Method for preparing pyrolytic oil from waste plastics

Abstract

The invention provides a method for preparing pyrolytic oil from waste plastics, which comprises the following steps: (S1) supplying a waste plastic raw material to a pyrolysis reactor for pyrolysis, discharging gaseous flow generated by pyrolysis through the top of the pyrolysis reactor, and condensing the gaseous flow to obtain liquid oil; (S2) carrying out decompression treatment and condensation on residual oil at the bottom of the pyrolysis reactor to additionally obtain liquid oil; and (S3) refining the liquid oil obtained in steps (S1) and (S2), in which the pyrolysis is carried out by controlling the internal pressure of the reactor in a range of greater than 1 bar to 40 bar.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0061366, filed on May 11, 2023, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to a method for preparing pyrolysis oil from waste plastics, 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 large amount of energy is required to produce plastics from crude oil, and a large amount of carbon is emitted in the process. In addition, when plastics used in various products are discarded, environmental pollution and huge processing costs are also caused. 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 can be generated, and highly viscous residual wax that is not completely decomposed can be discharged. According to 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 components, the yield of high value-added light hydrocarbon oil is limited, and the amount of heavy oil components produced 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 technology, the purpose of the present invention is to improve the pyrolysis efficiency of waste plastics by controlling the reaction pressure during the pyrolysis of waste plastics to suppress the evaporation of high-boiling components and selectively increase the residence time of liquid components, so as to prepare light hydrocarbon oil in high yield.

[0013] Technical Solution

[0014] In general, the method for preparing pyrolysis oil from waste plastics includes: (S1) supplying the waste plastic raw material to a pyrolysis reactor for pyrolysis, discharging the gaseous flow generated by the pyrolysis through the top of the pyrolysis reactor, and then condensing the gaseous flow to obtain liquid oil; (S2) decompressing and condensing the oil remaining at the bottom of the pyrolysis reactor to additionally obtain liquid oil; and (S3) refining the liquid oil obtained in steps (S1) and (S2), wherein the pyrolysis is carried out by controlling the internal pressure of the reactor in a range of greater than 1 bar to 40 bar.

[0015] Beneficial Effects

[0016] According to the present invention, the pyrolysis of waste plastics is carried out at a pressure higher than atmospheric pressure, thereby suppressing the evaporation of high-boiling components and selectively increasing the residence time of liquid components in the reactor, thereby improving the decomposition efficiency of waste plastics. Thus, the selectivity and productivity of light hydrocarbon oil in the pyrolysis product can be improved.

[0017] In addition, after pyrolysis under high pressure conditions, the oil remaining in the reactor is subjected to a decompression treatment to increase the evaporation of liquid hydrocarbons, thereby further increasing the yield of pyrolysis oil and minimizing the emission of residual wax.

[0018] In addition, the use of light hydrocarbon oils 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., saving energy consumption), and can be environmentally beneficial because no harmful gases are produced when processing waste plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figures 1 to 5 The high pressure pyrolysis results of waste plastics (PE / PP mixture) in Examples 1 to 5 are shown respectively.

[0020] Figure 6 The pyrolysis results of waste plastic (PE / PP mixture) in Comparative Example 1 at atmospheric pressure (1 bar) are shown. DETAILED DESCRIPTION

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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".

[0026] In addition, the “pressure” referred to in the present application refers to the absolute pressure measured based on a complete vacuum.

[0027] A method for preparing pyrolysis oil from waste plastics according to an embodiment of the present invention comprises (S1) pyrolyzing and condensing the waste plastic raw materials, (S2) heat treating and condensing the residual oil, and (S3) refining.

[0028] Hereinafter, each step of the method for preparing pyrolysis oil from waste plastics according to the present invention will be described in detail.

[0029] First, a waste plastic raw material is prepared and supplied to a pyrolysis reactor for pyrolysis (S1).

[0030] 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 and thermosetting resins etc.

[0031] 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.

[0032] 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.

[0033] 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 a stirrer (see Figures 1 to 5 ), the stirrer is not particularly limited as long as it can fully stir the waste plastic melt supplied as the raw material, and can be, for example, a spiral ribbon type or an anchor type, and advantageously, a gap of about 5 mm to 1 cm is maintained with the inner wall of the reactor to maximize 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 the pyrolysis reaction of the waste plastic melt is carried out.

[0034] The waste plastic melt is supplied to the stirred reactor and heated, and the stirrer is operated at the same time, so as to pyrolyze the waste plastic melt.

[0035] The heating of the waste plastic may be performed by transferring high-temperature heat to the waste plastic by passing high-temperature / high-pressure steam, hot water, a heat transfer fluid, etc. through a jacket provided outside the reactor, but is not particularly limited thereto.

