A method for producing natural gas from plastic

Abstract

The application discloses a method for producing natural gas by using plastic as raw material, and specifically comprises the following steps: mixing plastic and a catalyst in a solvent-free system, and reacting I in a closed pressure container containing a reducing atmosphere to obtain natural gas, wherein the catalyst is a Raney catalyst. The carbon yield of the natural gas prepared through the above steps can reach 89.1%, the process is simple and easy to operate, the environmental pollution caused by waste plastics can be reduced, high-purity natural gas is obtained, and a new path for producing natural gas is opened up.

Description

Technical Field

[0001] This application relates to a method for producing natural gas using plastics as raw materials, and belongs to the field of natural gas production. Background Technology

[0002] Plastics are among the most widely used materials in the world, indispensable in industries such as packaging, biomedical devices, automobiles, and electronics. This is primarily due to their low production costs and superior properties such as durability, low density, and corrosion resistance. Polyethylene and polypropylene are two commonly used types of plastics, accounting for 57.3% of global plastic consumption. However, due to the chemical inertness of plastics, large amounts of waste plastic accumulate in roads and oceans, causing a serious environmental crisis. Currently, one of the most common methods for disposing of plastic waste is landfill. Given the poor performance of mechanical recycling, chemical recycling is considered one of the most promising technologies, capable of transforming waste plastics into useful chemicals.

[0003] Natural gas is one of the world's basic energy sources, mainly composed of CH4 (70-90%) and small amounts of C2-C4 hydrocarbons, and can be used for power generation, heating, ammonia production, and hydrogen production. Therefore, effectively catalyzing the complete cleavage of elastic C-C bonds in polyolefin plastics into natural gas is of great significance.

[0004] In response to the current problems of high reaction temperatures and complex product composition in the chemical upgrading process of polyolefin plastics, there is an urgent need to develop efficient reaction systems. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method for producing natural gas from plastics. By using a Raney-type catalyst, lowering the reaction temperature, and breaking all carbon-carbon bonds, the process converts the plastics into natural gas with methane as the main gaseous component. This represents a revolutionary technology for producing natural gas from waste polyolefin plastics under mild conditions. Furthermore, the natural gas produced in this process meets the transportation requirements of urban natural gas pipelines, thus possessing significant economic value.

[0006] According to one aspect of this application, a method for producing natural gas from plastic is provided, wherein the plastic is mixed with a catalyst in a solvent-free system and reacted in a closed pressure vessel containing a reducing atmosphere to obtain natural gas.

[0007] The catalyst is a Raney-type catalyst.

[0008] Optionally, the solvent-free system refers to the reaction system in which no solvent is added.

[0009] Optionally, the Raney catalyst is Raney Ni.

[0010] Optionally, the Raney catalyst may further include a Raney catalyst supported on a bimetallic substrate.

[0011] Optionally, the Raney-type catalyst supported on a bimetallic substrate is selected from at least one of Raney Ni-Al, Raney Ni-Mo, Raney Ni-Sn, Raney Ni-Fe, or Raney Ni-Cu.

[0012] Optionally, the Raney-type catalyst needs to be activated before use.

[0013] Optionally, the specific operation of the activation treatment is as follows:

[0014] The Raney-type catalyst was added to a 20 wt% sodium hydroxide solution and kept in an oil bath for 1 hour. It was then washed with water until neutral to obtain a usable Raney-type catalyst.

[0015] Optionally, the plastic is a polyolefin plastic.

[0016] Optionally, the polyolefin plastic is selected from at least one of polyethylene plastics and polypropylene plastics.

[0017] Specifically, the polyethylene plastics are derived from at least one of polyethylene powder and plastic bags; the polypropylene plastics are derived from at least one of polypropylene powder, polypropylene granules, folders, takeout boxes, and masks.

[0018] Optionally, the method further includes the separation and reuse of the catalyst and the separation and reuse of the reducing gas.

[0019] Optionally, the catalyst is separated and reused by centrifugation to obtain the catalyst after the reaction, and then further recycled.

[0020] Optionally, the amount of catalyst added is 20% to 70% of the mass of the plastic.

