Polyol gradient synergistic depolymerization-esterification coupling reaction device for chemical recovery of PETG (Polyethylene Terephthalate Glycol)

Abstract

The invention discloses a polyol gradient synergetic depolymerization-esterification coupling reaction device for PETG chemical recovery, and belongs to the technical field of depolymerization-esterification coupling reaction devices, the polyol gradient synergetic depolymerization-esterification coupling reaction device comprises a main reaction kettle, the main reaction kettle is of a vertical cylindrical structure, the top of the main reaction kettle is fixedly connected with a sealing cover, the sealing cover is connected with a plurality of feeding ports, and the feeding ports are communicated with the main reaction kettle. A liquid collecting cavity is connected below the main reaction kettle, a return pipe is connected to the bottom of the liquid collecting cavity, a one-way valve is arranged on the return pipe, a multi-stage alcohol feeding system is arranged on one side of the main reaction kettle, a gradient temperature control jacket assembly is arranged on the other side of the main reaction kettle, and an in-situ esterification module is arranged on the inner side of the main reaction kettle. According to the method, multiple alcohol reagents are introduced according to the gradient synergistic effect, the breaking requirements of different types of ester bonds in PETG molecules are accurately matched, the depolymerization and esterification processes are coupled in situ, efficient, low-consumption and high-valued closed-loop recovery is achieved, and the defects that depolymerization is not thorough, products are complex, the technology is tedious and the like when PETG is treated in the prior art are effectively overcome.

Description

Technical Field

[0001] This invention relates to the field of depolymerization-esterification coupling reaction device technology, specifically a polyol gradient synergistic depolymerization-esterification coupling reaction device for the chemical recovery of PETG. Background Technology

[0002] The polyol gradient synergistic depolymerization-esterification coupling reaction in PETG chemical recovery is an efficient and controllable closed-loop process. It involves using multiple polyols to synergistically break the ester bonds of PETG in stages (depolymerization), simultaneously converting the depolymerization products into esterification products that can be directly used for repolymerization, achieving "one-step depolymerization-esterification coupling." The core of this process is gradient polyol-controlled reaction + efficient coupling + high-value product utilization. Acid is used as a catalyst, polyols as reagents, and heating is employed to achieve the above reaction. With the development of polyester material recycling technology, chemical recycling methods have received widespread attention due to their ability to achieve high-value regeneration. However, existing technologies still have significant shortcomings when processing specific types of polyesters (such as PETG). PETG (polyethylene terephthalate-1,4-cyclohexanediethanol ester) has low crystallinity, poor thermal stability, and is difficult to depolymerize due to the introduction of 1,4-cyclohexanediethanol (CHDM) structural units into its molecular chain, making traditional alcoholysis recovery methods for PET inefficient and unsuitable. Currently, most mainstream chemical recycling processes focus on conventional PET, lacking targeted depolymerization strategies for modified polyesters such as PETG, and there are significant bottlenecks, especially in terms of depolymerization efficiency, product purity, and process energy consumption.

[0003] A search revealed a method for the chemical recycling of waste PET products utilizing the phase transition properties of BHET crystals, disclosed in publication number CN115894223B on October 22, 2024. This method uses ethylene glycol as the alcoholysis agent, and under the action of a catalyst, waste PET is alcoholyzed to generate BHET, which is then purified through steps such as cooling crystallization and vacuum sublimation. Although this technology optimizes the purification path of BHET, its core is still based on a single ethylene glycol system and is designed for standard PET substrates. For PETG containing the CHDM structure, its alcoholysis products not only contain BHET but also generate a complex mixture of diol esters containing cyclohexane structures. It is difficult to effectively break all ester bonds using a single alcoholysis agent, and the products cannot form regular crystals. This results in incomplete depolymerization and difficult product separation when processing PETG, hindering efficient recycling.

