A system and method for large-scale industrial continuous production of PGA

Abstract

The application discloses a system and method for large-scale industrial continuous production of PGA. In a 100,000-3,000,000 tons / year polyglycolide PGA device, glycolide raw materials and catalyst are firstly sent into a first polymerization reactor to perform adiabatic polymerization, then are sent into a second polymerization reactor to perform further polymerization, part of polymerization heat is removed through heat conduction oil in a jacket of the second polymerization reactor and a winding pipe, then the glycolide raw materials and the catalyst are sent into a third polymerization reactor to perform adiabatic polymerization, after the polymerization reaction is completed, antioxidants and deactivation agents are added to terminate the reaction, then unreacted glycolide raw materials in the polymerization product are removed through a devolatilizer, finally, the polymerization product is subjected to crystallization, granulation and packaging and stacking to obtain a polyglycolide product with a molecular weight of 156,000-212,000, a melt viscosity of 460-540 Pa·S and a tensile strength of 65-73 MPa, which can be applied to large-scale commercial continuous industrial production of polyglycolide PGA.

Description

Technical Field

[0001] This invention relates to a system and method for producing polyglycolic acid (PGA), and more particularly to a system and method for large-scale industrial continuous production of PGA. Background Technology

[0002] Polyglycolic acid (PGA), also known as polyhydroxyacetic acid, is a highly crystalline, biodegradable aliphatic polymer. Using organometallic compounds, titanium compounds, or Lewis acids as catalysts, and ethanol as a molecular weight and reaction rate controller, PGA products are produced through cationic ring-opening polymerization of glycolide under high temperature and low pressure conditions. PGA is a synthetic polymer with excellent biocompatibility and biodegradability. Biodegradation mainly occurs through simple hydrolysis and biological reabsorption, ultimately transforming into water and carbon dioxide, which are harmless to humans, animals, plants, and the natural environment. Due to its rapid degradation and good processability, PGA applications are mainly in biomedicine and ecology. In biomedical applications, PGA is primarily used in surgical sutures, drug delivery carriers, scaffolds for cell culture and transplantation, and organ regeneration materials. In ecological applications, PGA is mainly used in autodegradable agricultural films, biodegradable forestry materials, biodegradable aquaculture materials, water-retaining materials for desert soil greening, and slow-release herbicides.

[0003] Patent 201911094857.3 discloses a method for preparing high molecular weight polylactic acid (PLA), comprising the steps of prepolymerization, polymerization, chain extension, and crosslinking. The chain extender in the crosslinking step is a dioxazoline chain extender, and the crosslinking agent in the crosslinking step is a polycarboxyl compound. This invention uses polycarboxyl compounds to induce intermolecular reactions in PLA to form a network crosslinked structure, further increasing the molecular weight of PLA and improving its mechanical properties. Unexpectedly, a synergistic effect was found between the dioxazoline chain extender and the polycarboxyl compound added in the crosslinking step; adjusting their ratio not only increases the molecular weight of PLA but also ensures that the product color is unaffected by chain extension and crosslinking. This invention also found that adding activated clay in the prepolymerization step not only improves the impact resistance of PLA but also reduces the reaction difficulty, further increasing the weight-average molecular weight of PLA. However, the polymerization of lactide to obtain PLA products suffers from problems such as long polymerization time, complex operation, and high overall energy consumption.

