Device and method for efficiently depolymerizing polycaprolactone to recover high-purity epsilon-CL

Abstract

The invention belongs to the technical field of high polymer material depolymerization, and particularly relates to a device for efficiently depolymerizing polycaprolactone to recover high-purity epsilon-CL and a depolymerization method based on the device. The device comprises a kettle cover and a kettle body, a heat insulation layer is arranged between the kettle cover and the kettle body, holes penetrating up and down are distributed in the heat insulation layer, and a heat insulation layer water inlet and a heat insulation layer water outlet are formed in the outer side of the heat insulation layer; a material opening, a kettle cover water inlet, a kettle cover water outlet and a gas outlet are formed in the kettle cover; a stirring paddle which penetrates through the heat insulation layer and extends into the kettle body is connected into the kettle cover; a baffle is embedded in the inner side of the kettle body, a discharge port is formed in the lower part of the kettle body, and the outer side of the kettle body is connected with an oil heating sleeve. According to the device disclosed by the invention, aiming at the characteristics of PCL depolymerization reaction, efficient depolymerization of PCL is realized by arranging a heat insulation layer and combining with design of precise temperature control and the like, so that epsilon-CL (99.9%) with high yield and high purity is obtained, the epsilon-CL is directly repolymerized, and complete conversion can be realized, so that regenerated PCL with excellent mechanical properties can be obtained.

Description

Technical Field

[0001] The 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, which is formed by ring-opening polymerization of ε-caprolactone (ε-CL) under the conditions of metal organic compound catalyst initiator. It belongs to polymerized polyester, has good biocompatibility and biodegradability, and is widely used in tissue engineering and medical fields. As the demand for PCL gradually increases, the market demand for the raw material monomer ε-CL also increases accordingly. However, during the preparation of ε-caprolactone, high temperature will cause the prepared ε-caprolactone monomer to rapidly open the ring to generate low molecular weight polycaprolactone. This part of polycaprolactone cannot meet practical applications and can only be discarded, resulting in a significant increase in the production cost of ε-caprolactone and a waste of resources. At the same time, since domestic production capacity is difficult to meet market demand, ε-caprolactone currently relies mainly on imports, and its expensive price limits the large-scale application of PCL. If the above-mentioned low molecular weight polycaprolactone and post-consumer waste polycaprolactone can be recovered and depolymerized into ε-caprolactone monomer raw materials, the high value utilization of polycaprolactone will be achieved.

[0003] At present, there is no depolymerization device specifically for PCL. When PCL is depolymerized using an ordinary reactor, due to the presence of the above-mentioned ε-caprolactone monomer, which is easy to undergo ring-opening polymerization at high temperature to generate low molecular weight polycaprolactone, such as dimers, trimers and other oligomers, this will not only cause the deposition of dimers, trimers and other oligomers in the pipeline, but also significantly affect the purity of the target product ε-caprolactone. This is also the reason why many literatures show that the ε-caprolactone obtained by PCL depolymerization is mixed with dimers, trimers and other by-products.

[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 the 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 can achieve efficient depolymerization of PCL, and the obtained product ε-CL has high yield, high purity and excellent reactivity, and can be directly repolymerized to obtain PCL, that is, reintroduced into the production cycle of PCL in a simple, effective and cheap way, and on an industrial scale. A closed-loop cycle of PCL from "polymer-monomer-polymer" is achieved.

[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 arranged between the kettle cover and the kettle body, the heat insulation layer is provided with holes penetrating from top to bottom, and a heat insulation layer water inlet and a heat insulation layer water outlet are arranged on the outer side of the heat insulation layer; a material port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet are arranged on the kettle cover, a stirring paddle penetrating the heat insulation layer and extending into the kettle body is connected inside the kettle cover; a baffle is embedded inside the kettle body, a discharge port is arranged at the lower part of the kettle body, and the outer side of the kettle body is connected to an oil heating sleeve.

