Method for producing pyrolysis oil from waste plastics

Abstract

The present invention comprises the steps of (S1) supplying waste plastic raw material to a first reactor to perform primary thermal decomposition and discharging the gas phase stream generated by the thermal decomposition to the top, and (S2) supplying the upper gas phase stream from the first reactor to one or more distillation columns to separate according to the boiling point, and C 5-12 Stream containing light oil (LO), C 13-22 Stream containing middle oil (MO), and C 23 The present invention provides a method for producing waste plastic pyrolysis oil, comprising the steps of: (S3) obtaining a stream containing heavy oil (HO) as described above; (S4) supplying a portion of the stream containing the medium oil (MO) separated in the distillation column to a second reactor for secondary pyrolysis, and supplying the gaseous stream generated by the pyrolysis to the distillation column; and (S5) recirculating the stream containing the heavy oil (HO) separated in the distillation column to the first reactor.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0110204 dated August 23, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference. The present invention relates to a method for producing pyrolysis oil from waste plastics, and more particularly, to a method for producing light hydrocarbon oil from waste plastic raw materials in high yield. [Background technology]

[0002] In recent years, the development and use of plastics with physical properties suited to various applications and purposes has increased. However, plastics require significant energy from crude oil extraction to manufacturing, and a large amount of carbon is emitted during this process. Furthermore, when plastics used in various products are discarded, environmental pollution and enormous disposal costs occur, making the recycling of waste plastics a crucial social issue.

[0003] Generally, there are three methods for recycling waste plastics (resins): mechanical recycling, chemical recycling, and thermal recycling. Mechanical recycling involves crushing and sorting the collected waste plastics, separating them by type, and then melting them into pellets using an extruder. The pellets are then mixed with new material in a certain proportion or reinforced with functional additives to produce resin products. Chemical recycling involves using various chemical means to extract only specific polymers or recover them as pure single molecules for repolymerization. Thermal recycling involves burning the waste plastics and recovering the resulting heat energy.

[0004] In particular, the aforementioned chemical recycling can reduce greenhouse gas emissions compared to the incineration of waste plastics, and has recently attracted attention from the perspective of alternative fuel development.

[0005] For example, when waste plastics such as polyethylene or polypropylene are heated and thermally decomposed at a specific temperature, a gaseous stream of non-condensable gas and liquid oil is produced, and a highly viscous residual wax that has not been completely decomposed may be discharged. Of the thermal decomposition products, the liquid oil is becoming increasingly important as a fuel for the manufacture of petrochemical products, and therefore, research is actively being conducted to increase the yield of the liquid oil.

[0006] The liquid oil produced by the thermal decomposition of the aforementioned waste plastic, i.e., the thermal decomposition oil, is usually a C2, such as naphtha. 5-12 This is a mixed oil containing light hydrocarbon oils and longer-chain hydrocarbon oils. When such a mixed oil contains a large amount of high-boiling-point components, the yield of high-value-added light hydrocarbon oil is limited, and there are problems with the production of heavy oil components and the discharge of residual wax.

[0007] To address these problems, methods have been proposed in which catalytic decomposition is carried out during the thermal decomposition of waste plastics, or in which heavy hydrocarbon (i.e., long-chain hydrocarbon) components in the thermal decomposition products of waste plastics are condensed using a contactor, a contact heat exchanger, and then circulated back into a thermal decomposition reactor for further thermal decomposition. However, these methods have limitations in improving the thermal decomposition efficiency of waste plastics and are limited to recycling as mixed oils.

[0008] In particular, the contactor is positioned above the pyrolysis reactor and is capable of improving selectivity only for pyrolysis oil components within a specific boiling point range (e.g., long-chain hydrocarbons at 240-280°C). Therefore, there is a need for technology that can improve the waste plastic pyrolysis process and increase the yield of high-grade light hydrocarbon oil. [Overview of the project] [Problems that the invention aims to solve]

[0009] The problem that this invention aims to solve is to solve the problems described in the background technology of the invention described above, and relates to a method for improving the yield of light hydrocarbon oil by connecting one or more distillation columns in series in place of a contactor (heat exchanger) at the top of a reactor for thermal decomposition of waste plastics, and then performing additional thermal decomposition after separating the high-boiling-point components in the thermal decomposition product into medium oil (MO) and heavy oil (HO). [Means for solving the problem]

