Refining method of glycolide and obtained glycolide

Abstract

The invention provides a refining method of glycolide and the obtained glycolide. The refining method of glycolide comprises the following steps: contacting a crude glycolide solution with particles with catalysis and adsorption functions, and filtering to obtain a glycolide solution; the method specifically comprises the following steps: dissolving crude glycolide in an organic solvent to obtain a dissolved solution, contacting the dissolved solution with particles with catalysis and adsorption functions, filtering to obtain a glycolide solution, crystallizing the obtained glycolide solution, carrying out solid-liquid separation, collecting a solid phase, and drying to obtain refined glycolide. According to the method, aldehyde impurities influencing polymerization in a system are converted into substances easy to remove to be removed through a catalysis method, the operation condition is mild, the polymerization performance of the product is improved, operation is easy, and industrialization is easy.

Description

Technical Field

[0001] The present invention relates to the field of glycolide, and more particularly, to a method for refining glycolide and the obtained glycolide. Background Art

[0002] Glycolide is the cyclic dimer of glycolic acid, that is, a cyclic substance formed by the dehydration condensation of two molecules of glycolic acid. Ring-opening polymerization of glycolide is a relatively mature method for preparing polyglycolic acid, and this method can obtain polyglycolic acid products with relatively high molecular weights. At present, the most mature and widely used synthesis methods of glycolide at home and abroad mainly include the polycondensation and depolymerization method using glycolic acid as the raw material.

[0003] The crude glycolide obtained from the above depolymerization reaction usually contains various aldehyde substances such as formaldehyde and acetaldehyde. The presence of a small amount of aldehyde substances during the ring-opening polymerization of glycolide will have a great impact on the molecular weight of the obtained polymer. And polyglycolic acid that needs to meet the requirements for uses such as surgical sutures needs to meet the requirements of an intrinsic viscosity greater than or equal to 1.0 dL / g and a weight-average molecular weight greater than one hundred thousand Da. Therefore, it is necessary to remove the influence of aldehydes during the refining process to improve its performance. Existing technologies generally catalyze the reaction of aldehyde substances through manganese-based catalysts. At the same time, noble metal (Pt, Au, Pb, Ag) catalysts and inexpensive metal (Mn, Cu, Fe, Co, etc.) catalysts are also active in the reaction of aldehyde substances. Of course, it is also a common practice to use them as the catalytic core and load them on a porous structure as a catalyst.

[0004] Chinese Patent CN107868075A proposes to use a dissolution and filtration method to remove oligomers. At the same time, this method can also remove low-level aldehydes with high solubility, such as formaldehyde, acetaldehyde, and propionaldehyde. It can also remove aldehydes with large molecular weights that exist as insoluble substances in the system. However, for substances with molecular weights between the two, this method cannot effectively remove them.

[0005] Chinese Patent CN114014835A proposes to dissolve the crude glycolide in an organic solvent and then use water as an extractant for liquid-liquid extraction, liquid separation, and then use an adsorbent for dehydration, filtration, crystallization, and drying to obtain a glycolide product. However, its use steps are numerous, using water as an extractant places restrictions on the operating conditions, and the adsorbent is also prone to adsorbing a large amount of organic solvents, resulting in difficult regeneration, which is not conducive to industrialization. And the pore size of the adsorbent is not described in this method, resulting in uncertainty about whether the adsorbent can adsorb aldehyde substances while adsorbing water.

[0006] Therefore, it is necessary to study a method for refining glycolide that can not only remove aldehyde impurities that affect polymerization in the system, thereby improving the polymerization performance of the product, but also has simple operation and is easy to industrialize. Summary of the Invention

[0007] To solve the technical problems existing in the prior art, the present invention provides a method for refining glycolide and the obtained glycolide.

[0008] In the prior art, methods for removing aldehydes from crude glycolide, such as distillation, are difficult to implement during the refining of glycolide due to the thermal sensitivity of glycolide; if the adsorption method is used, since the content of aldehyde impurities in crude glycolide is small, small molecule acids with a high content in the impurities will competitively be adsorbed as expected, resulting in an insignificant adsorption effect. To overcome the defects of the prior art, the technical solution of the present invention converts aldehyde impurities affecting polymerization in the system into substances that are easy to remove through a catalytic method, improving the polymerization performance of the product, with simple operation and easy industrialization.