[0004] A search revealed a method for recovering waste polyester based on alcoholysis using a two-component catalyst, publication number CN114890898B, published on April 16, 2024. This method employs a two-component catalyst composed of a nitrogen-containing polycyclic organic compound and a metal salt to alcoholyze PET at 120–200 °C using ethylene glycol as a solvent, thereby increasing the BHET yield. Although this technology improves reaction efficiency through catalyst synergy, it remains limited to a single alcoholysis agent (ethylene glycol) system and does not consider the selective cleavage ability of polyols on different ester bonds. The asymmetric ester bonds formed in the PETG molecule due to the introduction of CHDM are sensitive to the nucleophilicity and steric hindrance of the alcoholysis reagent. A single alcohol cannot simultaneously and efficiently attack the terephthalic acid-ethylene glycol bond and the terephthalic acid-CHDM bond, resulting in slow depolymerization rate, numerous side reactions, and low monomer yield. Furthermore, this method does not couple depolymerization with the subsequent esterification process, requiring additional steps for product purification and repolymerization, resulting in a lengthy process and high energy consumption. Summary of the Invention

[0005] To address the technical problems mentioned in the background section, this invention provides a polyol gradient synergistic depolymerization-esterification coupled reaction apparatus for the chemical recovery of PETG, employing the following technical solution:

[0006] The system includes a main reactor, which is a vertical cylindrical structure. A sealing cover is fixedly connected to the top of the main reactor, and several feeding ports are connected to the sealing cover. A liquid collection chamber is connected to the bottom of the main reactor, and a reflux pipe is connected to the bottom of the liquid collection chamber. A one-way valve is installed on the reflux pipe. The system is characterized in that a multi-stage alcohol feeding system is provided on one side of the main reactor, a gradient temperature control jacket assembly is provided on the other side of the main reactor, and an in-situ esterification module is provided inside the main reactor.

[0007] Furthermore, the multi-stage alcohol feeding system includes a first alcohol storage tank, a second alcohol storage tank, and a third alcohol storage tank located on one side of the main reactor. Each of the first, second, and third alcohol storage tanks is equipped with a feeding assembly. The feeding assembly includes a feeding pipe connected to the first, second, and third alcohol storage tanks, respectively. A metering pump is connected to the feeding pipe, and a feeding port is fitted onto the feeding pipe. The feeding port is fixedly connected to the outer wall of the main reactor. An L-shaped guide pipe is installed inside the main reactor and welded to the feeding port. The outlet of the L-shaped guide pipe faces the central axis of the main reactor and is inclined downward at 30° with the horizontal plane. The feeding port on the first alcohol storage tank is located 15 cm above the initial liquid level in the main reactor. The feeding port on the second alcohol storage tank is located 5 cm below the initial liquid level. The feeding port on the third alcohol storage tank is located 8 cm above the bottom of the main reactor.

[0008] Furthermore, the gradient temperature control jacket assembly includes an upper jacket, a middle jacket, and a lower jacket, which are fixed to the outer wall of the main reactor from top to bottom. The upper jacket covers the area from the top of the main reactor to 10 cm above the initial liquid level, the middle jacket covers the area 10 cm above and below the initial liquid level, and the lower jacket covers the area from the bottom of the main reactor to 10 cm below the initial liquid level. Each jacket has a spiral guide rib on its inner wall, with a rib height of 2 mm and a pitch of 50 mm. The heat transfer oil inlet of the upper jacket is located at its top, and the outlet is located at its bottom. The heat transfer oil inlet of the middle jacket is located in the middle of its side wall, and the outlet is symmetrically arranged in the middle of the other side. The heat transfer oil inlet of the lower jacket is located at its bottom, and the outlet is located at its top.

[0009] Furthermore, the in-situ esterification module is integrated inside the main reactor, including an annular distributor fixed to the inner side of the top of the main reactor and a microporous ceramic membrane assembly embedded in the bottom wall of the main reactor. The annular distributor has a hollow circular ring structure with an inner diameter of 0.6 times the inner diameter of the main reactor. It has 24 spray holes with a diameter of 1.2 mm evenly distributed at its bottom.

