Preparation method of glycolide and obtained glycolide

Abstract

The invention provides a preparation method of glycolide and the obtained glycolide. The preparation method comprises the following step: carrying out a depolymerization reaction on a glycollic acid oligomer in the presence of terphenyl and / or a hydrogenated product thereof to obtain glycolide. Terphenyl and / or a hydrogenated product thereof are / is added during a glycolic acid oligomer depolymerization reaction, so that a decarboxylation side reaction and a thermal degradation side reaction during the depolymerization reaction are inhibited, the generation of by-products such as CO2 and aldehyde ketonic acid small-molecular organic matters in depolymerization waste gas is reduced, and the glycolic acid oligomer depolymerization reaction is promoted to be carried out towards a back-biting ester exchange direction in a balanced manner; therefore, the yield and quality of glycolide are improved.

Description

Technical Field

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

[0002] As an aliphatic polyester, polyglycolide has high biodegradability and good biocompatibility. It can be hydrolyzed in organisms and can also be metabolized by microorganisms in the natural environment, ultimately decomposing into water and carbon dioxide. In addition, polyglycolide has good mechanical properties such as heat resistance and tensile strength, and has good gas barrier properties when used as a film or sheet.

[0003] Glycolide is a compound with a cyclic dimer structure formed by removing two molecules of water from two molecules of glycolic acid. The synthesis of glycolide monomers is usually carried out by depolymerizing glycolic acid oligomers through high-temperature distillation, and the gaseous crude product of glycolide is extracted from the reaction system.

[0004] The depolymerization reaction can be carried out either in the presence of a solvent, i.e., solution depolymerization, or in the absence of a solvent, i.e., bulk depolymerization. Whether it is bulk depolymerization or solution depolymerization, the depolymerization process is the key to controlling the quality of glycolide. In the related patents of solution depolymerization, in addition to technical points such as reaction conditions, raw materials, and reaction product transfer / processing, the optimization of the depolymerization solvent is an effective technical means to improve the reaction effect.

[0005] Chinese Patent CN104619690A discloses a method for manufacturing glycolide. The glycolic acid oligomer containing a high-boiling organic solvent or a solubilizer is heated to the depolymerization temperature for reaction, and the produced glycolide is distilled out from the reaction vessel and enters the rectifier for gas-liquid countercurrent contact to recover glycolide. The high-boiling organic solvent is at least selected from the group consisting of alkoxyalkyl esters of aromatic carboxylic acids, alkoxyalkyl esters of aliphatic carboxylic acids, polyalkylene glycol ethers, polyalkylene glycol esters, aromatic carboxylic esters, aliphatic carboxylic esters, aromatic ethers, aliphatic ethers, aromatic phosphates, aliphatic phosphates, aliphatic imide compounds, aliphatic imide compounds, and aromatic halides, and specifically points out that the high-boiling organic solvent is a polyalkylene glycol ether. A monohydric or polyhydric alcohol or phenol compound with a boiling point above 190 °C can be used as a solubilizer.

[0006] Chinese Patent CN112469759A provides a method for preparing glycolide from methyl glycolate oligomers. The method includes pyrolyzing methyl glycolate oligomers, and the pyrolysis reaction system contains no more than 1 wt% of polyesters, polyols, polyacids, or combinations thereof based on the total weight of the methyl glycolate oligomers. A viscosity reducer may or may not be present during the pyrolysis process, and the viscosity reducer is paraffin in a hydrocarbon mixture.

