Method for preparing pyrolytic fuel oil from waste plastics

Abstract

The invention provides a method for preparing pyrolytic oil from waste plastics. The method comprises the following steps: (S1) pyrolyzing a waste plastic raw material; (S2) condensing the gaseous stream produced by pyrolysis to obtain a liquid oil; and (S3) refining the liquid oil, wherein the pyrolysis is carried out under heating conditions in the range of 430 DEG C to 450 DEG C.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0061371, filed on May 11, 2023, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to pyrolyzing waste plastics into fuel oil, and more particularly to a method for preparing light hydrocarbon oil in high yield by improving the pyrolysis efficiency of waste plastics. Background Art

[0004] Recently, the development and use of plastics with physical properties required for various applications and purposes has increased. A lot of energy is required from crude oil extraction to the preparation of plastics, and a large amount of carbon is emitted in the process. In addition, when plastics used in various products are discarded, it also causes environmental pollution and huge processing costs. Therefore, the recycling of waste plastics has become an important social issue.

[0005] Generally, methods for recycling waste plastics (resins) include mechanical recycling, chemical recycling, and thermal recycling. Mechanical recycling is a method of crushing and screening the collected waste plastics, separating the waste plastics by type, melting the waste plastics using an extruder, and mixing the waste plastics with a certain proportion of new materials or adding functional additives when granulating the waste materials to prepare resin products. Chemical recycling is a method of using various chemical means to extract only specific polymers, or to recover and repolymerize pure single molecules. Thermal recycling is a method of burning waste plastics and recovering the waste plastics as heat energy.

[0006] In particular, chemical recycling can reduce greenhouse gases compared to the incineration of waste plastics and has recently attracted much attention in the development of alternative fuels.

[0007] For example, when waste plastics such as polyethylene or polypropylene materials are heated and pyrolyzed at a certain temperature, a gaseous stream containing a mixture of non-condensable gas and liquid oil is generated, leaving a highly viscous residual wax that is not completely decomposed. In view of the increasing importance of liquid oil in pyrolysis products as fuel oil for producing petrochemical products, research on improving the yield of liquid oil has been actively conducted.

[0008] The liquid oil produced by pyrolysis of waste plastics, namely pyrolysis oil, usually contains C 5-12 A mixture of light hydrocarbon oil (such as naphtha) and longer chain hydrocarbon oil. When such a mixture contains a large amount of high boiling point (heavy) components, the yield of high value-added light hydrocarbon oil is limited and the residual wax discharged is excessive.

[0009] In order to solve these problems, methods have been proposed, such as a method of performing a contact decomposition reaction by catalytic cracking during the pyrolysis of waste plastics; and a method of using a contactor to condense heavy hydrocarbon (i.e., long-chain hydrocarbon) components in the pyrolysis products of waste plastics and then recycling the components to a pyrolysis reactor to subject these components to a pyrolysis process again. However, these methods have limitations in improving the pyrolysis efficiency of waste plastics and are therefore only used for recycling mixed oil.

[0010] Therefore, there is a need to develop a technology that can improve the pyrolysis process of waste plastics and improve the yield of high-quality light hydrocarbon oil. Summary of the invention

[0011] Technical issues

[0012] In order to solve the problems mentioned in the background art, the object of the present invention relates to a method for preparing light hydrocarbon oil in high yield by improving the pyrolysis efficiency of waste plastics by pyrolyzing the waste plastics under elevated temperature conditions within a predetermined temperature range rather than at a single temperature.

[0013] Technical Solution

[0014] In general, the method for preparing pyrolysis oil from waste plastics includes: (S1) pyrolyzing the waste plastic raw material; (S2) condensing the gaseous stream generated by the pyrolysis to obtain liquid oil; and (S3) refining the liquid oil, wherein the pyrolysis is carried out under elevated temperature conditions in the range of 430°C to 450°C.

[0015] Beneficial Effects

[0016] According to the present invention, since the pyrolysis of waste plastics is carried out under elevated temperature conditions in the range of 430°C to 450°C, the decomposition efficiency of the waste plastics is improved, thereby increasing the yield of high-quality light hydrocarbon oil and minimizing the discharge of underutilized residual wax.