[0004] Patent 201920437990.3 discloses an apparatus for producing polyglycolic acid (PEG) using an ultrasonic method. The apparatus includes an inert gas replacement device, a dissolving vessel, a polymerization reactor, and a vacuum generator. The inert gas replacement device is connected to the dissolving vessel, which has a heating device on its outer side. The dissolving vessel has an inlet at the top and an outlet at the bottom. The polymerization reactor includes a polymerizer and an ultrasonic generator, with the polymerizer mounted on top of the ultrasonic generator. The polymerizer has an inlet at its top, and the outlet is positioned higher than the inlet. A material pipe connects the outlet and the inlet, and an electrically heated insulation belt is installed on the outside of the material pipe. The vacuum generator includes a vacuum tank and a vacuum pump connected to each other. The PEG polymer produced by this invention using ultrasonic polymerization has high purity, good reproducibility, controllable operation, and good thermal stability, which is beneficial for secondary molding and processing, making it suitable for large-scale industrial production. Patent 201811235062.5 discloses a method for the continuous ring-opening preparation of poly(lactic-coated lactide) and a catalyst preparation method, mainly addressing the problems of complex processes, long polymerization times, and unstable intrinsic viscosity and weight-average molecular weight of poly(lactic-coated lactide) products in existing continuous ring-opening polymerization processes. This invention employs a titanium-based catalyst comprising the following reactant products: a titanium compound having the general formula Ti(OR)4; R being an alkyl group with 1 to 10 carbon atoms; a diol having 2 to 10 carbon atoms; at least one aliphatic organic acid; and at least one phosphate ester compound; wherein, in molar ratios, the diol:titanium compound ratio is 1 to 150:1, the aliphatic organic acid:titanium compound ratio is 1 to 10:1, and the phosphate ester compound:titanium compound ratio is 0.1 to 5:1. This technical solution effectively solves the problem and can be used in the industrial production of continuous ring-opening poly(lactic-coated lactide). However, the two patents, 201920437990.3 and 201811235062.5, are only laboratory-scale and intermittent methods for preparing polyglycolic acid products in the process of obtaining PGA products through the polymerization of glycolide. The production scale is small and the polymerization reaction cycle is long. Once it is implemented in a large-scale continuous industrial polyglycolic acid production device, there will be a "scale-up effect" problem. Summary of the Invention

[0005] Purpose of the invention: The first purpose of the present invention is to provide a system for large-scale industrial continuous production of PGA, and the second purpose of the present invention is to provide a method for large-scale industrial continuous production of PGA using the system.

[0006] Technical solution: The present invention discloses a system for large-scale industrial continuous production of PGA, comprising a first polymerization reactor, a second polymerization reactor, a third polymerization reactor, a devolatilizer, a cold trap, a crystallizer, and a packaging palletizer; the second polymerization reactor is connected to the first polymerization reactor and the third polymerization reactor respectively via pipelines, the devolatilizer is connected to the third polymerization reactor and the cold trap respectively via pipelines, and the crystallizer is connected to the devolatilizer and the packaging palletizer respectively via a solid conveyor belt.

[0007] Preferably, the first polymerization reactor is an adiabatic reactor; the second polymerization reactor is equipped with an external jacket and an internal winding tube; the third polymerization reactor is an adiabatic polymerization reactor, and the devolatilizer is equipped with an external jacket.

[0008] The present invention discloses a method for large-scale industrial continuous production of PGA, comprising the following steps:

[0009] a. The mixture of molten glycolide feedstock and catalyst is fed into the first polymerization reactor for prepolymerization to obtain primary polymer feedstock; the temperature of the first polymerization reactor is controlled by the glycolide feedstock temperature, and the pressure of the first polymerization reactor is controlled by the introduction of nitrogen gas;

[0010] b. The primary polymer material enters the second polymerization reactor for further polymerization to obtain the secondary polymer material. Cooling medium is introduced into the jacket and winding pipe of the second polymerization reactor respectively. The temperature of the second polymerization reactor is controlled by the cooling medium introduced into the jacket and winding pipe, and the pressure of the second polymerization reactor is controlled by the introduction of nitrogen gas.

[0011] c. The secondary polymer material enters the third polymerization reactor to obtain the polymerization product; after the adiabatic polymerization reaction is completed, an antioxidant and a deactivating agent are introduced into the lower half of the third polymerization reactor to terminate the reaction; the temperature of the third polymerization reactor is controlled by introducing the antioxidant and deactivating agent, and the pressure of the third polymerization reactor is controlled by introducing nitrogen gas.

[0012] d. The polymerization product enters the devolatilizer, and heat transfer oil is introduced into the jacket of the devolatilizer for heating, to obtain PGA product and unreacted glycolide raw material. The unreacted glycolide raw material is sent to the cold trap for cooling to obtain unreacted glycolide for reuse.