[0007] When depolymerizing glycolic acid oligomers in the prior art, while preparing glycolide from glycolic acid oligomers by depolymerization, depolymerization waste gas will be generated, and its main components are CO2 and various small molecule organic compounds. The generation of CO2 is mainly because there is a certain amount of water in glycolide, and glycolide reacts with water to form glycolic acid dimer. Under the temperature and pressure conditions of depolymerization, the glycolic acid dimer will undergo decarboxylation reactions at the molecular chain ends and inside the molecular chain, that is, the carboxyl group (-COOH) is removed to generate formic acid, acetic acid, and release carbon dioxide. Small molecule organic compounds such as acetaldehyde, propionaldehyde, acrolein, methacrolein, acetone, butanone, and butanedione are produced by the thermal degradation of PGA. The yield of the backbiting transesterification reaction of glycolic acid oligomers should theoretically be close to 100%, but due to the existence of side reactions such as decarboxylation reactions and thermal degradation reactions, the yield of the backbiting transesterification reaction of oligomers decreases, and the effective utilization rate of oligomers drops significantly. Therefore, it is particularly important to reduce the generation amount of depolymerization waste gas and promote the equilibrium of the oligomer depolymerization reaction to shift towards the backbiting transesterification direction, thereby improving the yield and quality of glycolide. Summary of the Invention

[0008] In order to solve the technical problems existing in the prior art, the present invention provides a method for preparing glycolide and the obtained glycolide.

[0009] In the research on the depolymerization of glycolic acid oligomers, it is found that the essence of the depolymerization reaction is thermal degradation under controlled conditions, that is, the target degradation product (glycolide) is continuously removed from the system by using vacuum or inert gas flow, and the target degradation reaction (backbiting transesterification reaction) is accelerated through high temperature and catalyst.

[0010] The terphenyl and / or its hydrogenated product adopted by the present invention is mixed with glycolic acid oligomers, which can reduce the viscosity of the oligomers, is beneficial to heat transfer, reduce the depolymerization reaction temperature, thereby inhibiting the decarboxylation side reaction and thermal degradation side reaction during the depolymerization reaction, reducing the generation amount of depolymerization waste gas, promoting the equilibrium of the glycolic acid oligomer depolymerization reaction to shift towards the backbiting transesterification direction, and improving the yield and quality of glycolide.

[0011] The present invention can solve the problems that during the depolymerization process, the depolymerization reaction is prone to decarboxylation side reaction and thermal degradation side reaction, generating by-products such as CO2, aldehyde-ketone-acid small molecule organic compounds, resulting in high concentration of depolymerization waste gas, decreased yield of glycolide, decreased purity, and increased acid value.

[0012] One of the purposes of the present invention is to provide a method for preparing glycolide, including: performing a depolymerization reaction on glycolic acid oligomers in the presence of terphenyl and / or its hydrogenated product to obtain glycolide.

[0013] In a preferred embodiment of the present invention,

[0014] The terphenyl and / or its hydrogenated product is at least one of terphenyl and hydrogenated terphenyl.

[0015] In a preferred embodiment of the present invention,

[0016] The amount of the terphenyl and / or its hydrogenated product is 5 to 50% by weight of the glycolic acid oligomer, for example 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%, preferably 10 to 30%.

[0017] In a preferred embodiment of the present invention,

[0018] The weight-average molecular weight of the glycolic acid oligomer is 8000 to 20000, preferably 10000 to 15000;

[0019] The terminal carboxyl group content of the glycolic acid oligomer is 200 to 700 μmol / g, preferably 200 to 500 μmol / g;

[0020] The glycolic acid oligomer is a molten glycolic acid oligomer obtained by a method of the prior art, and the molten glycolic acid oligomer contains 5 to 50 wt% of the glycolic acid oligomer.

[0021] The glycolic acid oligomer of the present invention can be prepared by any method of the prior art. The following examples are for further illustration. The glycolic acid oligomers used in the present invention include but are not limited to the following preparation methods;

[0022] For example, the glycolic acid oligomer is prepared from an aqueous solution of 50 to 70% glycolic acid or methyl glycolate as a raw material. In a reactor, the aqueous glycolic acid solution or methyl glycolate is mixed and contacted with a catalyst, and the reaction is carried out at a reaction temperature of 100 to 220 °C and a reaction pressure of atmospheric pressure to 1 kPa until no water or methanol is distilled out, to obtain the glycolic acid oligomer. At least one of stannous octoate, stannous chloride, antimony trioxide, zinc oxide, and zinc acetylacetonate can be selected as the catalyst. Samples are taken to test the weight-average molecular weight and terminal carboxyl group content of the glycolic acid oligomer.

