A device and method for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL

Abstract

The present invention belongs to the technical field of polymer material depolymerization, and particularly relates to a device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL and a depolymerization method based thereon. The device of the present invention comprises a kettle cover and a kettle body, an insulation layer is provided between the kettle cover and the kettle body, the insulation layer is provided with holes running through it from top to bottom, and an insulation layer water inlet and an insulation layer water outlet are provided on the outside of the insulation layer; the kettle cover is provided with a feed port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet, and the inside of the kettle cover is connected with a stirring paddle that passes through the insulation layer and extends into the kettle body; a baffle is embedded in the inside of the kettle body, a discharge port is provided at the bottom of the kettle body, and the outside of the kettle body is connected to an oil heating jacket. The device of the present invention aims at the characteristics of the PCL depolymerization reaction, and by providing an insulation layer and combining with precise temperature control and other designs, it can achieve efficient depolymerization of PCL to obtain high-yield, high-purity ε-CL (99.9%), which can be directly repolymerized to achieve complete conversion to obtain regenerated PCL with excellent mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material depolymerization, and particularly relates to a device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL and a depolymerization method based thereon. Background Art

[0002] Polycaprolactone (PCL) is an organic polymer formed by the ring-opening polymerization of ε-caprolactone (ε-CL) using a metal-organic catalyst as an initiator. It is a polymeric polyester with excellent biocompatibility and biodegradability, making it widely used in tissue engineering and medical applications. As demand for PCL increases, so does the market demand for the raw material ε-CL. However, during the production process of ε-caprolactone, high temperatures cause the prepared ε-caprolactone monomer to rapidly undergo ring-opening polymerization, producing low-molecular-weight polycaprolactone. This polycaprolactone is unsuitable for practical applications and must be discarded, significantly increasing production costs and wasting resources. Furthermore, due to domestic production capacity being insufficient to meet market demand, ε-caprolactone currently relies primarily on imports. Its high price limits the large-scale application of PCL. Recycling and depolymerizing this low-molecular-weight polycaprolactone and post-consumer waste polycaprolactone into ε-caprolactone monomer would enable the high-value utilization of polycaprolactone.

[0003] Currently, there are no dedicated depolymerization devices for PCL. When depolymerizing PCL using conventional reactors, the presence of the aforementioned ε-caprolactone monomer readily undergoes ring-opening polymerization at high temperatures to form low-molecular-weight polycaprolactones, such as dimers and trimers. This not only causes the deposition of these oligomers in pipelines but also significantly affects the purity of the target product, ε-caprolactone. This is why many publications report that ε-caprolactone obtained from PCL depolymerization contains byproducts such as dimers and trimers.

[0004] Therefore, it is necessary to design a dedicated, efficient depolymerization device and depolymerization method for recovering high-purity ε-CL based on the characteristics of PCL. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL.

[0006] The device of the present invention can significantly improve the depolymerization efficiency of polycaprolactone, the yield and purity of ε-caprolactone in the product, thereby realizing high-value application of polycaprolactone.

[0007] Another object of the present invention is to provide application of the above device in polyester depolymerization.

[0008] Another object of the present invention is to provide a method for depolymerizing polycaprolactone based on the above device.

[0009] The method of the present invention achieves efficient depolymerization of PCL. The resulting product, ε-CL, has high yield, high purity, and excellent reactivity. This product can be directly repolymerized to give PCL, reintroducing it into the PCL production cycle in a simple, effective, and inexpensive manner, even on an industrial scale. This achieves a closed-loop cycle of PCL from polymer to monomer to polymer.

[0010] The purpose of the present invention is achieved through the following solutions:

[0011] A device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL comprises a kettle cover and a kettle body, wherein a heat insulation layer is provided between the kettle cover and the kettle body, the heat insulation layer is provided with holes running through it from top to bottom, and a heat insulation layer water inlet and a heat insulation layer water outlet are provided on the outside of the heat insulation layer; the kettle cover is provided with a feed port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet, and the inside of the kettle cover is connected to a stirring paddle that passes through the heat insulation layer and extends into the kettle body; a baffle is embedded in the inside of the kettle body, a discharge port is provided at the bottom of the kettle body, and the outside of the kettle body is connected to an oil heating jacket.