[0017] In addition, the use of light hydrocarbon fuel oil obtained from the pyrolysis of waste plastics can reduce greenhouse gas emissions caused by supplying raw materials to petrochemical processes, can improve process efficiency (such as saving energy consumption), and can be environmentally beneficial because no harmful gases are produced when processing waste plastics. DETAILED DESCRIPTION

[0018] The terms and words used in the specification and claims of the present invention should not be understood restrictively as having conventional or dictionary meanings, but should be understood as having meanings and concepts consistent with the technical concept of the present invention based on the principle that inventors can appropriately define the concepts of the terms in order to best describe their own inventions.

[0019] The meanings of “comprising” or “including” used in this application specify specific features, regions, integers, steps, operations, elements and / or components, and do not exclude other specific features, regions, integers, steps, operations, elements and / or components.

[0020] The term "stream" used in this application may refer to a fluid flow in a process, or may refer to a fluid flowing through a pipeline itself. Specifically, the stream may refer to the fluid itself flowing through pipelines connecting various devices, or may refer to a fluid stream. In addition, a fluid may include any one or more components of a gas, a liquid, and a solid.

[0021] The term "C n ” refers to all hydrocarbons with n carbon atoms, for example, “C 5-12 ” refers to all hydrocarbon molecules having 5 to 12 carbon atoms.

[0022] The term "liquid oil" used in the present application refers to the product obtained by converting the gaseous stream obtained in the pyrolysis step into a liquid state by condensation, and may also be referred to as "liquid distillate oil".

[0023] In addition, the “pressure” referred to in the present application refers to the absolute pressure measured based on a complete vacuum.

[0024] A method for preparing pyrolysis oil from waste plastics according to an embodiment of the present invention comprises: (S1) pyrolyzing the waste plastic raw material, (S2) condensing a gaseous stream generated by the pyrolysis to obtain liquid oil, and (S3) refining the liquid oil.

[0025] Hereinafter, each step of the method for preparing pyrolysis oil from waste plastics according to the present invention will be described in detail.

[0026] In the present invention, the waste plastic raw material is pyrolyzed under a temperature increase condition ranging from 430° C. to 450° C. ( S1 ).

[0027] Waste plastics can include natural polymers, synthetic polymers or mixtures thereof, and synthetic polymers can include thermoplastic resins, such as polyethylene, polypropylene and polystyrene. In addition, thermoplastic resins can also be other types of resins, such as mixtures of PVC and PET, thermosetting resins, etc.

[0028] Waste plastics (such as these materials) can be collected and screened, and then go through a pretreatment process including crushing, washing, drying and melting. The pretreatment process can be carried out by conventional methods in the art.

[0029] For example, the size of the pulverized waste plastic is not particularly limited, but the waste plastic can be pulverized to a size range of 0.5 cm to 6.0 cm, and then the washed and dried waste plastic pulverized material is placed in a tubular melter (e.g., an extruder) and then melted. The extruder has an extrusion function of melting and kneading, for example, it can be a twin-screw extruder. When the waste plastic is a thermoplastic resin, such as polyethylene, polypropylene, or a mixture thereof, the melting temperature can be 120° C. to 350° C., or 150° C. to 250° C., but is not limited thereto.

[0030] The waste plastic melt obtained by the pretreatment process can be supplied to the pyrolysis reactor as a raw material. The pyrolysis reactor that can be used in the present invention can be a stirred tank reactor equipped with an agitator, and the agitator is not particularly limited, as long as it can fully stir the waste plastic melt supplied as a raw material, and can be, for example, a spiral belt type or an anchor type, and advantageously, a gap of about 5mm to 1cm is maintained with the inner wall of the reactor to maximize the stirring of the waste plastic and heat transfer through the reactor wall. In addition, the reactor can be operated intermittently or continuously. In addition, the reactor can be purged with nitrogen to maintain an oxygen-free or low-oxygen atmosphere while performing the pyrolysis reaction of the waste plastic melt.

[0031] The waste plastic melt is supplied to the stirred reactor and heated, while the stirrer is operated, to pyrolyze the waste plastic melt. The heating of the waste plastic can be performed by transferring high temperature heat to the waste plastic by passing high temperature / high pressure steam, hot water, heat transfer fluid, etc. through a jacket provided outside the reactor, but is not particularly limited thereto.

[0032] Generally, when waste plastics are pyrolyzed, C 1-4 Gas composition, C 5-12 Light hydrocarbons (such as naphtha) and longer chain hydrocarbon components evaporate and are discharged through the top of the reactor, and high-viscosity residual wax is not evaporated and remains at the bottom of the reactor. When the amount of high-boiling point components in the evaporated top discharge is large, the yield of high value-added light hydrocarbon oil is limited, the high-viscosity residual wax is not fully utilized, and it becomes an obstacle to process operation or leads to a decrease in the quality of the final product.