[0023] In a preferred embodiment of the present invention,

[0024] The glycolic acid oligomer is mixed with the terphenyl and / or its hydrogenated product and then depolymerized; preferably,

[0025] The mixing temperature is 190 to 220 °C, for example 190 °C, 200 °C, 210 °C or 220 °C;

[0026] The mixing time is 5 to 20 minutes, preferably 10 to 15 minutes;

[0027] The purpose of the mixing is to achieve uniform mixing, which can be carried out in mixing equipment in the prior art, including but not limited to static mixers, single-screw extruders, and twin-screw extruders.

[0028] In a preferred embodiment of the present invention,

[0029] The temperature of the depolymerization reaction is 220 - 250 °C, such as 220 °C, 230 °C, 240 °C, or 250 °C;

[0030] The pressure of the depolymerization reaction is 0.5 - 8 kPa, more preferably 0.5 - 5 kPa, such as 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, or 8 kPa;

[0031] The reaction time of the depolymerization reaction is 10 - 40 minutes, more preferably 20 - 40 minutes.

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

[0033] Collect the organic matter in the depolymerization exhaust gas and discharge CO2.

[0034] The CO2 content in the exhaust gas generated by the depolymerization reaction is < 3 vol%, preferably < 2.5 vol%;

[0035] The organic matter content in the exhaust gas generated by the depolymerization reaction is < 0.5 vol%, preferably < 0.4 vol%;

[0036] The purity of the obtained glycolide is > 97.5%;

[0037] The acid value of the obtained glycolide is < 300 μmol / g.

[0038] The second object of the present invention is to provide a glycolide obtained by the above preparation method.

[0039] In the ranges and values disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article. In the following text, in principle, the various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed in this article.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] In the present invention, terphenyl and / or its hydrogenated product is added during the depolymerization reaction of glycolic acid oligomers, inhibiting the decarboxylation side reaction and thermal degradation side reaction during the depolymerization reaction, reducing the generation of by-products such as CO2 and small molecule organic compounds such as aldehyde-ketone acids in the depolymerization exhaust gas, and promoting the equilibrium of the glycolic acid oligomer depolymerization reaction to shift towards the back-biting transesterification direction, thereby improving the yield and quality of glycolide.

[0042] In the depolymerization exhaust gas of the present invention, the CO2 content is <3 vol%, the organic matter content is <0.5 vol%, the purity of the prepared glycolide is >97.5%, and the acid value is <300 μmol / g, achieving good technical effects. Detailed implementation manners

[0043] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the content of the present invention still fall within the protection scope of the present invention.

[0044] In addition, it should be noted that the various specific technical features described in the following detailed implementation manners can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0045] Furthermore, any combination can be made between different embodiments of the present invention as long as it does not violate the idea of the present invention. The technical solutions formed thereby belong to a part of the original disclosure content of this specification and also fall within the protection scope of the present invention.

[0046] If there is no special limitation on the raw materials used in the examples and comparative examples, they are all disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0047] Hydrogenated terphenyl: Commercially available, purity 99.0%.

[0048] Terphenyl: Commercially available, purity 99.0%.

[0049] The paraffin is solid paraffin with a melting point of 62 - 64 °C.

[0050] Analysis and determination methods for glycolic acid oligomers, glycolide products, and depolymerization exhaust gas in the present invention:

[0051] (1) Determination of the weight-average molecular weight of glycolic acid oligomers

[0052] The weight-average molecular weight of glycolic acid oligomers was determined using a gel permeation chromatograph (GPC). The sample was dissolved in a hexafluoroisopropanol solution. The column temperature was set at 40 °C; the hexafluoroisopropanol solution was used as the eluent; the flow rate was set at 1 mL / min; relative molecular mass calibration was performed using 5 different standard polymethyl methacrylates to obtain the weight-average molecular weight (M w ).