[0036] Since the existing waste plastic pyrolysis process is usually carried out under atmospheric pressure, C 1-4 Gas composition, C 5-12Light hydrocarbons (such as naphtha) and longer chain hydrocarbons evaporate and are discharged through the top of the reactor, and the unevaporated residual wax remains at the bottom of the reactor. In the pyrolysis process carried out under atmospheric pressure conditions, a large amount of high boiling point components are contained in the discharge from the top of the reactor, so the yield of high value-added light hydrocarbon oil is limited, and the amount of heavy oil components produced and the amount of residual wax discharged are excessive.

[0037] Therefore, in order to improve the selectivity of conversion into light hydrocarbons during the pyrolysis of waste plastics, in the present invention, when the pyrolysis of the waste plastic melt is carried out, the pressure of the reactor is controlled to be higher than the atmospheric pressure, for example, a high pressure of greater than 1 bar to 40 bars, preferably 2 bars to 30 bars, and more preferably 5 bars to 10 bars. More specifically, a control valve (PCV) is installed at the top of the reactor, and when a gas exceeding a certain pressure is generated during the pyrolysis reaction of the waste plastics, the internal pressure of the reactor is controlled to be higher than the atmospheric pressure by exhausting the gas using the valve, so that the gas generated during the pyrolysis reaction can be continuously discharged through the top of the reactor.

[0038] By controlling the high pressure of the pyrolysis reactor, the evaporation of high boiling point components during the pyrolysis reaction can be suppressed and the liquid residence time of high boiling point components can be increased. Increasing the liquid residence time improves the decomposition reaction efficiency of waste plastics and increases the selectivity of conversion to light hydrocarbons, thereby producing high value-added light hydrocarbon oil with high yield.

[0039] That is, when the pressure of the pyrolysis reactor is controlled to be higher than the atmospheric pressure, as the liquid residence time increases, the pyrolysis reaction of the waste plastic can be carried out for 1 to 8 hours, specifically, 2 to 6 hours, and in this process, the conversion of the polymer into light hydrocarbons (such as C 5-12 The conversion rate of hydrocarbons.

[0040] On the other hand, when the pyrolysis reaction is carried out at a pressure below atmospheric pressure, the evaporation of high-boiling components cannot be effectively suppressed, and the proportion of high-boiling components with a carbon number exceeding 12 in the discharge flow from the top of the reactor can increase. 5-12 The hydrocarbons cannot be discharged through the top of the reactor and can remain in the reactor for a long time, resulting in the pyrolysis byproduct gases (e.g., C 1-4 Gases are produced in excess, and these gases are non-condensable and cannot be liquefied at room temperature.

[0041] Meanwhile, the waste plastic raw material is mainly a thermoplastic resin, for example, considering that the waste plastic is a mixture containing polyethylene having a number average molecular weight of 10,000 to 500,000 (specifically 100,000 to 300,000) or polypropylene having a number average molecular weight of 5,000 to 300,000 (specifically 10,000 to 200,000), the pyrolysis reaction is advantageously carried out in the range of 400° C. to 450° C., specifically 420° C. to 430° C. When the pyrolysis temperature is lower than 400° C., the pyrolysis rate may be slow, and when the pyrolysis temperature is higher than 450° C., the pyrolysis rate may be fast, and an excessive amount of solid carbides (such as char) may be produced.

[0042] Through the pyrolysis reaction, 20 to 90 wt % or 25 to 80 wt % of the weight of the waste plastic raw material may be generated as pyrolysis gas and discharged through the top of the reactor.

[0043] Specifically, the top discharge stream of the reactor can be a stream containing C 1-4 Hydrocarbon, C 5-12 Light hydrocarbons, C 13-22 Medium hydrocarbons and C 23-40 A gaseous stream of heavy hydrocarbons. 1-4 Hydrocarbons such as methane, ethane and propane are separated by evaporation since they are not condensed, and the remaining hydrocarbons are condensed to obtain liquid distillate.

[0044] 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 quench oil or quench water, cooling and condensation can occur and liquid oil can be obtained, which can be discharged through the bottom of the condenser and transferred to a storage tank. The cooling temperature of the heat exchanger can be 0°C to 50°C, specifically 20°C to 30°C. At the same time, the gas components (such as C 1-4 The gas can be discharged through the top and can be used as a heat source in the petrochemical process through subsequent processes (such as compression).

[0045] The liquid oil condensed after pyrolysis and then transferred to the storage tank may contain C 5-12 Light oil (LO), C 13-22 Medium oil (MO) and C 23-40 Heavy oil (HO), where, relative to the total weight of liquid oil, C 5-12 The content of light oil (LO) may be 30 wt % to 100 wt %, specifically 35 wt % to 99 wt %. In addition, relative to the total weight of the waste plastic raw material before pyrolysis, C 5-12The light oil (LO) may be included in an amount of 20 to 70 wt %, specifically 25 to 50 wt %.

