A method for high value reutilization of polyglycolic acid recyclates

Abstract

The application relates to a method for recycling polyglycolic acid, which comprises the following steps: (1) granulating polyglycolic acid, and then dispersing and pretreating the polyglycolic acid to obtain pretreated material; (2) mixing the pretreated material with an ammonia source to perform an ammonolysis reaction, and then performing solid-liquid separation to obtain an ammonolysis solution; (3) concentrating the ammonolysis solution to obtain a concentrated solution with crystals precipitated, and then performing temperature reduction and crystallization, and then performing solid-liquid separation, and then washing and drying the obtained solid product to obtain ammonium glycolate, and the method is completed. Compared with the prior art, the method can efficiently convert recycled polyglycolic acid into ammonium glycolate, effectively realizes high-value recycling of waste carbon resources, and has good ecological and economic values.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling technology, and relates to a method for high-value recycling of polyglycolic acid recycled materials. Background Technology

[0002] Today, plastic has become one of the most widely used materials in people's production and daily life, and has had a significant impact on the development of human society. However, with the increasing use of plastic, the resulting accumulation of plastic waste has posed a serious threat to the ecological environment. Although people have adopted various recycling methods to minimize the damage of plastic waste to the environment, about 80% of plastic waste is still left in the environment as "garbage." To address this problem, converting plastic waste into chemicals with economic added value is an effective way to achieve carbon resource recycling and contribute to the goal of carbon neutrality.

[0003] In recent years, research and applications of biodegradable plastics have been beneficial to achieving green and sustainable development. Among many biodegradable plastics, polyglycolic acid (PEG) possesses excellent physicochemical properties and can be used in packaging and medical fields as a polymer material that can be degraded by the environment or metabolized by the human body. However, in practical applications, like most biodegradable plastics, PEG or methyl glycolate (PEG) degrades relatively quickly after use, but it still takes at least several months or even years for all PEG or PEG to completely decompose into water and carbon dioxide. Furthermore, allowing biodegradable plastics to degrade into water and carbon dioxide is a waste of resources from the perspective of material recycling. Therefore, compared to direct degradation in the natural environment, converting PEG into chemicals with economic added value is a better strategy.

[0004] Ammonium glycolate (also known as ammonium glycolate) has a wide range of applications in daily production and life. For example, it can be used as a raw material in the manufacture of cosmetics, as an additive in the production of polishing fluids for surface planarization of semiconductor chips, as an auxiliary agent in the production of buffers for the hydrothermal hydrogenation catalytic treatment of biomass, and as a complexing cleaning aid in the production of unblocking agents for use in the unblocking process of downhole mining operations, and so on. Therefore, ammonium glycolate is a chemical with good economic added value. Thus, if recycled polyglycolic acid materials can be converted into ammonium glycolate through certain means or methods, the recycling and reuse of waste carbon resources can be effectively achieved, possessing significant ecological and economic value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for high-value recycling of polyglycolic acid (PGA) waste materials, so as to realize the resource-based recycling and reuse of PGA waste materials.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for high-value recycling of polyglycolic acid (PGA) recycled materials includes the following steps:

[0008] (1) The polyglycolic acid recycled material is granulated and then dispersed for pretreatment to obtain pretreated material;

[0009] (2) The pretreated material is mixed with an ammonia source to carry out an ammonolysis reaction, followed by solid-liquid separation to obtain an ammonolysis solution;

[0010] (3) The ammonium hydrolysate is concentrated until crystals precipitate to obtain a concentrated solution. Then, gradient crystallization treatment is performed, followed by solid-liquid separation. The resulting solid product is then washed and dried to obtain ammonium glycolate.

[0011] As one implementation scheme, in step (1), the granulation is: crushing the polyglycolic acid recycled material into granular material with a particle size ≤1mm at -20 to 5℃.