[0021] Optionally, the amount of catalyst added is any value among 20%, 30%, 40%, 50%, and 70% of the mass of the plastic, or a range between two values.

[0022] Optionally, the amount of catalyst added is 50% to 70% of the mass of the plastic.

[0023] Optionally, the reducing atmosphere is a hydrogen atmosphere.

[0024] Optionally, the pressure of the reducing atmosphere is 0.1 to 7 MPa.

[0025] Optionally, the pressure of the reducing atmosphere is selected from any value or a range between two values ​​from 0.1 MPa, 1 MPa, 2 MPa, 4 MPa, and 7 MPa.

[0026] Optionally, the pressure of the reducing atmosphere is 1 to 4 MPa.

[0027] Optionally, the pressure of the reducing atmosphere is 2 to 4 MPa.

[0028] Optionally, the reaction temperature is 250–350°C.

[0029] Optionally, the temperature of the reaction is selected from any value of 250°C, 280°C, 300°C, 320°C, or 350°C, or a range between two values.

[0030] Optionally, the reaction temperature is 280–350°C.

[0031] Optionally, the reaction temperature is 300–350°C.

[0032] Optionally, the reaction time is 0.05 to 25 hours.

[0033] Optionally, the reaction time is selected from any value of 0.05h, 0.5h, 5h, 10h, 25h or a range between two values.

[0034] Optionally, the reaction time is 0.05 to 10 hours.

[0035] Optionally, the reaction time is 0.5 to 10 hours.

[0036] The above steps allow for the direct catalytic conversion of waste polyolefin plastics into natural gas under mild conditions, achieving a carbon yield of up to 89%. This process solves the environmental problems caused by the large accumulation of plastic waste, while simultaneously producing natural gas that meets the transportation requirements of urban natural gas pipelines.

[0037] This invention provides a method for producing natural gas using polyolefin plastics. This process is environmentally friendly, simple, easy to operate, and highly efficient, yielding high-purity biomass natural gas. The invention designs and develops a highly efficient catalytic reaction system that can almost completely break carbon-carbon bonds in a short time, catalyzing the direct conversion of plastics into natural gas. This transformative technology enables the production of natural gas from plastics under mild conditions, and the produced natural gas meets the transportation requirements of urban natural gas pipelines, providing important support for the sustainable development of my country's environment and economy, and opening up a new path for natural gas production.

[0038] The beneficial effects that this application can produce include:

[0039] 1) The method provided in this application realizes the upgrading and recycling of waste plastics, and the natural gas produced can be used for urban natural gas pipeline transportation, which has great economic value.

[0040] 2) The catalyst used in the method provided in this application can be centrifuged and further recycled, reducing the cost of the preparation process.

[0041] 3) The method provided in this application has simple operation steps, is green and pollution-free, and is an environmentally friendly process. Detailed Implementation

[0042] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0043] The Raney-type catalysts in this application embodiment—Raney Ni, Raney Ni-Mo, Raney Ni-Al, Raney Ni-Sn, Raney Ni-Fe, and Raney Ni-Cu—are obtained by activating their alloy powders. An appropriate amount of alloy powder is added to a 20wt% sodium hydroxide solution and kept in an oil bath for 1 hour. After the reaction is complete, it is washed with water until neutral to obtain the corresponding Raney-type catalyst, which is then used in the catalytic reaction.

[0044] The carbon yield calculation in this embodiment is as follows:

[0045]

[0046] Example 1

[0047] Weigh 0.5 g of Raney Ni-Al catalyst and add it to a 50 mL reactor, along with 1.0 g of polypropylene powder. Seal the reactor, purge with N2 3-5 times to expel air, then purge with H2 3-5 times to expel N2, and finally purge with H2 at 3 MPa. Heat to 300 °C using electric heating under magnetic stirring at 800 rpm for 60 min. After the reaction, stop stirring and cool the reactor to room temperature in an ice-water bath. Record the reaction termination temperature and pressure. Open the gas outlet and collect the generated gas using a gas bag for gas phase analysis. Add water to the reactor, remove the catalyst after reaction, centrifuge it, and recycle it.