[0012] In the device of the present invention, when the depolymerization product gas enters the kettle cover from the kettle body through the holes provided in the insulation layer, the gas temperature is adjusted by the insulation layer. By controlling the temperature of the insulation layer, the temperature of the product gas can be controlled, so that the product gas will neither condense and flow back to the reactor, nor react rapidly to generate by-products such as oligomers due to the high temperature, thereby significantly improving the depolymerization efficiency of PCL and the yield and purity of the target product ε-CL.

[0013] In the device of the present invention, before the depolymerization product gas is removed from the gas outlet through the kettle cover, the gas temperature is again adjusted by the kettle cover temperature, which can ensure that the product gas temperature gradually decreases, thereby reducing the generation of by-products and preventing condensation and reflux.

[0014] It is known that the temperature control of the heat insulation layer or the kettle cover can be achieved by conventional methods, such as by introducing a circulating cooling medium to achieve temperature control, such as introducing water flow to control the temperature.

[0015] Furthermore, the kettle cover and the insulation layer are each provided with circulating coolant for temperature control via a circulating refrigeration machine; the circulating refrigeration machine adjusts the refrigeration temperature by measuring the temperature of the water at the water outlet. Furthermore, the cooling medium of the coolant can be at least one of a saline solution, ethanol, ethylene glycol, and glycerol.

[0016] Furthermore, the temperature of the thermal insulation layer and the kettle cover can be controlled by various known methods.

[0017] If the insulation layer is provided with a pipe, the pipe connects the water inlet of the insulation layer with the water outlet of the insulation layer. By adopting the above technical solution, the temperature of the insulation layer can be controlled by passing the cooling medium into the pipe, thereby achieving temperature control of the product gas.

[0018] Alternatively, the insulation layer is a hollow structure, with the cavity connecting the insulation layer water inlet and the insulation layer water outlet. By adopting the above technical solution, the temperature of the insulation layer can be controlled by passing a cooling medium into the cavity, thereby achieving temperature control of the product gas.

[0019] For example, a pipe is provided on the inner wall of the kettle cover, connecting the water inlet and the water outlet of the kettle cover. By adopting the above technical solution, the temperature of the kettle cover can be controlled by passing a cooling medium into the pipe, thereby achieving temperature control of the product gas.

[0020] Alternatively, the kettle cover is a hollow structure, with the cavity connecting the kettle cover water inlet and the kettle cover water outlet. By adopting the above technical solution, the temperature of the kettle cover can be controlled by introducing a cooling medium into the kettle cover, thereby achieving temperature control of the product gas.

[0021] Furthermore, the diameter of the holes in the insulation layer can be 10 mm to 50 mm ± 5 mm, preferably 10 mm to 20 mm ± 5 mm. The number of holes can be greater than 100. Using a large number of smaller-diameter holes can increase the contact time between the product gas and the insulation layer, achieving better temperature control.

[0022] Furthermore, the material of the kettle body, kettle cover and stirring paddle base is preferably 316L.

[0023] Furthermore, the materials of the inner wall of the kettle body and kettle cover, the outer lining of the stirring paddle and the heat insulation layer are preferably polytetrafluoroethylene.

[0024] Furthermore, the baffles are longitudinally distributed on the inner side of the kettle. By adopting the above technical solution, the agitator paddles cooperate with the baffles on the inner wall of the kettle to generate a strong upward and downward circulation flow in the kettle, bringing stronger shear force and mixing efficiency, thereby increasing the contact area between polycaprolactone and the catalyst, and improving the depolymerization efficiency and degree.

[0025] Furthermore, there is one or more baffles; more preferably, there are six baffles distributed longitudinally on the inner wall of the kettle.

[0026] Furthermore, the baffle may be made of polytetrafluoroethylene.

[0027] Furthermore, the size of the baffle is preferably 40×10×4 unit lengths, and is vertically distributed on the inner wall of the kettle.

[0028] Furthermore, there is at least one or more material openings; preferably, one large material opening and one small material opening.

[0029] Furthermore, the gas outlet is connected to a condenser via an external pipe. The product gas generated by depolymerization is removed through the gas outlet and can be recovered to obtain the product after cooling.