[0009] The present invention contacts the prepared particles with catalytic and adsorption functions with the crude glycolide solution. The catalytic function oxidizes the aldehydes in the crude glycolide into acids, and the acid substances dissolve in the dissolution solution and can be removed during filtration. The main function of the adsorbent is to adsorb oxygen, and the adsorbed oxygen provides an oxidant for the catalytic reaction to oxidize aldehydes.

[0010] The content of aldehydes in the glycolide prepared by the present invention is very low, and the intrinsic viscosity of the polyglycolide after polymerization is higher.

[0011] One of the purposes of the present invention is to provide a method for refining glycolide, including the step of obtaining a glycolide solution after contacting and filtering a crude glycolide dissolution solution with particles having catalytic and adsorption functions.

[0012] In a preferred embodiment of the present invention,

[0013] the crude glycolide dissolution solution contains crude glycolide and an organic solvent; the contacting and filtering steps can be carried out simultaneously or first contact and then filter;

[0014] Preferably, it specifically includes the following steps:

[0015] (1) Dissolve crude glycolide in an organic solvent to obtain a dissolution solution;

[0016] (2) After contacting and filtering the dissolution solution obtained in step (1) with particles having catalytic and adsorption functions, the obtained glycolide solution is crystallized and then subjected to solid-liquid separation, and the solid phase is collected and dried to obtain refined glycolide.

[0017] In the above technical solution, the contacting is to oxidize the aldehydes in the crude glycolide into acids.

[0018] In a preferred embodiment of the present invention,

[0019] The contact and filtration methods are to add particles with catalytic and adsorption functions to the dissolution solution, mix them and then filter, or use the particles with catalytic and adsorption functions as a fixed bed to circulate and filter the dissolution solution; preferably,

[0020] When adding particles with catalytic and adsorption functions to the dissolution solution, the mass ratio of the particles with catalytic and adsorption functions to crude glycolide is (0.01 - 1):1, more preferably (0.3 - 0.7):1; and / or,

[0021] The temperature for contact and filtration is 20 - 80°C, preferably 40 - 70°C; and / or,

[0022] The time for contact and filtration is 0.5 - 3 h, preferably 0.8 - 2 h.

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

[0024] Step (1),

[0025] The crude glycolide is the product of the depolymerization reaction of glycolic acid oligomer or the intermediate glycolide obtained by subjecting the product to a purification process; the glycolic acid oligomer is obtained by the polycondensation reaction of glycolic acid or by the transesterification reaction of methyl glycolate;

[0026] For example, the crude glycolide can be prepared according to the method described in Chinese Patent CN104903306A (invention name: "Preparation method of glycolide"), specifically as follows:

[0027] In a reactor, mix a 50 - 70% aqueous glycolic acid solution with a catalyst in contact, and carry out the reaction at a reaction temperature of 100 - 220°C and a reaction pressure of normal pressure - 1 kPa(A) until no water is distilled out to obtain a glycolic acid oligomer; at least one of stannous octoate, stannous chloride, antimony trioxide, zinc oxide, and zinc acetylacetonate can be selected as the catalyst; the glycolic acid oligomer is subjected to a depolymerization reaction at a reaction temperature of 230 - 290°C and an absolute pressure of 0.5 - 10 kPa to obtain a crude product, and the crude product is washed with at least one of ethanol, propanol, and isopropanol and dried to obtain crude glycolide.

[0028] The acid value of the crude glycolide is 50 - 100 mmol / kg, and the purity is greater than or equal to 95%;

[0029] The organic solvent is at least one of acetone, n - propanol, isopropanol, ethanol, and ethyl acetate;

[0030] The mass ratio of the crude glycolide to the organic solvent is (0.05 - 1):1, preferably (0.2 - 0.8):1, to ensure sufficient solubility of the crude glycolide in the organic solvent;

[0031] The temperature at which the crude glycolide is dissolved is less than 80°C, preferably 40 - 70°C. Temperatures greater than 80°C will cause excessive side reactions in the glycolide solution.

[0032] The dissolution time of the crude glycolide is until it is completely dissolved, usually 0.5 - 4 h.

[0033] In a preferred embodiment of the present invention,

[0034] Step (2),

[0035] The particles with catalytic and adsorption functions are prepared from raw materials including catalyst particles and adsorbent particles.

[0036] The particles with catalytic and adsorption functions are porous solid particles with a pore diameter less than or equal to 0.04 nm, ensuring that a large amount of organic solvent does not enter the particles.