[0048] The natural gas yield was found to be 89.1%, and the gas distribution (volume fraction %) was: CH4 (99.1%), C2-C4 (0.1%), CO2 (0.8%).

[0049] Example 2

[0050] Weigh 0.6 g of Raney Ni catalyst and add it to a 50 mL reactor, along with 1.2 g of polypropylene powder. Seal the reactor, purge with N2 3-5 times to expel air, then purge with H2 3-5 times to expel N2, and finally purge with H2 at 2 MPa. Heat to 330 °C using electric heating under magnetic stirring at 800 rpm for 120 min. After the reaction, stop stirring and cool the reactor to room temperature in an ice-water bath. Record the reaction termination temperature and pressure. Open the gas outlet and collect the generated gas using a gas bag for gas phase analysis. Add water to the reactor, remove the catalyst after reaction, centrifuge it, and recycle it.

[0051] The natural gas yield was found to be 88.4%, and the gas distribution (volume fraction %) was: CH4 (99.3%), C2-C4 (0.4%), and CO2 (0.3%).

[0052] Example 3

[0053] Weigh 0.7g of Raney Ni-Mo catalyst and add it to a 50mL reactor, along with 1.5g of polypropylene powder. Seal the reactor, purge with N2 3-5 times to expel air, then purge with H2 3-5 times to expel N2, and finally purge with H2 at 4MPa. Heat to 310℃ using electric heating under magnetic stirring at 800rpm and react for 180min. After the reaction, stop stirring and cool the reactor to room temperature in an ice-water bath. Record the reaction termination temperature and pressure. Open the gas outlet and collect the generated gas using a gas bag for gas phase analysis. Add water to the reactor, remove the catalyst after reaction, centrifuge it, and recycle it.

[0054] The natural gas yield was found to be 86.4%, and the gas distribution (volume fraction %) was: CH4 (98.7%), C2-C4 (1.0%), and CO2 (0.3%).

[0055] Example 4

[0056] Weigh 0.5 g of Raney Ni-Fe catalyst and add it to a 50 mL reactor, along with 1.0 g of polypropylene powder. Seal the reactor, purge with N2 3-5 times to expel air, then purge with H2 3-5 times to expel N2, and finally purge with H2 at 4 MPa. Heat to 320 °C using electric heating under magnetic stirring at 800 rpm for 300 min. After the reaction, stop stirring and cool the reactor to room temperature in an ice-water bath. Record the reaction termination temperature and pressure. Open the gas outlet and collect the generated gas using a gas bag for gas phase analysis. Add water to the reactor, remove the catalyst after reaction, centrifuge it, and recycle it.

[0057] The natural gas yield was found to be 87.4%, and the gas distribution (volume fraction %) was: CH4 (99.0%), C2-C4 (0.4%), and CO2 (0.6%).

[0058] Example 5

[0059] Weigh 0.5 g of Raney Ni-Sn catalyst and add it to a 50 mL reactor, along with 1.0 g of polypropylene powder. Seal the reactor, purge with N2 3-5 times to expel air, then purge with H2 3-5 times to expel N2, and finally purge with H2 at 4 MPa. Heat to 300 °C using electric heating under magnetic stirring at 800 rpm for 30 min. After the reaction, stop stirring and cool the reactor to room temperature in an ice-water bath. Record the reaction termination temperature and pressure. Open the gas outlet and collect the generated gas using a gas bag for gas phase analysis. Add water to the reactor, remove the catalyst after reaction, centrifuge it, and recycle it.

[0060] The natural gas yield was found to be 83.4%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.4%), and CO2 (0.4%).

[0061] Example 6

[0062] Weigh 0.6 g of Raney Ni-Cu catalyst and add it to a 50 mL reactor, along with 1.2 g of polypropylene powder. Seal the reactor, purge with N2 3-5 times to expel air, then purge with H2 3-5 times to expel N2, and finally purge with H2 at 4 MPa. Heat to 310 °C using electric heating under magnetic stirring at 800 rpm for 300 min. After the reaction, stop stirring and cool the reactor to room temperature in an ice-water bath. Record the reaction termination temperature and pressure. Open the gas outlet and collect the generated gas using a gas bag for gas phase analysis. Add water to the reactor, remove the catalyst after reaction, centrifuge it, and recycle it.