[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. The temperature of the product gas can be controlled by controlling the temperature of the insulation layer, so that the product gas will neither condense and reflux 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 adjusted again by the kettle cover temperature, which can ensure that the product gas temperature gradually decreases, which can reduce the generation of by-products and prevent 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 a water flow to control the temperature.

[0015] Furthermore, the kettle cover and the heat insulation layer are respectively provided with circulating coolant for temperature control by a circulating refrigerator; the circulating refrigerator 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 heat insulation layer and the kettle cover can be controlled by various conventionally known methods.

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

[0018] Or the insulation layer is a hollow structure, and the cavity connects the water inlet of the insulation layer and 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 cavity, thereby achieving temperature control of the product gas.

[0019] For example, the inner wall of the kettle cover is provided with a pipeline, and the pipeline connects the water inlet of the kettle cover 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 the cooling medium into the pipeline, thereby achieving temperature control of the product gas.

[0020] Or the kettle cover is a hollow structure, and the cavity connects 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 passing the cooling medium into the kettle cover, thereby achieving temperature control of the product gas.

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

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

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

[0024] Furthermore, the baffles are longitudinally distributed on the inner side of the kettle. By adopting the above technical solution, the stirring paddle cooperates with the baffles on the inner wall of the kettle, which can generate a strong up and down circulation flow in the kettle, bring stronger shear force and mixing efficiency, thereby increasing the contact area between polycaprolactone and the catalyst, and improving the depolymerization efficiency and depolymerization degree.

[0025] Furthermore, there is one or more baffles; more preferably, there are six baffles longitudinally distributed 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, the material opening is at least one, or more than one; preferably includes a large material opening and a small material opening.

[0029] Furthermore, the gas outlet is connected to a condenser through an external pipeline. 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 sleeve is provided with a thermocouple and a circulating liquid. The circulating liquid medium can be selected from at least one of a saline solution, ethanol, ethylene glycol and glycerol. By adopting the above technical solution, the external pipe is wrapped with the insulation sleeve for insulation, and the temperature can be set to 50-70°C, which can prevent the ε-CL in the pipe from clogging the pipe or condensing back into the kettle when the temperature is too low, and prevent the ε-caprolactone at too high a temperature from repolymerizing to generate byproducts of oligomers such as dimers and trimers.

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

[0033] Furthermore, the condenser is preferably connected to the molecular sieve and then connected to the vacuum port and the collection tank respectively. Further adding the molecular sieve can effectively adsorb the by-products to improve 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 collecting 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, etc.; the cooling temperature can be adjusted to achieve a controllable change of -20 to 35°C. Specifically, the temperature of the cooling medium of the condenser is preferably controlled to be -5 to 5°C. The condenser is used to condense the product gas into liquid for recovery.

[0037] Furthermore, the condenser may be composed of a spherical condenser and a serpentine condenser. The product gas passes through the spherical condenser and the serpentine condenser in turn during the evaporation process. Although the serpentine condenser has a longer cooling path, it is very easy to get blocked, especially the by-products such as oligomers are solid after cooling and have no fluidity. By adopting the above technical solution, the spherical condenser and the serpentine condenser are combined, while ensuring a longer cooling path, the by-products can be prevented from getting blocked 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 and the external motor drive can be connected 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 blade is a turbine stirring blade, which can be a flat turbine stirring blade, a butterfly turbine stirring blade or a folding turbine stirring blade, and the stirring blade speed can be 50 to 500 rpm. The present invention uses a turbine stirring blade to cooperate with the baffle on the inner wall of the kettle, which can generate a strong up and down 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 depolymerization degree.

[0042] Furthermore, the diameter of the kettle body is the largest at the waist, and gradually narrows toward 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 material port and the vacuum port.

