Method for producing waste plastic pyrolysis oil

Abstract

The present invention provides a method for producing waste plastic pyrolysis oil, comprising the steps of: (S1) supplying waste plastic raw material to a pyrolysis reactor to perform pyrolysis, and discharging the gas phase stream produced by the pyrolysis to the top and condensing it to obtain liquid oil; (S2) reducing the pressure of the oil remaining in the bottom of the pyrolysis reactor and condensing it to obtain further liquid oil; and (S3) refining the liquid oil obtained in steps (S1) and (S2), wherein the pyrolysis is performed by adjusting the internal pressure of the reactor to a range of more than 1 bar to 40 bar.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0061366, filed May 11, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for producing waste plastic pyrolysis oil, and more particularly to a method for improving the efficiency of pyrolysis of waste plastics and producing light hydrocarbon oil in high yield. [Background technology]

[0003] In recent years, the development and use of plastics with properties suited to various uses and purposes has increased. Plastics require a lot of energy from crude oil extraction to manufacturing, and a large amount of carbon is emitted during the process. Furthermore, when plastics used in various products are discarded, environmental pollution and huge disposal costs occur, making waste plastic recycling an important social issue.

[0004] Generally, there are three methods for recycling waste plastics (resins): mechanical recycling, chemical recycling, and thermal recycling. Mechanical recycling involves crushing and sorting collected waste plastics, separating them by type, and then melting and pelletizing them using an extruder. The pellets are then mixed with new materials in a certain ratio or reinforced with functional additives to produce resin products. Chemical recycling involves using various chemical means to extract only specific polymers, or recovering them as pure monomolecules and repolymerizing them. Thermal recycling involves burning waste plastics and recovering the heat energy.

[0005] In particular, chemical recycling can reduce greenhouse gas emissions compared to incineration of waste plastics, and has been attracting attention in recent years in the development of alternative fuels. For example, when waste plastics such as polyethylene or polypropylene are heated and pyrolyzed at a certain temperature, a gaseous stream containing a mixture of non-condensable gases and liquid oil is generated, and highly viscous residual wax that has not been completely decomposed is discharged. Among the pyrolysis products, liquid oil is becoming increasingly important as a fuel oil for producing petrochemical products, and therefore, active research is being conducted to increase the yield of the liquid oil.

[0006] The liquid oil produced by the thermal decomposition of the waste plastic, i.e., the thermal decomposition oil, is usually a C 2 O 4 such as naphtha. 5-12 The mixed oil contains a light hydrocarbon oil of 100% or more and a hydrocarbon oil of a longer chain than that. When such a mixed oil contains a large amount of high-boiling-point components, there are problems in that 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 become excessive.

[0007] To solve these problems, methods have been proposed in which catalytic cracking reactions are carried out during the thermal decomposition of waste plastics, or a contactor is used to condense the heavy hydrocarbon (i.e., long-chain hydrocarbon) components in the thermal decomposition products of waste plastics, and then the condensed hydrocarbons are circulated to a thermal decomposition reactor and subjected to the thermal decomposition process again. However, these methods have limitations in terms of increasing the thermal decomposition efficiency of waste plastics, and are limited to recycling the waste plastics simply as mixed oil. Therefore, there is a need for a technology that can improve the waste plastic pyrolysis process and increase the yield of high-grade light hydrocarbon oil. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to solve the problems described above in the background of the invention, by adjusting the reaction pressure during the thermal decomposition of waste plastics to suppress the vaporization of high-boiling point components and selectively increasing the residence time of liquid components, thereby improving the thermal decomposition efficiency of waste plastics and producing light hydrocarbon oils at a high yield. [Means for solving the problem]

[0009] In order to solve the above problems, according to one embodiment of the present invention, there is provided a method for producing waste plastic pyrolysis oil, comprising the steps of: (S1) supplying waste plastic raw material to a pyrolysis reactor to perform pyrolysis, and discharging the gas phase stream produced by the pyrolysis to the top and condensing it to obtain liquid oil; (S2) decomposing and condensing the oil remaining in the bottom of the pyrolysis reactor to obtain further liquid oil; and (S3) refining the liquid oil obtained in steps (S1) and (S2), wherein the pyrolysis is performed by adjusting the internal pressure of the reactor to a range of more than 1 bar to 40 bar. [Effects of the Invention]

[0010] According to the present invention, the pyrolysis efficiency of waste plastics can be improved by conducting the pyrolysis of waste plastics under high-pressure conditions higher than atmospheric pressure, thereby suppressing the vaporization of high-boiling point components and selectively increasing the residence time of liquid components in the reactor, thereby increasing the selectivity and productivity of light hydrocarbon oils in the pyrolysis products.