[0010] To solve the above problems, according to one embodiment of the present invention, (S1) waste plastic raw material is supplied to a first reactor to perform primary pyrolysis, and the gas phase stream generated by the pyrolysis is discharged to the top, and (S2) the upper gas phase stream of the first reactor is supplied to one or more distillation columns and separated according to the boiling point, C 5-12 Stream containing light oil (LO), C 13-22 Stream containing middle oil (MO), and C 23 The present invention provides a method for producing waste plastic pyrolysis oil, comprising the steps of: (S3) obtaining streams containing heavy oil (HO) as described above; (S4) supplying a portion of the stream containing the medium oil (MO) separated in the distillation column to a second reactor for secondary pyrolysis, and supplying the gaseous stream generated by the pyrolysis to the distillation column; and (S4) recirculating the stream containing the heavy oil (HO) separated in the distillation column to the first reactor. [Effects of the Invention]

[0011] According to the present invention, in one or more distillation columns connected in series to a first reactor for thermally decomposing waste plastic raw materials, the thermally decomposed gas phase stream is separated according to its boiling point. Of the separated components, a portion of the medium oil (MO) is subjected to secondary thermal decomposition in a second reactor, while the heavy oil (HO) is recirculated to the first reactor, thereby improving the yield of high-grade diesel oil (LO).

[0012] In addition, by performing the pyrolysis of the first and second reactors under stepwise temperature increase conditions, the decomposition efficiency of waste plastics can be improved, the yield of higher-quality light hydrocarbon oil can be increased, and the discharge of residual wax with low utilization can be minimized.

[0013] Furthermore, by adjusting the upper operating temperature of the distillation column within a predetermined range, the fraction of light oil (LO) components in the vapor-phase stream separated by the distillation column can be increased. In the process where the vapor-phase stream is obtained in a liquid state by heat exchange with water in the condenser connected to the upper part of the distillation column, the water supplied to the condenser can recover the waste heat of the vapor-phase stream and be converted into steam.

[0014] Furthermore, the utilization of the light hydrocarbon oil obtained by the pyrolysis of waste plastics can reduce the emissions of greenhouse gases caused during the raw material supply in the petrochemical process, not only improving process efficiency such as reducing energy consumption, but also being environmentally advantageous because no harmful gases are generated during the treatment of waste plastics.

Brief Description of the Drawings

[0015] [Figure 1] It shows the pyrolysis process of waste plastics according to an embodiment of the present invention. [Figure 2] It shows the pyrolysis process of waste plastics according to a comparative example.

Modes for Carrying Out the Invention

[0016] The terms and words used in the description and claims of the present invention should not be construed as limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept that conform to the technical idea of the present invention, following the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0017] As used in this application, the meaning of "include" or "contain" embodies a particular characteristic, domain, integer, step, operation, element, or component, and does not preclude the addition of other particular characteristics, domains, integers, steps, operations, elements, or components.

[0018] As used in this application, the term "stream" means the flow of fluid during a process, and may also mean the fluid itself flowing through piping. Specifically, the stream may simultaneously mean the fluid itself and the flow of fluid within the piping connecting each device. Furthermore, the fluid may contain one or more components of gas, liquid, and solid.

[0019] The term "C" used in this application n " represents all hydrocarbons having n carbon atoms, for example, "C 5-12 " represents all hydrocarbon molecules with 5 to 12 carbon atoms.

[0020] The term "liquid oil" as used in this application refers to a substance obtained when the gaseous stream obtained in the thermal decomposition step is converted into a liquid by condensation, and can also be called "liquid distilled oil." Furthermore, in this application, "pressure" means absolute pressure measured relative to a perfect vacuum.

[0021] A method for producing waste plastic pyrolysis oil according to one embodiment of the present invention includes (S1) a primary pyrolysis step of waste plastic raw material, (S2) a separation step of the pyrolysis gas phase stream based on its boiling point, (S3) a secondary pyrolysis step of a portion of the separated intermediate oil, and (S4) a step of recirculating the separated heavy oil for raw material pyrolysis.

[0022] The above method can be carried out using a process system including a first reactor 10 to which waste plastic raw materials are supplied, one or more distillation columns 20 connected in series with the first reactor, a second reactor 11 connected to the distillation columns 20, and a residue treatment reactor 30, as shown in Figure 1.

[0023] The method for producing waste plastic pyrolysis oil according to the present invention will be described in detail step by step below with reference to the drawings. First, waste plastic raw materials are supplied to the first reactor 10 for primary thermal decomposition, and the gaseous stream generated by the thermal decomposition is discharged to the top (S1).