[0010] Furthermore, the microporous ceramic membrane assembly comprises three concentric ring-shaped microporous ceramic membranes: an inner ring microporous ceramic membrane, a middle ring microporous ceramic membrane, and an outer ring microporous ceramic membrane. These three membranes are fixedly stacked from top to bottom, each with a thickness of 5 mm and a pore size of 0.2 μm. The diameter of the outer ring microporous ceramic membrane is equal to the inner diameter of the main reactor. The diameter of the middle ring microporous ceramic membrane is 0.7 times the diameter of the outer ring microporous ceramic membrane, and the diameter of the inner ring microporous ceramic membrane is 0.4 times the diameter of the outer ring microporous ceramic membrane. A stainless steel support ring is fixedly connected to the bottom of the outer ring microporous ceramic membrane, and the stainless steel support ring is fixed to the bottom wall of the main reactor. The height of the stainless steel support ring is 8 mm.

[0011] Furthermore, a product separation unit is installed on one side of the main reactor. The product separation unit includes a gas phase condenser, a liquid phase settling tank, and a vacuum distillation column. A reboiler is connected to the bottom of the vacuum distillation column. The gas phase condenser is connected to the top of the main reactor through a gas phase outlet pipe. The gas phase outlet pipe has a built-in temperature sensor and pressure transmitter. A liquid phase outlet pipe is connected to the bottom of the liquid phase settling tank. The liquid phase outlet pipe is connected to a reflux pipe. A three-way switching valve is connected to the liquid phase outlet pipe. One branch of the three-way switching valve is connected to the vacuum distillation column. The vacuum distillation column is a packed tower structure and is filled with stainless steel θ-ring packing.

[0012] Furthermore, the heat transfer oil circulation loops of the upper jacket, middle jacket, and lower jacket are each equipped with independent flow regulating valves and temperature controllers, with set temperatures of 180℃, 210℃, and 230℃ for the upper jacket, middle jacket, and lower jacket, respectively.

[0013] Furthermore, the nozzles of the annular distributor are staggered along the circumference, with a central angle of 15° between adjacent nozzles, and the nozzle axis is deflected outward at a 10° angle to the radial direction of the annular distributor.

[0014] Furthermore, a 2mm gap is left between the inner ring microporous ceramic membrane, the middle ring microporous ceramic membrane and the outer ring microporous ceramic membrane, and the gap is filled with zirconia spherical packing with a particle size of 1mm, and the surface of the packing is loaded with tetrabutyl titanate catalyst.

[0015] Furthermore, the liquid phase sedimentation tank is equipped with three layers of partitions, with a vertical spacing of 20cm between the partitions. Each partition has a 5cm diameter through hole in the center, and a magnetic stirrer is installed below the bottom partition.

[0016] The present invention has the following advantages:

[0017] By combining a multi-stage alcohol feeding system with a gradient temperature control jacket assembly, different alcohols are brought into contact with their corresponding ester bonds in specific temperature regions. This solves the problem of incomplete depolymerization of asymmetric ester bonds in PETG due to steric hindrance and differences in nucleophilicity. The multi-stage alcohol feeding system allows ethylene glycol to selectively break standard ester bonds in the upper low-temperature region, 1,4-cyclohexanediethanol to efficiently attack CHDM-related ester bonds in the middle suitable temperature region, and propylene glycol to remove residual structures in the lower high-temperature region, forming a three-dimensional matching mechanism of space, temperature, and reagents. This invention introduces multiple alcohol reagents to work synergistically in a gradient manner, precisely matching the breaking requirements of different types of ester bonds in PETG molecules, and coupling the depolymerization and esterification processes in situ. This achieves efficient, low-consumption, and high-value closed-loop recycling, effectively overcoming the shortcomings of existing technologies in processing PETG, such as incomplete depolymerization, complex products, and cumbersome processes. Attached Figure Description

[0018] Figure 1 This is a structural diagram of the present invention.