[0033] Therefore, the present invention increases the selectivity of conversion into light hydrocarbons during pyrolysis of waste plastics by transferring heat to the waste plastics at a constant rate (e.g., 5°C / min to 20°C / min or 10°C / min to 15°C / min) to heat the waste plastic feedstock to 430°C, and maintaining a stepwise temperature increase condition from 430°C to 450°C.

[0034] In the temperature-increasing pyrolysis, as the reaction temperature gradually increases within a specific temperature range where the waste plastic decomposition reaction is active, the pyrolysis reaction efficiency is improved compared to pyrolysis at a single temperature, and the selectivity of conversion to light hydrocarbons can be increased. Therefore, the amount of residual wax can be minimized, while the yield of light hydrocarbon oil can be increased relative to the supply of waste plastic raw materials.

[0035] Meanwhile, the waste plastic raw material is mainly a thermoplastic resin, for example, considering that the waste plastic is a mixture containing polyethylene with a number average molecular weight of 10,000 to 500,000 (specifically 100,000 to 300,000) or polypropylene with a number average molecular weight of 5,000 to 300,000 (specifically 10,000 to 200,000), the pyrolysis reaction can be advantageously carried out within the range of 430° C. to 450° C. When the pyrolysis temperature is lower than 430° C., the pyrolysis rate can be slowed down, and the conversion to light hydrocarbons is reduced, and when the pyrolysis temperature is higher than 450° C., the yield of solid carbides (such as char) increases due to excessive reaction caused by high heat.

[0036] The pyrolysis under elevated temperature conditions may include pyrolysis by multi-stage temperature increase or linear temperature increase.

[0037] In the pyrolysis performed by multi-stage temperature increase, the pyrolysis of each stage can be performed under isothermal conditions or under temperature increase conditions, and the pyrolysis temperature of the latter stage is higher than the pyrolysis temperature of the previous stage. For example, when three-stage temperature increase is applied, the pyrolysis gas generated by heating the waste plastic raw material to 430°C and then maintaining the constant temperature at 430°C for a certain period of time while performing the pyrolysis reaction can be discharged through the top of the reactor, and the pyrolysis gas generated by heating the residue in the primary pyrolysis to 440°C and then maintaining the constant temperature at 440°C for a certain period of time while performing the pyrolysis reaction can be discharged through the top of the reactor again; then the pyrolysis gas generated by heating the residue in the secondary pyrolysis to 450°C and then maintaining the constant temperature at 450°C for a certain period of time while performing the pyrolysis reaction can be discharged through the top of the reactor. Alternatively, the waste plastic raw material can be heated to 430°C, and then the temperature can be gradually increased from 430°C to 440°C for a certain period of time, and the temperature can be gradually increased from 440°C to 450°C for a certain period of time. Then, the pyrolysis can be performed while heating the waste plastic raw material to 430°C, gradually increasing the temperature from 430°C to 440°C for a certain period of time, and then finally, the pyrolysis can be performed at 450°C for a certain period of time.

[0038] Meanwhile, the pyrolysis by linear temperature increase may be performed within a range of 430° C. to 450° C. at a heating rate of 0.1° C. / min to 0.2° C. / min.

[0039] In one embodiment of the present invention, the pyrolysis under the condition of temperature increase can be carried out at a pressure of 0.9 bar to 1.1 bar for 1 hour to 3 hours. The time of the pyrolysis reaction can be determined according to the time when the generation rate of light hydrocarbons with a carbon number of 12 or less in each temperature section of 430° C. to 450° C. increases after the pyrolysis reaction of the waste plastic starts.

[0040] In addition, the pyrolysis under the temperature increase conditions of the present invention can be carried out in the same reactor or in a plurality of reactors connected in series. For example, in one pyrolysis reactor, the components evaporated by the initial pyrolysis reaction can be discharged through the top, and then the remaining residue can be subjected to subsequent pyrolysis in sequence, or the residue can be transferred to another pyrolysis reactor connected in series at the bottom of the pyrolysis reactor, and the subsequent pyrolysis can be continuously carried out.

[0041] The pyrolysis gas produced by pyrolysis under elevated temperature conditions in the temperature range of 430°C to 450°C can be discharged through the top of the reactor. The gaseous stream discharged through the top of the reactor may contain C 1-4 Hydrocarbon, C 5-12 Hydrocarbon, C 13-22 Hydrocarbons and C 23-40 hydrocarbon.