[0037] The pore diameter refers to the molecular sieve of the adsorbent or the pore diameter of the molecular sieve with catalytic effect prepared by adding catalytic components. The pore diameter has a great influence on the invention effect. If the pore diameter is too large, a large amount of solvent will enter the molecular sieve, causing the molecular sieve to lose its adsorption capacity. The adsorbent in the present invention mainly adsorbs oxygen, and the oxygen molecule diameter is about 0.28 nm, indicating that the molecular sieve with a pore diameter greater than 0.28 nm can adsorb. Therefore, the preferred pore diameter range of the molecular sieve is 0.28 - 0.4 nm. If it is less than 0.28 nm, the oxygen molecule cannot be adsorbed.

[0038] Currently, the commonly commercially available molecular sieves that meet the requirements are 3A molecular sieve and 4A molecular sieve, corresponding to pore diameters of 0.3 nm and 0.4 nm respectively. The method for testing the pore diameter can use gas adsorption method.

[0039] In a preferred embodiment of the present invention,

[0040] The catalyst particles are at least one of the following catalyst particles: noble metal catalyst, inexpensive metal catalyst; preferably,

[0041] The noble metal catalyst is at least one of the following: elemental metal, oxide, hydroxide, chloride, complex, organometallic compound of Pt, Au, Pb, Ag;

[0042] The inexpensive metal catalyst is at least one of the following: elemental metal, oxide, hydroxide, chloride, complex, organometallic compound of Mn, Cu, Fe, Co;

[0043] The adsorbent particles are at least one of alumina, molecular sieve, silica gel, activated carbon, and mineral desiccant; the alumina is preferably at least one of α-Al2O3, β-Al2O3, or γ-Al2O3; the molecular sieve is preferably aluminosilicate or natural zeolite, more preferably at least one of 3A molecular sieve and 4A molecular sieve; the mineral desiccant is preferably at least one of montmorillonite and attapulgite;

[0044] The mass ratio of the catalyst particles to the adsorbent particles is (1 to 99):1, preferably (1 to 2.4):1.

[0045] In a preferred embodiment of the present invention,

[0046] The preparation method of the particles with catalytic and adsorption functions is as follows: The catalyst particles and the adsorbent particles are mixed, activated, cooled, and oxygen is passed through to obtain the particles with catalytic and adsorption functions.

[0047] In a preferred embodiment of the present invention,

[0048] The mixing can adopt the usual mixing methods in the art;

[0049] The activation is carried out under vacuum;

[0050] The activation temperature is 150 to 300 °C, such as 150 °C, 160 °C, 180 °C, 200 °C, 220 °C, 240 °C, 260 °C, 280 °C, 300 °C, etc.;

[0051] The activation time is more than 2 h, preferably 2 to 4 h;

[0052] After cooling to room temperature under vacuum conditions, oxygen is passed through for more than 15 min, preferably 15 to 40 min.

[0053] In a preferred embodiment of the present invention,

[0054] In step (2),

[0055] The crystallization method is cooling or evaporation; the cooling is preferably down to below 5 °C;

[0056] Drying can adopt the general drying methods in the prior art, such as a drying temperature of 50 to 80 °C and a drying time of 3 to 8 h.

[0057] The second object of the present invention is to provide a glycolide obtained by the above method.

[0058] The total aldehyde content of the glycolide is less than 10 ppm, preferably less than 5 ppm.

[0059] The third object of the present invention is to provide a polyglycolide prepared from the obtained glycolide.

[0060] The intrinsic viscosity of the polyglycolide is preferably 1.30 to 1.72 dL / g.

[0061] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0062] In the present invention, the particles with catalytic and adsorption functions are prepared and contacted with the crude glycolide solution. The catalytic function oxidizes the aldehydes in the crude glycolide to acids, and the acid substances dissolve in the dissolution liquid and can be removed during filtration. The main function of the adsorption function is to adsorb oxygen, and the adsorbed oxygen provides an oxidant for the catalytic reaction to oxidize the aldehydes. The pore diameter of the particles with catalytic and adsorption functions prepared in the present invention is less than or equal to 0.04 nanometers, which can avoid a large amount of solvent from entering and can be recycled for multiple uses.

[0063] The aldehyde content in the glycolide obtained after the refining treatment is less than 5 ppm, and the polyglycolide obtained by polymerization has a higher intrinsic viscosity.