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

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

[0050] When the depolymerized product ε-caprolactone is distilled out of the reactor, if the temperature is too high, ε-caprolactone will repolymerize to form by-products such as dimers and trimers, which will not only reduce the yield of ε-caprolactone, but also block the vacuum pipeline; while if the temperature is too low, ε-caprolactone will liquefy and reflux before entering the condenser, and cannot leave the reactor in time, which will reduce the efficiency of the depolymerization reaction. Therefore, the control of the product gas flow temperature is particularly important for the entire depolymerization process.

[0051] The device of the present invention is designed by setting a heat insulation layer, etc., combined with a unique vacuum control system and cooling system, to accurately control the temperature of the kettle cover, heat insulation layer, insulation sleeve, and condenser. For example, when the temperature of the coolant is adjusted to make the temperature of the heat insulation layer 70°C and the temperature of the kettle cover 60°C, the temperature of the product ε-caprolactone after passing through the heat insulation layer and the kettle cover will be controlled at 60-70°C. At this temperature, ε-caprolactone will neither condense and reflux to the reactor, nor generate by-products 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 by-products such as dimers and trimers, obtain efficient depolymerization of polycaprolactone and high-yield, high-purity ε-caprolactone monomer, and achieve the purpose of chemical recycling and efficient utilization of PCL.

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

[0053] The present invention also provides a method for depolymerizing polycaprolactone 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 by 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, and by-products such as oligomers are adsorbed by the molecular sieve, so that the target product ε-CL with better purity can be obtained.

[0060] Furthermore, during vacuuming, the pressure can be adjusted to 10Pa-101kPa, more preferably 10kPa-20kPa, 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 salt water solution, ethanol, ethylene glycol and glycerol.

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

[0064] According to the device and method of the present invention, PCL can be efficiently depolymerized to obtain high-yield, high-purity ε-CL (purity can reach 99.9%). During the depolymerization process, the product gas passes through the cooling system of the insulation layer, and the gas temperature is adjusted by the insulation layer, so that the product gas will neither condense and reflux to the reactor, nor react quickly to generate by-products such as dimers and trimers due to the high temperature; further combined with the cooling system of the reactor cover, the gas temperature is adjusted by the temperature of the reactor cover again, which can ensure that the product gas temperature gradually decreases, which can greatly reduce the generation of by-products and will not condense and reflux; at the same time, the molecular sieve connected to the condenser can effectively adsorb the by-products and achieve the removal of the by-products, thereby obtaining high-yield, high-purity ε-CL. The ε-CL recovered by depolymerization has excellent reactivity and can be directly repolymerized to obtain PCL, and the conversion rate can reach 99.9%, that is, it is reintroduced into the production cycle of PCL in a simple, effective and cheap way, and on an industrial scale, the closed-loop cycle of PCL from "polymer-monomer-polymer" is realized.

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

[0066] (1) The device of the present invention aims at the characteristics of the PCL depolymerization reaction. By setting a heat insulation layer and combining precise temperature control, 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 are effectively solved. ε-CL monomer with a high purity of 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 is designed with a unique stirring paddle and baffle structure to achieve efficient mixing of PCL and catalyst, increase the reaction interface, and improve the efficiency of catalytic depolymerization. The stirring paddle is a turbine stirring paddle, which cooperates with multiple baffles to generate a strong up and down circulation flow in the kettle, bringing 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 drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0069] Figure 1-Figure 3 It is a schematic diagram of the structure of the device of the present invention.

[0070] Figure 4 It is a schematic diagram of the top-sectional structure of one implementation method of the thermal insulation layer of the device of the present invention.

[0071] Figure 5 It is a schematic diagram of the top-sectional structure of one implementation method 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. collecting tank; 15. baffle; 16. stirring paddle; 17. high-precision vacuum regulating valve; 18. discharge ball valve. DETAILED DESCRIPTION

[0074] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto. The materials involved in the following examples can be obtained from commercial channels unless otherwise specified. 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 a heat insulation layer is provided between the kettle cover and the kettle body, the heat insulation layer is provided with holes penetrating from top to bottom, and a heat insulation layer water inlet and a heat insulation layer water outlet are provided on the outer side of the heat insulation layer; a material port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet are provided on the kettle cover, and a stirring paddle penetrating the heat insulation layer and extending into the kettle body is connected inside the kettle cover; a plurality of baffles are embedded inside the kettle body, a discharge port is provided at the lower part of the kettle body, and the outer side of the kettle body is connected to the oil heating sleeve.