[0013] e. The PGA product enters the crystallizer for cooling and crystallization, is heated to melt, and then cold-solidified, cut, and granulated to obtain polyglycolic acid granules.

[0014] f. Polyglycolic acid granules are packaged and stacked by a packaging and palletizing machine to obtain polyglycolic acid products which are then shipped out of the area.

[0015] Preferably, the cooling medium is heat transfer oil.

[0016] Preferably, the deactivating agent is one of sodium polysulfide or a sulfur-containing compound, and the antioxidant is one of octadecyl propionate or a phosphite.

[0017] Preferably, the first polymerization reactor operates at a temperature of 130–200°C, an operating pressure of 0.10–1.0 MPaG, and a polymerization residence time of 0.2–1.0 hours; the second polymerization reactor operates at an inlet temperature of 130–200°C, an outlet temperature of 150–220°C, an operating pressure of 0.00–0.50 MPaG, and a polymerization residence time of 1.0–2.0 hours; the third polymerization reactor operates fully filled with material, and its inlet operating temperature is 150–200°C. The operating temperature of the reactor is 220℃, the outlet operating temperature is 160~230℃, the operating pressure is 0.00~0.40MPaG, and the residence time of the polymerization reaction is 0.5~1.3 hours; the operating temperature of the devolatilizer is 180~240℃, the operating pressure is 2~14kPaA, and the residence time is 1~10 minutes; the vacuum degree of the devolatilizer is controlled by a vacuum system, and the operating pressure of the vacuum system is 1~8kPaA; the crystallization temperature of the crystallizer is 15~45℃, and the melting temperature is 215~245℃.

[0018] More preferably, the first polymerization reactor operates at a temperature of 140–190°C, an operating pressure of 0.20–0.90 MPaG, and a polymerization residence time of 0.3–0.9 hours; the second polymerization reactor operates at an inlet temperature of 140–190°C, an outlet temperature of 160–210°C, an operating pressure of 0.05–0.40 MPaG, and a polymerization residence time of 1.1–1.9 hours; and the third polymerization reactor operates at an inlet temperature of… The operating temperature of the polymerization reactor is 160–210℃, the outlet operating temperature is 170–220℃, the operating pressure is 0.05–0.35 MPaG, and the residence time is 0.5–1.2 hours; the operating temperature of the devolatilizer is 190–230℃, the operating pressure is 3–12 kPaA, and the residence time is 2–9 minutes; the operating pressure of the vacuum system controlling the devolatilizer is 2–7 kPaA; the crystallization temperature of the crystallizer is 20–40℃, and the melting temperature is 220–240℃.

[0019] Most preferably, the first polymerization reactor operates at a temperature of 150–180°C, an operating pressure of 0.30–0.80 MPaG, and a polymerization residence time of 0.4–0.8 hours; the second polymerization reactor operates at an inlet temperature of 150–180°C, an outlet temperature of 170–200°C, an operating pressure of 0.10–0.30 MPaG, and a polymerization residence time of 1.2–1.8 hours; and the third polymerization reactor operates at an inlet temperature of… The operating temperature of the polymerization reactor is 170–200℃, the outlet operating temperature is 180–210℃, the operating pressure is 0.10–0.30 MPaG, and the residence time is 0.6–1.1 hours; the operating temperature of the devolatilizer is 200–220℃, the operating pressure is 4–10 kPaA, and the residence time is 3–8 minutes; the operating pressure of the vacuum system controlling the devolatilizer is 3–6 kPaA; the crystallization temperature of the crystallizer granulator is 25–35℃, and the melting temperature is 225–235℃.

[0020] Preferably, the jacket outside the second polymerization reactor adopts a segmented heat transfer oil cooling system, dividing the heat transfer oil in the jacket into upper and lower sections. The inlet temperature of the heat transfer oil in the upper section is 150-155°C, and the outlet temperature is 155-160°C. The inlet temperature of the heat transfer oil in the lower section is 170-175°C, and the outlet temperature is 175-180°C.