[0064] The technical solution of the present invention converts the aldehyde impurities that affect polymerization in the system into substances that are easy to remove by a catalytic method. The operating conditions are mild, which reduces the deterioration of glycolide during the refining process, improves the polymerization performance of the product, is simple to operate, and is easy to industrialize. Detailed embodiments

[0065] 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 should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0066] The crude glycolide in the examples and comparative examples was synthesized in the laboratory by itself, and other raw materials used in the examples except for this were all conventional commercially available raw materials.

[0067] The preparation of the crude glycolide was carried out according to Chinese Invention Patent CN104903306A (the invention name is "Preparation method of glycolide"), specifically as follows:

[0068] Crude glycolide A: 70% aqueous glycolic acid solution and stannous octoate catalyst were mixed and contacted in a reactor, and the reaction was carried out at a reaction temperature of 220 °C and a reaction pressure of normal pressure to 1 kPa (A) until no water was distilled out, and a glycolic acid oligomer was obtained; the glycolic acid oligomer was depolymerized at a reaction temperature of 290 °C and an absolute pressure of 0.5 kPa to obtain a crude product, and the crude product was washed with absolute ethanol and dried to obtain crude glycolide A. The acid value of crude glycolide A was 54 mmol / kg, and the purity was 98.5%.

[0069] Crude glycolide B: In a reactor, 70% aqueous glycolic acid solution is mixed and contacted with stannous octoate as a catalyst. The reaction is carried out at a reaction temperature of 230 °C and a reaction pressure of atmospheric pressure to 1 kPa(A) until no water is distilled out, obtaining a glycolic acid oligomer; the glycolic acid oligomer is depolymerized at a reaction temperature of 290 °C and an absolute pressure of 0.5 kPa to obtain a crude product. The crude product is washed with isopropanol and dried to obtain crude glycolide B. The acid value of the crude glycolide B is 80 mmol / kg and the purity is 98.3%.

[0070] Crude glycolide C: In a reactor, 70% aqueous glycolic acid solution is mixed and contacted with stannous octoate as a catalyst. The reaction is carried out at a reaction temperature of 225 °C and a reaction pressure of atmospheric pressure to 1 kPa(A) until no water is distilled out, obtaining a glycolic acid oligomer; the glycolic acid oligomer is depolymerized at a reaction temperature of 285 °C and an absolute pressure of 0.5 kPa to obtain a crude product. The crude product is washed with isopropanol and dried to obtain crude glycolide C. The acid value of the crude glycolide C is 65 mmol / kg and the purity is 98.5%.

[0071] The above aqueous glycolic acid solution is a commercially available product from Chemours.

[0072] Manganese-modified zeolite SCR catalyst (manganese element content is 1%): Produced by Liuzhou Haida New Materials Technology Co., Ltd.

[0073] Analysis and testing methods:

[0074] (1) Evaluation of glycolide polymerization: Take 55.0 g of glycolide, add 3.0 mg of stannous chloride dihydrate as a catalyst, mix evenly, add the mixture to a mixer at 220 °C, set the rotation speed to 80 revolutions per minute, and react for 15 min to obtain polyglycolide. Take a part of the polyglycolide and measure the intrinsic viscosity of the polyglycolide using the Ubbelohde capillary viscometry method.

[0075] (2) Determination of the acid value of glycolide: The acid value content of glycolide before and after refining treatment is determined by the method of acid-base titration. Dissolve the glycolide sample in 20 mL of dry dimethyl sulfoxide. After it is dissolved, add a few drops of bromophenol blue indicator solution, and the solution turns yellow. Titrate it with a benzyl alcohol solution of sodium hydroxide with a standard concentration. The end point is when the solution color changes from yellow to green. Calculate the acid value content of glycolide by calculating the volume of the sodium hydroxide solution used when reaching the titration end point.

[0076] (3) Determination of total aldehydes: The aliphatic aldehydes in the sample react with 3-methyl-2-benzothiazolinone hydrazone (MBTH) in the presence of ferric chloride to form a blue-green fused cation, and the absorbance is measured at a wavelength of 620 nm using a spectrophotometer.

[0077] Weigh an appropriate amount of the sample, add 4.0 mL of acetone, measure the absorbance, and simultaneously conduct a reagent blank test. The net absorbance is the absorbance of the sample minus the absorbance of the blank. Calculate the aldehyde content (in terms of formaldehyde) of the sample based on the working curve.