[0053] (2) Determination of the terminal carboxyl group content of glycolic acid oligomers

[0054] The content of terminal carboxyl groups in glycolic acid oligomers was determined by acid-base titration. The sample was heated to 150 °C and dissolved in 40 mL of dry dimethyl sulfoxide. After dissolution, it was cooled to room temperature, and a few drops of bromophenol blue indicator solution were added, and the solution turned yellow. It was titrated with a benzyl alcohol solution of sodium hydroxide with a standard concentration until the solution color changed from yellow to green as the end point. The terminal carboxyl group content of the sample was calculated by calculating the volume of sodium hydroxide solution used at the titration end point.

[0055] (3) Determination of the purity of glycolide

[0056] GC analysis was carried out. 0.5 g of the sample was placed in a centrifuge tube and fully dissolved in 25 mL of dimethyl sulfoxide. The centrifugation speed was 10,000 r / min and the time was 5 min. The supernatant of the centrifuge tube was taken for analysis. The chromatographic column was DB-FFAP 30 m × 0.25 mm × 0.25 μm, and it was calculated using a (250 - 5000) μg / g standard curve.

[0057] (4) Determination of the acid value of glycolide

[0058] The acid value content of the crude glycolide product was determined by acid-base titration. The sample was dissolved in 20 mL of dry dimethyl sulfoxide. After dissolution, a few drops of bromophenol blue indicator solution were added, and the solution turned yellow. It was titrated with a benzyl alcohol solution of sodium hydroxide with a standard concentration until the solution color changed from yellow to green as the end point. The acid value content of the sample was calculated by calculating the volume of sodium hydroxide solution used at the titration end point.

[0059] (5) Determination of the depolymerization waste gas

[0060] GC-MS analysis was carried out. After sampling, the sample was directly injected for analysis. The chromatographic column was DM-FFAP (60 m × 0.25 mm × 0.5 μm), and single-point calibration with a standard gas was performed.

[0061]

Example 1

[0062] The molten glycolic acid oligomer with a terminal carboxyl group content of 254 μmol / g and hydrogenated terphenyl are mixed evenly. The mixing temperature is 209 °C and the mixing time is 15 minutes. The amount of hydrogenated terphenyl used is 28% of the weight of the glycolic acid oligomer, and the weight-average molecular weight of the glycolic acid oligomer is 13,800.

[0063] After mixing, the mixture is subjected to a depolymerization reaction. The temperature of the depolymerization reaction is gradually increased from 220 °C to 240 °C and maintained. The system pressure is reduced to 4.6 kPa by vacuum pumping to carry out the depolymerization reaction. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 28 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization waste gas is collected. The CO2 content in the depolymerization waste gas is measured to be 1.82 vol%, the content of small molecule organic compounds such as aldehydes, ketones and acids is 0.33 vol%, the purity of glycolide is 98.43%, and the acid value content is 201 μmol / g.

[0064]

Example 2

[0065] The molten glycolic acid oligomer with a terminal carboxyl group content of 278 μmol / g and hydrogenated terphenyl are mixed evenly. The mixing temperature is 218 °C and the mixing time is 10 minutes. The amount of hydrogenated terphenyl used is 17% of the weight of the glycolic acid oligomer, and the weight-average molecular weight of the glycolic acid oligomer is 12,200.

[0066] After mixing, the mixture is fed into a depolymerization reactor. The temperature of the depolymerization reaction is gradually increased from 220 °C to 235 °C and maintained. The system pressure is reduced to 3.4 kPa by vacuum pumping to carry out the depolymerization reaction. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 35 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization waste gas is collected. The CO2 content in the depolymerization waste gas is measured to be 2.14 vol%, the content of small molecule organic compounds such as aldehydes, ketones and acids is 0.36 vol%, the purity of glycolide is 98.01%, and the acid value content is 238 μmol / g.

