Byproduct purification process and preparation process for preparing high-quality polyglycolic acid by recycling byproduct

Abstract

The invention discloses a by-product purification process and a preparation process for preparing high-quality polyglycolic acid by recycling the by-product. The purification process comprises the following steps: (1) crushing the by-product to obtain by-product powder; (2) purifying the by-product powder to obtain a purified product; the purification operation comprises at least two of at least one first purification operation, at least one second purification operation and at least one third purification operation; (3) washing the purified product obtained in the step (2) to remove the residual solvent, and drying to obtain purified byproducts of glycolide and oligomer; according to the method, by recycling the byproduct and preparing the high-quality polyglycolic acid (PGA), the byproduct is recycled on the premise of guaranteeing the quality of the polyglycolic acid, so that the effects of improving the product yield and reducing the emission of solid wastes are achieved.

Description

Technical Field

[0001] The invention belongs to the field of polyglycolic acid, and particularly relates to a by-product purification process and a preparation process for recycling the by-product to prepare high-quality polyglycolic acid. Background Art

[0002] At present, biodegradable plastic products are mainly polylactic acid PLA, PBAT, PHA, PBS and modified starch, among which PLA is the largest in industry consumption, with a global output of more than 450,000 tons, and is widely used in packaging, film materials, construction and other fields. Develop engineering biodegradable polymer materials with better comprehensive performance than PLA and gradually replace PLA. The global market capacity of biodegradable polymer materials has reached one million tons, and the market demand is strong, which will bring significant economic benefits in the future.

[0003] Polyglycolic acid (PGA) has the advantages of excellent biocompatibility, mechanical properties, high barrier properties, high load deformation temperature, etc. It is a rare degradable engineering polymer material. Its biodegradability is similar to that of natural cellulose. At the same time, it meets the requirements of industrial composting, household composting and seawater degradation. It has been certified as a safe biodegradable plastic material in the United States, the European Union, Japan and other countries. It is widely used in high-end biomedicine, food packaging, shale and oil extraction, agricultural production and other fields. It has broad market space. It is expected that the global PGA market will reach 10 billion yuan in 2030.

[0004] At present, the synthesis methods of polyglycolic acid with industrial value include direct polycondensation and glycolide ring-opening polymerization. At present, the synthesis of PGA at home and abroad is mainly based on glycolide ring-opening polymerization, which has high requirements for the purity of glycolide and high product cost. It is mainly produced on a large scale in Japan and the United States.

[0005] In recent years, with the development of coal chemical technology and the breakthrough of key technology for preparing glycolic acid (methyl ester) from dimethyl oxalate at low cost, my country's PGA industry has brought important turning points and hope. The rapid growth of domestic glycolic acid monomer production scale and the reduction of costs make direct polymerization more likely to become the preferred solution for large-scale production of PGA in the future.

[0006] The method of synthesizing PGA by direct polycondensation of glycolic acid is shorter and less expensive than the ring-opening polymerization of glycolide, and is more suitable for the production of bulk products. However, it is generally reported that this method has the problem of too low product yield. Because in the late stage of the polycondensation reaction, a large amount of by-product glycolide and oligomers are extracted under high vacuum, resulting in a decrease in product yield. The by-product glycolide and oligomers contain some trace impurities (the main components of the by-products are shown in Table 1 below). Direct reuse will cause the color of the PGA product to darken, affecting product quality.

[0007] Table 1 The by-product components mainly include:

[0008] Summary of the invention

[0009] The object of the present invention is to provide a by-product purification process and a preparation process for preparing high-quality polyglycolic acid by recycling the by-products, so as to realize the recycling of the by-products and improve the purification and yield of the polyglycolic acid.