[0019] Attached Figures: 1. Main Reactor; 2. Sealing Cap; 3. Feed Port; 4. Collection Chamber; 5. Reflux Pipe; 6. Check Valve; 7. First Alcohol Storage Tank; 8. Second Alcohol Storage Tank; 9. Third Alcohol Storage Tank; 10. Feed Pipe; 11. Metering Pump; 12. Feed Port; 13. L-shaped Guide Pipe; 14. Upper Jacket; 15. Middle Jacket; 16. Lower Jacket; 17. Annular Distributor; 18. Spray Orifice; 19. Inner Ring Microporous Ceramic Membrane; 20. Middle Ring Microporous Ceramic Membrane; 21. Outer Ring Microporous Ceramic Membrane; 22. Stainless Steel Support Ring; 23. Gas Phase Condenser; 24. Liquid Phase Settling Tank; 25. Vacuum Distillation Column; 26. Liquid Phase Outlet Pipe; 27. Three-Way Switching Valve; 28. Baffle Plate; 29. ​​Through Hole; 30. Magnetic Stirrer; 31. Reboiler. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please refer to Figure 1 This invention provides a polyol gradient synergistic depolymerization-esterification coupled reaction device for the chemical recovery of PETG, including a main reactor 1, which is a vertical cylindrical structure. A sealing cover 2 is fixedly connected to the top of the main reactor 1, and several feeding ports 3 are connected to the sealing cover 2. PETG liquid enters the main reactor 1 through the feeding ports 3. A collection chamber 4 is connected to the bottom of the main reactor 1, and the reacted liquid is collected in the collection chamber 4. A reflux pipe 5 is connected to the bottom of the collection chamber 4, and a one-way valve 6 is provided on the reflux pipe 5. The one-way valve 6 controls the opening and closing of the reflux pipe 5. By opening the one-way valve 6, the liquid in the collection chamber 4 is discharged through the reflux pipe 5. A multi-stage alcohol feeding system is provided on one side of the main reactor 1, and a gradient temperature control jacket assembly is provided on the other side of the main reactor 1. An in-situ esterification mold is provided inside the main reactor 1.

[0022] The multi-stage alcohol feeding system includes a first alcohol storage tank 7, a second alcohol storage tank 8, and a third alcohol storage tank 9 located on one side of the main reactor 1. The first alcohol storage tank 7 contains ethylene glycol, the second alcohol storage tank 8 contains 1,4-cyclohexanediethanol, and the third alcohol storage tank 9 contains propylene glycol. The molar ratio of the three alcohols is ethylene glycol:1,4-cyclohexanediethanol:propylene glycol = 4:3:2. Each of the first alcohol storage tank 7, the second alcohol storage tank 8, and the third alcohol storage tank 9 is equipped with a feeding assembly, which feeds the alcohols from the first alcohol storage tank 7, the second alcohol storage tank 8, and the third alcohol storage tank 9 into the main reactor 1. Ethylene glycol, 1,4-cyclohexanediethanol, and propylene glycol are reagents for the chemical recovery reaction of PETG liquid.

[0023] (Hereinafter, "alcohols" refers to ethylene glycol, 1,4-cyclohexanediethanol, and propylene glycol collectively.) The feeding assembly includes feed pipes 10 connected to the first alcohol storage tank 7, the second alcohol storage tank 8, and the third alcohol storage tank 9, respectively. A metering pump 11 is connected to the feed pipes 10, and a feed inlet 12 is fitted onto the feed pipes 10. The feed inlet 12 is fixedly connected to the outer wall of the main reactor 1. An L-shaped guide pipe 13 is installed inside the main reactor 1, and the L-shaped guide pipe 13 is welded to the feed inlet 12. The alcohols from the first alcohol storage tank 7, the second alcohol storage tank 8, and the third alcohol storage tank 9 are metered and fed into the feed pipes 10 by the metering pump 11, then into the feed inlet 12, and finally into the L-shaped guide pipe 12. The alcohol is fed into the main reactor 1 through the guide pipe 13 and the L-shaped guide pipe 13. The outlet of the L-shaped guide pipe 13 faces the central axis of the main reactor 1 and is inclined downward at 30° with the horizontal plane to facilitate the discharge of alcohol. The feed port 12 on the first alcohol storage tank 7 is located 15cm above the initial liquid level in the main reactor 1. This is the liquid level layer of ethylene glycol in the main reactor 1. The feed port 12 on the second alcohol storage tank 8 is located 5cm below the initial liquid level. This is the liquid level layer of 1,4-cyclohexanediethanol in the main reactor 1. The feed port 12 on the third alcohol storage tank 9 is located 8cm above the bottom of the main reactor 1. This is the liquid level layer of propylene glycol in the main reactor 1.