[0077] The inner wall of the kettle cover is provided with a pipe, which connects the kettle cover water inlet and kettle cover water outlet. The heat insulation layer is provided with a pipe, which connects the heat insulation layer water inlet and heat insulation layer water outlet. The kettle cover and the heat insulation layer are respectively provided with circulating coolant temperature control by a circulating refrigerator; the circulating refrigerator adjusts the refrigeration temperature by measuring the temperature of the water outlet.

[0078] The diameter of the holes on the insulation layer can be 10mm-50mm±5mm, preferably 10mm-20mm±5mm. The number of holes can be more than 100. Six baffles are longitudinally distributed on the inner wall of the kettle. The gas outlet is connected to the condenser through an external pipeline. The external pipeline is provided with an insulation sleeve. The insulation sleeve is provided with a thermocouple and a circulating fluid. The condenser is preferably connected to the molecular sieve and then connected to the vacuum port and the collection tank respectively. The product gas can be extracted from the vacuum port by a vacuum pump, etc., to accelerate the evaporation of the product gas 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. The product gas passes through the spherical condenser and the serpentine condenser in turn during the evaporation process. The discharge port is connected to a discharge ball valve through a discharge pipe. The discharge of the remaining material after the reaction is controlled by the ball valve. The stirring blade is a turbine stirring blade, and the stirring blade speed can be 50-500rpm; the stirring blade is connected to the external motor drive by a magnetic coupler. The kettle body, kettle cover, insulation layer, and oil heating jacket are all equipped with thermocouples for measuring temperature.

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

[0080] Embodiment 2:

[0081] On the basis of the above-mentioned embodiment 1, another temperature control method is realized 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 kettle cover water inlet and the kettle cover water outlet to achieve temperature control.

[0083] Embodiment three:

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

[0085] See also 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] Embodiment 4:

[0087] On the basis of the above-mentioned embodiment 3, another temperature control method is realized 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 kettle cover water inlet and the kettle cover water outlet 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 continued to be increased to the depolymerization temperature of polycaprolactone; the circulating refrigerator passes coolant into the kettle cover and the insulation layer through the water inlet and the water inlet, respectively, and passes coolant into the insulation jacket and the condenser, respectively, to accurately control the temperatures of the kettle cover, the insulation layer, the insulation jacket and the condenser; the pressure in the reactor is reduced to a specified value by vacuuming through the vacuum port, 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 quickly 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; 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 will it generate by-products such as oligomers, thereby significantly improving the depolymerization efficiency of ε-caprolactone. By combining a spherical condenser with a serpentine condenser, while ensuring a longer cooling path, clogging of by-products in the serpentine condenser can be avoided. 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 device comprises the following steps: adding polycaprolactone with a number average molecular weight of 8000-100000 and a catalyst into a kettle body and sealing the device; respectively introducing cooling liquid into the heat insulation layer, kettle cover, insulation jacket and condenser, 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 cooling liquid; heating the kettle body to the polycaprolactone depolymerization temperature (160-250°C) by using an oil heating jacket; starting a stirring blade (a butterfly turbine stirring blade with a rotation speed of 100 rpm) to start the reaction; and during the reaction, evacuating the system (system pressure of 10 kPa-20 kPa) 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.