[0012] As one implementation scheme, in step (1), the dispersion pretreatment process is as follows:

[0013] The granulated polyglycolic acid recycled material is placed in a pressure-bearing and sealable stirring container. After the stirring container is sealed, supercritical CO2 fluid is injected and stirred. Then it is transferred to a filter press for filtration to separate the supercritical CO2 fluid from the material. The supercritical CO2 fluid can be recovered and the material can be collected to obtain the pretreated material.

[0014] In this granulation and dispersion pretreatment process, supercritical CO2 fluid is used to stir and disperse the granular material. Because supercritical CO2 fluid has a strong swelling effect on polymer particles, the stirring and shearing action of the agitator further breaks the granular material into relatively small fine particles. The resulting pretreated material exhibits better dispersibility in ammonia water, facilitating the efficient ammonolysis reaction. Furthermore, the use of supercritical CO2 fluid is beneficial for dissolving impurities such as grease and other chemical residues adhering to the surface of the granular material. These impurities are carried away after the supercritical CO2 fluid separates from the material.

[0015] Furthermore, the stirring process is as follows: control the pressure inside the stirring container to be 7.4-8.2 MPa and the temperature to be 35-60℃, stir at low speed for 5-15 minutes, and then stir at high speed for 15-30 minutes.

[0016] More preferably, the low-speed stirring is 200-400 r / min, and the high-speed stirring is 800-1200 r / min. Compared with general stirring, the present invention first uses "low-speed stirring", which on the one hand allows for a relatively gentle pre-dispersion of the particulate material, and on the other hand allows sufficient time for the supercritical CO2 fluid to swell the particulate material; then "high-speed stirring" is used to utilize its strong shearing and disturbance effect to break down and pulverize the fully swollen particulate material into smaller fine particles.

[0017] Furthermore, the mass of the supercritical CO2 fluid injected into the stirring vessel is 1.1-2.6 times the mass of the granulated polyglycolic acid recycled material.

[0018] Furthermore, supercritical CO2 fluid is injected into the stirred vessel at a rate of 0.1-0.5 kg / min.

[0019] As one embodiment, the ammonia source is an ammonia source that can generate NH3 or NH in water. 4+ Inorganic compounds, preferably ammonia or similar substances.

[0020] As one implementation scheme, the ammonia source contains NH3 or NH 4+ The molar ratio of repeating units of polyglycolic acid in the pretreatment material to the repeating units is 1.05-10:1.

[0021] As one implementation scheme, the ammonolysis reaction is carried out under the following conditions: absolute pressure of 100-2500 kPa and temperature of 60-200 °C for 0.5-24 h.

[0022] In one implementation scheme, in step (3), the conditions for concentrating the ammonia hydrolysate are: evaporation and concentration at a temperature not exceeding 185°C until crystals precipitate. Since the ammonia hydrolysate has a relatively high water content, and water has a high solubility for ammonium glycolate, directly crystallizing without concentration would lead to a significant decrease in product yield. Furthermore, ammonia gas can be recovered during the concentration process of the ammonia hydrolysate. Therefore, preferably, the ammonia hydrolysate needs to be concentrated before gradient crystallization.

[0023] As one implementation scheme, in step (3), the process conditions for the gradient crystallization treatment are as follows: first, the temperature is lowered to 40-60℃ at a rate of 5-10℃ / min, and kept at a constant temperature for 1-4h; then, the temperature is raised to 72-86℃ at a rate not higher than 5℃ / min, and kept at a constant temperature for 0.5-2h; then, the temperature is lowered to -15~10℃ at a rate of 5-10℃ / min, and kept at a constant temperature for 2-10h.

[0024] As one implementation scheme, in step (3), the washing process specifically involves repeatedly washing with a detergent at a temperature not exceeding 20°C until neutral. Since the main impurities in the generated ammonium glycolate are water and glycolic acid, the selected solvent has low solubility for ammonium glycolate at this temperature, but can still effectively dissolve the impurities and improve the yield. Therefore, the detergent is further selected from at least one of alcohols, esters, ethers, or ketones, preferably a low-carbon alcohol of C1 to C5, and more preferably methanol or ethanol.