[0078]

Example 1

[0079] Particle preparation: Mix manganese dioxide and 4A molecular sieve in a mass ratio of 1:1 to make catalytic particles, vacuum at 200 °C for 2 h, maintain the vacuum and cool down to 25 °C, then purge with oxygen for 15 min.

[0080] Product refinement: Add 300 g of crude glycolide (acid value is 54 mmol / kg, purity is 98.5%) to 700 g of ethyl acetate, heat to 70 °C, stir for 3 h, add 200 g of catalytic particles, keep the temperature at 60 °C, stir for 2 h, filter, cool the received filtrate to 5 °C to precipitate crystals, filter, and dry at 60 °C for 5 h to obtain glycolide crystals (acid value 3 mmol / kg, total aldehyde content is 3.7 ppm)

[0081] The intrinsic viscosity of the obtained polyglycolide from the polymerization evaluation is 1.45 dL / g.

[0082]

Example 2

[0083] Particle preparation: Mix a commercially available manganese-modified molecular sieve SCR catalyst (manganese element content is 1%) and 4A molecular sieve in a mass ratio of 1:1 to make catalytic particles, vacuum at 200 °C for 4 h, maintain the vacuum and cool down to 25 °C, then purge with oxygen for 15 min.

[0084] Product refinement: Add 300 g of crude glycolide (acid value is 80 mmol / kg, purity is 98.3%) to 700 g of ethyl acetate, heat to 60 °C, stir for 1 h, add 200 g of catalytic particles, keep the temperature at 60 °C, stir for 2 h, filter, cool the received filtrate to 5 °C to precipitate crystals, filter, and dry at 60 °C for 5 h to obtain glycolide crystals (acid value 4 mmol / kg, total aldehyde content is 2.5 ppm)

[0085] The intrinsic viscosity of the obtained polyglycolide from the polymerization evaluation is 1.47 dL / g.

[0086]

Example 3

[0087] Particle preparation: Mix silver chloride and 4A molecular sieve in a mass ratio of 1:1 to make catalytic particles, vacuum at 250 °C for 2 h, maintain the vacuum and cool down to 25 °C, then purge with oxygen for 15 min.

[0088] Product Refinement: Add 300 g of crude glycolide (acid value 54 mmol / kg, purity 98.5%) to 400 g of acetone, heat to 60 °C, stir for 1 h, add 200 g of catalytic particles, keep the temperature at 60 °C, stir for 1 h, filter, evaporate and crystallize the filtrate received, precipitate crystals, filter, and dry at 60 °C for 5 h to obtain glycolide crystals (acid value 2.7 mmol / kg, total aldehyde content 3.2 ppm).

[0089] The intrinsic viscosity of the polyglycolide obtained by polymerization evaluation is 1.53 dL / g.

[0090]

Example 4

[0091] Particle Preparation: Mix manganese dioxide and α-Al2O3 (pore size 0.41 nm) in a mass ratio of 1:1 to make catalytic particles, vacuum at 300 °C for 2 h, keep the vacuum and cool to 25 °C, then purge with oxygen for 40 min.

[0092] Product Refinement: Add 300 g of crude glycolide (acid value 54 mmol / kg, purity 98.5%) to 650 g of mixed solvent (mass ratio of ethyl acetate to isopropanol 80:20), heat to 60 °C, stir for 1 h, add 200 g of catalytic particles, keep the temperature at 60 °C, stir for 0.8 h, filter, cool the filtrate received to 5 °C, precipitate crystals, filter, and dry at 60 °C for 5 h to obtain glycolide crystals (acid value 4.2 mmol / kg, total aldehyde content 3.7 ppm).

[0093] The intrinsic viscosity of the polyglycolide obtained by polymerization evaluation is 1.39 dL / g.

[0094]

Example 5

[0095] Particle Preparation: Mix manganese dioxide and 4A molecular sieve in a mass ratio of 1:1 to make catalytic particles, vacuum at 300 °C for 3 h, keep the vacuum and cool to 25 °C, then purge with oxygen for 15 min.

[0096] Product Refinement: Add 300 g of crude glycolide (acid value 54 mmol / kg, purity 98.5%) to 700 g of ethyl acetate, heat to 40 °C, stir for 1 h, add 100 g of catalytic particles, keep the temperature at 40 °C, stir for 2 h, filter, cool the filtrate received to 5 °C, precipitate crystals, filter, and dry at 60 °C for 5 h to obtain glycolide crystals (acid value 2.1 mmol / kg, total aldehyde content 3.4 ppm).