[0042] Subsequently, the gaseous stream produced by the pyrolysis is condensed to obtain liquid oil (S2).

[0043] Condensation is a process of cooling the pyrolysis gas, by which the polymerization reaction of hydrocarbons in the high-temperature pyrolysis gas discharged from the pyrolysis reactor can be suppressed, thereby reducing the heat load of the subsequent process (refining process). For example, when the gaseous stream discharged through the top of the pyrolysis reactor is supplied to the condenser and heat-exchanged with quenching oil or quenching water, the gaseous stream can be cooled and condensed and liquid oil can be obtained thereby, and the liquid oil can be discharged through the bottom of the condenser and transferred to a storage tank. At the same time, the gas components (such as C 1-4 Hydrocarbons) can be discharged through the top and can be used as a heat source in petrochemical processes through subsequent processes (such as compression).

[0044] If necessary, the operating temperature of the condenser may be varied within a range of 430° C. to 450° C. in consideration of the temperatures of pyrolysis products discharged at various temperature sections during pyrolysis under elevated temperature conditions. For example, when pyrolysis under elevated temperature conditions is performed in three reactors, the temperature may be set according to the liquid level of the reactor connected to the condenser, so that the operating temperature of the condenser may be adjusted in various ways.

[0045] The amount of liquid oil obtained by condensation is 80 to 90 wt % based on the weight of the waste plastic raw material, which means that residual wax that is not decomposed due to high viscosity is discharged in a small amount of 20 wt % or less.

[0046] Specifically, the liquid oil may contain C 5-12 Light oil (LO), C 13-22 Medium oil (MO) and C 23-40 Heavy oil (HO).

[0047] Among them, based on the total weight of liquid oil, C 5-12 The amount of light oil (LO) may be 40 wt % to 60 wt %. In addition, based on the weight of the waste plastic raw material before pyrolysis, C 5-12 The amount of light oil (LO) may range from 35 wt% to 50 wt%.

[0048] That is, in the present invention, when the waste plastic is pyrolyzed under an elevated temperature condition ranging from 430° C. to 450° C., the decomposition efficiency of the waste plastic is improved, so that C 5-12 Light oil (LO).

[0049] Thereafter, the liquid oil is refined to separate components (S3).

[0050] Since the liquid oil obtained by temperature-raising pyrolysis and condensation is a mixed oil containing light hydrocarbons and longer-chain hydrocarbons, the liquid oil is supplied to a multi-stage distillation column and subjected to a refining process of stepwise separation according to boiling points.

[0051] The refining process can be carried out in a conventional manner in the art without particular limitation. For example, the feed stream supplied to the distillation tower may contain all light oil and heavy oil components obtained by pyrolysis of waste plastics, a stream containing low-boiling light hydrocarbons may be discharged through the top of the distillation tower, and a stream containing high-boiling heavy hydrocarbons may be discharged through the bottom of the distillation tower.

[0052] Meanwhile, when the temperature-raising pyrolysis of the present invention is carried out in a plurality of pyrolysis reactors connected in series, the pipes connecting the various reactors and the distillation towers may be connected at different positions to optimize the operating heat of the towers.

[0053] The feed stream supplied to the distillation column is a stream containing an oil component (i.e., C 5-12 Light oil (LO), C 13-22 Medium oil (MO) and C 23-40 Heavy oil (HO)) mixed oil, containing C 5-12 A stream of light components can be separated and discharged through the top of the distillation column.

[0054] In one embodiment of the present invention, the C separated at the top of the distillation tower 5-12The amount of light hydrocarbons can be 40% to 60% by weight of the total weight of the feed stream (i.e., liquid oil (mixed oil)), or 35% to 50% by weight of the weight of the waste plastic raw material. 5-12 The light hydrocarbons are condensed and then efficiently used as high-quality fuel oil.

[0055] In particular, the present invention finally obtains C 5-12 Light hydrocarbon fuel oil has a boiling point of 0°C to 230°C, specifically 30°C to 216°C, a kinematic viscosity at 40°C of 0.3 cSt to 1.0 cSt, specifically 0.4 cSt to 0.9 cSt, and a flash point of above -80°C (eg -40°C), and can therefore be effectively used as a petrochemical raw material.

[0056] As described above, according to the present invention, when pyrolysis of waste plastics is performed under elevated temperature conditions of 430°C to 450°C, the decomposition efficiency of the waste plastics can be improved, thereby increasing the yield of high-quality light hydrocarbon oil and minimizing the discharge of underutilized residual wax.