[0025] Furthermore, in the present invention, solid-liquid separation can be carried out using conventional methods in the art, such as, but not limited to, filtration, vacuum filtration, centrifugation, etc.

[0026] Compared with existing technologies, this invention can convert polyglycolic acid recycled materials into ammonium glycolate, effectively realizing the high-value recycling and reuse of waste carbon resources, and has great ecological and economic value. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] The endpoints and any values ​​of the ranges disclosed herein 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. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. For example, "a range from 1 to 10" should be understood to represent every and every possible number consecutive between approximately 1 and approximately 10. Therefore, even if specific data points within the range, or even if no data points within the range are explicitly identified or only a few specific points are referred to, it should be understood that any and all data points within the range are considered to be explicitly stated. In this document, when the term "approximately" is used to modify numerical values, it indicates an error tolerance of ±5% of the measured value.

[0029] It should be noted that the purity of the obtained ammonium glycolate product in the following examples was tested using an ion chromatograph. The specific test conditions were as follows: Instrument model: ICS-900; Column: IonPac CG12A, CS12A, 4mm; Eluent: 18mN methanesulfonic acid eluent; Flow rate: 1.0mL / min; Injection volume: 10μL; Detector: Suppressive conductivity, CSRS-ULTRA 4mm, automatic suppression cycling mode.

[0030] The technical solution of the present invention will be further described below through specific embodiments. Unless otherwise specified, the other raw materials or processing technologies are conventional commercially available raw materials or conventional processing technologies in the field.

[0031] Example 1:

[0032] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then cryogenically pulverized at 5°C to form granules with a particle size ≤1mm. Approximately 1kg of these granules is transferred to a pressure-resistant, sealable mixing container. After sealing, the pressure inside the container is controlled at 7.4MPa and the temperature at 35°C. Approximately 1.1kg of supercritical CO2 fluid is injected into the container at a rate of 0.1kg / min. The mixture is then stirred at 200r / min for 5 minutes, followed by stirring at 800r / min for 15 minutes. The mixture is then transferred to a filter press to separate the supercritical CO2 fluid from the solid material. The supercritical CO2 fluid is recovered, and the solid material is collected to obtain the pretreated material (approximately 1kg, corresponding to approximately 17.2mol of glycolic acid per repeating unit). Ammonia water with a concentration of 25wt% is used as the ammonia source. Approximately 1 kg of material was added to approximately 1230 g of ammonia water (corresponding to approximately 18.1 mol of NH3). The ammonolysis reaction was carried out at an absolute pressure of 100 kPa and 60 °C for 24 hours. After the ammonolysis reaction was completed, the mixture was filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent ammonolysis solution. This solution was then heated and concentrated at 105 °C until it began to turn cloudy. Heating was then stopped to obtain the concentrated solution. The solution was then cooled at a rate of 10 °C / min. The temperature of the liquid was lowered to 60°C and kept at a constant temperature for 1.5 hours. Then, the temperature was increased to 80°C at a rate of 1°C / min and kept at a constant temperature for 1 hour. Subsequently, the temperature was lowered to 10°C at a rate of 5°C / min and kept at a constant temperature for 2 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at approximately 20°C until neutral. After vacuum drying, 1132.5 g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6 g. The actual yield in this example is 70.8%, and the purity is 95.2%.