[0011] In addition, after pyrolysis under the high-pressure conditions, the oil remaining in the reactor is subjected to a reduced pressure treatment to increase the vaporization of liquid hydrocarbons, thereby further increasing the yield of pyrolysis oil and minimizing the discharge of residual wax.

[0012] Furthermore, the use of light hydrocarbon oils obtained by the thermal decomposition of waste plastics can reduce greenhouse gas emissions caused by the supply of raw materials to petrochemical processes, and improve process efficiency by reducing energy consumption. It is also environmentally friendly as no harmful gases are generated during the treatment of waste plastics. [Brief explanation of the drawings]

[0013] [Figure 1] 1 shows the results of high-pressure pyrolysis of waste plastics (PE / PP mixture) in Example 1. [Figure 2] 1 shows the results of high-pressure pyrolysis of waste plastics (PE / PP mixture) in Example 2. [Figure 3] 1 shows the results of high-pressure pyrolysis of waste plastics (PE / PP mixture) in Example 3. [Figure 4] 1 shows the results of high-pressure pyrolysis of waste plastics (PE / PP mixture) in Example 4. [Figure 5] 1 shows the results of high-pressure pyrolysis of waste plastics (PE / PP mixture) in Example 5. [Figure 6] 1 shows the results of thermal decomposition of waste plastic (PE / PP mixture) of Comparative Example 1 at normal pressure (1 bar). DETAILED DESCRIPTION OF THE INVENTION

[0014] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their inventions.

[0015] As used herein, the meaning of "comprise" or "contain" is to embody a particular property, region, integer, step, operation, element, or component, and does not exclude the addition of other particular properties, regions, integers, steps, operations, elements, or components.

[0016] The term "stream" as used herein refers to the flow of fluid during a process, and may also refer to the fluid itself flowing in a pipe. Specifically, the term "stream" may refer simultaneously to the fluid itself flowing in a pipe connecting each device and the flow of the fluid. The fluid may also contain one or more components of gas, liquid, and solid.

[0017] As used herein, the term "C n " denotes all hydrocarbons having n carbon atoms, e.g., "C 5-12 " refers to all hydrocarbon molecules with 5 to 12 carbon atoms.

[0018] The term "liquid oil" as used herein means the product obtained by condensing the vapor stream obtained in the thermal cracking step into a liquid form, and may also be referred to as "liquid distilled oil." In addition, in this application, "pressure" means absolute pressure measured relative to a perfect vacuum.

[0019] A method for producing waste plastic pyrolysis oil according to one embodiment of the present invention includes (S1) a step of thermal decomposition and condensation of waste plastic raw material, (S2) a step of thermal treatment and condensation of residual oil, and (S3) a step of purification.

[0020] Hereinafter, the method for producing waste plastic pyrolysis oil according to the present invention will be described in detail step by step. First, waste plastic raw material is prepared and fed to a pyrolysis reactor to undergo pyrolysis (S1).

[0021] The waste plastic may include natural polymers, synthetic polymers, or mixtures thereof, and the synthetic polymers may include thermoplastic resins such as polyethylene, polypropylene, polystyrene, etc. The thermoplastic resins may also be mixed with other types of resins such as PVC and PET, thermosetting resins, etc.

[0022] After being collected and sorted, such waste plastic materials may be subjected to a pre-treatment process including crushing, washing, drying, and melting, which may be carried out in a manner conventional in the art.

[0023] For example, the size of the crushed waste plastic is not particularly limited, but may typically be in the range of 0.5 to 6.0 cm. After that, the crushed waste plastic may be washed and dried and then fed into a tubular melting machine such as an extruder to melt it. The extruder has the function of melting, kneading, and extruding, and may be, for example, a twin-screw extruder. When the waste plastic is a thermoplastic resin, such as polyethylene, polypropylene, or a mixture thereof, the melting temperature may be, but is not limited to, 120 to 350°C or 150 to 250°C.