[0097] The intrinsic viscosity of the polyglycolide obtained by polymerization evaluation is 1.46 dL / g.

[0098]

Example 6

[0099] Particle preparation: Manganese dioxide, 4A molecular sieve, and 3A molecular sieve are mixed in a mass ratio of 2:1:1 to form catalytic particles, which are vacuum-treated at 200 °C for 2 h. After maintaining the vacuum and cooling to 25 °C, they are purged with oxygen for 15 min.

[0100] Product refinement: 300 g of crude glycolide (acid value: 54 mmol / kg, purity: 98.5%) is added to 700 g of ethyl acetate, and the mixture is heated to 60 °C. 200 g of catalytic particles are fixed in the filter layer of a circulating filtration device. Using the catalytic particles as a fixed bed, the solution is pumped through the fixed bed in a cycle at 60 °C for 1 h. The received filtrate is cooled to 5 °C to precipitate crystals, which are then filtered and dried at 60 °C for 5 h to obtain glycolide crystals (acid value: 3 mmol / kg, total aldehyde content: 3.5 ppm).

[0101] The intrinsic viscosity of the polyglycolide obtained from the polymerization evaluation is 1.42 dL / g.

[0102]

Example 7

[0103] Particle preparation: A commercially available manganese-modified molecular sieve SCR catalyst (manganese element content: 1%) and 4A molecular sieve are mixed in a mass ratio of 1:1 to form catalytic particles, which are vacuum-treated at 200 °C for 2 h. After maintaining the vacuum and cooling to 25 °C, they are purged with oxygen for 15 min.

[0104] Product refinement: 300 g of crude glycolide (acid value: 54 mmol / kg, purity: 98.5%) is added to 650 g of a mixed solvent (mass ratio of ethyl acetate to isopropanol: 80:20), and the mixture is heated to 60 °C and stirred for 1 h. 200 g of catalytic particles are added, and the temperature is maintained at 60 °C and stirred for 2 h. After filtration, the received filtrate is cooled to 5 °C to precipitate crystals, which are then filtered and dried at 60 °C for 5 h to obtain glycolide crystals (acid value: 2.7 mmol / kg, total aldehyde content: 4.1 ppm).

[0105] The intrinsic viscosity of the polyglycolide obtained from the polymerization evaluation is 1.45 dL / g.

[0106]

Example 8

[0107] Particle preparation: Manganese dioxide and 4A molecular sieve are mixed in a mass ratio of 2.4:1 to form catalytic particles, which are vacuum-treated at 200 °C for 2 h. After maintaining the vacuum and cooling to 25 °C, they are purged with oxygen for 15 min.

[0108] Product Refining: Add 300 g of crude glycolide (acid value: 54 mmol / kg, purity: 98.5%) to 650 g of a mixed solvent (mass ratio of ethyl acetate to isopropanol is 80:20). Heat to 50°C, stir for 1 h, add 100 g of catalytic particles, keep the temperature at 60°C, stir for 2 h, filter. Cool the obtained filtrate to 5°C to precipitate crystals, filter, and dry at 60°C for 5 h to obtain glycolide crystals (acid value: 3.2 mmol / kg, total aldehyde content: 4.0 ppm).

[0109] The intrinsic viscosity of the polyglycolide obtained from the polymerization evaluation is 1.62 dL / g.

[0110]

Example 9

[0111] Particle Preparation: Mix manganese dioxide and 4A molecular sieve in a mass ratio of 1:1 to make catalytic particles. Vacuum at 200°C for 2 h, keep the vacuum and cool to 25°C, then purge with oxygen for 20 min.

[0112] Product Refining: Add 300 g of commercially available crude glycolide (acid value: 65 mmol / kg, purity: 98.0%) to 1200 g of ethyl acetate. Heat to 20°C, stir for 1 h, add 200 g of catalytic particles, keep the temperature at 60°C, stir for 2 h, filter. Cool the obtained filtrate to 0°C to precipitate crystals, filter, and dry at 60°C for 5 h to obtain glycolide crystals (acid value: 3.2 mmol / kg, total aldehyde content: 2.7 ppm).

[0113] The intrinsic viscosity of the polyglycolide obtained from the polymerization evaluation is 1.59 dL / g.