[0024] The gradient temperature control jacket assembly includes an upper jacket 14, a middle jacket 15, and a lower jacket 16, fixed from top to bottom to the outer wall of the main reactor 1. These upper jackets 14, 15, and 16 are all existing technologies. Their core function is to precisely control the temperature of the medium inside the container. They are jacketed structures attached to the outer wall of equipment such as reactors, storage tanks, and pipelines. By introducing heating or cooling media into the jacket, the temperature of the material inside the container is indirectly adjusted. The key point of this invention is that the gradient arrangement of the upper jacket 14, 15, and 16 from top to bottom corresponds to the gradient arrangement of the first alcohol storage tank 7, the second alcohol storage tank 8, and the third alcohol storage tank 9 from top to bottom. The upper jacket 14 covers the area from the top of the main reactor 1 to 10 cm above the initial liquid level, heating the ethylene glycol liquid level layer. The middle jacket 15 covers... The upper jacket 14 covers an area 10cm above and below the initial liquid level of the main reactor 1 to heat the 1,4-cyclohexanediethanol liquid level layer. The lower jacket 16 covers an area 10cm below the initial liquid level of the main reactor 1 to heat the propylene glycol liquid level layer. Each jacket has a spiral guide rib on its inner wall, with a rib height of 2mm and a pitch of 50mm. The heat transfer oil inlet of the upper jacket 14 is located at its top and the outlet at its bottom. The heat transfer oil inlet of the middle jacket 15 is located in the middle of its side wall, and the outlet is symmetrically located in the middle of the other side. The heat transfer oil inlet of the lower jacket 16 is located at its bottom and the outlet at its top. The heat transfer oil is spirally guided into each jacket through the spiral guide ribs. The heat transfer oil is used as a heating medium to heat the jackets. The three jackets are isolated from each other and connected to the temperature control system through an independent heat transfer oil circulation loop. This is also existing technology and is briefly described here.

[0025] The in-situ esterification module is integrated inside the main reactor 1, including an annular distributor 17 fixed to the inner side of the top of the main reactor 1 and a microporous ceramic membrane assembly embedded in the bottom wall of the main reactor 1. The annular distributor 17 is a hollow ring structure with an inner diameter 0.6 times the inner diameter of the main reactor 1. It has 24 nozzles 18 with a diameter of 1.2 mm evenly distributed at its bottom. The annular distributor 17 is connected to an external acid catalyst storage tank through a pipe. The acid liquid, as a catalyst, enters the annular distributor 17 through the acid catalyst storage tank and is then atomized and sprayed out through the nozzles 18. The in-situ esterification module adopts an upper and lower coordinated structure of the top annular distributor 17 and the bottom microporous ceramic membrane assembly. The catalyst atomization distribution and membrane catalytic esterification are carried out simultaneously, avoiding the loss of intermediate products and increased energy consumption caused by the step-by-step operation of depolymerization and esterification in traditional processes.

[0026] The microporous ceramic membrane module comprises three concentric rings: an inner ring microporous ceramic membrane 19, a middle ring microporous ceramic membrane 20, and an outer ring microporous ceramic membrane 21. The multi-layered concentric ring design of the microporous ceramic membrane expands the effective reaction area, while the catalyst supported by the zirconia packing provides additional active sites. The microporous ceramic membrane is centrally connected to the esterification reaction, serving as a core material for efficient separation and process intensification. Embedded in different stages of the esterification reaction, it solves problems such as low separation efficiency, difficult catalyst recovery, and poor product purity in traditional esterification processes. The inner ring microporous ceramic membrane 19, the middle ring... The microporous ceramic membrane 20 and the outer ring microporous ceramic membrane 21 are fixedly stacked from top to bottom. Each membrane is 5 mm thick and has a pore size of 0.2 μm. The diameter of the outer ring microporous ceramic membrane 21 is equal to the inner diameter of the main reactor 1. The diameter of the middle ring microporous ceramic membrane 20 is 0.7 times the diameter of the outer ring microporous ceramic membrane 20. The diameter of the inner ring microporous ceramic membrane 19 is 0.4 times the diameter of the outer ring microporous ceramic membrane 21. A stainless steel support ring 22 is fixedly connected to the bottom of the outer ring microporous ceramic membrane 21. The stainless steel support ring 22 is fixed to the bottom wall of the main reactor 1 and has a height of 8 mm.