[0024] The aforementioned waste plastic may contain natural polymers, synthetic polymers, or mixtures thereof, and the synthetic polymer may include thermoplastic resins such as polyethylene, polypropylene, and polystyrene. Furthermore, the thermoplastic resin may be a mixture with other types of resins such as PVC and PET, or thermosetting resins.

[0025] After being collected and sorted, such waste plastics may undergo a pretreatment process that includes crushing, washing, drying, and melting. The pretreatment process may be carried out in a manner that is common in the field.

[0026] For example, the size of the crushed waste plastic is not particularly limited, but is usually in the range of 0.5 to 6.0 cm. The crushed waste plastic, after being washed and dried, may then be fed into a tubular melting machine such as an extruder and melted. The extruder has the function of melting, kneading, and extruding, and may be, for example, a twin-screw extruder. If 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.

[0027] The molten waste plastic obtained in the aforementioned pretreatment process is supplied to the first reactor for thermal decomposition. The pyrolysis reactor usable in this invention may be a stirred tank reactor equipped with an agitator, and the agitator is not particularly limited as long as it can sufficiently stir the waste plastic molten material supplied as raw material. For example, it may be a helical ribbon type or an anchor type, and maintaining a distance of about 5 mm to 1 cm between the agitator and the inner wall of the reactor is advantageous for maximizing the stirring of the waste plastic and heat transfer through the reactor wall. Furthermore, the reactor can be operated in either a batch type or a continuous type. In addition, nitrogen purging may be performed on the reactor to maintain an oxygen-free or low-oxygen atmosphere while the pyrolysis reaction of the waste plastic molten material is carried out.

[0028] The molten waste plastic is supplied to the first reactor equipped with such a stirrer, and the reactor is heated while the stirrer is operated to perform thermal decomposition of the molten waste plastic.

[0029] The heating of the waste plastic may be carried out by passing high-temperature / high-pressure steam, hot water, or a heat transfer fluid through a jacket provided outside the reactor to transfer high-temperature heat to the waste plastic, and is not particularly limited to this method.

[0030] In one embodiment of the present invention, the primary pyrolysis in the first reactor may be carried out at 400 to 450 °C. Considering that the waste plastic raw material is mainly 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 based on the number average molecular weight, or polypropylene with a number average molecular weight of 5,000 to 300,000, specifically 10,000 to 200,000, it is advantageous for the pyrolysis reaction to be carried out in the range of 400 to 450 °C, specifically 420 to 430 °C. When the primary pyrolysis temperature is less than 400 °C, the pyrolysis rate may become slow. When it exceeds 450 °C, although the pyrolysis rate is fast, excessive solid carbides such as char may be generated due to high heat.

[0031] Also, the primary pyrolysis in the first reactor may be carried out at a pressure of 0.9 to 1.1 bar for 1 to 5 hours, specifically 2 to 4 hours. The primary pyrolysis reaction time can be determined considering the point at which the production rate of light hydrocarbons with 12 or fewer carbon atoms increases in the temperature range of 400 to 450 °C after the start of the decomposition reaction of the waste plastic. [[ID=​​​​​​​​​​​​​​​The one or more distillation columns 20 are arranged in series above the first reactor 10, and selective heating and condensation can separate the pyrolysis products transferred from the first reactor according to their boiling points. For example, the stream supplied to each distillation column is heated by heat provided by a reactor connected to the bottom of the column, and the vapor generated by the heating moves to the top of the column and is discharged, and the discharged vapor can be partially or completely condensed in a condenser connected to the top of the column. A portion of the condensate can be recycled back into the column.

[0034] Unlike conventional waste plastic pyrolysis processes that apply a contactor (heat exchanger) to the pyrolysis reactor, the present invention allows for the placement of one or more distillation columns at the top of the first reactor to separate pyrolysis products according to their boiling points, and enables the selective recirculation of high-boiling-point oil discharged from the middle or bottom of the distillation column to the first reactor or supply to the second reactor to carry out additional pyrolysis reactions, thereby improving the yield of light oil (LO).

[0035] Furthermore, in this invention, the carbon range of the target pyrolysis oil (distilled oil) can be changed by adjusting the upper operating temperature of the distillation column.

[0036] Specifically, increasing the upper operating temperature of the distillation column shifts the carbon range of the pyrolysis oil to a higher boiling point, and decreasing the upper operating temperature of the distillation column shifts the carbon range of the pyrolysis oil to a lower boiling point, thereby increasing the yield of light oil such as naphtha.