[0067]

Example 3

[0068] The molten glycolic acid oligomer with a terminal carboxyl group content of 233 μmol / g and terphenyl are mixed evenly. The mixing temperature is 203 °C and the mixing time is 10 minutes. The amount of terphenyl used is 45% of the weight of the glycolic acid oligomer, and the weight-average molecular weight of the glycolic acid oligomer is 14,300.

[0069] After mixing, the mixture is fed into a depolymerization reactor. The temperature of the depolymerization reaction is gradually increased from 220 °C to 228 °C and maintained. The system pressure is reduced to 2.1 kPa by vacuum pumping, and the depolymerization reaction is carried out. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 40 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization exhaust gas is collected. The CO2 content in the depolymerization exhaust gas is measured to be 1.94 vol%, the content of small molecule organic compounds such as aldehydes, ketones and acids is 0.34 vol%, the purity of glycolide is 98.16%, and the acid value content is 221 μmol / g.

[0070]

Example 4

[0071] The molten glycolic acid oligomer with a terminal carboxyl group content of 281 μmol / g and hydrogenated terphenyl are mixed evenly. The mixing temperature is 192 °C and the mixing time is 10 minutes. The amount of hydrogenated terphenyl used is 20% of the weight of the glycolic acid oligomer, and the weight-average molecular weight of the glycolic acid oligomer is 12700.

[0072] After mixing, the mixture is subjected to a depolymerization reaction. The temperature of the depolymerization reaction is gradually increased from 220 °C to 240 °C and maintained. The system pressure is reduced to 0.6 kPa by vacuum pumping, and the depolymerization reaction is carried out. The total time of the depolymerization reaction of the molten glycolic acid oligomer in the depolymerization reactor is 26 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization exhaust gas is collected. The CO2 content in the depolymerization exhaust gas is measured to be 2.58 vol%, the content of small molecule organic compounds such as aldehydes, ketones and acids is 0.43 vol%, the purity of glycolide is 97.64%, and the acid value content is 279 μmol / g.

[0073]

Example 5

[0074] The molten glycolic acid oligomer with a terminal carboxyl group content of 464 μmol / g and terphenyl are mixed evenly. The mixing temperature is 210 °C and the mixing time is 15 minutes. The amount of terphenyl used is 18% of the weight of the glycolic acid oligomer, and the weight-average molecular weight of the glycolic acid oligomer is 10800.

[0075] After mixing, the mixture is fed into a depolymerization reactor. The temperature of the depolymerization reactor is gradually increased from 220 °C to 250 °C and maintained. The system pressure is reduced to 3.5 kPa by vacuum pumping, and the depolymerization reaction is carried out. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 30 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization exhaust gas is collected. The CO2 content in the depolymerization exhaust gas is measured to be 2.84 vol%, the content of small molecule organic compounds such as aldehydes, ketones and acids is 0.39 vol%, the purity of glycolide is 97.81%, and the acid value content is 264 μmol / g.

[0076]

Example 6

[0077] The molten glycolic acid oligomer with a terminal carboxyl group content of 238 μmol / g and hydrogenated terphenyl are mixed evenly. The mixing temperature is 210 °C and the mixing time is 10 minutes. The dosage of hydrogenated terphenyl is 40% of the weight of the glycolic acid oligomer, and the weight-average molecular weight of the glycolic acid oligomer is 14400.

[0078] After mixing, the mixture is subjected to a depolymerization reaction. The temperature of the depolymerization reaction is gradually increased from 220 °C to 222 °C and maintained. The system pressure is reduced to 1.5 kPa by vacuum pumping for the depolymerization reaction. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 25 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization waste gas is collected. The CO2 content in the depolymerization waste gas is measured to be 1.98 vol%, the content of small molecular organic compounds such as aldehydes, ketones and acids is 0.37 vol%, the purity of glycolide is 97.92%, and the acid value content is 271 μmol / g.