[0027] A product separation unit is installed on one side of the main reactor 1. This unit includes a vapor-phase condenser 23, a liquid-phase settling tank 24, and a vacuum distillation column 25. A reboiler 31 is connected to the bottom of the vacuum distillation column 25. The vapor-phase condenser 23 is connected to the top of the main reactor 1 via a vapor-phase outlet pipe. Vapor generated during the depolymerization-esterification reaction in the main reactor 1 enters the vapor-phase condenser 23 through the vapor-phase outlet pipe for condensation and collection. The vapor-phase outlet pipe is equipped with a temperature sensor and a pressure transmitter to control the temperature and pressure of the vapor entering the vapor-phase condenser 23. A liquid-phase outlet pipe 26 is connected to the bottom of the liquid-phase settling tank 24 and is connected to a reflux pipe 5. After the reaction in the main reactor 1, the liquid enters the liquid phase outlet pipe 26 through the reflux pipe 5, and then enters the liquid phase settling tank 24 for settling. A three-way switching valve 27 is connected to the liquid phase outlet pipe 26. One branch of the three-way switching valve 27 is connected to the vacuum distillation tower 25. By switching the three-way switching valve 27, when the liquid in the main reactor 1 enters the liquid phase settling tank 24, the three-way switching valve 27 closes the valve port with the same port as the reflux pipe 5 and opens the other valve port, so that the liquid in the liquid phase settling tank 24 enters the vacuum distillation tower 25 for distillation. The vacuum distillation tower 25 is a packed tower structure, and the vacuum distillation tower 25 is filled with stainless steel θ ring packing to accelerate the distillation efficiency.

[0028] The heat transfer oil circulation loops of the upper jacket 14, middle jacket 15, and lower jacket 16 are each equipped with independent flow regulating valves and temperature controllers. The set temperatures of the upper jacket 14, middle jacket 15, and lower jacket 16 are 180℃, 210℃, and 230℃, respectively. The upper jacket 14, middle jacket 15, and lower jacket 16 on the main reactor 1 are set with a three-way heating system (essentially segmented temperature control) from top to bottom, with a temperature gradient from high to low, to precisely heat the three liquid level layers of ethylene glycol, 1,4-cyclohexanediol, and propylene glycol. The core purpose is to adapt to the differences in phase, concentration, and reaction rate of the materials in the main reactor 1. Through the structural cooperation of the multi-stage alcohol feeding system and the gradient temperature control jacket assembly, different alcohols are heated in specific temperature zones. By contacting the corresponding ester bonds, the system solves the problem of incomplete depolymerization of asymmetric ester bonds in PETG caused by steric hindrance and nucleophilicity differences. The multi-stage alcohol feeding system enables ethylene glycol to selectively break standard ester bonds in the upper low-temperature zone, 1,4-cyclohexanediethanol to efficiently attack CHDM-related ester bonds in the middle suitable temperature zone, and propylene glycol to remove residual structures in the lower high-temperature zone, forming a three-dimensional matching mechanism of space-temperature-reagent. By introducing multiple alcohol reagents to work synergistically in a gradient manner, the system accurately matches the breaking requirements of different types of ester bonds in PETG molecules and couples the depolymerization and esterification processes in situ, achieving efficient, low-consumption, and high-value closed-loop recycling. This effectively overcomes the shortcomings of existing technologies in processing PETG, such as incomplete depolymerization, complex products, and cumbersome processes.

[0029] The nozzles 18 of the annular distributor 17 are staggered along the circumference, with a central angle of 15° between adjacent nozzles 18, and the axis of the nozzles 18 is deflected outward at 10° radially relative to the annular distributor 17, which facilitates spraying over a larger area.