[0033] Example 2:

[0034] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then cryogenically pulverized at 1°C to form granules with a particle size ≤1mm. Approximately 1kg of these granules is transferred to a pressure-resistant, sealable mixing container. After sealing, the pressure inside the container is controlled at 7.6MPa and the temperature at 42°C. Approximately 1.5kg of supercritical CO2 fluid is injected into the container at a rate of 0.1kg / min. The mixture is then stirred at 200r / min for 8 minutes, followed by stirring at 1000r / min for 22 minutes. The mixture is then transferred to a filter press to separate the supercritical CO2 fluid from the solid material. The supercritical CO2 fluid is recovered, and the solid material is collected to obtain the pretreated material (approximately 1kg, corresponding to approximately 17.2mol of glycolic acid per repeating unit). Ammonia water with a concentration of 25wt% is used as the ammonia source. Approximately 1 kg of the treated material was added to approximately 2340 g of ammonia water (corresponding to approximately 34.4 mol of NH3). The ammonolysis reaction was carried out at an absolute pressure of 600 kPa and 80 °C for 24 hours. After the ammonolysis reaction was completed, the mixture was filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent ammonolysis solution. This solution was then heated and concentrated at 120 °C until it began to become cloudy. Heating was then stopped to obtain the concentrated solution. The solution was then cooled at a rate of 8 °C / min. The temperature of the concentrate was lowered to 53°C and kept at that temperature for 1 hour. Then, the temperature was increased to 72°C at a rate of 4°C / min and kept at that temperature for 1 hour. Subsequently, the temperature was lowered to 2°C at a rate of 8°C / min and kept at that temperature for 5 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at approximately 10°C until neutral. After vacuum drying, 1236.5 g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6 g. The actual yield in this example was 77.3%, and the purity was 96.1%.

[0035] Example 3:

[0036] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then cryogenically pulverized at -5°C to form granules with a particle size ≤1mm. Approximately 1kg of these granules is transferred to a pressure-resistant, sealable mixing container. After sealing, the pressure inside the container is controlled at 7.8MPa and the temperature at 50°C. Approximately 2.0kg of supercritical CO2 fluid is injected into the container at a rate of 0.2kg / min. The mixture is then stirred at 320r / min for 10min, followed by stirring at 1000r / min for 25min. The mixture is then transferred to a filter press to separate the supercritical CO2 fluid from the solid material. The supercritical CO2 fluid is recovered, and the solid material is collected to obtain the pretreated material (approximately 1kg, corresponding to approximately 17.2mol of glycolic acid per repeating unit). Ammonia water with a concentration of 25wt% is used as the ammonia source. Approximately 1 kg of raw material was added to approximately 5850 g of ammonia water (corresponding to approximately 86 mol of NH3). The ammonolysis reaction was carried out at an absolute pressure of 1000 kPa and 120 °C for 12 hours. After the ammonolysis reaction was completed, the mixture was filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent ammonolysis solution. This solution was then heated and concentrated at 146 °C until it began to turn cloudy. Heating was then stopped to obtain the concentrated solution. The concentrated solution was then cooled at a rate of 5 °C / min. The liquid temperature was lowered to 48℃ and kept at a constant temperature for 4 hours. Then, the temperature was increased to 82℃ at a rate of 2℃ / min and kept at a constant temperature for 2 hours. Subsequently, the temperature was lowered to -5℃ at a rate of 10℃ / min and kept at a constant temperature for 8.5 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at approximately 10℃ until neutral. After vacuum drying, 1366.1g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6g. The actual yield in this example is 85.4%, and the purity is 98.1%.

[0037] Example 4:

[0038] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then cryogenically pulverized at -12°C to form granules with a particle size ≤1mm. Approximately 1kg of these granules is transferred to a pressure-resistant, sealable mixing container. After sealing, the pressure inside the container is controlled at 8.0MPa and the temperature at 56°C. Approximately 2.4kg of supercritical CO2 fluid is injected into the container at a rate of 0.4kg / min. The mixture is then stirred at 400r / min for 15min, followed by stirring at 1200r / min for 30min. The mixture is then transferred to a filter press to separate the supercritical CO2 fluid from the solid material. The supercritical CO2 fluid is recovered, and the solid material is collected to obtain the pretreated material (approximately 1kg, corresponding to approximately 17.2mol of glycolic acid per repeating unit). Ammonia water with a concentration of 25wt% is used as the ammonia source. Approximately 1 kg of material was added to approximately 7020 g of ammonia water (corresponding to approximately 103.2 mol of NH3). The ammonolysis reaction was carried out at an absolute pressure of 1600 kPa and 135 °C for 6 hours. After the ammonolysis reaction was completed, the mixture was filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent ammonolysis solution. This solution was then heated and concentrated at 158 ​​°C until it began to turn cloudy. Heating was then stopped to obtain the concentrated solution. The concentrated solution was then cooled at a rate of 6 °C / min. The liquid temperature was lowered to 40℃ and kept at a constant temperature for 2 hours. Then, the temperature was increased to 86℃ at a rate of 5℃ / min and kept at a constant temperature for 0.5 hours. Subsequently, the temperature was lowered to -10℃ at a rate of 10℃ / min and kept at a constant temperature for 10 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous methanol at a temperature of about 5℃ until neutral. After vacuum drying, 1428.4g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6g. The actual yield in this example is 89.3%, and the purity is 98.5%.

[0039] Example 5:

[0040] The scraps generated during the machining of polyglycolic acid materials are collected and crushed into appropriately sized recyclable materials. These recyclable materials are then cryogenically pulverized at -6°C to form granules with a particle size ≤1mm. Approximately 1kg of these granules is then transferred to a pressure-resistant, sealable mixing container. After sealing, the pressure inside the container is controlled at 7.7MPa and the temperature at 60°C. Approximately 1.6kg of supercritical CO2 fluid is injected into the mixing container at a rate of 0.2kg / min. The mixture is then stirred at 250r / min for 10min, followed by stirring at 1000r / min for 25min. The mixture is then transferred to a filter press for filtration to separate the supercritical CO2 fluid from the solid material. The supercritical CO2 fluid is recovered, and the solid material is collected to obtain the pretreated material (approximately 1kg, corresponding to approximately 17.2mol of glycolic acid repeating units). Ammonia water with a concentration of 25wt% is used as the ammonia source. The pretreated material (… Approximately 1 kg of ammonia solution was added to approximately 9360 g of ammonia water (corresponding to approximately 137.6 mol of NH3). The ammonolysis reaction was carried out at an absolute pressure of 2000 kPa and 200 °C for 3.5 h. After the ammonolysis reaction was completed, the solution was filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent ammonolysis solution. This solution was then heated and concentrated at 185 °C until it began to turn cloudy. Heating was then stopped to obtain the concentrated solution. The concentrated solution was then cooled at a rate of 10 °C / min. The liquid temperature was lowered to 46℃ and kept at a constant temperature for 2.5 hours. Then, the temperature was increased to 76℃ at a rate of 0.5℃ / min and kept at a constant temperature for 2 hours. Subsequently, the temperature was lowered to -15℃ at a rate of 10℃ / min and kept at a constant temperature for 6 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at a temperature of about 2℃ until neutral. After vacuum drying, 1510.4g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6g. The actual yield in this example is 94.4%, and the purity is 99.6%.

[0041] Compare with Example 1:

[0042] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then soaked and washed with anhydrous ethanol to remove grease, and then pulverized at room temperature into granules with a particle size ≤1mm. Approximately 1kg of these granules (corresponding to approximately 17.2 mol of glycolic acid repeating units) are added to approximately 9360g of 25wt% ammonia solution (corresponding to approximately 137.6 mol of NH3). The mixture is then subjected to ammonolysis at 2000kPa and 200℃ for 3.5 hours. After the ammonolysis reaction is complete, the mixture is filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent product. The ammonium hydrolysate was heated and concentrated at 185°C until it began to become turbid. Heating was then stopped to obtain a concentrated solution. The temperature of the concentrated solution was then lowered to 46°C at a rate of 10°C / min and held at that temperature for 2.5 hours. The temperature was then increased to 76°C at a rate of 0.5°C / min and held at that temperature for 2 hours. Subsequently, the temperature was lowered to -15°C at a rate of 10°C / min and held at that temperature for 6 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at approximately 2°C until neutral. After vacuum drying, 1177.3 g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6 g. The actual yield in this example was 73.6%, and the purity was 86.1%.