[0021] This invention first feeds glycolide raw material and catalyst into a first polymerization reactor for adiabatic polymerization; then into a second polymerization reactor for further polymerization, where some of the polymerization heat is removed by heat transfer oil in the jacket and winding pipes of the second polymerization reactor; then into a third polymerization reactor for adiabatic polymerization. After the polymerization reaction is completed, antioxidants and deactivators are added to terminate the polymerization reaction; then, unreacted glycolide raw material is removed from the polymerization product by a devolatilizer, and the glycolide is cooled and returned to the unit for recycling; finally, the polymerization product is crystallized, granulated, packaged, and stacked to obtain the polyethylene glycolide product.

[0022] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: In a 10,000-300,000 tons / year polyglycolic acid (PGA) plant, the polymerization reaction is carried out through three polymerization reactors. Unreacted glycolide raw materials are recovered by a devolatilizer and returned to the reaction unit. The product is then obtained through a crystallizer, granulator, and packaging / palletizer, achieving the goal of large-scale commercial continuous industrial production of PGA. PGA products with molecular weights of 156,000-212,000, melt viscosity of 460-540 Pa·s, and tensile strength of 65-73 MPa are obtained, achieving good technical results. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0025] Example 1

[0026] The process flow of this invention is as follows: Figure 1 As shown, the mixture 11 of molten glycolide feedstock and catalyst enters the first polymerization reactor 1 for prepolymerization of glycolide. The temperature of the first polymerization reactor 1 is regulated by the feed temperature of glycolide, and nitrogen gas 12 is introduced to control the pressure of the first polymerization reactor. The primary polymer 13 flowing out from the bottom of the first polymerization reactor enters the second polymerization reactor 2 for further polymerization. The heat transfer oil 15 from the first stage enters the lower half of the jacket and winding pipe of the second polymerization reactor 2 to remove some of the polymerization heat, and then the heat transfer oil 16 flows out from the lower half of the jacket and winding pipe to the outside. The heat transfer oil 17 from the second stage enters the upper half of the jacket and winding pipe of the second polymerization reactor 2 to remove some of the polymerization heat, and then the heat transfer oil 18 flows out from the upper half of the jacket and winding pipe to the outside. The secondary polymer 14 from the second polymerization reactor directly enters the third polymerization reactor 3 for adiabatic polymerization. After the adiabatic polymerization reaction is completed, antioxidant 20 and deactivator 21 are sent to the lower half of the third polymerization reactor 3 to terminate the reaction. The polymerization product 19 at the bottom of the third polymerization reactor 3 is fed into the devolatilizer 4 to remove unreacted glycolide raw material 23. Heat transfer oil 24 enters the jacket of the devolatilizer 4 for heating, and the heated heat transfer oil 25 flows out of the jacket of the devolatilizer 4 and is sent outside the facility. The unreacted glycolide raw material 23 removed by the devolatilizer 4 is cooled and partially condensed by the cold trap 5. The uncondensed gaseous component 26 is sent to the vacuum system, and the condensed unreacted liquid glycolide 27 is returned to the unit for reuse. The PGA product 22 obtained in the devolatilizer 4 is fed into the crystallizer granulator 6, where it is cooled and crystallized to obtain polyethylene glycolide powder. This powder is then heated and melted to obtain molten polyethylene glycolide, which is then cold-cured, cut, and granulated to obtain polyethylene glycolide granules 28. The polyethylene glycolide granules 28 enter the packaging and palletizing machine 7, where they are packaged and palletized to obtain polyethylene glycolide product 29, which is then sent outside the facility.

[0027] The deactivating agent 14 can be one of sodium polysulfide or sulfur-containing compounds, and the antioxidant 15 can be one of octadecyl propionate or phosphite.