[0030] Furthermore, the external pipe is wrapped with a thermal insulation sleeve.

[0031] Furthermore, the insulation jacket contains a thermocouple and circulating fluid. The circulating fluid medium can be selected from at least one of a saline solution, ethanol, ethylene glycol, and glycerol. By employing this technical solution, the insulation jacket wraps around the external piping to insulate the temperature, which can be set to, for example, 50-70°C. This prevents ε-caprolactone in the piping from clogging the piping or condensing back into the kettle when the temperature is too low, and also prevents ε-caprolactone from repolymerizing at excessively high temperatures, forming byproducts such as dimers and trimers.

[0032] Furthermore, the condenser is connected to a vacuum port and a collection tank respectively. By using a vacuum pump or the like to extract gas from the vacuum port, the product gas can be led out of the device, thereby accelerating the evaporation of the product gas and achieving separation.

[0033] Furthermore, the condenser is preferably connected to a molecular sieve and then to a vacuum port and a collection tank, respectively. The addition of a molecular sieve can effectively adsorb by-products, thereby improving the purity of the target product, ε-caprolactone.

[0034] Furthermore, the vacuum port is connected to a high-precision vacuum regulating valve, which can precisely control the vacuum degree.

[0035] Furthermore, the collection tank is used to collect the condensed product.

[0036] Furthermore, the cooling medium of the condenser can be selected from at least one of a saline solution, ethanol, ethylene glycol, and glycerol; and the cooling temperature can be adjusted to achieve a controllable range of -20°C to 35°C. Specifically, the temperature of the cooling medium of the condenser is preferably controlled to be -5°C to 5°C. The condenser is used to condense the product gas into a liquid for recovery.

[0037] Furthermore, the condenser can be composed of a spherical condenser and a serpentine condenser. The product gas passes through the spherical condenser and the serpentine condenser sequentially during evaporation. Although the serpentine condenser has a longer cooling path, it is prone to clogging, especially since byproducts such as oligomers become solid and lack fluidity after cooling. By adopting the above technical solution, combining the spherical condenser with the serpentine condenser, a longer cooling path can be ensured while preventing byproduct clogging in the serpentine condenser.

[0038] Furthermore, the discharge port is connected to a discharge ball valve via a discharge pipe. By adopting the above technical solution, the discharge of the remaining material after the reaction is controlled by the ball valve.

[0039] Furthermore, the stirring paddle is driven by an external motor.

[0040] Furthermore, the stirring blade can be connected to the external motor drive by a magnetic coupling. By adopting the above technical solution, due to its contactless torque transmission, the dynamic seal is replaced by a static seal, which can improve the sealing performance of the device.

[0041] Furthermore, the stirring paddle is a turbine stirring paddle, specifically one of a flat turbine stirring paddle, a butterfly turbine stirring paddle, or a folding blade turbine stirring paddle, and the stirring paddle rotation speed can be 50 to 500 rpm. The present invention uses a turbine stirring paddle in conjunction with a baffle on the inner wall of the kettle to generate a strong upward and downward circulation flow in the kettle, bringing stronger shear force and mixing efficiency, thereby increasing the contact area between the polycaprolactone and the catalyst, and improving the depolymerization efficiency and degree of depolymerization.

[0042] Furthermore, the diameter of the kettle body is the largest at the waist and gradually narrows towards the upper and lower sides of the waist. By adopting the above technical solution, the sealing area can be reduced and the sealing performance of the device can be improved.

[0043] Furthermore, the oil heating jacket can use dimethyl silicone oil or the like as a heating medium, and a circulating oil bath machine can provide circulating hot oil to control the temperature in the kettle.

[0044] Furthermore, double sealing rings of silicone rubber and polytetrafluoroethylene are used between the kettle cover and the heat insulation plate, and between the heat insulation and the kettle body.

[0045] Furthermore, the material of the kettle body, kettle cover and stirring paddle base is preferably 316L; the material of the inner wall of the kettle body, the inner wall of the kettle cover, the outer lining of the stirring paddle and the insulation layer is preferably polytetrafluoroethylene.