[0043] Compare with Example 2:

[0044] This comparative example is basically the same as Example 5, except that in this comparative example, when the concentrated solution is crystallized, the temperature of the concentrated solution is directly reduced to -15°C at a cooling rate of 10°C / min, kept at a constant temperature for 10.5 hours, and then separated by centrifugation. The solid is retained and repeatedly washed with anhydrous ethanol at a temperature of about 2°C until neutral. After vacuum drying, 1324.5g of ammonium glycolate can be obtained. The theoretical yield of ammonium glycolate is 1599.6g. The actual yield of this example is 82.8%, and the purity is 96.3%.

[0045] Compare with Example 3:

[0046] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then soaked and washed with anhydrous ethanol to remove grease, and then pulverized at room temperature into granules with a particle size ≤1mm. Approximately 1kg of these granules (corresponding to approximately 17.2mol of glycolic acid repeating units) are added to approximately 9360g of 25wt% ammonia solution (corresponding to approximately 137.6mol of NH3). The mixture is then subjected to ammonolysis at 2000kPa and 200℃ for 3.5 hours. After completion, the solid-liquid mixture was separated by filtration, and the liquid was retained to obtain a clear and transparent ammonium hydrolysate. The ammonium hydrolysate was heated and concentrated at 185°C until it began to turn cloudy. Heating was then stopped to obtain a concentrated solution. The temperature of the concentrated solution was then directly reduced to -15°C at a cooling rate of 10°C / min and allowed to stand at a constant temperature for 10.5 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at approximately 2°C until neutral. After vacuum drying, 980.6 g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6 g. The actual yield in this example was 61.3%, and the purity was 77.4%.

[0047] Compare with Example 4:

[0048] This comparative example is basically the same as Example 5, except that after obtaining the ammonia hydrolysate, it is not concentrated. Instead, it is subjected to gradient crystallization treatment: the temperature is lowered to 46°C at a rate of 10°C / min, and held at that temperature for 2.5 hours. Then, the temperature is increased to 76°C at a rate of 0.5°C / min, and held at that temperature for 2 hours. Subsequently, the temperature is lowered to -15°C at a rate of 10°C / min, and held at that temperature for 6 hours. After centrifugation, the solid is retained and repeatedly washed with anhydrous ethanol at approximately 2°C until neutral. After vacuum drying, 737.4 g of ammonium glycolate is obtained. The theoretical yield of ammonium glycolate is 1599.6 g. The actual yield of this example is 46.1%, and the purity is 82.7%.

[0049] Example 6:

[0050] Scrap materials generated during the machining of polyglycolic acid (PGA) are collected and crushed into appropriately sized recyclables. These recyclables are then cryogenically pulverized at -20°C to form granules with a particle size ≤1mm. Approximately 1kg of these granules is transferred to a pressure-resistant, sealable mixing container. After sealing, the pressure inside the container is controlled at 8.2MPa and the temperature at 52°C. Approximately 2.6kg of supercritical CO2 fluid is injected into the container at a rate of 0.5kg / min. The mixture is then stirred at 300r / min for 10min, followed by stirring at 1100r / min for 30min. The mixture is then transferred to a filter press to separate the supercritical CO2 fluid from the solid material. The supercritical CO2 fluid is recovered, and the solid material is collected to obtain the pretreated material (approximately 1kg, corresponding to 17.2mol of glycolic acid repeating unit). Ammonia water with a concentration of 25wt% is used as the ammonia source. Approximately 1 kg of raw material was added to approximately 11700 g of ammonia water (corresponding to 172 mol of NH3). Ammonolysis was carried out at an absolute pressure of 2500 kPa and 185 °C for 0.5 h. After the ammonolysis reaction was completed, the mixture was filtered to separate the solid and liquid phases, retaining the liquid to obtain a clear and transparent ammonolysis solution. This solution was then heated and concentrated at 170 °C until it began to turn cloudy. Heating was then stopped to obtain the concentrated solution. The solution was then cooled at a rate of 5 °C / min. The temperature of the concentrate was lowered to 50°C and kept at that temperature for 4 hours. Then, the temperature was increased to 85°C at a rate of 1°C / min and kept at that temperature for 2 hours. Subsequently, the temperature was lowered to -15°C at a rate of 5°C / min and kept at that temperature for 10 hours. After centrifugation, the solid was retained and repeatedly washed with anhydrous ethanol at approximately 2°C until neutral. After vacuum drying, 1479.8 g of ammonium glycolate was obtained. The theoretical yield of ammonium glycolate is 1599.6 g. The actual yield in this example is 92.5%, and the purity is 98.9%.