[0057] In addition, the use of light hydrocarbon oil obtained from the pyrolysis of waste plastics can reduce greenhouse gas emissions caused by supplying raw materials to petrochemical processes, can improve process efficiency (e.g., energy saving), and can be environmentally beneficial because no harmful gases are produced when processing waste plastics.

[0058] Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are provided for illustration of the present invention. It will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0059] Embodiment 1:

[0060] 100 parts by weight of a waste plastic melt containing polyethylene (PE) and polypropylene (PP) in a weight ratio of 6:4 was prepared and pyrolyzed under three-stage temperature rising conditions using three stirred reactors connected in series.

[0061] Specifically, the waste plastic melt is supplied to the first reactor, heated to 430° C. at atmospheric pressure (1 bar), primary pyrolysis is performed while the temperature is kept constant at 430° C. for 40 minutes, and the generated pyrolysis gas is discharged through the top of the first reactor. The stream discharged through the top of the first reactor is introduced into a condenser connected to the reactor, and then cooled to 25° C. to obtain condensed liquid distillate oil, and uncondensed gas components are discharged.

[0062] The residue from the primary pyrolysis at the bottom of the first reactor is supplied to the second reactor connected in series with the first reactor, heated to 440° C. at atmospheric pressure (1 bar), and while the temperature is kept constant at 440° C. for 40 minutes, secondary pyrolysis is performed, and the generated gas is discharged from the top of the second reactor. The stream discharged through the top of the second reactor is introduced into a condenser connected to the reactor, and then cooled to 25° C. to obtain condensed liquid oil, and uncondensed gas components are discharged.

[0063] The residue from the secondary pyrolysis at the bottom of the second reactor was supplied to a third reactor connected in series with the second reactor, heated to 450° C. at atmospheric pressure (1 bar), and the generated gas was discharged through the top of the third reactor while the temperature was kept constant at 450° C. for 40 minutes. The stream discharged through the top of the third reactor was introduced into a condenser connected to the reactor, and then cooled to 25° C. to obtain condensed liquid oil, and uncondensed gas components were discharged.

[0064] The liquid oil obtained by passing through each of the first to third reactors and the condenser connected thereto is supplied to a distillation column and separated and purified according to the boiling point, thereby finally preparing C 5-12 Light hydrocarbon fuel oil.

[0065] Embodiment 2:

[0066] The same process as in Example 1 was performed, except that the pyrolysis of the waste plastic melt was performed under three-stage heating conditions of 430°C for 30 minutes, 440°C for 60 minutes, and 450°C for 30 minutes.

[0067] Embodiment 3:

[0068] The same process as in Example 1 was performed, except that the pyrolysis of the waste plastic melt was performed under linear temperature increasing conditions of gradually increasing the temperature from 430° C. to 450° C. over 120 minutes.

[0069] Comparative Example 1:

[0070] 100 parts by weight of a waste plastic melt containing polyethylene (PE) and polypropylene (PP) in a weight ratio of 6:4 was supplied to a pyrolysis reactor and heated to 430° C., and then pyrolyzed while maintaining the temperature of 430° C. for 180 minutes.

[0071] The stream discharged from the top of the reactor was introduced into a condenser connected to the reactor, and then cooled to 25° C. to obtain condensed liquid oil, and uncondensed gas components were discharged.

[0072] The liquid oil is supplied to a distillation column and refined by separation according to the boiling point, thereby finally preparing C 5-12 Light hydrocarbon fuel oil.

[0073] Comparative Example 2:

[0074] The same process as in Comparative Example 1 was performed except that the waste plastic melt was heated to 440° C. and then pyrolyzed while being maintained at a temperature of 440° C. for 120 minutes.

[0075] Comparative Example 3:

[0076] The same process as in Comparative Example 1 was performed, except that the waste plastic melt was heated to 450° C. and then pyrolyzed while being maintained at a temperature of 450° C. for 120 minutes.

[0077] Comparative Example 4:

[0078] The same process as in Example 1 was performed, except that the pyrolysis of the waste plastic melt was performed under three-stage temperature rising conditions of 410°C for 40 minutes, 420°C for 40 minutes, and 430°C for 40 minutes.

[0079] Comparative Example 5:

[0080] The same process as in Example 1 was performed, except that the pyrolysis of the waste plastic melt was performed under three-stage heating conditions of 420° C. for 40 minutes, 430° C. for 40 minutes, and 440° C. for 40 minutes.