[0037] For example, when adjusting the temperature of the top of the distillation column to 220°C to 300°C, C 5-12 Low boiling point hydrocarbons and C 13-22 A gaseous stream containing 80% or more medium-boiling point hydrocarbons can be discharged. On the other hand, when adjusting the upper temperature of the distillation column to less than 150°C to 220°C, C 5-12A gaseous stream containing 70% or more low-boiling hydrocarbons can be discharged. The gaseous stream can be cooled and condensed into liquid oil by heat exchange with water connected to the top of the distillation column, and any gaseous components that were not condensed by the heat exchange (e.g., C 1-4 The hydrocarbons can be discharged to the top. At this time, some of the components contained in the condensed liquid oil, i.e., the medium-boiling or high-boiling point components, can be rerefluxed to the top of the distillation column and moved downwards. As a result, C is released in the upper tray of the column. 5-12 Light oil (LO) is discharged, and in the middle of the column C 13-22 Middle oil (MO) is discharged, and C is discharged in the lower part of the column. 23 For example, C 23-40 Heavy oil (HO) can be discharged.

[0038] Furthermore, the distillation column 20 can be a distillation column (DWC) with a separation wall type structure that includes two regions separated by a central separation wall, and C is placed at the top of the DWC. 5-12 A stream containing light hydrocarbons, with C on the side of the DWC 13-22 A stream containing intermediate hydrocarbons, C at the bottom of the DWC 23 Streams containing the above high-boiling-point hydrocarbons can be separated.

[0039] On the other hand, when multiple distillation columns 20 are arranged, the temperature of the condenser connected to the top of each column can be varied. That is, by setting the top temperature of the preceding column relatively higher and the top temperature of the succeeding column relatively lower, the carbon range of the pyrolysis oil (distilled oil) can be changed. For example, the top temperature of the preceding column can be adjusted to 220°C to 300°C, and the top temperature of the succeeding column can be adjusted to 150°C to less than 220°C. The upper gas phase stream discharged from the preceding and succeeding columns can be discharged as liquid oil after condensation, as described above, or a portion of it can be recirculated back to the top of each column. In addition, in the middle and lower parts of each column, C 13-22 Medium Oil (MO) or C 23 The above heavy oil (HO) can be selectively discharged.

[0040] In this way, in one or more distillation columns, the gas phase stream generated by the primary thermal decomposition of waste plastic raw materials is separated according to its boiling point, C 5-12 Stream containing diesel fuel (LO), C 13-22 Stream containing medium oil (MO), and C 23 A stream containing the above heavy fuel oil (HO) can be obtained.

[0041] Furthermore, in the process in which the gas phase stream is obtained as a liquid through heat exchange with water in a condenser connected to the top of the distillation column, the water supplied to the condenser can be converted into steam by recovering the waste heat from the gas phase stream.

[0042] In order to generate steam through such waste heat recovery, the present invention uses hot water at 60 to 100°C as the water that undergoes heat exchange in the upper condenser of the distillation column. The temperature of the water can be adjusted according to the composition of the target pyrolysis oil.

[0043] In particular, when multiple distillation columns are arranged, as described above, steam at different pressures can be generated by operating the condenser temperature of the preceding column at a high temperature and the condenser temperature of the succeeding column at a low temperature. For example, if the upper operating temperature of the distillation column is set high and the carbon range of the pyrolysis oil moves to a high boiling point, high-pressure steam can be generated by the heat absorbed by the condenser connected to the upper part of the column. On the other hand, if the upper operating temperature of the distillation column is set low and the carbon range of the pyrolysis oil moves to a low boiling point, low-pressure steam can be generated.

[0044] Subsequently, C separated in the distillation column 20 13-22 A portion of the stream containing the medium oil (MO) is supplied to the second reactor 11 for secondary pyrolysis, and the gaseous stream generated by the pyrolysis is supplied to the distillation column 20 (S3).

[0045] The second reactor 11 can be arranged in series with the distillation column 20. That is, the first reactor 10 can be arranged on one side of the distillation column 20, and the second reactor 11 can be arranged on the other side of the distillation column 20, so that the first reactor, the distillation column, and the second reactor can be arranged in series in that order.

[0046] The thermal decomposition of a portion of the intermediate oil (MO) in the second reactor may be carried out at a higher temperature than the thermal decomposition of the waste plastic raw material carried out in the first reactor. In other words, in the present invention, it is advantageous to carry out the thermal decomposition in the first and second reactors under stepwise heating conditions in order to increase the efficiency of waste plastic decomposition.