[0010] In order to achieve one aspect of the above-mentioned invention object, the purification process provided by the present invention adopts the following technical scheme:

[0011] A purification process for by-product glycolide and oligomers comprises the following steps:

[0012] (1) crushing the by-product to obtain by-product powder;

[0013] (2) performing a purification operation on the by-product powder to obtain a purified product; the purification operation includes at least two of at least one first purification operation, at least one second purification operation, and at least one third purification operation; wherein:

[0014] The first purification operation is: taking the by-product powder and mixing it evenly with solution A so that the soluble impurities therein are dissolved in the solution A; filtering to separate the solution A containing dissolved impurities to obtain a purified solvent A;

[0015] The second purification operation is: uniformly mixing the solvent A purified product with solution B so that the soluble impurities therein are dissolved in the solution B; filtering to separate the solution B containing the impurities, thereby obtaining the solvent B purified product;

[0016] The third purification operation is: dissolving the purified product of solvent A or the purified product of solvent B in solution C, filtering, and then subjecting the filtrate to recrystallization and secondary filtration to obtain the purified product of solvent C;

[0017] (3) washing the purified product obtained in step (2) to remove the residual solvent and drying the product to obtain purified byproducts of glycolide and oligomers;

[0018] Wherein, the solution A is one or more of deionized water, anhydrous methanol, anhydrous ethanol, ethylene glycol and propylene glycol;

[0019] The solution B is one or more of deionized water, anhydrous methanol, anhydrous ethanol, ethylene glycol and propylene glycol, and the solution B is selected differently from the solution A;

[0020] The solution C is one or more of ethyl acetate, dichloromethane and DMSO.

[0021] In step (1) of the present invention, in order to facilitate the dissolution and removal of impurities in the subsequent by-products, the by-products are crushed to obtain by-product powders; in the process of direct polycondensation of glycolic acid to synthesize PGA, in the late stage of the polycondensation reaction, a large amount of by-product glycolide and oligomers are extracted and collected under high vacuum (for example, the pressure is not higher than 100 Pa), thereby obtaining the by-products, wherein the glycolide content can be higher than 92%, and the oligomer content can be higher than 7.5%. In some embodiments, the particle size of the by-product powder is above 20 mesh (Taylor standard sieve), such as 20-2000 mesh; preferably, the particle size is 200-1000 mesh.

[0022] In step (2) of the present invention, the by-product powder is subjected to a purification operation to obtain a purified product; the purification operation includes at least two of at least one first purification operation, at least one second purification operation and at least one third purification operation; for example, the purification operation may be a first purification operation repeated multiple times, or a second purification operation repeated multiple times, or a third purification operation repeated multiple times; or, the purification operation may be at least one first purification operation and at least one second purification operation followed by a subsequent purification operation, or at least one first purification operation and at least one third purification operation followed by a subsequent purification operation, or at least one second purification operation and at least one third purification operation followed by a subsequent purification operation. Of course, it is understood in the art that when the first purification operation is not included, the processing object of the second purification operation is directly the by-product powder, and other situations are similar; or, the purification operation may be at least one first purification operation, at least one second purification operation and at least one third purification operation performed in sequence.

[0023] It is understood in the art that the more times the purification operation is performed, the lower the impurity content is, but the yield of glycolide and oligomers (e.g., a degree of polymerization of 5-10) in the by-product will be reduced accordingly, so it is sufficient to purify until the impurity content in the by-product meets the standard. Preferably, the impurity content in the purified by-product of the present invention is less than 10ppm, such as 7ppm, 8ppm or 9ppm, and there is no need for excessive purification, thereby reducing costs.

[0024] In a preferred embodiment, in step (2), the purification operation includes a first purification operation, a second purification operation and a third purification operation performed sequentially.

[0025] In the first purification operation, the by-product powder is mixed evenly with solution A so that the soluble impurities therein are dissolved in the solution A; the solution A containing dissolved impurities is filtered to separate to obtain a purified solvent A; in a preferred embodiment, the solution A is deionized water; it can be understood in the art that the amount of solvent A should be sufficient to fully mix with the by-product powder and dissolve the impurities therein, for example, the amount thereof can be 1-10 times, for example 2-5 times, such as 3 or 4 times, the mass of the by-product powder.

[0026] In the second purification operation, the solvent A purified product is mixed evenly with solution B so that the soluble impurities therein are dissolved in the solution B; the solution B containing dissolved impurities is filtered to obtain a solvent B purified product; in a preferred embodiment, the solution B is one or more of anhydrous methanol, anhydrous ethanol, ethylene glycol and propylene glycol; it can be understood in the art that the amount of solvent B should be sufficient to fully mix with the by-product powder and dissolve the impurities therein, for example, its amount can be 1-10 times the mass of the by-product powder, for example, 2-5 times, such as 3 or 4 times.