[0046] That is, in the present invention, since the evaporation of high boiling point components is suppressed by pyrolyzing waste plastics at a pressure higher than atmospheric pressure, the selectivity of light hydrocarbons in the pyrolysis product is improved, so that C 5-12 Light oil (LO).

[0047] Meanwhile, during the pyrolysis reaction, part of the waste plastic melt may not be evaporated and remain at the bottom of the reactor in the form of liquid oil, and decompression treatment and condensation are performed to promote additional evaporation of the residual oil (S2).

[0048] The reduced pressure treatment may be carried out by a flash method, in which the pressure is reduced to atmospheric pressure (1 bar) after the previous pyrolysis reaction, and the evaporation of the components that have not evaporated in the previous pyrolysis reaction and remain at the bottom of the reactor may be promoted, thereby increasing the yield of liquid oil and minimizing the discharge amount of residual wax. In this case, when the heat treatment is carried out under high pressure conditions as in the previous pyrolysis, it is difficult to cause sufficient evaporation of the residual oil.

[0049] In this decompression treatment process, heat treatment can be performed while heating the reactor. The heat treatment can be performed at a temperature range of 400°C to 450°C, and the residual oil can be additionally pyrolyzed during this process. In this case, when the heat treatment temperature is lower than 400°C, it is difficult to cause sufficient evaporation of the residual oil, and when the heat treatment temperature is higher than 450°C, the formation of solid carbides (such as char) can be accelerated.

[0050] Furthermore, the reduced pressure treatment can be appropriately determined according to the composition of the residual oil remaining at the bottom of the reactor, and can be performed for, for example, 1 hour to 8 hours, specifically 2 hours to 6 hours.

[0051] If necessary, additional screw or plug flow reactors can be used to carry out reduced pressure treatment and heat treatment.

[0052] The gas produced by the decompression treatment can be obtained as liquid oil by condensation. The condensation can be carried out in the same way as in the pyrolysis process. The liquid oil obtained by the thermal treatment can also be collected in a storage tank before being transferred to the subsequent refining step.

[0053] Thereafter, the liquid oil obtained in the pyrolysis and decompression treatment steps is refined to separate components (S3).

[0054] Since the liquid oil obtained in the previous step 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 that performs separation stepwise according to boiling points.

[0055] 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.

[0056] 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.

[0057] In one embodiment of the present invention, relative to the total weight of the feed stream (i.e., liquid oil (mixed oil)), the C separated by the top of the distillation column is 5-12 The light hydrocarbons may be 30 wt % to 99 wt %, specifically 35 wt % to 99 wt %. The high yield of C 5-12 The light hydrocarbons are condensed and then efficiently used as high-quality fuel oil.

[0058] 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.

[0059] According to the present invention as described above, the pyrolysis of waste plastics is carried out at a pressure higher than atmospheric pressure, thereby suppressing the evaporation of high-boiling components and selectively increasing the residence time of liquid components in the reactor, thereby improving the decomposition efficiency of waste plastics. Thus, the selectivity and productivity of light hydrocarbon oil in the pyrolysis product can be improved.

[0060] Furthermore, after pyrolysis under high pressure conditions, the oil remaining in the reactor is decompressed at a lower pressure (eg, 1 bar atmospheric pressure) to increase vaporization of liquid hydrocarbons, thereby increasing the yield of pyrolysis oil and minimizing the emission of residual wax.

[0061] 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.

[0062] 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.

[0063] Embodiment 1:

[0064] like Figure 1 As shown, 100 parts by weight of a waste plastic melt containing polyethylene (PE) and polypropylene (PP) in a weight ratio of 6:4 is supplied to a stirred tank reactor, the reactor is heated by an external heating device, and when the temperature reaches 430° C., a pyrolysis reaction is performed for 2 hours while maintaining a constant temperature. At this time, the internal pressure of the reactor is controlled to 2 bar by exhausting the gas generated during the pyrolysis reaction using a pressure control valve provided at the top of the reactor.

[0065] The gas generated during the pyrolysis reaction was continuously discharged through the top of the reactor, introduced into a condenser connected to the reactor, and then cooled to 25°C to obtain condensed liquid oil, while the uncondensed gas components were discharged.

[0066] Subsequently, the oil remaining at the bottom of the reactor was transferred to a post-screw reactor arranged in series, heat-treated at 450° C. while being depressurized to atmospheric pressure (1 bar), and then condensed to obtain additional liquid oil.

[0067] The liquid oil obtained above is supplied to a distillation column and refined by separation according to boiling point, thereby finally preparing C 5-12 Light hydrocarbon pyrolysis oil.