[0024] The waste plastic melt obtained in the pretreatment process is supplied as a raw material to a pyrolysis reactor. The pyrolysis reactor usable in the present invention may be a stirred tank reactor equipped with an agitator (see Figures 1 to 5). The agitator is not particularly limited as long as it can sufficiently agitate the waste plastic melt supplied as a raw material. For example, it may be a helical ribbon type or an anchor type. Maintaining a gap of approximately 5 mm to 1 cm from the inner wall of the reactor is advantageous for maximizing the agitation of the waste plastic and heat transfer through the reactor wall. The reactor can be operated in either a batch or continuous mode. Furthermore, the reactor may be purged with nitrogen to maintain an oxygen-free or low-oxygen atmosphere during the pyrolysis reaction of the waste plastic melt.

[0025] The molten waste plastic is supplied to such an agitation reactor, and heated while the agitator is operated, to thermally decompose the molten waste plastic. The waste plastic may be heated by passing high-temperature / high-pressure steam, hot water, a heat transfer fluid, or the like through a jacket installed outside the reactor to transfer high-temperature heat to the waste plastic, but is not particularly limited thereto.

[0026] Conventional waste plastic pyrolysis processes are usually carried out under atmospheric pressure conditions, and C 1-4 gas components, such as naphtha 5-12 The light hydrocarbons and longer-chain hydrocarbons are vaporized and discharged to the top of the reactor, while the unvaporized residual wax remains at the bottom of the reactor. In such a thermal cracking process under atmospheric pressure, the upper discharge of the reactor contains a large amount of high-boiling-point components, which limits the yield of high-value-added light hydrocarbon oil and results in excessive production of heavy oil components and discharge of residual wax.

[0027] Therefore, in order to increase the selectivity of conversion to light hydrocarbons during the thermal decomposition of waste plastics, in the present invention, the pressure in the reactor is adjusted to a pressure higher than atmospheric pressure, for example, a pressure higher than 1 bar to 40 bar, preferably 2 to 30 bar, and more preferably 5 to 10 bar, during the thermal decomposition of the molten waste plastics. More specifically, a pressure control valve (PCV) is provided at the top of the reactor, and when gas above a certain pressure is generated during the thermal decomposition reaction of the waste plastics, the internal pressure of the reactor is adjusted to a pressure higher than atmospheric pressure by venting using the valve, thereby allowing the gas generated during the thermal decomposition reaction to be continuously discharged to the top of the reactor.

[0028] By controlling the high pressure of the thermal cracking reactor, vaporization of high boiling point components during the thermal cracking reaction can be suppressed, and the liquid residence time of the high boiling point components in the reactor can be increased. This increase in liquid residence time improves the efficiency of the waste plastic cracking reaction and increases the selectivity of conversion to light hydrocarbons, allowing for the production of high-value-added light hydrocarbon oils at a high yield.

[0029] That is, when the pressure of the pyrolysis reactor is adjusted to be higher than atmospheric pressure, the liquid residence time increases, and the pyrolysis reaction of waste plastics may be carried out for 1 to 8 hours, specifically 2 to 6 hours. During this process, polymers are converted into light hydrocarbons, such as C 5-12 The proportion of the carbon dioxide converted into hydrocarbons can be increased.

[0030] On the other hand, if the thermal decomposition reaction is carried out at atmospheric pressure or lower, the vaporization of high boiling point components cannot be effectively suppressed, and the proportion of high boiling point components with carbon numbers exceeding 12 may increase in the top discharge stream of the reactor. If the thermal decomposition reaction is carried out at a pressure exceeding 40 bar, 5-12 The hydrocarbons cannot be discharged to the top of the reactor and remain inside the reactor for a long time. Therefore, the pyrolysis by-product gases (e.g., C 1-4 gas) may be produced in excess.

[0031] Meanwhile, considering that the waste plastic raw material is primarily a thermoplastic resin, for example, 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, it is advantageous to carry out the pyrolysis reaction at a temperature in the range of 400 to 450°C, specifically 420 to 430°C. If the pyrolysis temperature is less than 400°C, the pyrolysis rate may be slow, whereas if it exceeds 450°C, the pyrolysis rate is fast, but the high heat may result in the excessive production of solid carbonized materials such as char.

[0032] Through the pyrolysis reaction, 20 to 90 wt % or 25 to 80 wt % of the weight of the waste plastic raw material is generated as pyrolysis gas, which can be discharged to the top of the reactor.