[0027] In a preferred embodiment, in the first purification operation and the second purification operation, while the impurities are mixed and dissolved, the mixture of the by-product and the solvent is simultaneously subjected to ultrasonic treatment, for example, ultrasonic treatment for 0.5-1.5 h, such as 1 h, to promote the dissolution of impurities in the by-product.

[0028] In the third purification operation, the purified product of solvent A or the purified product of solvent B is dissolved in solution C, filtered, and the filtrate is recrystallized and filtered twice to obtain the purified product of solvent C; the specific recrystallization and filtration processes are well known in the art and will not be described here. In a preferred embodiment, the solution C is ethyl acetate.

[0029] In step (3) of the present invention, the purified product obtained in step (2) is washed to remove the residual solvent and then dried to obtain purified byproducts of glycolide and oligomers; in a preferred embodiment, in step (3), cold water is used for washing, preferably cold water with a temperature below 15° C. to reduce washing losses. In the present invention, the yield of the purified byproducts can reach about 85%.

[0030] To achieve another aspect of the above-mentioned invention object, the preparation process provided by the present invention adopts the following technical scheme:

[0031] A by-product purification process and a preparation process for recycling high-quality polyglycolic acid, comprising the following steps:

[0032] The first step: adding glycolic acid and / or methyl glycolate as polymerization raw materials and a catalyst mixture into a reactor, heating to 190° C. and reacting until no distillate is evaporated from the reaction system, changing the reaction system to a rough vacuum (preferably 2000-3000 Pa) to increase the reaction rate, and further reacting until the theoretical water yield of the reaction system reaches more than 98%, thereby obtaining PGA oligomers;

[0033] Step 2: Add the purified by-product, antioxidant and stabilizing agent to the reaction system, increase the temperature of the reaction system to 220-225° C., and maintain the rough vacuum reaction polymerization for 0.5-1.5 hours, for example, 1 hour;

[0034] Step 3: increasing the vacuum degree of the reaction system to below 70 Pa to continue the polymerization reaction to obtain a PGA crystalline polymer; at the same time, collecting the mixture of glycolide and oligomers evaporated from the reaction system in the third step as a by-product, and purifying the collected by-product using the above-mentioned purification process to obtain the purified by-product;

[0035] Step 4: Cut the prepared PGA crystalline polymer into pellets, dry and remove water, and then perform solid phase polymerization at 195-210° C. to further increase the molecular weight of PGA.

[0036] In the second step of the present invention, purified by-products, antioxidants and stabilizing agents are added to the reaction system to control side reactions such as oxidation and decomposition during the reaction to achieve the purpose of inhibiting yellowing of the product; in a preferred embodiment, the antioxidant is one or more of pentaerythritol tetrakis (di-tert-butyl hydroxyhydrocinnamate) ester (Antioxidant 1010), α-tocopherol, and 5-tert-butyl-4-hydroxy-2-methylphenylene sulfide (Antioxidant 300).

[0037] In a preferred embodiment, the stabilizer is one or more of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite (THP-24), diphenyl phosphite, triphenyl phosphite (TPP), and triethyl phosphate (TEP).

[0038] In a preferred embodiment, in the second step, based on the mass of the polymer raw material, the total usage ratio of the antioxidant and the stabilizer is 1 / 10,000 to 1 / 1000, preferably 4 / 10,000 to 6 / 10,000, that is, the total usage is 1 / 10,000 to 1 / 10,000, preferably 4 / 10,000 to 6 / 10,000 of the mass of the polymer raw material. Preferably, the usage ratio of the antioxidant to the stabilizer is (2-4):1, such as 3:1.

[0039] In some embodiments, in the second step, based on the mass of the polymerization raw material, the amount of the purified by-product added is 10%-30% of the mass of the polymerization raw material, such as 20% or 25%, so as to reuse the by-product without affecting the quality of the product and prepare a high-yield and high-quality PGA product.

[0040] In a preferred embodiment, in the third step, the vacuum degree of the reaction system is increased to below 70Pa, such as to below 70Pa, such as 60, 40 or 20Pa within 1 hour, such as 20 or 40 minutes, and then the polymerization is continued for 1-3 hours, such as 2 hours, to obtain a PGA crystalline polymer.