[0094] 30 parts by mass of PCL (number average molecular weight of 89,000) and 2 mol% of stannous isooctanoate (catalyst) were reacted. The temperature of the thermal 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 and a conventional two-blade stirring impeller, that is, the cooling system without a heat insulation layer or a reactor cover, and the baffle plate was not embedded in the reactor body. The 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 the use of conventional reactors and conventional stirring paddles, 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; and 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 product ε-CL and pure ε-CL obtained by depolymerization using the device of the present invention are shown in FIG. As can be seen from the figure, the ε-CL product obtained by depolymerization using the method of the present invention has high purity and is free of other impurities.

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

[0101] As can be seen from the table, the ε-CL obtained by depolymerization based on the method of the present invention has excellent reactivity. Directly polymerizing under the catalysis of the catalyst can obtain a regenerated PCL with a number average molecular weight of 81000, a tensile strength and a breaking elongation of 30.7 MPa and 856%, respectively. The tensile performance test is in accordance with GB / T 1040-2006, and the tensile rate is set to 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 Regeneration PCL 30.7 856

[0106] The mechanical properties of the regenerated PCL of the present invention are compared with those of the raw PCL, and the results are shown in Table 2. As can be seen from Table 2, the regenerated PCL obtained by the present invention has excellent properties, high tensile strength, which can reach 30.7MPa, which is 77.3% of the tensile strength of native polycaprolactone; and elongation at break is 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 equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A device for efficiently depolymerizing polycaprolactone to recover high-purity ε-CL, comprising a kettle cover and a kettle body, characterized in that: An insulation layer is arranged between the kettle cover and the kettle body, and the insulation layer is provided with holes penetrating from top to bottom, and an insulation layer water inlet and an insulation layer water outlet are arranged on the outer side of the insulation layer; a material port, a kettle cover water inlet, a kettle cover water outlet and a gas outlet are arranged on the kettle cover, and a stirring paddle penetrating the insulation layer and extending into the kettle body is connected inside the kettle cover; a baffle is embedded inside the kettle body, a discharge port is arranged at the lower part of the kettle body, and the outer side of the kettle body is connected to the oil heating sleeve.

2. The device according to claim 1, characterized in that: The thermal insulation layer is provided with a pipeline, which connects the water inlet of the thermal insulation layer 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 of the thermal insulation layer and the water outlet of the thermal insulation layer.

3. The device according to any one of claims 1 to 2, characterized in that: The inner wall of the kettle cover is provided with a pipeline, and the pipeline connects the kettle cover water inlet and the kettle cover water outlet; or the kettle cover is a hollow structure, and the cavity connects the kettle cover water inlet and the kettle cover water outlet.

4. The device according to any one of claim 1, characterized in that: 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 device according to claim 1, characterized in that: The gas outlet is connected to the condenser through an external pipeline; the condenser is connected to the vacuum port and the collecting tank respectively; or the condenser is connected to the molecular sieve and then connected to the vacuum port and the collecting 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 device according to claim 5, characterized in that: The external pipeline is wrapped with a heat preservation sleeve; the cooling medium of the heat preservation sleeve is selected from at least one of saline solution, ethanol, ethylene glycol and propylene glycol; the vacuum port is connected with a high-precision vacuum regulating valve.

7. The device according to claim 1, characterized in that: There is one or more material ports; the discharge port is connected to a discharge ball valve via a discharge pipeline; and the collecting tank is used to collect the condensed product.

8. Use of the device according to any one of claims 1 to 7 in polyester depolymerization.

9. A method for depolymerizing polycaprolactone based on the device according to any one of claims 1 to 7, characterized in that The method comprises the following steps: adding polycaprolactone and a catalyst into a kettle body and sealing the device; respectively introducing a coolant into the heat insulation layer and the kettle cover, 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; turning on a stirring paddle to start the reaction; and during the reaction, vacuumizing the system 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.

10. The method according to claim 9, characterized in that: The depolymerization temperature is 160-250°C; the temperature of the cooling liquid introduced into the heat insulation layer is controlled at 60-80°C; the temperature of the cooling liquid introduced into the kettle cover is controlled at 50-70°C.

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