Method for recovering polycaprolactone by low-temperature plasma coupling catalytic depolymerization

Abstract

The application belongs to the field of solid waste plastic resource utilization, and discloses a method for depolymerization and recovery of polycaprolactone by low-temperature plasma coupling catalysis. Polycaprolactone particles are subjected to plasma discharge treatment together with a catalyst to make the polycaprolactone particles depolymerize, thereby realizing the depolymerization and recovery of polycaprolactone. The application utilizes the Joule heat generated by plasma discharge to liquefy polycaprolactone, and after liquefaction, the polycaprolactone fully contacts the active sites of the catalyst, and meanwhile, under the action of active free radicals generated by plasma treatment and the catalyst, realizes fast polycaprolactone depolymerization and recovery without external heat source, solvent and pressure. The complete conversion of polycaprolactone is realized within 1 hour, and the yield of gamma-caprolactone monomer can be as high as 88.9%, which is significantly better than the current solvent thermal method.

Description

Technical Field

[0001] This invention belongs to the technical field of polycaprolactone depolymerization and recycling and solid waste plastic resource utilization, specifically relating to a method for low-temperature plasma-coupled catalytic depolymerization and recycling of polycaprolactone. Background Technology

[0002] Polycaprolactone (PCL), a petroleum-based biodegradable synthetic polyester plastic, is widely used in biomedicine, 3D printing, and composite materials due to its excellent biocompatibility, flexibility, and processing properties. Although PCL can biodegrade naturally in the environment, the oligomers and other metabolites produced during this degradation process pose potential health and environmental hazards, and natural degradation cannot fully utilize PCL as a resource. Recycling PCL demonstrates both environmental advantages and economic potential. γ-Caprolactone (γ-CL), a six-membered ring ester compound with a coconut aroma, is one of the high-value products of PCL depolymerization and is widely used in fragrances, polymer materials, pharmaceuticals, and energy. As a food additive, it provides natural cream and coconut flavor to confectionery, dairy products, and daily chemical products. Furthermore, γ-caprolactone serves as a green solvent and organic intermediate in the preparation of pharmaceutical, pesticide, and coating plasticizers. Compared to natural extraction, the recovery of γ-caprolactone from polycaprolactone (PCL) via chemical depolymerization offers advantages such as high yield, low cost, and high added value, while also enabling closed-loop recycling of waste PCL plastics. However, current chemical depolymerization methods for recovering γ-caprolactone from PCL still have low yields, and existing methods require the use of solvents containing metal ions and heating conditions for PCL depolymerization. This results in the generated γ-caprolactone dissolving in the solvent and being difficult to separate, and also leads to unavoidable metal ion residues in the product, causing degradation. Furthermore, the depolymerization process lasts for tens of hours and requires continuous heating, resulting in high energy consumption. The subsequent disposal of the solvent increases the end-of-pipe treatment cost of the PCL depolymerization process, thus affecting its economic viability. Therefore, there is an urgent need to develop a simple, rapid, solvent-free method for depolymerizing PCL into γ-caprolactone under mild conditions. Summary of the Invention

[0003] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a method for the depolymerization and recovery of polycaprolactone using low-temperature plasma-coupled catalysis.

[0004] This invention employs a coaxial cylindrical dielectric barrier discharge plasma reactor. The discharge reaction cavity is filled with a blend of polycaprolactone (PCL) and a catalyst, and a plasma carrier gas is introduced. Applying a sinusoidal voltage to the reactor ionizes the internal carrier gas, forming plasma and generating Joule heating during the discharge process. This Joule heating causes PCL to dissolve and liquefy, allowing it to fully contact the active sites on the catalyst surface, thereby achieving the catalytic depolymerization of PCL into smaller molecules such as caprolactone. During the catalytic conversion, active substances generated in the plasma gas phase, such as high-temperature electrons and active free radicals, participate in the solid-liquid two-phase catalytic depolymerization of PCL, promoting the dissociation of its long chains into monomer units. These monomer units then move out of the plasma discharge region and cool to obtain smaller molecules such as γ-caprolactone. This achieves PCL depolymerization and caprolactone monomer recovery under normal pressure conditions without solution or external heating sources, improving the process's economic efficiency and environmental friendliness, as well as the economic value and usability of the products.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for the depolymerization and recovery of polycaprolactone via low-temperature plasma-coupled catalysis includes the following steps:

[0007] Polycaprolactone particles and catalyst are mixed evenly and placed in the discharge reaction cavity of a dielectric barrier discharge plasma reactor. First, the reactor is purged with a carrier gas, and then plasma discharge is performed under the carrier gas atmosphere. The polycaprolactone particles undergo depolymerization under the action of plasma and catalyst. After the depolymerization reaction is completed, the product is collected, separated and purified to obtain a mixture of caprolactone monomers, thus realizing the depolymerization of polycaprolactone and the recovery of caprolactone monomers.

[0008] Preferably, the plasma discharge treatment is a room temperature and atmospheric pressure plasma treatment; the duration of the plasma discharge treatment is 0.1 to 5 h; the carrier gas flow rate is 10 to 2000 mL / min, more preferably 30 to 40 mL / min; the Joule heat generated during the plasma discharge treatment causes the temperature inside the discharge reaction cavity to reach and be maintained at 150 to 400 °C, more preferably 170 to 200 °C.

[0009] Preferably, the carrier gas includes at least one of hydrogen, hydrocarbon gas, nitrogen, carbon dioxide, carbon monoxide, and rare gas; more preferably, it is at least one of hydrogen and hydrocarbon gas. The carrier gas can generate free radicals during plasma discharge, thereby achieving the effect of selective depolymerization of polycaprolactone to produce caprolactone monomer under solvent-free, external heating source-free, and normal pressure conditions.

[0010] Preferably, the carrier gas purging conditions are: a purging flow rate of 20–100 mL / min and a purging time of 5–60 minutes.

[0011] Preferably, the mass ratio of the polycaprolactone particles to the catalyst is 1:4 to 4:1, more preferably 1:4 to 1:1.

[0012] Preferably, the size of the polycaprolactone particles is 10-500 mesh, more preferably 20-100 mesh, and even more preferably 60-80 mesh.

[0013] Preferably, the molecular weight of the polycaprolactone is Mn = 40,000 to 160,000; more preferably, it is 40,000 to 80,000.

[0014] Preferably, the catalyst comprises a molecular sieve and / or a metal-supported molecular sieve, wherein the metal comprises at least one selected from iron, nickel, cobalt, manganese, copper, zinc, and ruthenium.

[0015] More preferably, the molecular sieve is an aluminosilicate molecular sieve, and even more preferably, HY molecular sieve; the metal loading in the metal-loaded molecular sieve is 3 to 20 wt.% (the mass percentage of metal in the metal-loaded molecular sieve), and even more preferably, 5 to 20 wt.%.

[0016] The metal-loaded molecular sieve is derived from commercial sources or obtained by conventional preparation methods. Conventional preparation methods involve loading metal salts onto molecular sieve powder and then calcining and reducing them to metal.

[0017] More preferably, the metal-supported molecular sieve is obtained by the following method:

[0018] Molecular sieve powder is added to a metal salt solution for impregnation. After removing the solvent, it is calcined and reduced to obtain a metal-supported molecular sieve catalyst.

[0019] More preferably, the calcination conditions are: calcination at 500-600 °C for 2-6 h.

[0020] More preferably, the reduction conditions are: maintaining the temperature at 500-600°C for 1-5 h in an H2-Ar mixed atmosphere with a hydrogen content of 1-20 vol.%.

[0021] Preferably, the dielectric barrier discharge plasma reactor is a coaxial cylindrical dielectric barrier discharge plasma reactor, and its dielectric layer is cylindrical quartz glass.

[0022] Preferably, the separation and purification includes extraction.