[0041] In the present invention, unless otherwise specified, all ratios or percentages involved are mass ratios or mass percentages.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] According to the purification process of the present invention, after purification, the final purified by-product components mainly include glycolide and oligomers with a polymerization degree of 5-10, and the total content of other impurities is reduced to <10ppm level; compared with the glycolide ring-opening polymerization, the extremely high requirements for the purity of glycolide, the glycolide purification process is complicated, the equipment requirements are high, and the cost is high. The by-products purified by the purification process of the present invention are simple to operate, low cost, and effectively reduce the impurity content. Although the purity requirements of glycolide ring-opening polymerization PGA cannot be met, the impurity content of the by-product glycolide and oligomers meets the reuse requirements and can be directly reused in the polymerization system for preparing PGA by direct polymerization, so as to achieve the effect of improving product yield and reducing solid waste emissions.

[0044] In summary, by recycling the by-products and preparing high-quality light-colored polyglycolic acid (PGA), the present invention has the effect of recycling the by-products while ensuring the quality of the polyglycolic acid, so as to achieve the effect of improving the product yield and reducing the discharge of solid waste. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0046] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values, such as values ​​of ±10% of the endpoint values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range 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 considered as specifically disclosed in this article. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0047] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatus.

[0048] The present invention is further described below in conjunction with the following embodiments / comparative examples. In the following embodiments / comparative examples, unless otherwise specified, all reagents used are analytically pure.

[0049] Purification Example 1

[0050] 1. Take 500g of by-product powder (200 mesh, the same below) and put it into a beaker. Add 2L of deionized water and stir evenly. Then put it into an ultrasonic cleaner for 1h to remove water-soluble impurities.

[0051] 2. Take out the beaker and use a suction filtration device to filter to obtain a primary purified product, the impurity content of the primary purified product (dry basis, the same below) is greater than 100 ppm;

[0052] 3. Pour the primary purified product into a beaker, add 1L of anhydrous ethanol, stir evenly, and continue to put it into an ultrasonic cleaner for 1 hour to further remove impurities; repeat the suction filtration operation in step 2 to obtain a secondary purified product, and the impurity content of the secondary purified product is less than 50ppm;

[0053] 4. The secondary purified product was dissolved in ethyl acetate, filtered, and the filtrate was recrystallized to obtain a solid product, which was washed with cold water and dried to obtain the final purified product; the impurity content of the final purified product was less than 10 ppm (about 5 ppm). The product yield was 85%.

[0054] Purification Example 2

[0055] 1. Take 500g of by-product powder and put it into a beaker. Add 2L of deionized water and stir evenly. Then put it into an ultrasonic cleaner for 1h to remove water-soluble impurities.

[0056] 2. Take out the beaker and use a suction filtration device to filter to obtain a primary purified product, the impurity content of which is greater than 100 ppm;

[0057] 3. Pour the primary purified product into a beaker, add 1L of ethylene glycol, stir evenly, and continue to put it into an ultrasonic cleaner for 1 hour to further promote the dissolution of impurities; repeat the suction filtration operation in step 2 and wash the obtained product with cold water and dry it to obtain a secondary purified product, the impurity content of which is less than 50ppm;

[0058] 4. Repeat the operation of step 3 to obtain a purified product three times with an impurity content of less than 30 ppm.

[0059] 5. Repeat the operation of step 3 again to obtain a fourth purified product with an impurity content of less than 15 ppm.

[0060] 6. Repeat step 3 to obtain a purified product for the fifth time, with an impurity content of less than 10 ppm (about 7 ppm). The product yield is 82%.

[0061] Purification Example 3

[0062] 1. Take 500g of by-product powder and put it into a beaker. Add 2L of deionized water and stir evenly. Then put it into an ultrasonic cleaner for 1h to remove water-soluble impurities.

[0063] 2. Take out the beaker and use a suction filtration device to filter to obtain a primary purified product, the impurity content of which is greater than 100 ppm;

[0064] 3. The secondary purified product is dissolved in ethyl acetate, filtered, and the filtrate is recrystallized to obtain a solid product. The obtained product is washed with cold water and dried to obtain a secondary purified product, and the impurity content of the secondary purified product is less than 30 ppm;

[0065] 4. Repeat the operation of step 3 to obtain a purified product three times with an impurity content of less than 15 ppm.

[0066] 5. Repeat the operation of step 3 to obtain four purified products with impurity content less than 10 ppm. The product yield is 75% (about 5 ppm).