[0046] By adopting the above technical solution, the reactor can have excellent sealing performance, and both polytetrafluoroethylene and 316L stainless steel have good corrosion resistance and surface lubricity, which can extend the service life and reduce wear.

[0047] Furthermore, mechanical seals are used for connection parts such as the feed port and the vacuum port.

[0048] By adopting the above technical solution, through mechanical sealing and the interaction between rotating parts and stationary parts, the sealing performance of the device can be improved, and air leakage in pipeline connection parts such as the material inlet and vacuum port can be effectively avoided.

[0049] Furthermore, the kettle body, kettle cover, thermal insulation layer and oil heating jacket are all equipped with thermocouples for measuring temperature.

[0050] When the depolymerization product, ε-caprolactone, is distilled from the reactor, excessively high temperatures can cause it to repolymerize, forming byproducts such as dimers and trimers. This not only reduces the yield of ε-caprolactone but can also clog the vacuum line. Excessively low temperatures can cause ε-caprolactone to liquefy and reflux before entering the condenser, preventing it from leaving the reactor in time and reducing the efficiency of the depolymerization reaction. Therefore, controlling the product airflow temperature is crucial for the entire depolymerization process.

[0051] The device of the present invention, by providing an insulation layer and other designs, combined with a unique vacuum control system and cooling system, precisely controls the temperature of the kettle cover, insulation layer, insulation jacket, and condenser. For example, when the coolant temperature is adjusted so that the insulation layer temperature is 70°C and the kettle cover temperature is 60°C, the temperature of the product ε-caprolactone after passing through the insulation layer and kettle cover will be controlled at 60-70°C. At this temperature, ε-caprolactone will neither condense and reflux into the reactor nor generate byproducts such as oligomers, which can significantly improve the depolymerization efficiency of ε-caprolactone. The device of the present invention can significantly improve the depolymerization efficiency of polycaprolactone and the yield of ε-caprolactone monomer, reduce byproducts such as dimers and trimers, and obtain efficient depolymerization of polycaprolactone and high-yield, high-purity ε-caprolactone monomer, thereby achieving the chemical recycling recovery and efficient utilization of PCL.

[0052] The present invention also provides application of the device in polyester depolymerization.

[0053] The present invention also provides a polycaprolactone depolymerization method based on the above-mentioned device, comprising the following steps: adding materials such as polycaprolactone and a catalyst into a kettle body and sealing the device; respectively introducing a coolant into the insulation layer and the kettle cover, and controlling the temperature of the insulation layer and the kettle cover to a specified value by adjusting the temperature of the coolant; heating the kettle body to the polycaprolactone depolymerization temperature using an oil heating jacket; turning on a stirring paddle to start the reaction; and evacuating the system during the reaction to quickly remove the depolymerization product gas from the device, and recovering the depolymerization product through cooling.

[0054] Furthermore, the depolymerization temperature may be 160-250°C.

[0055] Furthermore, the temperature of the coolant entering the heat insulation layer is preferably controlled to be 60-80°C.

[0056] Furthermore, the temperature of the cooling liquid introduced into the kettle cover is preferably controlled to be 50-70°C.

[0057] Furthermore, the depolymerization gas is extracted from the device and then cooled and recovered through a condenser.

[0058] Furthermore, the temperature of the cooling liquid introduced into the condenser is preferably controlled to be -5 to 5°C.

[0059] Furthermore, the condenser is connected to a molecular sieve; the depolymerization gas is cooled by the condenser and then passes through the molecular sieve, where by-products such as oligomers are adsorbed by the molecular sieve, thereby obtaining the target product ε-CL with better purity.

[0060] Furthermore, during vacuuming, the pressure can be adjusted to 10 Pa-101 kPa, more preferably 10 kPa-20 kPa, by a high-precision vacuum regulating valve.

[0061] Furthermore, the number average molecular weight of the polycaprolactone may be 8,000-100,000.

[0062] Furthermore, the cooling medium of the kettle cover, the insulation layer, and the condenser is selected from at least one of a saline solution, ethanol, ethylene glycol, and glycerol.

[0063] Furthermore, the oil heating jacket uses dimethyl silicone oil as the heating medium.