[0023] In the above method, the low-temperature plasma catalytic process is monitored in situ in real time by emission spectroscopy. The disappearance of the CO group spectral line in the plasma emission spectrum indicates the end of the depolymerization reaction.

[0024] The dielectric barrier discharge plasma reactor used in the method is a coaxial cylindrical dielectric barrier discharge plasma reactor, which includes a cylindrical shell that runs vertically through the top and bottom, an upper end cap, a lower end cap, an inner electrode, and an outer electrode.

[0025] The upper end cap is disposed at the top of the shell, and the lower end cap is disposed at the bottom of the shell. A discharge reaction cavity is formed between the shell, the upper end cap, and the lower end cap, which is the discharge reaction cavity of the reaction device.

[0026] The inner electrode is coaxially disposed at the center of the housing, extends outward through the central hole of the upper end cap, and is connected to the output end of the plasma power supply.

[0027] The outer electrode is arranged around the outer wall of the housing;

[0028] A plasma discharge region is formed between the inner and outer electrodes.

[0029] Preferably, the cylindrical shell that runs vertically through the top and bottom is made of quartz glass.

[0030] Preferably, the lower part of the lower end cap is provided with a condensation chamber communicating with the interior of the shell to condense and collect the liquid products after the decomposition of polycaprolactone.

[0031] Preferably, the external electrode has a mesh structure.

[0032] Preferably, the upper end cap is provided with an air inlet for receiving carrier gas, and the lower end cap is provided with an air outlet for discharging carrier gas.

[0033] Preferably, a thermocouple thermometer and / or an infrared thermal imager are installed inside the discharge reaction cavity formed between the shell, the upper end cap, and the lower end cap.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] (1) This invention is the first to use low-temperature plasma (plasma produced at room temperature and pressure) to selectively depolymerize polycaprolactone, thereby realizing the recovery of caprolactone monomer. The reaction process does not require an external heating source and is carried out under normal pressure and solvent-free conditions, which improves the cleanliness and economy of polycaprolactone chemical recovery.

[0036] (2) This invention utilizes the Joule heat waste heat in the low-temperature plasma coupled catalysis process for the first time, and uses it for the heated liquefaction of solid plastic powder, so as to further contact the catalyst in liquid form and combine it with plasma free radicals to carry out a multiphase catalytic process.

[0037] (3) The carrier gas used in the low-temperature plasma synergistic catalytic process of this invention can be non-hydrogen gas, which is cheaper. The catalyst is depolymerized in situ through plasma coupling to form a large number of free radicals. These free radicals can be used in situ to participate in the heterogeneous catalytic reaction of polycaprolactone depolymerization, which further improves the economy of polycaprolactone depolymerization process.

[0038] (4) The present invention uses low-temperature plasma synergistic catalysis to depolymerize polycaprolactone, which can achieve complete conversion of polycaprolactone in as little as 1 hour, and the yield of γ-caprolactone monomer can be as high as 88.9 wt.%. The technical indicators such as reaction time, reaction conditions, reactant conversion rate and monomer yield are significantly better than the current solvothermal method. Attached Figure Description

[0039] Figure 1 The image shows a scanning electron microscope image of the Ni / HY catalyst used in the embodiments and comparative examples of this invention at a resolution of 300 nm.

[0040] Figure 2 The powder X-ray diffraction patterns of the HY and Ni / HY catalysts used in the embodiments and comparative examples of this invention are shown below.

[0041] Figure 3 This is a schematic diagram of a coaxial cylindrical dielectric barrier discharge plasma reaction device in an embodiment of the present invention; wherein, 1 is the inner electrode; 2 is the upper end cap; 3 is the air inlet; 4 is the outer electrode; 5 is a cylindrical shell (quartz glass tube) that runs vertically through the body; 6 is the lower end cap; 7 is the air outlet; and 8 is the condensation chamber.