[0033] Specifically, the reactor top discharge stream is C 1-4 hydrocarbons, C 5-12 Light hydrocarbons, C 13-22 intermediate hydrocarbons, and C 23-40 The gaseous stream may contain heavy hydrocarbons such as methane, ethane, and propane. 1-4 The non-condensable hydrocarbons are evaporated and separated, and the remaining hydrocarbons are condensed to obtain a liquid distillate oil.

[0034] The condensation is a process for cooling the pyrolysis gas, which suppresses the polymerization reaction of hydrocarbons in the high-temperature pyrolysis gas discharged from the pyrolysis reactor and reduces the thermal load of the subsequent process (refining process). For example, when the gas phase stream discharged from the upper part of the pyrolysis reactor is supplied to a condenser and subjected to heat exchange with quench oil or quench water, cooling and condensation occur to obtain a liquid oil, which is discharged to the bottom of the condenser and can be transferred to a storage tank. The cooling temperature by the heat exchange may be 0 to 50°C, specifically 20 to 30°C. Meanwhile, gas components (e.g., C) that are not condensed by the heat exchange may be cooled to a temperature of 0 to 50°C, specifically 20 to 30°C. 1-4 The gas is discharged from the top and can be used as a heat source for petrochemical processes after further processing such as compression.

[0035] After the thermal cracking, the liquid oil is condensed and transferred to a storage tank. 5-12 Light oil (LO), C 13-22 Middle oil (MO), and C 23-40 The heavy oil (HO) may contain the above C 5-12 The content of the light oil (LO) may be 30 to 100% by weight, specifically 35 to 99% by weight, based on the total weight of the liquid oil. 5-12 The content of light oil (LO) may be 20 to 70% by weight, specifically 25 to 50% by weight, based on the weight of the waste plastic raw material before thermal decomposition.

[0036] That is, the present invention performs thermal decomposition of waste plastics under pressure conditions higher than atmospheric pressure to suppress vaporization of high boiling point components and improve the selectivity of light hydrocarbons in the thermal decomposition products, thereby achieving the C 5-12 Light oil (LO) can be obtained in high yield.

[0037] Meanwhile, during the thermal decomposition reaction, a portion of the molten waste plastic cannot be vaporized and remains in the form of liquid oil at the bottom of the reactor. In order to induce additional vaporization of this residual oil, decompression and condensation are performed (S2).

[0038] The decompression treatment may be performed using a flash method in which the pressure is reduced to atmospheric pressure (1 bar) after the previous thermal cracking reaction, and it can promote the vaporization of components that remained in the bottom of the reactor without being vaporized in the previous thermal cracking step, thereby increasing the yield of liquid oil and minimizing the discharge of residual wax. In this case, if the thermal treatment is performed under high-pressure conditions like in the previous thermal cracking, it is difficult to induce sufficient vaporization of the residual oil.

[0039] During the decompression treatment, the reactor may be heated to simultaneously carry out a heat treatment. The heat treatment may be carried out at a temperature in the range of 400 to 450°C, and additional pyrolysis of the residual oil may be carried out during this process. In this case, if the heat treatment temperature is less than 400°C, it may be difficult to induce sufficient vaporization of the residual oil, and if it exceeds 450°C, the formation of solid carbonized materials such as char may be accelerated.

[0040] The decompression treatment may be carried out for an appropriate period, taking into consideration the composition of the residual oil remaining in the bottom of the reactor, and may be carried out for, for example, 1 to 8 hours, specifically 2 to 6 hours. If necessary, the decompression and heat treatment may be carried out using a separate reactor of the screw or plug flow type.

[0041] The gas produced by the decompression treatment can be condensed to obtain a liquid oil. The condensation can be carried out in a manner similar to that used in thermal cracking. The liquid oil obtained by the thermal treatment can also be collected in a storage tank before being transferred to a subsequent refining step.

[0042] Thereafter, the liquid oil obtained from the thermal cracking and decompression treatment steps is refined for component separation (S3). The liquid oil obtained in the previous step is a mixed oil containing light and longer-chain hydrocarbons, so it is fed into a multi-stage distillation tower and undergoes a refining process in which it is separated into stages based on boiling point differences.