[0064] The apparatus and method of the present invention efficiently depolymerizes PCL and produces high-yield, high-purity ε-CL (up to 99.9%). During the depolymerization process, the product gas passes through a cooling system within the insulation layer, where its temperature is regulated. This prevents the product gas from condensing and refluxing back into the reactor, nor does it react rapidly to form oligomers such as dimers and trimers due to the high temperature. Furthermore, the gas temperature is further regulated by the temperature of the reactor lid, ensuring a gradual decrease in the product gas temperature, significantly reducing the production of byproducts while preventing condensation and reflux. Furthermore, a molecular sieve connected to the condenser effectively adsorbs and removes byproducts, resulting in high-yield, high-purity ε-CL. The ε-CL recovered from depolymerization exhibits excellent reactivity and can be directly repolymerized to produce PCL with a conversion rate of up to 99.9%. This simple, efficient, and inexpensive method allows for reintroduction into the PCL production cycle, achieving a closed-loop "polymer-monomer-polymer" cycle for PCL on an industrial scale.

[0065] The present invention has the following originality in the prior art:

[0066] (1) The device of the present invention is based on the characteristics of the PCL depolymerization reaction. By setting a heat insulation layer and combining it with precise temperature control, it effectively solves the problems of low depolymerization efficiency, large number of by-products and low purity of the target product ε-CL in the existing PCL depolymerization process. The ε-CL monomer with a high purity of up to 99.9% can be recovered. The recovered ε-CL has high reaction activity and can be directly repolymerized to obtain PCL with a conversion rate of up to 99.9%. The obtained regenerated PCL has excellent performance and a tensile strength of up to 30.7 MPa, which is 77.3% of the tensile strength of polycaprolactone before depolymerization.

[0067] (2) The device of the present invention features a unique agitator and baffle structure, which achieves efficient mixing of PCL and catalyst, increases the reaction interface, and improves the efficiency of catalytic depolymerization. The agitator is a turbine agitator, which, in conjunction with multiple baffles, generates a strong upward and downward circulation flow within the reactor, resulting in stronger shear force and mixing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0069] Figure 1-Figure 3 Schematic diagram of the structure of the device of the present invention.

[0070] Figure 4 This is a schematic top-sectional view of one implementation of the thermal insulation layer of the device of the present invention.

[0071] Figure 5 This is a schematic top-sectional view of one implementation of the thermal insulation layer of the device of the present invention.

[0072] Figure 6 These are the NMR data of the liquid product ε-CL and pure ε-CL obtained by depolymerization using the device of the present invention.

[0073] In the figure: 1. Kettle body; 2. Oil heating jacket; 3. Discharge port; 301. Discharge pipe; 4. Insulation layer; 41. Insulation layer water inlet; 42. Insulation layer water outlet; 5. Kettle cover; 6. Kettle cover water inlet; 7. Large material port; 8. Small material port; 9. Kettle cover water outlet; 10. Gas outlet; 1001. External pipeline; 1002. Insulation jacket; 11. Condenser; 1101. Spherical condenser; 1102. Serpentine condenser; 12. Molecular sieve; 13. Vacuum port; 14. Collection tank; 15. Baffle; 16. Agitator; 17. High-precision vacuum regulating valve; 18. Discharge ball valve. DETAILED DESCRIPTION

[0074] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the materials involved in the following examples can be obtained from commercial channels. The methods described are conventional methods unless otherwise specified.

[0075] Example 1: A device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL

[0076] A device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL, such as Figure 1-Figure 4As shown, it includes a kettle cover and a kettle body, wherein an insulation layer is provided between the kettle cover and the kettle body, the insulation layer is provided with holes running through it from top to bottom, and an insulation layer water inlet and an insulation layer water outlet are provided on the outside of the insulation layer; the kettle cover is provided with a material port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet, and the inside of the kettle cover is connected to a stirring paddle that passes through the insulation layer and extends into the kettle body; a plurality of baffles are embedded in the inside of the kettle body, a discharge port is provided at the lower part of the kettle body, and the outside of the kettle body is connected to the oil heating jacket.