[0042] Figure 4 This is the plasma emission spectrum of the plasma-coupled catalytic process in Example 3 of the present invention;

[0043] Figure 5 This is the total ion current chromatography (TIC) chromatogram of the product obtained in Example 3 of the present invention;

[0044] Figure 6 This is a temperature diagram of the reaction region during the plasma discharge process in Embodiment 1 of the present invention. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments of the present invention, conventional conditions or conditions recommended by the manufacturer shall apply. Raw materials, reagents, etc., used without specified manufacturers are all conventional products that can be purchased commercially.

[0046] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0047] The molecular sieve supported metal catalyst Ni / HY described in the following examples and comparative examples is prepared by the following methods:

[0048] 1.232 g of nickel nitrate hexahydrate was dissolved in 100 mL of deionized water by thorough stirring to prepare a metal salt solution. The prepared metal salt solution was added to 4.75 g of HY molecular sieve powder, stirred at room temperature for 1 hour, then transferred to a water bath and evaporated to dryness at 80 °C. The dried sample was then transferred to an oven and dried overnight at 110 °C. The sample was subsequently calcined in a muffle furnace at 550 °C in air for 4 hours, followed by natural cooling. The calcined catalyst powder was transferred to a tube furnace, and a hydrogen-Ar mixture with a hydrogen concentration of 10 vol.% was introduced at a flow rate of 100 mL / min. The temperature was increased to 550 °C at a rate of 5 °C / min and held for 3 hours to reduce the catalyst, resulting in a Ni / HY catalyst with a metal loading of 5 wt.%.

[0049] The Ni-supported HY catalyst obtained in the above steps was characterized, and the morphology and structure of the Ni / HY catalyst are as follows: Figure 1 As shown, the supported active nickel metal is uniformly distributed on the surface of HY. The crystal structure of the catalyst is as follows. Figure 2 As shown, the diffraction peak signals of the prepared HY molecular sieve are consistent with the standard diffraction card PDF#43-0168, indicating that it exhibits a FAU channel structure. The positions and intensities of the diffraction peaks did not change significantly after loading the active metal, indicating that the structure of the HY molecular sieve remained stable after metal loading.

[0050] The cylindrical dielectric barrier discharge plasma reactor used in the following embodiments has the following structure: Figure 3As shown, the system includes: a cylindrical shell extending vertically through the shell, an upper end cap, a lower end cap, an inner electrode, and an outer electrode. The upper end cap is located at the top of the shell, and the lower end cap is located at the bottom of the shell. A cavity for reaction is formed between the shell, the upper end cap, and the lower end cap. The inner electrode is coaxially located at the center of the shell and extends outward through a central hole in the upper end cap, connecting to the output terminal of the plasma power supply. The outer electrode is arranged around the outer wall of the shell. The upper end cap has an inlet for receiving carrier gas, and the lower end cap has an outlet for discharging carrier gas. A condensation chamber communicating with the interior of the shell is located at the bottom of the lower end cap to condense and collect liquid products during the plastic depolymerization process. The shell (i.e., the dielectric layer) is a cylindrical quartz glass, the inner electrode is a stainless steel rod, and the outer electrode is a stainless steel mesh, forming a plasma discharge region between the outer and inner electrodes. The blend of catalyst and polycaprolactone particles is placed in the plasma discharge region formed by the outer and inner electrodes, and is also located in the cavity formed between the shell, upper end cap and lower end cap for reaction, and is clamped at both ends with quartz wool.

[0051] The dielectric barrier discharge plasma reactor is connected to a plasma power supply (external voltage). The plasma power supply outputs a sine wave to the internal electrodes to generate high-temperature electrons, active free radicals, and Joule heat through plasma discharge. Thermocouples and infrared thermal imagers placed inside the plasma discharge reaction cavity (the cavity formed between the shell, upper head, and lower head) monitor the temperature inside the discharge reaction cavity in real time. By adjusting the external voltage of the plasma reactor, the generated Joule heat is used to adjust the temperature inside the discharge reaction cavity to the target reaction temperature. The plasma reactor is placed at room temperature without an external heating source; it only performs room temperature discharge.