[0079]

Comparative Example 1

[0080] The molten glycolic acid oligomer used is the same as that in Example 1.

[0081] The molten glycolic acid oligomer with a terminal carboxyl group content of 254 μmol / g and a weight-average molecular weight of 13800 is gradually heated from 220 °C to 240 °C and maintained. The system pressure is reduced to 4.6 kPa by vacuum pumping for the depolymerization reaction. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 28 minutes. The crude product of glycolide distilled out is condensed and collected. The depolymerization waste gas is collected. The CO2 content in the depolymerization waste gas is measured to be 13.88 vol%, the content of small molecular organic compounds such as aldehydes, ketones and acids is 1.64 vol%, the purity of glycolide is 88.04%, and the acid value content is 518 μmol / g.

[0082]

Comparative Example 2

[0083] The molten glycolic acid oligomer used is the same as that in Example 1.

[0084] The molten glycolic acid oligomer with a terminal carboxyl group content of 254 μmol / g and a weight-average molecular weight of 13800 and polyethylene glycol dimethyl ether (molecular weight 350) are mixed evenly. The mixing temperature is 209 °C and the mixing time is 15 minutes. The dosage of polyethylene glycol dimethyl ether is 28% of the weight of the glycolic acid oligomer.

[0085] After mixing, the mixture is depolymerized. The temperature of the depolymerization reaction is gradually increased from 220 °C to 240 °C and maintained. The system pressure is reduced to 4.6 kPa by vacuum pumping, and the depolymerization reaction is carried out. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 28 minutes. The crude product of the distilled glycolide is collected after condensation, and the depolymerization waste gas is collected. The CO2 content in the depolymerization waste gas is measured to be 12.03 vol%, the content of small molecule organic compounds such as aldehyde, ketone and acid is 2.38 vol%, the purity of glycolide is 89.19%, and the acid value content is 487 μmol / g.

[0086]

Comparative Example 3

[0087] The molten glycolic acid oligomer used is the same as that in Example 1.

[0088] The molten glycolic acid oligomer with a terminal carboxyl group content of 254 μmol / g and a weight average molecular weight of 13,800 and paraffin are mixed evenly. The mixing temperature is 209 °C and the mixing time is 15 minutes. The amount of paraffin used is 28% of the weight of the glycolic acid oligomer.

[0089] After mixing, the mixture is depolymerized. The temperature of the depolymerization reaction is gradually increased from 220 °C to 240 °C and maintained. After feeding, the system pressure is reduced to 4.6 kPa by vacuum pumping, and the depolymerization reaction is carried out. The total time of the depolymerization reaction of the molten glycolic acid oligomer is 28 minutes. The crude product of the distilled glycolide is collected after condensation, and the depolymerization waste gas is collected. The CO2 content in the depolymerization waste gas is measured to be 10.94 vol%, the content of small molecule organic compounds such as aldehyde, ketone and acid is 2.07 vol%, the purity of glycolide is 89.63%, and the acid value content is 461 μmol / g.

[0090] The differences between Example 1 and Comparative Examples 1-3 are that there is no hydrogenated terphenyl, polyethylene glycol dimethyl ether is used to replace hydrogenated terphenyl, and paraffin is used to replace hydrogenated terphenyl, respectively.