[0114]

Comparative Example 1

[0115] Product Refining: Add 300 g of crude glycolide (acid value: 54 mmol / kg, purity: 98.5%) to 700 g of ethyl acetate. Heat to 70°C, stir for 3 h, filter. Cool the obtained filtrate to 5°C to precipitate crystals, filter, and dry at 60°C for 5 h to obtain glycolide crystals (acid value: 3 mmol / kg, total aldehyde content: 453 ppm).

[0116] The intrinsic viscosity of the polyglycolide obtained from the polymerization evaluation is 1.13 dL / g.

[0117]

Comparative Example 2

[0118] Particle Preparation: Mix manganese dioxide and 4A molecular sieve in a mass ratio of 1:1 to make catalytic particles. Vacuum at 200°C for 2 h, keep the vacuum and cool to below 25°C.

[0119] Product refinement: 300 g of commercially available crude glycolide (acid value 65 mmol / kg, purity 98.5%) was added to 1200 g of ethyl acetate, heated to 60 °C, stirred for 1 h, 200 g of catalytic particles were added, the temperature was 60 °C, stirred for 2 h, filtered, the obtained filtrate was cooled to 5 °C, crystals were precipitated, filtered, and dried at 60 °C for 5 h to obtain glycolide crystals (acid value 2.7 mmol / kg, total aldehyde content 356 ppm).

[0120] The intrinsic viscosity of the polyglycolide obtained by polymerization evaluation was 1.21 dL / g.

[0121]

Comparative Example 3

[0122] Particle preparation: 4A molecular sieve, vacuum at 200 °C for 2 h, after maintaining the vacuum and cooling to 25 °C, purged with oxygen for 25 min.

[0123] Product refinement: 300 g of commercially available crude glycolide (acid value 65 mmol / kg, purity 98.5%) was added to 1200 g of ethyl acetate, heated to 60 °C, stirred for 1 h, 200 g of particles were added, the temperature was 60 °C, stirred for 2 h, filtered, the obtained filtrate was cooled to 5 °C, crystals were precipitated, filtered, and dried at 60 °C for 5 h to obtain glycolide crystals (acid value 2.7 mmol / kg, total aldehyde content 432 ppm).

[0124] The intrinsic viscosity of the polyglycolide obtained by polymerization evaluation was 1.15 dL / g.

[0125] Compared with Example 1, in Comparative Example 1, the particles with catalytic and adsorption functions were not added. The total aldehyde content of the obtained glycolide crystals was 453 ppm, and the intrinsic viscosity of the polyglycolide obtained by polymerization was 1.13 dL / g. While the total aldehyde content of the glycolide crystals obtained in Example 1 was 3.7 ppm, and the intrinsic viscosity of the polyglycolide obtained by polymerization was 1.45 dL / g; it was proved that the aldehyde removal ability of the particles with catalytic and adsorption functions was outstanding, which could greatly reduce the total aldehyde content of glycolide. At the same time, the intrinsic viscosity of the polyglycolide obtained by polymerization was higher.

[0126] Compared with Example 9, in Comparative Example 2, when preparing the particles with catalytic and adsorption functions, there was no step of purging with oxygen. Therefore, not enough oxygen was adsorbed in the adsorbent and it could not act as an oxidant; the total aldehyde content of the obtained glycolide crystals was 356 ppm, and the intrinsic viscosity of the polyglycolide obtained by polymerization was 1.21 dL / g. While the total aldehyde content of the glycolide crystals obtained in Example 9 was 2.7 ppm, and the intrinsic viscosity of the polyglycolide obtained by polymerization was 1.59 dL / g; it was proved that the particles with catalytic and adsorption functions could have the function of an oxidant only after adsorbing oxygen.

[0127] Compared with Example 9, in Comparative Example 3, when preparing the particles with catalytic and adsorption functions, although there is a step of oxygen purging, when preparing the particles, manganese dioxide catalyst was not added, and only 4A molecular sieve was used; the total aldehyde content of the obtained glycolide crystals was 432 ppm, and the intrinsic viscosity of the polyglycolide obtained by polymerization was 1.15 dL / g. Compared with the performance of Example 9, it was proved that the effect of insufficient aldehyde removal could not be achieved with only adsorption function and no catalytic function.