[0052] Example 1

[0053] Polycaprolactone particles were sieved to obtain 60-80 mesh polycaprolactone particles with a molecular weight Mn=80000. Polycaprolactone and HY molecular sieve catalyst powder were mixed in a centrifuge tube at a mass ratio of 1:1 and then placed in the plasma discharge region (i.e., the discharge reaction cavity) of the cylindrical dielectric barrier discharge plasma reactor of this application. The structure of the reactor is as follows: Figure 3As shown. The reaction mixture was clamped and fixed in the discharge reaction cavity of the plasma reactor by filling both ends with quartz wool. After sealing the reactor, hydrogen gas was introduced as a carrier gas and purged at a flow rate of 30 mL / min for 30 minutes. Then, the plasma power supply was turned on, and plasma discharge treatment was performed by adjusting the voltage. The resulting Joule heat raised the internal temperature of the discharge reaction cavity to 200°C and maintained it. Hydrogen gas was continued to be introduced at a flow rate of 30 mL / min. Product collection began immediately after plasma discharge. After 1 hour of reaction, the plasma power supply was turned off. The solid residue in the reactor (to recover the adsorbed product on the solid residue) and the condensed liquid product in the condensation chamber were placed in a centrifuge tube. The caprolactone monomers were extracted by shaking with dichloromethane. After extraction, the liquid product was taken as the target product, which is a mixture of caprolactone monomers.

[0054] The yield of caprolactone monomer was qualitatively and quantitatively determined using gas chromatography-mass spectrometry (GC-MS). The mixture of catalyst and polycaprolactone plastic after the reaction was pyrolyzed using a thermogravimetric analysis (TGA-DSC), and the mass percentage of polycaprolactone plastic in the residual solids was determined by the weight loss during pyrolysis, thus determining the conversion rate of polycaprolactone plastic.

[0055] Example 2

[0056] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is described. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Example 1. The difference is that the catalyst used in this example is a Ni / HY catalyst with a metal loading of 5 wt.%.

[0057] Example 3

[0058] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is disclosed. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Example 1. The difference is that the plasma carrier gas used in this example is methane, and the catalyst used is a Ni / HY catalyst with a metal loading of 5 wt.%.

[0059] Figure 4 Plasma emission spectroscopy results show that when methane is used as the plasma carrier gas and Ni / HY is used as the catalyst, CH4 is the main component present in the plasma discharge region. + Ions, CH· radicals, CO· radicals, C2 radicals, and H· radicals, CH + Ions, CH· radicals, and C2 radicals are characteristic groups of methane low-temperature plasma, while the presence of CO· radical signals indicates that PCL decomposes.

[0060] Example 4

[0061] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is provided. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Example 1. The difference is that the mass ratio of polycaprolactone to catalyst in this example is 1:4.

[0062] Example 5

[0063] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is described. The steps, reagents, process parameters, and product detection methods used in each step are the same as in Example 1. The difference is that in this example, the plasma discharge treatment is performed by adjusting the voltage, and the resulting Joule heat causes the temperature inside the discharge reaction cavity to reach and be maintained at 150°C.

[0064] Example 6

[0065] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is described. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Example 1. The difference is that the hydrogen carrier gas flow rate in this example is 40 mL / min.

