity content was tested, and the aldehyde impurity content was 3340 ppm, the ketone impurity content was 920 ppm, and the ether impurity content was 690 ppm.

[0103] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt %, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 5 kPa by vacuum pumping, and the reaction was continued for 2 h, and then the system pressure was reduced to 0.1 kPa, and the reaction was continued for 1.5 h to obtain glycolic acid oligomers, which were crushed after cooling.

[0104] 400 g of glycolic acid oligomer and 400 g of benzene were placed in a three-necked flask and mixed, the mixture was heated to 75°C and stirred for 50 min. The mixture was cooled to 25°C and filtered to remove the solvent.

[0105] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 0.1kPa. React at this pressure for 2h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 255.3g crude glycolide with a yield of 85.1%. 250g crude glycolide and 250g ethyl acetate are placed in a three-necked flask and mixed. The mixture is heated to 75°C, stirred for 60min, cooled to 25°C to precipitate glycolide crystals, and filtered to remove the solvent. The solid filter cake is vacuum dried at 65°C and 50Pa (absolute pressure) for 14h to obtain refined glycolide. The acid value content of the refined glycolide is measured to be 22.47mol / t. The linear dimer content of liquid chromatography analysis is 538ppm, and the total content of cyclic polymers (tetramers to octamers) is 626ppm.

[0106] [Comparative Example 3]

[0107] Using glycolic acid aqueous solution C as raw material, its impurity content was tested, and the aldehyde impurity content was 3960 ppm, the ketone impurity content was 560 ppm, and the ether impurity content was 380 ppm.

[0108] 800 g of 70% aqueous glycolic acid solution and 2.8 g of stannous octoate (0.5 wt%, based on glycolic acid) were added to a four-necked flask, and the temperature was gradually raised from room temperature to 220°C to distill off the water generated in the reaction. At this temperature, the system pressure was reduced to 1 kPa by vacuum, and the reaction was continued for 2 h to obtain glycolic acid oligomers, which were then crushed after cooling.

[0109] 400 g of glycolic acid oligomer and 400 g of cyclohexane were placed in a three-necked flask and mixed, the mixture was heated to 75°C and stirred for 50 min. The mixture was cooled to 25°C and filtered to remove the solvent.

[0110] Add 300g washed glycolic acid oligomers to a four-necked flask, gradually heat from room temperature to 230°C, and simultaneously vacuumize to reduce the system pressure to 3kPa. React at this pressure for 4.5h. During the reaction, gradually raise the temperature to 290°C. The distilled glycolide crude product is condensed and collected to obtain 259.8g crude glycolide with a yield of 86.6%. 250g crude glycolide and 250g ethyl acetate are placed in a three-necked flask and mixed. The mixture is heated to 75°C, stirred for 60min, cooled to 25°C to precipitate glycolide crystals, and filtered to remove the solvent. The solid filter cake is vacuum dried at 50°C and 40Pa (absolute pressure) for 18h to obtain refined glycolide. The acid value content of the refined glycolide is measured to be 18.94mol / t. The linear dimer content of liquid chromatography analysis is 476ppm, and the total content of cyclic polymers (tetramers to octamers) is 513ppm.

[0111] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing glycolide, the method comprising: (1) reacting an aqueous glycolic acid solution in the presence of a catalyst to obtain glycolic acid oligomers, wherein the aqueous glycolic acid solution is an industrial-grade aqueous glycolic acid solution obtained from a coal-to-ethylene glycol route, and contains at least one of an aldehyde compound, a ketone compound, and an ether compound; and the catalyst is selected from at least one of stannous octoate, stannous chloride, antimony trioxide, zinc oxide, and zinc acetylacetonate; (2) washing the glycolic acid oligomers to obtain purified glycolic acid oligomers; in step (2), washing is performed with a polar organic solvent; the polar organic solvent is selected from at least one of an alcohol solvent and a ketone solvent or a combination of two of them and ethyl acetate, and the washing is performed at a temperature in the range of 40 to 100° C.; (3) depolymerizing the purified glycolic acid oligomers to obtain a crude glycolide product; (4) Refining the crude glycolide product to obtain glycolide; the refining includes one or more recrystallizations and drying.

2. The preparation method according to claim 1, characterized in that: In step (1), in the aqueous glycolic acid solution, the content of aldehyde compounds is greater than 2000 ppm, and / or the content of ketone compounds is greater than 700 ppm, and / or the content of ether compounds is greater than 400 ppm.

3. The preparation method according to claim 1, characterized in that: The usage ratio of the catalyst to glycolic acid is 0.05-1 wt %.

4. The preparation method according to claim 1, characterized in that: The usage ratio of the catalyst to glycolic acid is 0.1-0.5 wt %.

5. The preparation method according to claim 1, characterized in that: The reaction in step (1) is carried out as follows: the temperature is raised to 160-260° C. for preliminary reaction, and then the vacuum degree of the reaction system is controlled to 0.05-10 kPa to continue the reaction for 0.5-10 h.

6. The preparation method according to claim 1, characterized in that: The weight ratio of the glycolic acid oligomer to the polar organic solvent is 1:(0.5-1.5).

7. The preparation method according to claim 1, characterized in that: In step (2), after washing, the temperature is lowered and filtering is performed.

8. The preparation method according to claim 1, characterized in that: In step (2), the washing is carried out at a temperature in the range of 50 to 80°C.

9. The preparation method according to claim 1, characterized in that: In step (3), the depolymerization is carried out as follows: the temperature is raised to 210-300° C., the vacuum degree is increased to 0.05-10 kPa, and the reaction is carried out for 0.5-10 hours to obtain a crude glycolide product.

10. The preparation method according to claim 1, characterized in that: The recrystallization is carried out as follows: the crude glycolide product is added into a solvent, heated and stirred, then cooled and crystallized, and finally filtered to remove the solvent.

11. The preparation method according to claim 10, characterized in that: The solvent is selected from polar organic solvents.

12. The preparation method according to claim 10, characterized in that: The solvent is selected from at least one of ethyl acetate, isopropanol, ethanol and acetone.

13. The preparation method according to claim 1, characterized in that: The drying temperature is 40-90° C., and / or the drying pressure is 10-100 Pa absolute pressure, and the drying time is not less than 8 hours.

14. The preparation method according to claim 13, characterized in that: The drying temperature is 50-70° C., and / or the drying pressure is 30-100 Pa absolute pressure, and the drying time is not less than 10 hours.

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