[0028] The process operating parameters in this embodiment are as follows: In a polyglycolic acid (PGA) production unit with a production scale of 10,000 tons / year, the operating temperature of the first polymerization reactor 1 is 142°C, the operating pressure is 0.3 MPaG, and the polymerization residence time is 0.3 hours; the inlet operating temperature of the second polymerization reactor 2 is 142°C, the outlet operating temperature is 162°C, the operating pressure is 0.11 MPaG, and the polymerization residence time is 1.2 hours; the third polymerization reactor 3 is fully filled with material, and its inlet operating temperature is 162°C, and its outlet operating temperature is... The operating temperature of the first polymerization reactor was 172℃, the operating pressure was 0.08 MPaG, and the residence time was 0.7 hours. The operating temperature of the devolatilizer 4 was 187℃, the operating pressure was 4 kPaA, and the residence time was 3 minutes. The vacuum system operating pressure of the devolatilizer 4 was controlled at 2 kPaA. The crystallization temperature of the crystallizer granulator 6 was 20℃, and the melting temperature was 240℃. The inlet temperature of the upper section of the heat transfer oil in the outer jacket of the second polymerization reactor 2 was 151℃, and the outlet temperature was 156℃. The inlet temperature of the lower section of the heat transfer oil was 171℃, and the outlet temperature was 176℃. During the polymerization reaction and devolatilization process, the heat transfer oil removed from the second polymerization reactor amounted to 127,000 kcal / h, and the heat removed by the glycolide through the cold trap amounted to 88,900 kcal / h. This yielded a polyglycolic acid (PGA) product with a molecular weight of 164,000, a melt viscosity of 470 Pa·s, and a tensile strength of 66 MPa, achieving good technical results.

[0029] Example 2

[0030] Similar to Example 1, but with changes to the production scale and operating conditions, the polyglycolic acid (PGA) unit has a production scale of 50,000 tons / year, and the process parameters are modified as follows: The operating temperature of the first polymerization reactor 1 is 186°C, the operating pressure is 0.8 MPaG, and the polymerization residence time is 0.9 hours; the inlet operating temperature of the second polymerization reactor 2 is 186°C, the outlet operating temperature is 206°C, the operating pressure is 0.47 MPaG, and the polymerization residence time is 1.8 hours; the third polymerization reactor 3 is fully filled with material, with an inlet operating temperature of 206°C and an outlet operating temperature of 206°C. The operating temperature of the inlet reactor was 216℃, the operating pressure was 0.32 MPaG, and the residence time of the polymerization reaction was 1.1 hours. The operating temperature of the devolatilizer 4 was 231℃, the operating pressure was 10 kPaA, and the residence time was 6 minutes. The operating pressure of the vacuum system controlling the devolatilizer 4 was 5 kPaA. The crystallization temperature of the crystallizer granulator 6 was 35℃, and the melting temperature was 235℃. The inlet temperature of the upper section of the heat transfer oil in the outer jacket of the second polymerization reactor 2 was 153℃, and the outlet temperature was 158℃. The inlet temperature of the lower section of the heat transfer oil was 173℃, and the outlet temperature was 178℃. During the polymerization reaction and devolatilization process, the heat transfer oil removed from the second polymerization reactor amounted to 635,000 kcal / h, and the heat removed by the glycolide through the cold trap amounted to 444,500 kcal / h. This yielded a polyglycolic acid (PGA) product with a molecular weight of 186,000, a melt viscosity of 520 Pa·s, and a tensile strength of 70 MPa, achieving good technical results.

[0031] Example 3

[0032] Similar to Example 1, but with different production scale and operating conditions, the polyglycolic acid (PGA) plant has a production scale of 200,000 tons / year and is equipped with two production lines. The process parameters are modified as follows: the operating temperature of the first polymerization reactor 1 is 153°C, the operating pressure is 0.4 MPaG, and the polymerization residence time is 0.5 hours; the inlet operating temperature of the second polymerization reactor 2 is 153°C, the outlet operating temperature is 173°C, the operating pressure is 0.21 MPaG, and the polymerization residence time is 1.3 hours; the third polymerization reactor 3 is fully filled with material, and its inlet operating temperature is 1... The operating temperature of the reactor is 73℃, the outlet operating temperature is 183℃, the operating pressure is 0.12MPaG, and the residence time of the polymerization reaction is 0.8 hours; the operating temperature of the devolatilizer 4 is 198℃, the operating pressure is 6kPaA, and the residence time is 5 minutes; the operating pressure of the vacuum system of the devolatilizer 4 is controlled at 4kPaA; the crystallization temperature of the crystallizer granulator 6 is 30℃, and the melting temperature is 230℃; the inlet temperature of the upper section of the heat transfer oil in the outer jacket of the second polymerization reactor 2 is 152℃, and the outlet temperature is 157℃; the inlet temperature of the lower section of the heat transfer oil is 172℃, and the outlet temperature is 177℃. During the polymerization reaction and devolatilization process, the heat transfer oil removed 2,540,000 kcal / h of polymerization heat from the second polymerization reactor, and the glycolide removed 1,778,000 kcal / h of heat through the cold trap. As a result, a polyglycolic acid (PGA) product with a molecular weight of 172,000, a melt viscosity of 480 Pa·s, and a tensile strength of 68 MPa was obtained, achieving good technical results.