[0067] Example 1

[0068] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst (stannous octoate, the same below) into a 10 L polymerization reactor, heat to 190 ° C, react at normal pressure for 0.5 h, then change the reaction system to 3000 Pa and continue to react for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0069] 2000 g of the final purified material obtained in Purification Example 1 was added, and an antioxidant and a stabilizer (0.314 g Antioxidant 1010, 0.371 g α-tocopherol, 0.26 g THP-24, the same below) were added, and the system was heated to 220°C, the vacuum degree of the system was controlled at 65 Pa, and the polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain white PGA pellets with a number average molecular weight of about 47000 Da.

[0070] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a white PGA solid material with a yield of 61%. The polymer B value was 2.2, the number average molecular weight was about 62,000 Da, the weight average molecular weight was about 88,000, and the molecular weight distribution was 1.43.

[0071] The collected by-product glycolide and oligomers were purified by purification example 1 and then the above polymerization steps were repeated 5 times. The total yield of PGA was 95%.

[0072] Example 2

[0073] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, change the reaction system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0074] 2000 g of the final purified product obtained in Purification Example 2 was added, and an antioxidant and a stabilizer were added. The system was heated to 220° C. The vacuum degree of the system was controlled at 65 Pa. The polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain white PGA with a number average molecular weight of about 45,000 Da.

[0075] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a white PGA solid material with a yield of 62%. The polymer B value was 2.1, the number average molecular weight was about 61,000 Da, the weight average molecular weight was about 87,000, and the molecular weight distribution was 1.41.

[0076] The collected by-product glycolide and oligomers were purified by purification example 2 and then the above polymerization steps were repeated 5 times. The total yield of PGA was 95%.

[0077] Example 3

[0078] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, then change the system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0079] 2000 g of the final purified product obtained in Purification Example 3 was added, and an antioxidant and a stabilizer were added. The system was heated to 220° C. The vacuum degree of the system was controlled at 65 Pa. The polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain white PGA with a number average molecular weight of about 45,000 Da.

[0080] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a white PGA solid material with a yield of 62%. The polymer B value was 2.2, the number average molecular weight was about 63,000 Da, the weight average molecular weight was about 86,000, and the molecular weight distribution was 1.37.

[0081] The collected by-product glycolide and oligomers were purified as in Example 3 and then the above polymerization steps were repeated 5 times. The total yield of PGA was 95%.

[0082] Example 4

[0083] Add 100 mol of methyl glycolate and 8 mmol of polyester catalyst (stannous octoate, the same below) into a 10 L polymerization reactor, heat to 190 ° C, react at normal pressure for 0.5 h, then change the reaction system to 3000 Pa and continue to react for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0084] 2000 g of the final purified material obtained in Purification Example 1 was added, and an antioxidant and a stabilizer were added. The system was heated to 220°C, the vacuum degree of the system was controlled at 765 Pa, and polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain white PGA pellets with a number average molecular weight of about 45,000 Da.

[0085] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a white PGA solid material with a yield of 63%. The polymer B value was 2.0, the number average molecular weight was about 60,000 Da, the weight average molecular weight was about 86,000, and the molecular weight distribution was 1.45.

[0086] The collected by-product glycolide and oligomers were purified by purification example 1 and then the above polymerization steps were repeated 5 times. The total yield of PGA was 94%.

[0087] Comparative Example 1

[0088] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, change the reaction system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0089] Antioxidants and stabilizers were added, the reaction system was heated to 220°C, and the vacuum degree of the reaction system was controlled at 65 Pa. The polycondensation was carried out for 4 hours, and the material was cooled and granulated under vacuum conditions to obtain white PGA with a number average molecular weight of about 46,000 Da. A total of 2,000 grams of glycolide and PGA oligomers were collected during the polycondensation process.

[0090] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a white PGA solid material with a yield of 61%, a polymer B value of 2.2, a number average molecular weight of 60,000 Da, a weight average molecular weight of 87,600, and a molecular weight distribution of 1.46.

[0091] The PGA oligomer collected during the polymerization process was mixed with 2000 g of glycolide and 5000 g of glycolic acid, and the above experiment was repeated to obtain a dark yellow PGA solid material with a yield of 61%, a polymer B value of 7.3, a number average molecular weight of 68500 Da, a weight average molecular weight of 89500, and a molecular weight distribution of 1.57.