[0063] The natural gas yield was found to be 80.4%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.4%), and CO2 (0.4%).

[0064] Example 7

[0065] The preparation process described in Example 1 was repeated, except that polypropylene powder was replaced with polypropylene particles. The resulting gaseous product was natural gas with a yield of 88.2% and a gas distribution (volume fraction %) of: CH4 (99.0%), C2-C4 (0.4%), and CO2 (0.6%).

[0066] Example 8

[0067] The preparation process described in Example 1 was repeated, except that the polypropylene powder was replaced with a folder. The resulting gaseous product was natural gas with a yield of 87.1% and a gas distribution (volume fraction %) of: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0068] Example 9

[0069] The preparation process described in Example 1 was repeated, except that the polypropylene powder was replaced with a takeout box. The resulting gaseous product was natural gas with a yield of 83.4%, and the gas distribution (volume fraction %) was: CH4 (99.0%), C2-C4 (0.1%), and CO2 (0.9%).

[0070] Example 10

[0071] The preparation process described in Example 1 was repeated, except that the polypropylene powder was replaced with a mask. The resulting gaseous product was natural gas with a yield of 86.2%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0072] Example 11

[0073] The preparation process described in Example 1 was repeated, except that the polypropylene powder was replaced with polyethylene powder. The resulting gaseous product was natural gas with a yield of 83.5% and a gas distribution (volume fraction %) of: CH4 (99.0%), C2-C4 (0.1%), and CO2 (0.9%).

[0074] Example 12

[0075] The preparation process described in Example 1 was repeated, except that the polypropylene powder was replaced with a plastic bag. The resulting gaseous product was natural gas with a yield of 86.3%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0076] Example 13

[0077] The preparation process described in Example 2 was repeated, except that polypropylene powder was replaced with polypropylene particles. The resulting gaseous product was natural gas with a yield of 87.1% and a gas distribution (volume fraction %) of CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0078] Example 14

[0079] The preparation process described in Example 2 was repeated, except that the polypropylene powder was replaced with a folder. The resulting gaseous product was natural gas with a yield of 84.2% and a gas distribution (volume fraction %) of: CH4 (98.2%), C2-C4 (1.2%), and CO2 (0.6%).

[0080] Example 15

[0081] The preparation process described in Example 2 was repeated, except that the polypropylene powder was replaced with a takeout box. The resulting gaseous product was natural gas with a yield of 83.3%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0082] Example 16

[0083] The preparation process described in Example 2 was repeated, except that the polypropylene powder was replaced with a mask. The resulting gaseous product was natural gas with a yield of 85.4%, and the gas distribution (volume fraction %) was: CH4 (99.5%), C2-C4 (0.2%), and CO2 (0.3%).

[0084] Example 17

[0085] The preparation process described in Example 2 was repeated, except that the polypropylene powder was replaced with polyethylene powder. The resulting gaseous product was natural gas with a yield of 84.1% and a gas distribution (volume fraction %) of: CH4 (99.4%), C2-C4 (0.1%), and CO2 (0.5%).

[0086] Example 18

[0087] The preparation process described in Example 2 was repeated, except that the polypropylene powder was replaced with a plastic bag. The resulting gaseous product was natural gas with a yield of 86.2%, and the gas distribution (volume fraction %) was: CH4 (99.3%), C2-C4 (0.2%), and CO2 (0.5%).