[0047] In one embodiment of the present invention, the temperature of the secondary pyrolysis in the second reactor 11 may be in the range of 420°C to 450°C. If the secondary pyrolysis is carried out at a higher temperature than the primary pyrolysis, the production of light oil (LO) by the decomposition of intermediate oil (MO) can be further increased. If the secondary pyrolysis temperature is 420°C or lower, it is difficult to induce sufficient pyrolysis of intermediate oil (MO), and if it exceeds 450°C, the formation of solid carbides such as char may be accelerated.

[0048] Furthermore, the secondary pyrolysis may be carried out at a pressure of 0.9 to 1.1 bar for 1 to 3 hours, more specifically for 1.5 to 2.5 hours. The duration of the secondary pyrolysis reaction can be determined by considering the point in time after the start of the decomposition reaction of the medium oil (MO) when the rate of production of light hydrocarbons with 12 or fewer carbon atoms increases.

[0049] Through this secondary thermal decomposition, C obtained from waste plastic raw materials 13-22 The intermediate oil (MO) can be sufficiently thermally decomposed to convert it to an even lower carbon number, thereby ultimately yielding C 5-12 This can increase the yield of diesel fuel (LO).

[0050] On the other hand, C separated in the distillation column 20 23 The stream containing the above heavy oil (HO) is recirculated to the first reactor 10 (S4). The heavy oil (HO) contained in the gas phase product obtained by primary pyrolysis of the waste plastic raw material can be discharged to the bottom of the distillation column as a high-boiling point hydrocarbon having a boiling point of 360°C or higher. The stream containing such high-boiling point heavy oil is then transferred back to the first reactor and pyrolyzed again, thereby producing C 5-12 Diesel fuel (LO) and C 13-22 It can be converted into medium oil (MO).

[0051] Furthermore, the lower residue from the first reactor 10 and the lower residue from the second reactor 11 may be supplied to the residue treatment reactor 30 for additional thermal decomposition.

[0052] The residue treatment reactor 30 may include an upper section where a thermal decomposition reaction takes place, and a lower section for discharging highly viscous residual wax. In the upper section of the residue treatment reactor, the lower residue from the first reactor and the lower residue from the second reactor may be supplied to carry out additional thermal decomposition, and in this case, it is preferable that the additional thermal decomposition is carried out at a higher temperature than the thermal decomposition in the first reactor or the second reactor.

[0053] Furthermore, the additional thermal decomposition in the residue treatment reactor may be carried out at a pressure of 0.9 to 1.1 bar for 1 to 3 hours, more specifically 1.5 to 2.5 hours. The duration of this additional thermal decomposition reaction can be determined by considering the point in time after the start of the residue decomposition reaction when the rate of low-boiling hydrocarbon production increases.

[0054] The pyrolysis oil obtained through the pyrolysis process described above is a high value-added C 5-12 It can contain a high fraction of diesel fuel (LO). For example, the final obtained C 5-12 The diesel fuel (LO) content may be 50-70% by weight, more specifically 50-60% by weight, based on the weight of the waste plastic raw material. C obtained in this high yield 5-12 These light hydrocarbons can be condensed and used as high-grade fuel oils.

[0055] In particular, in the present invention, the final obtained C 5-12 This 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), making it useful as a petrochemical raw material.

[0056] According to the present invention as described above, in one or more distillation columns connected in series to a first reactor for thermal decomposition of waste plastic raw materials, the thermally decomposed gas phase stream is separated according to its boiling point. Of the separated components, a portion of the medium oil (MO) is subjected to secondary thermal decomposition in a second reactor, while the heavy oil (HO) is recirculated to the first reactor, thereby improving the yield of higher-grade diesel oil (LO).

[0057] Furthermore, by performing the thermal decomposition of the first and second reactors under stepwise heating conditions, the decomposition efficiency of waste plastics can be improved, the yield of high-grade light hydrocarbon oil can be increased, and the discharge of less useful residual wax can be minimized.

[0058] Furthermore, by adjusting the upper operating temperature of the distillation column to a predetermined range, the fraction of light oil (LO) component in the gas phase stream separated by the distillation column can be increased. In the process in which the gas phase stream is liquefied by heat exchange with water in a condenser connected to the upper part of the distillation column, the water supplied to the condenser can recover the waste heat from the gas phase stream and be converted into steam.