[0051] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for high-value recycling of polyglycolic acid (PGA) recycled materials, characterized in that, Includes the following steps: (1) The polyglycolic acid recycled material is granulated and then dispersed for pretreatment to obtain pretreated material; (2) The pretreated material is mixed with an ammonia source for ammonolysis reaction, followed by solid-liquid separation to obtain ammonolysis solution; (3) The ammonium hydrolysate is concentrated until crystals precipitate to obtain a concentrated solution. Then, a gradient crystallization treatment is performed, followed by solid-liquid separation. The resulting solid product is then washed and dried to obtain ammonium glycolate. In step (1), the dispersion pretreatment process is as follows: The granulated polyglycolic acid recycled material is placed in a pressure-bearing and sealable stirring container. After the stirring container is sealed, supercritical CO2 fluid is injected and stirred. Then it is transferred to a filter press for filtration to separate the supercritical CO2 fluid from the material. The material is collected to obtain the pretreated material. The ammonia source is one that can generate NH3 or NH4 in water. + Inorganic compounds; The ammonia source contains NH3 or NH4. + The molar ratio of repeating units of polyglycolic acid in the pretreated material to the pretreated material is 1.05-10:1; In step (3), the process conditions for the gradient crystallization treatment are as follows: first, the temperature is lowered to 40-60℃ at a rate of 5-10℃ / min, and kept at a constant temperature for 1-4 hours; then, the temperature is raised to 72-86℃ at a rate not exceeding 5℃ / min, and kept at a constant temperature for 0.5-2 hours; then, the temperature is lowered to -15~10℃ at a rate of 5-10℃ / min, and kept at a constant temperature for 2-10 hours.

2. The method for high-value recycling of polyglycolic acid reclaimed materials according to claim 1, characterized in that, In step (1), the granulation is: the polyglycolic acid recycled material is crushed into granular material with a particle size ≤1mm at -20~5℃.

3. The method for high-value recycling of polyglycolic acid reclaimed materials according to claim 1, characterized in that, The stirring process is as follows: control the pressure inside the stirring container to be 7.4-8.2 MPa and the temperature to be 35-60℃, stir at low speed for 5-15 minutes, and then stir at high speed for 15-30 minutes.

4. The method for high-value recycling of polyglycolic acid reclaimed materials according to claim 1, characterized in that, The mass of the supercritical CO2 fluid injected into the stirring container is 1.1-2.6 times the mass of the granulated polyglycolic acid recycled material.

5. The method for high-value recycling of polyglycolic acid reclaimed materials according to claim 1, characterized in that, The conditions for the ammonolysis reaction are: absolute pressure 100-2500 kPa, 60-200℃, reaction time 0.5-24 h.

6. The method for high-value recycling of polyglycolic acid reclaimed materials according to claim 1, characterized in that, In step (3), the process conditions for concentrating the ammonia hydrolysate are: evaporation and concentration at a temperature not exceeding 185°C until crystals precipitate.

7. The method for high-value recycling of polyglycolic acid reclaimed materials according to claim 1, characterized in that, In step (3), the washing process is as follows: using a detergent with a temperature not exceeding 20°C, repeatedly wash until neutral.