[0091] Comparing the test data shows that:

[0092] The CO2 content in the depolymerization waste gas of Example 1 is 1.82 vol%, and those of Comparative Examples 1-3 are 13.88 vol%, 12.03 vol%, and 10.94 vol%, respectively;

[0093] The content of small molecule organic compounds such as aldehyde, ketone and acid in Example 1 is 0.33 vol%, and those of Comparative Examples 1-3 are 1.64 vol%, 2.38 vol%, and 2.07 vol%, respectively;

[0094] The purity of glycolide in Example 1 is 98.43%, and those of Comparative Examples 1-3 are 88.04%, 89.19%, and 89.63%, respectively;

[0095] The acid value content of glycolide in Example 1 was 201 μmol / g, and those in Comparative Examples 1 to 3 were 518 μmol / g, 487 μmol / g, and 461 μmol / g, respectively;

[0096] The comparison results of the above test data show that when terphenyl or hydrogenated terphenyl is added during the depolymerization reaction, compared with the addition of dimethyl polyethylene glycol ether, paraffin, or without addition, the content of CO2 and small molecule organic compounds such as aldehydes, ketones, and acids in the depolymerization waste gas is significantly reduced, and the obtained glycolide has higher purity and lower acid value.

[0097] It is proved that the addition of terphenyl or hydrogenated terphenyl can inhibit the decarboxylation side reaction and thermal degradation side reaction during the depolymerization reaction, reduce the generation amount of depolymerization waste gas, and promote the equilibrium of the glycolic acid oligomer depolymerization reaction to shift towards the back-biting transesterification direction, thereby improving the yield and quality of glycolide.

[0098] After the depolymerization of Examples 1 to 6 was completed, the CO2 content in the depolymerization waste gas was measured to be <3 vol%, the organic matter content was <0.5 vol%, the purity of the prepared glycolide was >97.5%, and the acid value was <300 μmol / g, solving the problems that during the depolymerization process, the depolymerization reaction is prone to decarboxylation side reaction and thermal degradation side reaction, generating by-products such as CO2, small molecule organic compounds such as aldehydes, ketones, and acids, resulting in high concentration of depolymerization waste gas, decreased yield of glycolide, decreased purity, and increased acid value.

Claims

1. A method for preparing glycolide, comprising: The glycolic acid oligomer is depolymerized in the presence of terphenyl and / or its hydrogenated product to obtain glycolide.

2. The method for preparing glycolide according to claim 1, characterized in that: The terphenyl and / or its hydrogenated product is at least one of terphenyl and hydrogenated terphenyl.

3. The method for preparing glycolide according to claim 1, characterized in that: The dosage of the terphenyl and / or its hydrogenated product is 5-50% by weight of the glycolic acid oligomer.

4. The method for preparing glycolide according to claim 3, characterized in that: The dosage of the terphenyl and / or its hydrogenated product is 10-30% by weight of the glycolic acid oligomer.

5. The method for preparing glycolide according to claim 1, characterized in that: The weight-average molecular weight of the glycolic acid oligomer is 8000-20000; and / or, The terminal carboxyl group content of the glycolic acid oligomer is 200-700 μmol / g.

6. The method for preparing glycolide according to claim 5, characterized in that: The weight-average molecular weight of the glycolic acid oligomer is 10000-15000; and / or, The terminal carboxyl group content of the glycolic acid oligomer is 200-500 μmol / g.

7. The method for preparing glycolide according to claim 1, characterized in that: The glycolic acid oligomer is mixed with terphenyl and / or its hydrogenated product and then undergoes depolymerization reaction; preferably, The mixing temperature is 190-220 °C; and / or, The mixing time is 5-20 minutes, preferably 10-15 minutes.

8. The method for preparing glycolide according to claim 1, characterized in that: The temperature of the depolymerization reaction is 220-250 °C; and / or, The pressure of the depolymerization reaction is 0.5-8 kPa, more preferably 0.5-5 kPa; and / or, The reaction time of the depolymerization reaction is 10-40 minutes, preferably 20-40 minutes.

9. The method for preparing glycolide according to any one of claims 1-8, characterized in that: The CO2 content in the waste gas generated by the depolymerization reaction is <3 vol%; and / or, The organic matter content in the waste gas generated by the depolymerization reaction is <0.5 vol%; and / or, The purity of the obtained glycolide is >97.5%; and / or, The acid value of the obtained glycolide is <300 μmol / g.

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