[0092] The above experimental operation was repeated to form a semi-continuous preparation of PGA. The cycle was repeated 5 times, and the total yield of PGA was 95%.

[0093] Comparative Example 2

[0094] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, change the reaction system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0095] 2000 g of the primary purified material obtained in Purification Example 1 was added, and antioxidants and stabilizers were added. The system was heated to 220°C, the system vacuum was controlled at 65 Pa, and polycondensation was performed for 4 hours. The material was cooled under vacuum conditions and granulated to obtain brown-yellow PGA with a number average molecular weight of about 30,000 Da.

[0096] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a brown-yellow PGA solid material with a yield of 60%. The polymer B value was 11.2, the number average molecular weight was about 43,000 Da, the weight average molecular weight was about 56,000, and the molecular weight distribution was 2.13.

[0097] Comparative Example 3

[0098] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, then change the system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0099] 2000 g of the secondary purified material obtained in Purification Example 1 was added, and an antioxidant and a stabilizer were added. The system was heated to 220° C. The vacuum degree of the system was controlled at 65 Pa. The polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain yellow PGA with a number average molecular weight of about 39,000 Da.

[0100] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a yellow PGA solid material with a yield of 61%. The polymer B value was 7.2, the number average molecular weight was about 54,000 Da, the weight average molecular weight was about 69,000, and the molecular weight distribution was 2.01.

[0101] Comparative Example 4

[0102] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, then change the system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0103] 2000 g of the fourth purified material obtained in Purification Example 2 was added, and antioxidants and stabilizers were added. The system was heated to 220°C, the vacuum degree of the system was controlled at 65 Pa, and polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain light yellow PGA with a number average molecular weight of about 42,000 Da.

[0104] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a light yellow PGA solid material with a yield of 61%. The polymer B value was 4.2, the number average molecular weight was about 60,000 Da, the weight average molecular weight was about 71,000, and the molecular weight distribution was 1.88.

[0105] Comparative Example 5

[0106] Add 100 mol of glycolic acid and 5 mmol of polyester catalyst into a 10 L polymerization reactor, heat to 190°C, react at normal pressure for 0.5 h, then change the system to 3000 Pa and continue the reaction for 1 h to obtain PGA oligomers with a number average molecular weight of 5000-10000 Da;

[0107] 2000 g of the tertiary purified material obtained in Purification Example 3 was added, and an antioxidant and a stabilizer were added. The system was heated to 220°C, the vacuum degree of the system was controlled at 65 Pa, and polycondensation was carried out for 4 hours. The material was cooled under vacuum conditions and granulated to obtain light yellow PGA with a number average molecular weight of about 42,000 Da.

[0108] The PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a temperature of 198°C for 20 hours to obtain a light yellow PGA solid material with a yield of 61%. The polymer B value was 4.5, the number average molecular weight was about 61000Da, the weight average molecular weight was about 72000, and the molecular weight distribution was 1.75.

[0109] It can be seen from purification examples 1, 2, 3 and 4 that after the by-products are purified by the one-step or multi-step process of the present invention, the impurity content in glycolide and oligomers is significantly reduced to <10 ppm;

[0110] It can be seen from Examples 1-3 that the by-products are directly recycled into the polymerization system for preparing PGA by direct polymerization according to the present invention, and the product quality is stable and the yield is significantly improved;

[0111] It can be seen from Comparative Examples 1-5 that when the by-product glycolide and oligomers do not meet the standards of the present invention after purification, recycling them into the polymerization system for preparing PGA by direct polymerization will lead to problems such as product quality degradation and yellowing.

[0112] Obviously, the present invention is not limited to the above embodiments, and many variations are possible. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as falling within the protection scope of the present invention.