[0030] A 2mm gap is left between the inner ring microporous ceramic membrane 19, the middle ring microporous ceramic membrane 20 and the outer ring microporous ceramic membrane 21. The gap is filled with zirconia spherical packing with a particle size of 1mm. The surface of the packing is loaded with tetrabutyl titanate catalyst. The catalyst loaded on the zirconia packing provides additional active sites.

[0031] The liquid settling tank 24 has three layers of baffles 28 inside, with a vertical spacing of 20cm between the baffles 28. The core function of the multi-layer baffles 28 inside the liquid settling tank 24 is to optimize the fluid flow pattern, enhance the solid-liquid / liquid-liquid separation effect, improve the settling efficiency, and avoid problems such as short-circuit flow and dead zones, ensuring the stability of the process in each area of ​​the tank. Each baffle 28 has a 5cm diameter through hole 29 in the center, through which the liquid falls to the bottom of the liquid settling tank 24. A magnetic stirrer 30 is installed below the bottom baffle 28. The core function of the magnetic stirrer 30 is to use a magnetic field to drive the stir bar to rotate, so as to achieve uniform mixing, dissolution, or temperature and material homogenization of the liquid material reaction system.

[0032] This invention is simple to operate, convenient to use, and suitable for widespread promotion and application. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG, comprising a main reactor (1), the main reactor (1) being a vertical cylindrical structure, a sealing cover (2) fixedly connected to the top of the main reactor (1), a plurality of feeding ports (3) connected to the sealing cover (2), a liquid collection chamber (4) connected to the bottom of the main reactor (1), a reflux pipe (5) connected to the bottom of the liquid collection chamber (4), and a one-way valve (6) provided on the reflux pipe (5), characterized in that, A multi-stage alcohol feeding system is provided on one side of the main reactor (1), a gradient temperature control jacket assembly is provided on the other side of the main reactor (1), and an in-situ esterification module is provided inside the main reactor (1).

2. The polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG according to claim 1, characterized in that, The multi-stage alcohol feeding system includes a first alcohol storage tank (7), a second alcohol storage tank (8), and a third alcohol storage tank (9) located on one side of the main reactor (1). Each of the first alcohol storage tank (7), the second alcohol storage tank (8), and the third alcohol storage tank (9) is equipped with a feeding assembly. The feeding assembly includes a feeding pipe (10) connected to the first alcohol storage tank (7), the second alcohol storage tank (8), and the third alcohol storage tank (9), respectively. A metering pump (11) is connected to the feeding pipe (10), and a feed inlet (12) is fitted onto the feeding pipe (10). The feed inlet (12) is fixedly connected to the outer wall of the main reactor (1). The main reactor (1) is equipped with an L-shaped guide pipe (13), which is welded to the feed inlet (12). The outlet of the L-shaped guide pipe (13) faces the central axis of the main reactor (1) and is inclined downward at 30° with the horizontal plane. The feed inlet (12) on the first alcohol storage tank (7) is located 15cm above the initial height of the liquid level in the main reactor (1). The feed inlet (12) on the second alcohol storage tank (8) is located 5cm below the initial liquid level. The feed inlet (12) on the third alcohol storage tank (9) is located 8cm above the bottom of the main reactor (1).

3. The polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG according to claim 2, characterized in that, The gradient temperature control jacket assembly includes an upper jacket (14), a middle jacket (15), and a lower jacket (16) fixed from top to bottom on the outer wall of the main reactor (1). The upper jacket (14) covers the area from the top of the main reactor (1) to 10cm above the initial height of the liquid surface. The middle jacket (15) covers the area 10cm above and below the initial height of the liquid surface. The lower jacket (16) covers the area from the bottom of the main reactor (1) to 10cm below the initial height of the liquid surface. The inner wall of each jacket is provided with a spiral guide rib with a rib height of 2mm and a pitch of 50mm. The heat transfer oil inlet of the upper jacket (14) is located at its top and the outlet is located at its bottom. The heat transfer oil inlet of the middle jacket (15) is located in the middle of its side wall, and the outlet is symmetrically arranged in the middle of the other side; the heat transfer oil inlet of the lower jacket (16) is located at its bottom, and the outlet is located at its top.