[0033] Example 4

[0034] Similar to Example 1, but with changes to the production scale and operating conditions, the polyglycolic acid (PGA) plant has a production scale of 300,000 tons / year and is equipped with three production lines. The process parameters are modified as follows: the operating temperature of the first polymerization reactor 1 is 175°C, the operating pressure is 0.9 MPaG, and the polymerization residence time is 0.8 hours; the inlet operating temperature of the second polymerization reactor 2 is 175°C, the outlet operating temperature is 195°C, the operating pressure is 0.45 MPaG, and the polymerization residence time is 1.7 hours; the third polymerization reactor 3 is fully filled with material, and its inlet operating temperature is 19... The operating temperature of the first polymerization reactor is 5℃, the outlet operating temperature is 205℃, the operating pressure is 0.34MPaG, and the residence time of the polymerization reaction is 1.2 hours; the operating temperature of the devolatilizer 4 is 220℃, the operating pressure is 12kPaA, and the residence time is 8 minutes; the operating pressure of the vacuum system of the devolatilizer 4 is controlled at 7kPaA; the crystallization temperature of the crystallizer granulator 6 is 40℃, and the melting temperature is 220℃; the inlet temperature of the upper section of the heat transfer oil in the outer jacket of the second polymerization reactor 2 is 154℃, and the outlet temperature is 159℃; the inlet temperature of the lower section of the heat transfer oil is 174℃, and the outlet temperature is 179℃. During the polymerization reaction and devolatilization process, the heat transfer oil removed 3,810,000 kcal / h of polymerization heat from the second polymerization reactor, and the glycolide removed 2,667,000 kcal / h of heat through the cold trap. As a result, a polyglycolic acid (PGA) product with a molecular weight of 200,000, a melt viscosity of 530 Pa·s, and a tensile strength of 72 MPa was obtained, achieving good technical results.

[0035] Example 5

[0036] Similar to Example 1, but with changes to the production scale and operating conditions, the polyglycolic acid (PGA) unit has a production scale of 100,000 tons / year, and the process parameters are modified as follows: the operating temperature of the first polymerization reactor 1 is 130°C, the operating pressure is 0.1 MPaG, and the polymerization residence time is 0.2 hours; the inlet operating temperature of the second polymerization reactor 2 is 130°C, the outlet operating temperature is 150°C, the operating pressure is 0.00 MPaG, and the polymerization residence time is 1.0 hour; the third polymerization reactor 3 is fully filled with material, and its inlet operating temperature is 150°C. The outlet operating temperature is 160℃, the operating pressure is 0.00MPaG, and the residence time of the polymerization reaction is 0.5 hours; the operating temperature of devolatilizer 4 is 180℃, the operating pressure is 2kPaA, and the residence time is 1 minute; the operating pressure of the vacuum system controlling devolatilizer 4 is 1kPaA; the crystallization temperature of crystallizer granulator 6 is 15℃, and the melting temperature is 215℃; the inlet temperature of the upper section of the heat transfer oil in the outer jacket of the second polymerization reactor 2 is 150℃, and the outlet temperature is 155℃; the inlet temperature of the lower section of the heat transfer oil is 170℃, and the outlet temperature is 175℃. During the polymerization reaction and devolatilization process, the heat transfer oil removes 1,260,000 kcal / h of polymerization heat from the second polymerization reactor, and the heat removed by the glycolide through the cold trap is 882,000 kcal / h. This yields a polyglycolic acid (PGA) product with a molecular weight of 156,000, a melt viscosity of 460 Pa·s, and a tensile strength of 65 MPa, achieving good technical results.