[0043] The refining step may be carried out in a manner conventional in the art, and is not particularly limited. For example, the feed stream supplied to the distillation column may contain all of the light and heavy oil components obtained by thermal decomposition of waste plastics, and a stream containing low-boiling light hydrocarbons may be discharged from the top of the distillation column, and a stream containing high-boiling heavy hydrocarbons may be discharged to the bottom of the distillation column.

[0044] The feed stream supplied to the distillation column is an oil component obtained by thermal decomposition of waste plastics, i.e., C 5-12 Diesel oil (LO), C 13-22 Medium oil (MO), and C 23-40 The distillation column may be a mixed oil containing heavy oil (HO), and the distillation column may be a distillation column having ... 5-12 A stream containing the light components of the sulphur dioxide can be separated and discharged.

[0045] In one embodiment of the present invention, the C separated at the top of the distillation column 5-12 The light hydrocarbons may be 30 to 99% by weight, specifically 35 to 99% by weight, of the total weight of the feed stream, i.e., the liquid oil (mixed oil). 5-12 These light hydrocarbons can be usefully used as high-grade fuel oils after condensation.

[0046] In particular, the C finally obtained in this invention 5-12 The light hydrocarbon fuel oil has a boiling point of 0 to 230°C, specifically 30 to 216°C, a kinematic viscosity at 40°C of 0.3 to 1.0 cSt, specifically 0.4 to 0.9 cSt, and a flash point of -80°C or higher (e.g., -40°C), and can be usefully used as a petrochemical feedstock.

[0047] According to the present invention as described above, the pyrolysis of waste plastics is carried out under high-pressure conditions higher than atmospheric pressure, thereby suppressing the vaporization of high-boiling point components and selectively increasing the residence time of liquid components in the reactor, thereby improving the cracking efficiency of waste plastics, thereby increasing the selectivity and productivity of light hydrocarbon oils in the pyrolysis products.

[0048] In addition, after pyrolysis under the high-pressure conditions, the oil remaining in the reactor can be decompressed at a lower pressure (e.g., atmospheric pressure of 1 bar) to increase the vaporization of liquid hydrocarbons, thereby increasing the yield of pyrolysis oil and minimizing the discharge of residual wax.

[0049] Furthermore, the use of light hydrocarbon oils obtained by the thermal decomposition of waste plastics can reduce greenhouse gas emissions caused by the supply of raw materials to petrochemical processes, and improve process efficiency by reducing energy consumption. It is also environmentally friendly as no harmful gases are generated during the treatment of waste plastics.

[0050] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention, and the scope of the present invention is not limited to these examples.

[0051] Example 1: As shown in Figure 1, 100 parts by weight of molten waste plastic containing polyethylene (PE) and polypropylene (PP) in a weight ratio of 6:4 was supplied to a stirred tank reactor, and the reactor was heated using an external heating means. When the temperature reached 430°C, the temperature was maintained constant and a pyrolysis reaction was carried out for 2 hours. During this process, the internal pressure of the reactor was adjusted to 2 bar by venting gas generated during the pyrolysis reaction using a pressure control valve installed at the top of the reactor.

[0052] The gas produced during the thermal cracking reaction was continuously discharged from the top of the reactor and then flowed into a condenser connected to the reactor, where it was cooled to 25°C to obtain a condensed liquid oil, and uncondensed gas components were discharged.

[0053] Next, the oil remaining in the bottom of the reactor was transferred to a subsequent screw-type reactor arranged in series, where it was heat-treated at 450°C while being reduced to atmospheric pressure (1 bar), and then condensed to obtain additional liquid oil. The liquid oil obtained above is fed to a distillation column, where it is purified by separating it according to its boiling point, and C 5-12 of light hydrocarbon pyrolysis oil was finally produced.

[0054] Example 2: The same procedure as in Example 1 was carried out, except that the internal pressure of the reactor in which the pyrolysis was carried out was adjusted to 5 bar.

[0055] Example 3: The same procedure as in Example 1 was carried out, except that the internal pressure of the reactor in which the pyrolysis was carried out was adjusted to 10 bar.

[0056] Example 4: The same procedure as in Example 1 was carried out, except that the internal pressure of the reactor in which the pyrolysis was carried out was adjusted to 20 bar.

[0057] Example 5: The same procedure as in Example 1 was carried out, except that the internal pressure of the reactor in which the pyrolysis was carried out was adjusted to 30 bar.

[0058] Comparative Example 1: The same procedure as in Example 1 was carried out, except that the internal pressure of the reactor where the pyrolysis was carried out was adjusted to atmospheric pressure.