[0077] The inner wall of the kettle cover is provided with a pipe connecting the water inlet and outlet of the kettle cover. The insulation layer is also provided with a pipe connecting the water inlet and outlet of the insulation layer. The kettle cover and insulation layer are each provided with circulating coolant for temperature control via a circulating chiller. The circulating chiller adjusts the cooling temperature by measuring the temperature of the water at the outlet.

[0078] The diameter of the holes in the insulation layer can be 10mm-50mm±5mm, preferably 10mm-20mm±5mm. The number of holes can be more than 100. Six baffles are distributed longitudinally on the inner wall of the kettle. The gas outlet is connected to the condenser via an external pipe. The external pipe is wrapped with an insulation jacket. The insulation jacket is equipped with a thermocouple and circulating fluid. The condenser is preferably connected to a molecular sieve and then to a vacuum port and a collection tank. Extraction from the vacuum port using a vacuum pump or the like can be achieved to remove the product gas from the device, accelerate its evaporation, and achieve separation. The vacuum port is connected to a high-precision vacuum regulating valve. The collection tank is used to collect the condensed product. The condenser consists of a spherical condenser and a serpentine condenser. During evaporation, the product gas passes through the spherical condenser and the serpentine condenser in sequence. The discharge port is connected to a discharge ball valve via a discharge pipe. The ball valve controls the discharge of residual material after the reaction. The stirring paddle is a turbine paddle with a rotational speed of 50-500 rpm. A magnetic coupling is used to connect the stirring paddle to the external motor drive. Thermocouples are installed in the kettle body, lid, insulation layer, and oil heating jacket for temperature measurement.

[0079] The oil heating jacket can use dimethyl silicone oil or other media as the heating medium, with a circulating oil bath providing circulating hot oil to control the temperature within the reactor. The coolant and circulating fluid, whether the same or different, can be selected from at least one of a saline solution, ethanol, ethylene glycol, and glycerol. Furthermore, the condenser cooling medium can be ethylene glycol.

[0080] Example 2:

[0081] On the basis of the above embodiment 1, another temperature control method is achieved by changing the kettle cover.

[0082] In the above embodiment, the kettle cover is an internal hollow structure, and the cavity is connected with the water inlet and the water outlet of the kettle cover to achieve temperature control.

[0083] Example 3:

[0084] On the basis of the above-mentioned embodiment 1, another temperature control method is achieved by changing the heat insulation board.

[0085] See Figure 5 In the above embodiment, the insulation layer is provided with a condensation pipe, and the condensation pipe is connected with the water inlet and the water outlet of the insulation layer to achieve temperature control.

[0086] Example 4:

[0087] On the basis of the above-mentioned embodiment 3, another temperature control method is achieved by changing the kettle cover.

[0088] In the above embodiment, the kettle cover is an internal hollow structure, and the cavity is connected with the water inlet and the water outlet of the kettle cover to achieve temperature control.

[0089] Based on the above device, weighed polycaprolactone, catalyst and other materials are added to the kettle body, and the device is sealed; dimethyl silicone oil is provided as circulating hot oil into the oil heating jacket through a circulating oil bath machine to heat the kettle body to a specified temperature; the temperature of the reactor is continuously increased to the depolymerization temperature of polycaprolactone; a circulating refrigerator introduces coolant into the kettle cover and the insulation layer through a water inlet and a water inlet, respectively, and introduces coolant into the insulation jacket and the condenser, respectively, to precisely control the temperatures of the kettle cover, the insulation layer, the insulation jacket and the condenser; vacuum is drawn through a vacuum port to reduce the pressure in the reactor to a specified value, and the pressure can be adjusted by a high-precision vacuum regulating valve; the stirring paddle is turned on to start the reaction; the depolymerization product is removed from the reaction device after vacuuming and recovered after cooling.

[0090] When the depolymerization product gas enters the kettle cover from the kettle body through the holes (10mm±5mm) provided in the insulation layer, the gas temperature is adjusted by the insulation layer, so that the product gas will neither condense and reflux into the reactor, nor react rapidly to generate oligomers and other by-products due to the high temperature, thereby significantly improving the depolymerization efficiency of PCL and the yield and purity of the target product ε-CL; before the depolymerization product gas is removed from the gas outlet through the kettle cover, the gas temperature is again adjusted by the kettle cover temperature, which can ensure that the product gas temperature gradually decreases, which can greatly reduce the generation of by-products and prevent condensation and reflux.