[0037] Example 6

[0038] Similar to Example 1, but with changes to the production scale and operating conditions, the polyglycolic acid (PGA) unit has a production scale of 100,000 tons / year. The process parameters are modified as follows: the operating temperature of the first polymerization reactor 1 is 200°C, the operating pressure is 1.0 MPaG, and the polymerization residence time is 1.0 hour; the inlet operating temperature of the second polymerization reactor 2 is 200°C, the outlet operating temperature is 220°C, the operating pressure is 0.50 MPaG, and the polymerization residence time is 2.0 hours; the third polymerization reactor 3 is fully filled with material, with an inlet operating temperature of 220°C and an outlet operating temperature of 220°C. The operating temperature of the inlet reactor was 230℃, the operating pressure was 0.40 MPaG, and the residence time of the polymerization reaction was 0.3 hours. The operating temperature of the devolatilizer 4 was 240℃, the operating pressure was 14 kPaA, and the residence time was 10 minutes. The operating pressure of the vacuum system of the devolatilizer 4 was controlled at 8 kPaA. The crystallization temperature of the crystallizer granulator 6 was 45℃, and the melting temperature was 245℃. The inlet temperature of the upper section of the heat transfer oil in the outer jacket of the second polymerization reactor 2 was 155℃, and the outlet temperature was 160℃. The inlet temperature of the lower section of the heat transfer oil was 175℃, and the outlet temperature was 180℃. During the polymerization reaction and devolatilization process, the heat transfer oil removed from the second polymerization reactor was 1,280,000 kcal / h, and the heat removed by the glycolide through the cold trap was 896,000 kcal / h. As a result, a polyglycolic acid (PGA) product with a molecular weight of 212,000, a melt viscosity of 540 Pa·s, and a tensile strength of 73 MPa was obtained, achieving good technical results.