[0059] 1 to 6 show the compositions of the pyrolysis products of Examples 1 to 5 and Comparative Example 1, respectively. Specifically, the compositions were calculated by dividing the non-condensable carbons by the peak area ratios of the regions according to the carbon number in the mass spectrum obtained by GC-MS analysis. 1-4 Gas, condensed liquid distillate oil (C 5-12 Diesel oil (LO), C 13-22 Medium oil (MO), and C 23-40 The fractions of heavy oil (HO) and residual oil were calculated. Table 1 below shows the LO(C) in liquid oil under different thermal cracking conditions. 5-12 ) fraction and the amount of waste plastic raw material supplied. 5-12 ) yield was shown.

[0060] [Table 1] JPEG2025528090000003.jpg150130JPEG2025528090000004.jpg135131

[0061] From Table 1, it can be seen that in Examples 1 to 5, in which the thermal decomposition of waste plastics was carried out under high pressure conditions of 2 to 30 bar, the LO(C) in the liquid oil was lower than in Comparative Example 1, in which the thermal decomposition was carried out under normal pressure. 5-12 ) fraction and the amount of waste plastic raw material supplied. 5-12 These results are attributable to the improved decomposition efficiency of waste plastics due to the increased residence time of liquid components in the reactor, which is achieved by controlling the internal pressure of the reactor higher than atmospheric pressure, which suppresses the vaporization of high-boiling point components.

[0062] More specifically, in Examples 1 to 3, C was obtained from waste plastic raw materials by pyrolysis at a pressure of 2 to 10 bar. 5-12 In Examples 4 and 5, the light hydrocarbons were not vaporized completely and remained as residual oil due to the relatively high pressures of 20 bar and 30 bar, but by lowering the pressure during the additional pyrolysis and vaporizing the light hydrocarbons from the residual oil due to the flash effect, the overall yield of light hydrocarbon pyrolysis oil based on the amount of raw material supplied was improved.

[0063] On the other hand, in Comparative Example 1, by carrying out thermal decomposition under normal pressure conditions at 430°C, the content of vaporized components in the decomposition reaction of the molten waste plastic increased, but the selectivity of higher light hydrocarbons in the resulting liquid oil decreased.

Claims

1. (S1) supplying waste plastic raw materials to a thermal decomposition reactor to perform thermal decomposition, discharging the gas phase stream generated by the thermal decomposition to the top, and then condensing it to obtain liquid oil; (S2) subjecting the oil remaining in the lower part of the pyrolysis reactor to decompression and condensation to obtain further liquid oil; (S3) refining the liquid oil obtained in steps (S1) and (S2); Including, The method for producing waste plastic pyrolysis oil, wherein the thermal decomposition in step (S1) is carried out by adjusting the internal pressure of the reactor to a range of more than 1 bar to 40 bar.

2. 2. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the thermal decomposition in step (S1) is carried out by adjusting the internal pressure of the reactor to a range of 2 to 30 bar.

3. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the thermal decomposition in step (S1) is carried out at 400 to 450°C.

4. The method for producing waste plastic pyrolysis oil according to claim 1, wherein an additional heat treatment is performed during the decompression treatment in step (S2).

5. The liquid oil obtained in the step (S1) is C ５－１２ Light oil (LO), C １３－２２ middle oil (MO), and C ２３－４０ 2. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the mixed oil contains heavy oil (HO).

6. Said C ５－１２ The method for producing waste plastic pyrolysis oil according to claim 5, wherein the content of light oil (LO) is 30 to 100 wt % based on the total weight of the liquid oil.

7. Said C ５－１２ The method for producing waste plastic pyrolysis oil according to claim 5, wherein the content of light oil (LO) is 20 to 70 wt % based on the weight of the waste plastic raw material.

8. The method for producing waste plastic pyrolysis oil according to claim 1 , wherein the pyrolysis reactor is a reactor equipped with an agitator.

9. The method for producing waste plastic pyrolysis oil according to any one of claims 1 to 8, wherein the waste plastic raw material is a mixture containing polyethylene (PE) or polypropylene (PP).

10. The method for producing waste plastic pyrolysis oil according to any one of claims 1 to 8, wherein the waste plastic raw material is supplied to a pyrolysis reactor after undergoing a pretreatment process including crushing, washing, drying, and melting.

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