[0091] For example, when the temperature of the coolant is adjusted so that the temperature of the insulation layer is 60-80°C and the temperature of the kettle cover is 50-70°C, the temperature of the product ε-caprolactone will be controlled at 60-70°C after it passes through the insulation layer and the kettle cover and is removed from the reaction device. At this temperature, ε-caprolactone will neither condense and reflux into the reactor, nor generate by-products such as oligomers, which can significantly improve the depolymerization efficiency of ε-caprolactone. The combination of a spherical condenser and a serpentine condenser can avoid clogging of by-products in the serpentine condenser while ensuring a longer cooling path. The molecular sieve connected to the tail of the condenser can effectively adsorb by-products.

[0092] Example 5: Polycaprolactone depolymerization method based on device

[0093] A polycaprolactone depolymerization method based on the above-mentioned device comprises the following steps: adding polycaprolactone with a number average molecular weight of 8,000-100,000 and a catalyst into a kettle, and sealing the device; introducing a coolant into the heat insulation layer, kettle cover, insulation jacket, and condenser, respectively, and controlling the temperatures of the heat insulation layer (60-80°C), kettle cover (50-70°C), insulation jacket (50-70°C), and condenser (-5-5°C) to specified values ​​by adjusting the temperature of the coolant; heating the kettle to a polycaprolactone depolymerization temperature (160-250°C) using an oil heating jacket; starting a stirring blade (a butterfly turbine stirring blade with a rotation speed of 100 rpm) to initiate a reaction; and evacuating the system during the reaction (system pressure of 10 kPa-20 kPa) to quickly remove depolymerization product gas from the device, and recovering the depolymerization product through cooling.

[0094] The reaction was carried out with 30 parts by mass of PCL (number average molecular weight of 89,000) and 2 mol% of stannous isooctanoate (catalyst). The temperature of the insulation layer was controlled at 70°C, and the temperature of the kettle cover and the insulation jacket was controlled at 60°C. The temperature of the reactor was raised to 250°C, the pressure was reduced to 0.01 MPa by vacuum, and the reaction product was collected by condensation.

[0095] The same materials were reacted in a conventional reactor with a conventional two-blade impeller, i.e., without a heat insulation layer, a cooling system for the reactor cover, or baffles embedded in the reactor. All other experimental parameters were the same. The results are shown in Table 1.

[0096] Calculate the depolymerization efficiency and the liquid yield in the collection tank after the depolymerization reaction. The calculation formula is shown in formula (1), the liquid yield in the depolymerization product is The calculation formula is shown in formula (2).

[0097]

[0098] Among them, m0 is the input mass of PCL before depolymerization, m1 is the residual mass after depolymerization, and m2 is the mass of the liquid collected in the collection bottle (i.e., ε-CL).

[0099] As can be seen from the table, compared with using a conventional reactor and a conventional stirring paddle, the depolymerization time using the device of the present invention is shortened from 4 hours to 2.5 hours, and the depolymerization efficiency is significantly improved; the depolymerization efficiency is increased from 48.8% to 95.4%; the liquid yield in the depolymerization product is increased to 97%, and the monomer purity is 99.9%. Figure 6 The NMR data of the liquid ε-CL product and pure ε-CL obtained by depolymerization using the device of the present invention are shown in Figure 1. As can be seen from the figure, the ε-CL product obtained by depolymerization using the method of the present invention is of high purity and free of other impurities.

[0100] The ε-CL liquid recovered after depolymerization was directly used to repolymerize PCL. The reaction conditions were: the product monomer and a stannous isooctoate catalyst (0.25 mol%) were placed in a nitrogen atmosphere, reacted at 140°C for 10 hours, then heated to 220°C for 1 hour, and finally ring-opening polycondensed to obtain regenerated PCL. The results are shown in Table 1.

[0101] As shown in the table, the ε-CL obtained by depolymerization using the present method exhibits excellent reactivity. Direct polymerization under the catalytic influence of the catalyst yielded regenerated PCL with a number-average molecular weight of 81,000, a tensile strength of 30.7 MPa, and an elongation at break of 856%, respectively. Tensile properties were tested according to GB / T 1040-2006 at a rate of 500 mm / min.