Claims

1. A method for large-scale industrial continuous production of PGA using a system for large-scale industrial continuous production, characterized in that, The system includes a first polymerization reactor (1), a second polymerization reactor (2), a third polymerization reactor (3), a devolatilizer (4), a cold trap (5), a crystallizer (6), and a packaging palletizer (7); the second polymerization reactor (2) is connected to the first polymerization reactor (1) and the third polymerization reactor (3) through pipes respectively; the devolatilizer (4) is connected to the third polymerization reactor (3) and the cold trap (5) through pipes respectively; the crystallizer (6) is connected to the devolatilizer (4) and the packaging palletizer (7) through a solid conveyor belt respectively; the first polymerization reactor (1) is an insulated reactor; the second polymerization reactor (2) is equipped with a jacket on the outside and a winding tube on the inside; the third polymerization reactor (3) is an insulated polymerization reactor; the devolatilizer (4) is equipped with a jacket on the outside; Includes the following steps: a. The mixture of molten glycolide raw material and catalyst (11) enters the first polymerization reactor (1) to carry out a prepolymerization reaction to obtain primary polymer material (13). b. The primary polymer material (13) enters the second polymerization reactor (2) for further polymerization to obtain the secondary polymer material (14); at the same time, the jacket of the second polymerization reactor (2) is circulated with cooling medium (15), and the spiral tube of the second polymerization reactor (2) is circulated with cooling medium (17); the cooling medium (15) and cooling medium (17) are heat transfer oil; the jacket outside the second polymerization reactor (2) adopts segmented heat transfer oil heat removal, dividing the heat transfer oil in the jacket into upper and lower sections. The inlet temperature of the heat transfer oil in the upper section is 150~155℃, and the outlet temperature is 155~160℃; the inlet temperature of the heat transfer oil in the lower section is 170~175℃, and the outlet temperature is 175~180℃. c. Secondary polymer material (14) enters the third polymerization reactor (3) for adiabatic polymerization reaction to obtain polymer product (19); after the adiabatic polymerization reaction is completed, antioxidant (20) and deactivator (21) are introduced into the lower half of the third polymerization reactor (3) to terminate the reaction; d. The polymerization product (19) enters the devolatilizer (4). Heat transfer oil (24) is introduced into the jacket of the devolatilizer (4) for heating to obtain PGA product (22) and unreacted glycolide raw material (23). The unreacted glycolide raw material (23) is sent to the cold trap (5) to cool down and obtain unreacted glycolide (27) for reuse. e. PGA product (22) enters the crystallizer (6) for cooling and crystallization, heating and melting, and then cold solidification and cutting to obtain polyglycolic acid granules (28). f. Polyglycolic acid granules (28) are packaged and stacked by a packaging and palletizing machine (7) to obtain polyglycolic acid products (29) which are then sent out of the boundary. The deactivating agent (21) is one of sodium polysulfide and sulfur-containing compounds, and the antioxidant (20) is one of octadecyl propionate and phosphite. The first polymerization reactor (1) operates at a temperature of 130~200℃, an operating pressure of 0.10~1.0 MPaG, and a polymerization residence time of 0.2~1.0 hours; the second polymerization reactor (2) operates at an inlet temperature of 130~200℃, an outlet temperature of 150~220℃, an operating pressure of 0.00~0.50 MPaG, and a polymerization residence time of 1.0~2.0 hours; the third polymerization reactor (3) operates fully filled with material, and its inlet operating temperature is 150~220℃. The outlet operating temperature is 160~230℃, the operating pressure is 0.00~0.40MPaG, and the residence time of the polymerization reaction is 0.5~1.3 hours; the operating temperature of the devolatilizer (4) is 180~240℃, the operating pressure is 2~14kPaA, and the residence time is 1~10 minutes; the vacuum degree of the devolatilizer (4) is controlled by a vacuum system, and the operating pressure of the vacuum system is 1~8kPaA; the crystallization temperature of the crystallizer (6) is 15~45℃, and the melting temperature is 215~245℃.

2. The method for large-scale industrial continuous production of PGA according to claim 1, characterized in that, The first polymerization reactor (1) operates at a temperature of 140~190℃, an operating pressure of 0.20~0.90MPaG, and a polymerization residence time of 0.3~0.9 hours; the second polymerization reactor (2) operates at an inlet temperature of 140~190℃, an outlet temperature of 160~210℃, an operating pressure of 0.05~0.40MPaG, and a polymerization residence time of 1.1~1.9 hours; the third polymerization reactor (3) operates at an inlet temperature of 160~190℃. The operating temperature of the de-explosion reactor (4) is 190-230°C, the operating pressure is 3-12 kPaA, and the residence time is 2-9 minutes. The vacuum system operating pressure of the de-explosion reactor (4) is controlled to be 2-7 kPaA. The crystallization temperature of the crystallizer (6) is 20-40°C, and the melting temperature is 220-240°C.

3. The method for large-scale industrial continuous production of PGA according to claim 2, characterized in that, The first polymerization reactor (1) operates at a temperature of 150~180℃, an operating pressure of 0.30~0.80 MPaG, and a polymerization residence time of 0.4~0.8 hours; the second polymerization reactor (2) operates at an inlet temperature of 150~180℃, an outlet temperature of 170~200℃, an operating pressure of 0.10~0.30 MPaG, and a polymerization residence time of 1.2~1.8 hours; the third polymerization reactor (3) operates at an inlet temperature of 17℃. The operating temperature is 0~200℃, the outlet operating temperature is 180~210℃, the operating pressure is 0.10~0.30MPaG, and the residence time of the polymerization reaction is 0.6~1.1 hours; the operating temperature of the devolatilizer (4) is 200~220℃, the operating pressure is 4~10kPaA, and the residence time is 3~8 minutes; the operating pressure of the vacuum system of the devolatilizer (4) is controlled to be 3~6kPaA; the crystallization temperature of the crystallizer (6) is 25~35℃, and the melting temperature is 225~235℃.

Images