[0068] Embodiment 2:

[0069] The same process as in Example 1 was performed except that the internal pressure of the reactor where the pyrolysis was performed was controlled to 5 bar.

[0070] Embodiment 3:

[0071] The same process as in Example 1 was performed except that the internal pressure of the reactor where the pyrolysis was performed was controlled to 10 bar.

[0072] Embodiment 4:

[0073] The same process as in Example 1 was performed except that the internal pressure of the reactor where the pyrolysis was performed was controlled to 20 bar.

[0074] Embodiment 5:

[0075] The same process as in Example 1 was performed except that the internal pressure of the reactor where the pyrolysis was performed was controlled to 30 bar.

[0076] Comparative Example 1:

[0077] The same process as in Example 1 was performed except that the internal pressure of the reactor where the pyrolysis was performed was controlled to be atmospheric pressure.

[0078] Figures 1 to 6 The compositions of the pyrolysis products of Examples 1 to 5 and Comparative Example 1 are shown respectively. Specifically, the uncondensed C in the composition was calculated by using the peak area of ​​each region according to the carbon number in the mass spectrum obtained by GC-MS analysis. 1-4 Gas, condensed liquid distillate oil (including C 5-12 Light oil (LO), C 13-22 Medium oil (MO), C 23-40 Heavy oil (HO) and residual oil fractions.

[0079] Table 1 shows the LO (C 5-12 ) fraction and LO (C 5-12 ) yield.

[0080] [Table 1]

[0081]

[0082] From Table 1, it can be confirmed that the LO (C) in the liquid oil of Examples 1 to 5 in which the waste plastics were pyrolyzed under high pressure of 2 bar to 30 bar was higher than that of Comparative Example 1 in which the waste plastics were pyrolyzed under atmospheric pressure. 5-12 ) fraction and LO(C) relative to the supply of waste plastic raw materials 5-12 These results are due to the fact that the pyrolysis reaction controls the pressure inside the reactor to be higher than the atmospheric pressure, which inhibits the evaporation of high-boiling components and increases the residence time of the liquid components in the reactor, thereby improving the decomposition efficiency of waste plastics.

[0083] More specifically, in Examples 1 to 3, when pyrolysis was performed at a pressure of 2 to 10 bar, all C 5-12 The light hydrocarbons are vaporized and discharged. In Examples 4 and 5, when the pressure is controlled at a relatively high pressure of 20 bar and 30 bar, not all of the light hydrocarbons are vaporized and some of them remain in the form of residual oil, but the light hydrocarbons are vaporized from the residual oil by reducing the pressure in the additional pyrolysis process, and therefore, the overall yield of the light hydrocarbon pyrolysis oil relative to the feedstock supply is improved.

[0084] Meanwhile, in Comparative Example 1, since the pyrolysis was performed at 430° C. under atmospheric pressure, the content of components evaporated in the decomposition reaction of the waste plastic melt increased, but the selectivity to high-quality light hydrocarbons in the resulting liquid oil decreased.

Claims

1. A method for preparing pyrolysis oil from waste plastics, the method comprising: (S1) supplying the waste plastic raw material to a pyrolysis reactor for pyrolysis, discharging a gaseous stream generated by the pyrolysis through the top of the pyrolysis reactor, and then condensing the gaseous stream to obtain liquid oil; (S2) decompressing and condensing the oil remaining at the bottom of the pyrolysis reactor to obtain additional liquid oil; and (S3) refining the liquid oil obtained in steps (S1) and (S2), The pyrolysis in step (S1) is carried out by controlling the internal pressure of the pyrolysis reactor within a range of greater than 1 bar to 40 bar.

2. The method according to claim 1, wherein: The pyrolysis in step (S1) is performed by controlling the internal pressure of the pyrolysis reactor within a range of 2 bar to 30 bar.

3. The method according to claim 1, wherein: The pyrolysis in step (S1) is performed at 400°C to 450°C.

4. The method according to claim 1, wherein: In the decompression treatment in step (S2), an additional heat treatment is also performed.

5. The method according to claim 1, wherein: The liquid oil obtained in step (S1) contains C 5-12 Light oil (LO), C 13-22 Medium oil (MO) and C 23-40 A mixture of heavy oil (HO).

6. The method according to claim 5, wherein: Relative to the total weight of the liquid oil, C 5-12 The content of light oil (LO) is 30 wt % to 100 wt %.

7. The method according to claim 5, wherein: Relative to the total weight of the waste plastic raw material, C 5-12 The content of light oil (LO) is 20 wt % to 70 wt %.

8. The method according to claim 1, wherein: The pyrolysis reactor is a reactor equipped with a stirrer.

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

10. The method according to claim 1, wherein: The waste plastic raw material is supplied to the pyrolysis reactor after undergoing a pretreatment process including crushing, washing, drying and melting.

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