[0066] Comparative Example 1

[0067] Polycaprolactone particles were sieved to obtain 60-80 mesh particles with a molecular weight Mn=80000. Polycaprolactone particles and HY molecular sieve catalyst powder were mixed in a centrifuge tube at a mass ratio of 1:1. The mixture was then placed in the plasma discharge region (i.e., the discharge reaction cavity) of the cylindrical dielectric barrier discharge plasma reactor of this application. The reaction mixture was clamped and fixed in the discharge reaction cavity of the plasma reactor by filling both ends with quartz wool. After sealing the reactor, hydrogen gas was introduced as a carrier gas and purged at a flow rate of 30 mL / min for 30 minutes. Unlike Example 1, in this comparative example, the reactor was not connected to a plasma power source; that is, no power was supplied, and no plasma discharge treatment was performed. Instead, the reactor was placed in a tube furnace, and the tube furnace heating rate was set to 20 °C / min to heat the internal temperature of the discharge reaction cavity to 200 °C, followed by holding at that temperature for 50 minutes for a thermocatalytic comparative experiment. Product collection begins immediately upon heating in the tubular furnace. After the reaction, the tubular furnace is shut off, and the plasma reactor is removed from the furnace for natural cooling. Subsequently, the solid residue in the reactor and the condensed liquid product in the condensation chamber are placed in centrifuge tubes, and the γ-caprolactone monomer is extracted by shaking with dichloromethane. After extraction, the yield of the γ-caprolactone monomer is detected by gas chromatography-mass spectrometry.

[0068] Comparative Example 2

[0069] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is disclosed. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Comparative Example 1. The difference is that the catalyst used in this comparative example is a Ni / HY catalyst with a metal loading of 5 wt.%.

[0070] Comparative Example 3

[0071] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is disclosed. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Comparative Example 1. The difference is that the carrier gas used in this comparative example is methane, and the catalyst used is a Ni / HY catalyst with a metal loading of 5 wt.%.

[0072] Comparative Example 4

[0073] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is described. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Example 1. The difference is that no catalyst is added in this comparative example, and polycaprolactone is only filled into the reaction area.

[0074] Comparative Example 5

[0075] A method for depolymerizing and recovering polycaprolactone using low-temperature plasma-coupled catalysis is described. The steps, reagents, process parameters, and product detection methods used in each step are the same as those in Example 1. The difference is that no catalyst is added in this comparative example, and polycaprolactone is only filled into the reaction zone. Methane is used as the carrier gas.

[0076] The products obtained in the above examples and comparative examples were qualitatively and quantitatively detected by gas chromatography-mass spectrometry (GC-MS). Figure 5 The total ion current chromatogram (TIC) of the liquid reaction products in Example 3 is shown. Mass spectrometry analysis identified the liquid products as mainly containing C6 ketones, C6 acids, and three structural types of caprolactone monomers (γ-CL, ε-CL, and δ-CL). The ketones and acids are likely products of ring-opening side reactions of the cyclic caprolactone structure during plasma discharge. Table 1 shows the polycaprolactone conversion and γ-caprolactone yield in Examples 1-6 and Comparative Examples 1-5. The structure and yield of γ-caprolactone were determined by quantifying the peak area of ​​the γ-caprolactone signal measured by the FID detector using the external standard method. The yield of γ-caprolactone (…) S γ-CL The following formula is used to calculate:

[0077]

[0078] in m PCLThe total mass of PCL used in each experiment. m γ-CL The mass of γ-caprolactone obtained in each experiment. m PCL-remain This represents the mass of the unconverted portion of PCL in each experiment.

[0079] Conversion rate of polycaprolactone (PVP) C PCL The following formula is used to calculate:

[0080]

[0081] in m PCL The total mass of PCL used in each experiment. m PCL-remain This represents the mass of the unconverted portion of PCL in each experiment.

[0082] Table 1 Polycaprolactone conversion rate and γ-caprolactone yield

[0083]

[0084] Based on the performance test results of Example 1 and Comparative Example 1 in Table 1, it can be seen that the plasma-coupled catalytic process of the present invention can effectively promote the decomposition of polycaprolactone (PCL) and simultaneously improve the conversion rate of PCL and the yield of γ-caprolactone monomer. Under the conditions of 200°C and a reaction time of one hour, when Comparative Example 1 only heated the mixture of PCL and HY to achieve thermal catalytic decomposition, the PCL decomposition rate was only 2.7%, while Example 1 achieved a 100% conversion rate through plasma-coupled catalysis. When using thermal catalysis (Comparative Example 1), the yield of γ-caprolactone monomer was 7.3%, while the yield achieved by plasma-coupled catalysis (Example 1) was 88.1%, representing a 12-fold increase.