Claims

1. A purification process for by-product glycolide and oligomers, comprising the following steps: (1) crushing the by-product to obtain by-product powder; (2) performing a purification operation on the by-product powder to obtain a purified product; the purification operation includes at least two of at least one first purification operation, at least one second purification operation, and at least one third purification operation; wherein: The first purification operation is: taking the by-product powder and mixing it evenly with solution A so that the soluble impurities therein are dissolved in the solution A; filtering to separate the solution A containing dissolved impurities to obtain a purified solvent A; The second purification operation is: uniformly mixing the solvent A purified product with solution B so that the soluble impurities therein are dissolved in the solution B; filtering to separate the solution B containing the impurities, thereby obtaining the solvent B purified product; The third purification operation is: dissolving the purified product of solvent A or the purified product of solvent B in solution C, filtering, and then subjecting the filtrate to recrystallization and secondary filtration to obtain the purified product of solvent C; (3) washing the purified product obtained in step (2) to remove the residual solvent and drying the product to obtain purified byproducts of glycolide and oligomers; Wherein, the solution A is one or more of deionized water, anhydrous methanol, anhydrous ethanol, ethylene glycol and propylene glycol; The solution B is one or more of deionized water, anhydrous methanol, anhydrous ethanol, ethylene glycol and propylene glycol, and the solution B is selected differently from the solution A; The solution C is one or more of ethyl acetate, dichloromethane and DMSO.

2. The purification process according to claim 1, characterized in that In the first purification operation and the second purification operation, when the impurities are mixed and dissolved, the mixture of the by-product and the solvent is simultaneously subjected to ultrasonic treatment to promote the dissolution of the impurities in the by-product.

3. The purification process according to claim 1 or 2, characterized in that: In step (2), the purification operation includes a first purification operation, a second purification operation and a third purification operation performed sequentially.

4. The purification process according to any one of claims 1 to 3, characterized in that: The solution A is deionized water; the solution B is one or more of anhydrous methanol, anhydrous ethanol, ethylene glycol and propylene glycol; the solution C is one or more of ethyl acetate, dichloromethane and DMSO.

5. The purification process according to any one of claims 1 to 4, characterized in that: The glycolide content of the by-product is greater than 92%, and the oligomer content is greater than 7.5%; The impurity content in the purified by-product is less than 10 ppm.

6. The purification process according to any one of claims 1 to 5, characterized in that: In step (1), the byproduct powder has a particle size of 20-2000 mesh; preferably, the particle size is 200-1000 mesh; In step (3), cold water is used for washing, preferably cold water with a temperature below 15°C.

7. A by-product purification process and a process for recycling the by-product to prepare high-quality polyglycolic acid, characterized in that: The preparation process comprises the following steps: The first step: adding glycolic acid or methyl glycolate as a polymerization raw material and a catalyst mixture into a reactor, heating to 190° C. and reacting until no distillate is evaporated from the reaction system, then changing the reaction system to a rough vacuum (3000-2000 Pa) to increase the reaction rate, and further reacting until the theoretical water yield of the reaction system reaches more than 98%, thereby obtaining PGA oligomers; Step 2: Add the purified byproduct, antioxidant and stabilizing agent to the reaction system, increase the temperature of the reaction system to 220-225° C., and maintain the vacuum degree at 3000-2000 Pa for polymerization for 0.5-1.5 hours; Step 3: increasing the vacuum degree of the reaction system to below 70 Pa to continue the polymerization reaction to obtain a PGA crystalline polymer; at the same time, collecting the mixture of glycolide and oligomers evaporated from the reaction system in the third step as a by-product, and purifying the collected by-product using the purification process described in any one of claims 1 to 6 to obtain the purified by-product; Step 4: Cut the prepared PGA crystalline polymer into pellets, dry and remove water, and then perform solid phase polymerization at 195-210° C. to further increase the molecular weight of PGA.

8. The preparation process according to claim 7, characterized in that: The antioxidant is one or more of pentaerythritol tetrakis (di-tert-butyl hydroxyhydrocinnamate), α-tocopherol, and 5-tert-butyl-4-hydroxy-2-methylphenyl sulfide; The stabilizer is one or more of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, diphenyl phosphite, triphenyl phosphite and triethyl phosphate.

9. The preparation process according to claim 8, characterized in that: In the second step, based on the mass of the polymer raw materials, the total usage ratio of the antioxidant and the stabilizing agent is 1 / 10,000 to 1 / 1,000, preferably 4 / 10,000 to 6 / 10,000; preferably, the usage ratio of the antioxidant to the stabilizing agent is 2-4:

1.

10. The preparation process according to claim 9, characterized in that: In the third step, the vacuum degree of the reaction system is increased to below 70 Pa and the polymerization is continued for 1-3 hours to obtain a PGA crystalline polymer.

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