[0102] Table 1

[0103] parameter Device of the present invention Comparative Example Depolymerization time (h) 2.5 4 Depolymerization efficiency (%) 95.4 48.8 Liquid yield (%) 97 87 Number average molecular weight after repolymerization 81000 30000 Tensile strength after repolymerization (MPa) 30.7 12.2 Elongation at break after repolymerization (%) 856 507

[0104] Table 2

[0105] Material Tensile strength (MPa) Elongation at break (%) Raw material PCL 39.7 1070 Regenerated PCL 30.7 856

[0106] The mechanical properties of the recycled PCL of the present invention were compared with those of raw PCL, and the results are shown in Table 2. As can be seen from Table 2, the recycled PCL obtained by the present invention has excellent properties. It has a high tensile strength of 30.7 MPa, which is 77.3% of the tensile strength of native polycaprolactone; and an elongation at break of 856%, which is 80% of the elongation at break of native polycaprolactone.

[0107] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for depolymerizing polycaprolactone based on a device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL, characterized in that The method comprises the following steps: adding polycaprolactone and a catalyst into a kettle body and sealing the device; introducing a coolant into the heat insulation layer and the kettle cover respectively, and controlling the temperature of the heat insulation layer and the kettle cover to a specified value by adjusting the temperature of the coolant; heating the kettle body to the polycaprolactone depolymerization temperature by using an oil heating jacket; starting a stirring paddle to start a reaction; evacuating the system during the reaction to allow the depolymerization product gas to be quickly removed from the device, and recovering the depolymerization product through cooling to obtain the depolymerization product; The device comprises a kettle cover and a kettle body, an insulation layer is provided between the kettle cover and the kettle body, the insulation layer is provided with holes running through it from top to bottom, and an insulation layer water inlet and an insulation layer water outlet are provided on the outside of the insulation layer; the kettle cover is provided with a material port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet, and the inside of the kettle cover is connected to a stirring paddle that penetrates the insulation layer and extends into the kettle body; a baffle is embedded in the inside of the kettle body, a discharge port is provided at the bottom of the kettle body, and the outside of the kettle body is connected to an oil heating jacket; The depolymerization temperature is 160-250°C; the temperature of the cooling liquid entering the heat insulation layer is controlled at 60-80°C; the temperature of the cooling liquid entering the kettle cover is controlled at 50-70°C.

2. The method according to claim 1, wherein: The thermal insulation layer is provided with a pipe, which connects the water inlet and the water outlet of the thermal insulation layer; or the thermal insulation layer is a hollow structure, and the cavity connects the water inlet and the water outlet of the thermal insulation layer.

3. The method according to claim 1, wherein: The inner wall of the kettle cover is provided with a pipe, which connects the water inlet of the kettle cover and the water outlet of the kettle cover; or the kettle cover is a hollow structure, and the cavity connects the water inlet of the kettle cover and the water outlet of the kettle cover.

4. The method according to claim 1, wherein: There is one or more baffles; the baffles are longitudinally distributed inside the kettle body; and the stirring paddle is a turbine stirring paddle.

5. The method according to claim 1, wherein: The gas outlet is connected to the condenser through an external pipeline; the condenser is connected to the vacuum port and the collection tank respectively; or the condenser is connected to the molecular sieve and then connected to the vacuum port and the collection tank respectively; the cooling medium of the kettle cover, the insulation layer, and the condenser is selected from at least one of saline solution, ethanol, ethylene glycol, and glycerol; the oil heating jacket uses dimethyl silicone oil as the heating medium.

6. The method according to claim 5, characterized in that: The external pipeline is wrapped with an insulation sleeve; the cooling medium of the insulation sleeve is selected from at least one of saline solution, ethanol, ethylene glycol and glycerol; the vacuum port is connected to a high-precision vacuum regulating valve.

7. The method according to claim 1, wherein: There is one or more material ports; the discharge port is connected to a discharge ball valve through a discharge pipe; and the collection tank is used to collect the condensed product.

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