4. The polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG according to claim 3, characterized in that, The in-situ esterification module is integrated inside the main reactor (1), including an annular distributor (17) fixed to the inner side of the top of the main reactor (1) and a microporous ceramic membrane assembly embedded in the bottom wall of the main reactor (1). The annular distributor (17) is a hollow ring structure with an inner diameter of 0.6 times the inner diameter of the main reactor (1). It has 24 spray holes (18) with a diameter of 1.2 mm evenly opened at its bottom.

5. The polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG according to claim 4, characterized in that, The microporous ceramic membrane assembly includes three concentric ring-shaped inner ring microporous ceramic membranes (19), middle ring microporous ceramic membranes (20), and outer ring microporous ceramic membranes (21). The inner ring microporous ceramic membrane (19), middle ring microporous ceramic membrane (20), and outer ring microporous ceramic membrane (21) are fixedly stacked from top to bottom. Each membrane is 5 mm thick and has a pore size of 0.2 μm. The diameter of the outer ring microporous ceramic membrane (21) is equal to the inner diameter of the main reactor (1). The diameter of the middle ring microporous ceramic membrane (20) is 0.7 times the diameter of the outer ring microporous ceramic membrane (20). The diameter of the inner ring microporous ceramic membrane (19) is 0.4 times the diameter of the outer ring microporous ceramic membrane (21). A stainless steel support ring (22) is fixedly connected to the bottom of the outer ring microporous ceramic membrane (21). The stainless steel support ring (22) is fixed to the bottom wall of the main reactor (1). The height of the stainless steel support ring (22) is 8 mm.

6. The polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG according to claim 1, characterized in that, A product separation unit is provided on one side of the main reactor (1). The product separation unit includes a gas phase condenser (23), a liquid phase settling tank (24), and a vacuum distillation tower (25). A reboiler (31) is connected to the bottom of the vacuum distillation tower (25). The gas phase condenser (23) is connected to the top of the main reactor (1) through a gas phase outlet pipe. A temperature sensor and a pressure transmitter are built into the gas phase outlet pipe. A liquid phase outlet pipe (26) is connected to the bottom of the liquid phase settling tank (24). The liquid phase outlet pipe (26) is connected to the reflux pipe (5). A three-way switching valve (27) is connected to the liquid phase outlet pipe (26). One branch of the three-way switching valve (27) is connected to the vacuum distillation tower (25). The vacuum distillation tower (25) is a packed tower structure. The vacuum distillation tower (25) is filled with stainless steel θ ring packing.

7. The polyol gradient synergistic depolymerization-esterification coupled reaction device for chemical recovery of PETG according to claim 1, characterized in that, The heat transfer oil circulation loops of the upper jacket (14), middle jacket (15) and lower jacket (16) are equipped with independent flow regulating valves and temperature controllers, and the set temperatures of the upper jacket (14), middle jacket (15) and lower jacket (16) are 180℃, 210℃ and 230℃, respectively.

8. The polyol gradient synergistic depolymerization-esterification coupled reaction apparatus for chemical recovery of PETG according to claim 5, characterized in that, The nozzles (18) of the annular distributor (17) are staggered along the circumference, with a central angle of 15° between adjacent nozzles (18), and the axis of the nozzles (18) is deflected outward at 10° from the radial direction of the annular distributor (17).

9. The polyol gradient synergistic depolymerization-esterification coupled reaction apparatus for chemical recovery of PETG according to claim 5, characterized in that, A 2mm gap is left between the inner ring microporous ceramic membrane (19), the middle ring microporous ceramic membrane (20) and the outer ring microporous ceramic membrane (21). The gap is filled with zirconia spherical fillers with a particle size of 1mm, and the surface of the fillers is loaded with tetrabutyl titanate catalyst.

10. The polyol gradient synergistic depolymerization-esterification coupled reaction apparatus for chemical recovery of PETG according to claim 6, characterized in that, The liquid phase sedimentation tank (24) is equipped with three layers of partitions (28), with a vertical spacing of 20cm between the partitions (28). Each partition (28) has a through hole (29) with a diameter of 5cm in the center, and a magnetic stirrer (30) is provided below the bottom partition (28).

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