[0128] In Examples 1 to 9, the particles with catalytic and adsorption functions prepared were contacted with the crude glycolide solution. The catalytic function oxidized the aldehydes in the crude glycolide to acids, and the acid substances were dissolved in the dissolution solution and could be removed during filtration. The main function of the adsorption function was to adsorb oxygen, and the adsorbed oxygen provided an oxidant for the catalytic reaction to oxidize aldehydes. The aldehyde content in the glycolide obtained after refining treatment was less than 5 ppm, and the intrinsic viscosity of the polyglycolide obtained by polymerization was higher.

Claims

1. A method for refining glycolide, comprising the steps of contacting a crude glycolide solution with particles having catalytic and adsorption functions, and then filtering to obtain a glycolide solution.

2. The method for refining glycolide according to claim 1, wherein: The crude glycolide solution contains crude glycolide and an organic solvent; the contacting and filtering steps can be carried out simultaneously, or first contact and then filter; Preferably, it specifically includes the following steps: (1) Dissolving crude glycolide in an organic solvent to obtain a solution; (2) Contacting the solution obtained in step (1) with particles having catalytic and adsorption functions, filtering, crystallizing the obtained glycolide solution, performing solid-liquid separation, collecting the solid phase and drying to obtain refined glycolide.

3. The method for refining glycolide according to claim 1 or 2, wherein: The manner of contacting and filtering is to add particles having catalytic and adsorption functions to the solution for mixing and then filtering, or use particles having catalytic and adsorption functions as a fixed bed and circulate and filter the solution; preferably, When adding particles having catalytic and adsorption functions to the solution, the mass ratio of the particles having catalytic and adsorption functions to the crude glycolide is (0.01 - 1):1, more preferably (0.3 - 0.7):1; and / or, The temperature of the contacting and filtering is 20 - 80 °C, preferably 40 - 70 °C; and / or, The time of the contacting and filtering is 0.5 - 3 h, preferably 0.8 - 2 h.

4. The method for refining glycolide according to claim 2, wherein: Step (1), The crude glycolide is a product obtained by depolymerizing a glycolic acid oligomer or an intermediate glycolide obtained by subjecting the product to a purification process; the glycolic acid oligomer is obtained by polycondensing glycolic acid or by transesterifying methyl glycolate; and / or, The acid value of the crude glycolide is 50 - 100 mmol / kg, and the purity is greater than or equal to 95%; and / or, The organic solvent is at least one of acetone, n-propanol, isopropanol, ethanol, ethyl acetate; and / or, The mass ratio of the crude glycolide to the organic solvent is (0.05 - 1):1, preferably (0.2 - 0.8):1; and / or, The temperature for dissolving the crude glycolide is less than 80 °C, preferably 40 - 70 °C; and / or: Step (2), The particles having catalytic and adsorption functions are prepared from raw materials including catalyst particles and adsorbent particles; and / or, The particles having catalytic and adsorption functions are porous solid particles with a pore diameter less than or equal to 0.04 nm.

5. The method for refining glycolide according to claim 4, wherein: The catalyst particles are at least one of the following catalyst particles: noble metal catalysts, inexpensive metal catalysts; preferably, The noble metal catalysts are at least one of the following metals in the form of single substances, oxides, hydroxides, chlorides, complexes, organometallic compounds: Pt, Au, Pb, Ag; and / or, The inexpensive metal catalyst is at least one of the simple substances, oxides, hydroxides, chlorides, complexes, and organometallic compounds of the following metals: Mn, Cu, Fe, Co; and / or, The adsorbent particles are at least one of alumina, molecular sieve, silica gel, activated carbon, and mineral desiccant; and / or, The mass ratio of the catalyst particles to the adsorbent particles is (1-99):1, preferably (1-2.4):

1.

6. The method for refining glycolide according to claim 1 or 2, wherein: The preparation method of the particles with catalytic and adsorption functions is: mixing the catalyst particles and the adsorbent particles, activating, cooling, and passing oxygen to obtain the particles with catalytic and adsorption functions.

7. The method for refining glycolide according to claim 6, wherein: The activation is carried out under vacuum; and / or, The activation temperature is 150-300°C; and / or, The activation time is more than 2 h, preferably 2-4 h; and / or, After cooling to room temperature under vacuum conditions, oxygen is passed in for more than 15 min, preferably 15-40 min.

8. The method for refining glycolide according to claim 2, wherein: In step (2), the crystallization method is cooling or evaporation.

9. Glycolide obtained by the method for refining glycolide according to any one of claims 1-8.

10. Poly-glycolide prepared from the glycolide according to claim 9.