[0088] Example 19

[0089] The preparation process described in Example 3 was repeated, except that polypropylene powder was replaced with polypropylene particles. The resulting gaseous product was natural gas with a yield of 87.1% and a gas distribution (volume fraction %) of: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0090] Example 20

[0091] The preparation process described in Example 3 was repeated, except that the polypropylene powder was replaced with a folder. The resulting gaseous product was natural gas with a yield of 87.2% and a gas distribution (volume fraction %) of: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0092] Example 21

[0093] The preparation process described in Example 3 was repeated, except that the polypropylene powder was replaced with a takeout box. The resulting gaseous product was natural gas with a yield of 87.5%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0094] Example 22

[0095] The preparation process described in Example 3 was repeated, except that the polypropylene powder was replaced with a mask. The resulting gaseous product was natural gas with a yield of 87.2%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0096] Example 23

[0097] The preparation process described in Example 3 was repeated, except that the polypropylene powder was replaced with polyethylene powder. The resulting gaseous product was natural gas with a yield of 84.1% and a gas distribution (volume fraction %) of CH4 (99.4%), C2-C4 (0.1%), and CO2 (0.5%).

[0098] Example 24

[0099] The preparation process described in Example 3 was repeated, except that the polypropylene powder was replaced with a plastic bag. The resulting gaseous product was natural gas with a yield of 86.3%, and the gas distribution (volume fraction %) was: CH4 (99.3%), C2-C4 (0.2%), and CO2 (0.5%).

[0100] Example 25

[0101] The preparation process described in Example 4 was repeated, except that polypropylene powder was replaced with polypropylene particles. The resulting gaseous product was natural gas with a yield of 88.2% and a gas distribution (volume fraction %) of: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0102] Example 26

[0103] The preparation process described in Example 4 was repeated, except that the polypropylene powder was replaced with a folder. The resulting gaseous product was natural gas with a yield of 79.1% and a gas distribution (volume fraction %) of: CH4 (97.3%), C2-C4 (1.1%), and CO2 (1.6%).

[0104] Example 27

[0105] The preparation process described in Example 4 was repeated, except that the polypropylene powder was replaced with a takeout box. The resulting gaseous product was natural gas with a yield of 78.2%, and the gas distribution (volume fraction %) was: CH4 (97.2%), C2-C4 (0.4%), and CO2 (2.4%).

[0106] Example 28

[0107] The preparation process described in Example 4 was repeated, except that the polypropylene powder was replaced with a mask. The resulting gaseous product was natural gas with a yield of 84.1%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0108] Example 29

[0109] The preparation process described in Example 4 was repeated, except that the polypropylene powder was replaced with polyethylene powder. The resulting gaseous product was natural gas with a yield of 84.2% and a gas distribution (volume fraction %) of: CH4 (99.4%), C2-C4 (0.1%), and CO2 (0.5%).

[0110] Example 30

[0111] The preparation process described in Example 4 was repeated, except that the polypropylene powder was replaced with a plastic bag. The resulting gaseous product was natural gas with a yield of 86.3%, and the gas distribution (volume fraction %) was: CH4 (99.3%), C2-C4 (0.2%), and CO2 (0.5%).

[0112] Example 31

[0113] The preparation process described in Example 5 was repeated, except that polypropylene powder was replaced with polypropylene particles. The resulting gaseous product was natural gas with a yield of 85.3% and a gas distribution (volume fraction %) of: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0114] Example 32

[0115] The preparation process described in Example 5 was repeated, except that the polypropylene powder was replaced with a folder. The resulting gaseous product was natural gas with a yield of 86.2% and a gas distribution (volume fraction %) of: CH4 (99.6%), C2-C4 (0.1%), and CO2 (0.3%).

[0116] Example 33

[0117] The preparation process described in Example 5 was repeated, except that the polypropylene powder was replaced with a takeout box. The resulting gaseous product was natural gas with a yield of 82.6%, and the gas distribution (volume fraction %) was: CH4 (99.1%), C2-C4 (0.3%), and CO2 (0.6%).

[0118] Example 34

[0119] The preparation process described in Example 5 was repeated, except that the polypropylene powder was replaced with a mask. The resulting gaseous product was natural gas with a yield of 86.4%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0120] Example 35

[0121] The preparation process described in Example 5 was repeated, except that the polypropylene powder was replaced with polyethylene powder. The resulting gaseous product was natural gas with a yield of 84.2% and a gas distribution (volume fraction %) of: CH4 (99.4%), C2-C4 (0.1%), and CO2 (0.5%).