[0081] Comparative Example 6:

[0082] The same process as in Example 1 was performed, except that the pyrolysis of the waste plastic melt was performed under three-stage heating conditions of 440° C. for 40 minutes, 450° C. for 40 minutes, and 460° C. for 40 minutes.

[0083] Comparative Example 7:

[0084] The same process as in Example 1 was performed, except that the pyrolysis of the waste plastic melt was performed under three-stage heating conditions of 450°C for 40 minutes, 460°C for 40 minutes, and 470°C for 40 minutes.

[0085] The composition of the liquid oil obtained by condensation after pyrolysis of the waste plastics in the examples and comparative examples was analyzed by GC-MS, and the uncondensed C 1-4 Gas, condensed liquid oil (C 5-12 Light oil (LO), C 13-22 Medium oil (MO), C 23-40 Fractions of heavy oil (HO) and residue.

[0086] Table 1 shows the LO (C5-12 ) fraction and LO(C) based on the supply of waste plastic raw materials 5-12 ) yield.

[0087] [Table 1]

[0088]

[0089]

[0090] In Table 1, it can be confirmed that in Examples 1 to 3, when the pyrolysis of waste plastics is carried out under the condition of increasing temperature within the range of 430°C to 450°C, C 5-12 The yield of light oil (LO) was improved compared with the comparative example.

[0091] Specifically, in Comparative Examples 1 to 3 where pyrolysis was performed at a single temperature, the yield distribution of light hydrocarbons was unstable. In particular, in Comparative Example 3 where pyrolysis was performed at 450° C., the decomposition rate increased, but the yield of solid carbides (such as char) increased. Therefore, the yield of liquid oil decreased based on the supply amount of the raw material.

[0092] Meanwhile, in Comparative Example 4, in which pyrolysis was performed under elevated temperature conditions, the pyrolysis rate decreased as the pyrolysis start and end temperatures decreased. As a result, a small amount of the raw material remained in the form of high-viscosity wax, and the yield of liquid oil could not be measured.

[0093] In Comparative Examples 5 to 7 where the temperature increase condition is outside the range of 430°C to 450°C, C 5-12 The yield of light oil (LO) decreases. In particular, in Comparative Examples 6 and 7, as the start and end temperatures of pyrolysis increase, the yield of liquid oil based on the supply amount decreases, and the amount of discharged residue increases.

Claims

1. A method for preparing pyrolysis oil from waste plastics, the method comprising: (S1) pyrolyzing the waste plastic raw material; (S2) condensing a gaseous stream produced by pyrolysis to obtain liquid oil; as well as (S3) refining the liquid oil, The pyrolysis is carried out under elevated temperature conditions ranging from 430°C to 450°C.

2. The method according to claim 1, wherein: The pyrolysis is carried out in the same reactor or in a plurality of reactors connected in series.

3. The method according to claim 1, wherein: The pyrolysis includes pyrolysis performed by multi-stage temperature increase or linear temperature increase.

4. The method according to claim 1, wherein: The pyrolysis is carried out by multi-stage temperature increase, wherein each stage is maintained at an isothermal or temperature increase condition, and the pyrolysis temperature of the latter stage is higher than the pyrolysis temperature of the former stage.

5. The method according to claim 1, wherein: The pyrolysis is performed by linearly increasing the temperature in the range of 430° C. to 450° C. at a temperature increase rate of 0.1° C. / min to 0.2° C. / min.

6. The method according to claim 1, wherein: The pyrolysis is carried out for 1 hour to 3 hours.

7. The method according to claim 1, wherein: The liquid oil is obtained in an amount of 80 wt % to 90 wt % relative to the weight of the waste plastic raw material.

8. The method according to claim 1, wherein: The liquid oil contains C 5-12 Light oil (LO), C 13-22 Medium oil (MO) and C 23-40 A mixture of heavy oil (HO).

9. The method according to claim 8, wherein: C 5-12 The content of light oil (LO) is 40 to 60 wt % based on the total weight of the liquid oil.

10. The method according to claim 8, wherein: Relative to the weight of the waste plastic raw material, 35 wt % to 50 wt % of C is obtained. 5-12 Light oil (LO).

11. The method according to claim 1, wherein: The waste plastic raw material comprises a mixture containing polyethylene (PE) or polypropylene (PP).

12. The method according to claim 1, wherein: Before the waste plastic raw materials are supplied to the pyrolysis reactor, the waste plastic raw materials are subjected to a pretreatment process including crushing, washing, drying and melting.

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