[0085] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for recovering polycaprolactone by low-temperature plasma coupling catalytic depolymerization, characterized in that, The method comprises the following steps: The polycaprolactone particles are mixed with the catalyst, and then placed in a discharge reaction cavity of a dielectric barrier discharge plasma reaction device. After purging with a carrier gas, the polycaprolactone particles are subjected to plasma discharge treatment in the carrier gas atmosphere. Under the action of the plasma and the catalyst, the polycaprolactone particles are subjected to depolymerization reaction. After the depolymerization reaction is completed, the product is collected, and then separated and purified to obtain gamma-caprolactone, thereby realizing depolymerization of the polycaprolactone and recovery of the caprolactone monomer; The catalyst is a molecular sieve and / or a metal-loaded molecular sieve; The metal in the metal-loaded molecular sieve is at least one of iron, nickel, cobalt, manganese, copper, zinc and ruthenium; The molecular sieve in the molecular sieve and / or the metal-loaded molecular sieve is a silicoaluminate molecular sieve; The carrier gas comprises at least one of hydrogen and a hydrocarbon gas.

2. The method of claim 1, wherein, The plasma discharge treatment is normal-temperature and normal-pressure plasma treatment; And / or, the flow rate of the carrier gas during the plasma discharge treatment is 10-2000 mL / min; And / or, the temperature in the discharge reaction cavity reaches and is maintained at 150-400 DEG C. due to the Joule heat generated during the plasma discharge treatment.

3. The method of claim 1 or 2, wherein, The mass ratio of the polycaprolactone particles to the catalyst is 1:4-4:1; And / or, the loading amount of the metal in the metal-loaded molecular sieve is 3-20 wt.%. And / or, the duration of the plasma discharge treatment is 0.5-5 h.

4. The method of claim 3, wherein, The mass ratio of the polycaprolactone particles to the catalyst is 1:4-1:1; And / or, the loading amount of the metal in the metal-loaded molecular sieve is 5-20 wt.%.

5. The method of claim 1 or 2, wherein, The size of the polycaprolactone particles is 10-500 mesh; And / or, the molecular weight of the polycaprolactone is Mn=40000-160000.

6. The method of claim 5, wherein, The carrier gas comprises at least one of hydrogen and a hydrocarbon gas. And / or, the size of the polycaprolactone particles is 20-100 mesh; And / or, the molecular weight of the polycaprolactone is Mn=40000-80000.

7. The method of claim 1 or 2, wherein, The dielectric barrier discharge plasma reaction device is a coaxial cylindrical dielectric barrier discharge plasma reaction device, and the dielectric layer is a cylindrical quartz glass.

8. The method of claim 1 or 2, wherein, The dielectric barrier discharge plasma reaction device comprises a cylindrical shell penetrating from top to bottom, an upper head, a lower head, an inner electrode and an outer electrode. The upper head is arranged at the top of the shell, and the lower head is arranged at the bottom of the shell. The shell, the upper head and the lower head form a discharge reaction cavity. The inner electrode is coaxially arranged at the center position inside the shell and extends outward through the center hole of the upper head. The outer electrode is annularly arranged on the outer wall of the shell. The inner electrode and the outer electrode form a plasma discharge zone.

9. The method of claim 8, wherein, The cylindrical shell penetrating from top to bottom is made of quartz glass. And / or, the inside of the discharge reaction cavity formed between the shell, the upper head and the lower head is provided with a thermocouple thermometer and / or an infrared thermal imager.

10. The method of claim 8, wherein, The upper head is provided with a gas inlet for receiving the carrier gas, and the lower head is provided with a gas outlet for discharging the carrier gas. And / or, the lower part of the lower head is provided with a condensation cavity communicating with the inside of the shell. And / or, the outer electrode is in a mesh structure. And / or, the inner electrode is connected to an output of a plasma power supply.

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