[0122] Example 36

[0123] The preparation process described in Example 5 was repeated, except that the polypropylene powder was replaced with a plastic bag. The resulting gaseous product was natural gas with a yield of 86.2%, and the gas distribution (volume fraction %) was: CH4 (99.3%), C2-C4 (0.2%), and CO2 (0.5%).

[0124] Example 37

[0125] The preparation process described in Example 6 was repeated, except that polypropylene powder was replaced with polypropylene particles. The resulting gaseous product was natural gas with a yield of 84.4% and a gas distribution (volume fraction %) of: CH4 (97.2%), C2-C4 (1.2%), and CO2 (1.6%).

[0126] Example 38

[0127] The preparation process described in Example 6 was repeated, except that the polypropylene powder was replaced with a folder. The resulting gaseous product was natural gas with a yield of 78.2% and a gas distribution (volume fraction %) of: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0128] Example 39

[0129] The preparation process described in Example 6 was repeated, except that the polypropylene powder was replaced with a takeout box. The resulting gaseous product was natural gas with a yield of 79.6%, and the gas distribution (volume fraction %) was: CH4 (96.4%), C2-C4 (2.2%), and CO2 (1.4%).

[0130] Example 40

[0131] The preparation process described in Example 6 was repeated, except that the polypropylene powder was replaced with a mask. The resulting gaseous product was natural gas with a yield of 79.2%, and the gas distribution (volume fraction %) was: CH4 (99.2%), C2-C4 (0.2%), and CO2 (0.6%).

[0132] Example 41

[0133] The preparation process described in Example 6 was repeated, except that the polypropylene powder was replaced with polyethylene powder. The resulting gaseous product was natural gas with a yield of 86.1% and a gas distribution (volume fraction %) of CH4 (99.2%), C2-C4 (0.1%), and CO2 (0.7%).

[0134] Example 42

[0135] The preparation process described in Example 6 was repeated, except that the polypropylene powder was replaced with a plastic bag. The resulting gaseous product was natural gas with a yield of 86.2%, and the gas distribution (volume fraction %) was: CH4 (99.3%), C2-C4 (0.2%), and CO2 (0.5%).

[0136] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for producing natural gas from plastics, characterized in that, Natural gas is obtained by mixing plastic with a catalyst in a solvent-free system and reacting the mixture in a closed pressure vessel containing a reducing atmosphere. The catalyst is a Raney-type catalyst; The Raney catalyst is Raney Ni or a Raney catalyst supported on a bimetallic substrate; The amount of catalyst added is 20% to 70% of the mass of the plastic; The reducing atmosphere is introduced at a pressure of 0.1~7 MPa; The reaction temperature is 250~350℃.

2. The method according to claim 1, characterized in that, The Raney-type catalyst supported on a bimetallic substrate is selected from at least one of Raney Ni-Al, Raney Ni-Mo, Raney Ni-Sn, Raney Ni-Fe, or Raney Ni-Cu.

3. The method according to claim 1, characterized in that, The plastic is a polyolefin plastic.

4. The method according to claim 3, characterized in that, The polyolefin plastic is selected from at least one of polyethylene plastics and polypropylene plastics.

5. The method according to claim 1, characterized in that, The method also includes the separation and reuse of catalysts and the separation and reuse of reducing atmospheres.

6. The method according to claim 1, characterized in that, The amount of catalyst added is 50% to 70% of the mass of the plastic.

7. The method according to claim 1, characterized in that, The reducing atmosphere is a hydrogen atmosphere.

8. The method according to claim 1, characterized in that, The reducing atmosphere is introduced at a pressure of 1-4 MPa.

9. The method according to claim 1, characterized in that, The reducing atmosphere is introduced at a pressure of 2-4 MPa.

10. The method according to claim 1, characterized in that, The reaction temperature is 280~350℃.

11. The method according to claim 1, characterized in that, The reaction temperature is 300~350℃.

12. The method according to claim 1, characterized in that, The reaction time is 0.05~25h.

13. The method according to claim 1, characterized in that, The reaction time is 0.05~10h.

14. The method according to claim 1, characterized in that, The reaction time is 0.5 to 10 hours.

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