[0059] Furthermore, utilizing light hydrocarbon oil obtained from the thermal decomposition of waste plastics can reduce greenhouse gas emissions caused during the supply of raw materials in petrochemical processes, improve process efficiency such as reducing energy consumption, and is also environmentally advantageous because no harmful gases are generated during the processing of waste plastics. [Examples]

[0060] 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 obvious to an ordinary person that various changes and modifications are possible within the scope and technical concept of the present invention, and the scope of the present invention is not limited to these examples alone.

[0061] Example 1: As shown in Figure 1, the thermal decomposition of waste plastics was carried out using a process system including a first reactor 10, a distillation column 20, a second reactor 11, and a residue treatment reactor 30.

[0062] First, 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 first reactor 10 of the stirring type. After heating the first reactor 10 with an external heating means, when it reached 430°C, a primary pyrolysis reaction was carried out for 4 hours while maintaining a constant temperature.

[0063] The gaseous stream discharged from the top of the first reactor 10 was supplied to the distillation column 20 and separated into components according to their boiling points. Specifically, the column was operated at a top temperature of 210°C to discharge the gaseous stream upwards, and the condensed liquid C was cooled to 25°C in a condenser. 5-12 Diesel fuel (LO) was obtained, and the uncondensed gaseous components were discharged. Next, in the middle tray of the column, C 13-22 A stream containing medium oil (MO) is obtained, and in the lower part of the column C 23-40 The lower stream containing heavy fuel oil (HO) was discharged.

[0064] A portion of the neutral oil (MO) separated in the distillation column 20 was supplied to the second reactor 11 for secondary thermal decomposition at 430°C for 2 hours, and the gaseous stream generated by the secondary thermal decomposition was recirculated to the distillation column 20. Meanwhile, the lower discharge stream of the distillation column 20 was recirculated to the first reactor 10 for further thermal decomposition.

[0065] Furthermore, the lower residue from the first reactor 10 and the lower residue from the second reactor 11 were supplied to the residue treatment reactor 30 for an additional 2 hours of thermal decomposition at 450°C, and the resulting upper gas phase stream was recirculated to the lower part of the distillation column 20, and the residue remaining at the bottom was discharged.

[0066] Example 2: In the second reactor 11, the same process as in Example 1 was carried out, except that a secondary thermal decomposition of a portion of the intermediate oil (MO) was performed at 440°C for 2 hours.

[0067] Example 3: In the second reactor 11, the same process as in Example 1 was carried out, except that a secondary thermal decomposition of a portion of the intermediate oil (MO) was performed at 450°C for 2 hours.

[0068] Comparative Example 1: As shown in Figure 2, the thermal decomposition of waste plastics was carried out using a process system including a first reactor 10, a distillation column 20, and a residue treatment reactor 30. Specifically, the process was the same as in Example 1, except that secondary thermal decomposition was not performed on a portion of the intermediate oil (MO) separated in the distillation column 20.

[0069] Table 1 below shows the composition (weight %) of the pyrolysis products obtained based on the feed amount in the above examples and comparative examples, as analyzed by GC-MS.

[0070] [Table 1]

[0071] As shown in Table 1 above, in Examples 1 to 3, in which one or more distillation columns connected in series with the first reactor for thermal decomposition of waste plastic raw materials were separated according to their boiling points, and then a portion of the intermediate oil (MO) from the separated components was subjected to secondary thermal decomposition in the second reactor, the yield of low-boiling point diesel oil (LO) was improved compared to Comparative Example 1, in which secondary thermal decomposition was not performed. Furthermore, in Examples 2 and 3, where primary and secondary pyrolysis were carried out under stepwise heating conditions, diesel fuel was obtained with a higher yield than in Example 1, which was carried out at the same temperature.

Claims

1. (S1) A step of supplying waste plastic raw material to a first reactor to perform primary thermal decomposition, and discharging the gas phase stream generated by the primary thermal decomposition to the upper part, (S2) The upper gas phase stream from the first reactor is supplied to one or more distillation columns and separated according to the boiling point, C ５－１２ Stream containing light oil (LO), C １３－２２ A stream containing middle oil (MO), and C ２３ The steps include obtaining a stream containing the above heavy oil (HO), (S3) A portion of the stream containing the intermediate oil (MO) separated in the distillation column is supplied to a second reactor for secondary pyrolysis, and the gaseous stream generated by the secondary pyrolysis is supplied to the distillation column. (S4) The step of recirculating the stream containing heavy oil (HO) separated in the distillation column to the first reactor, A method for producing waste plastic pyrolysis oil, including the oil described.

2. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the first reactor, the distillation column, and the second reactor are connected in series.

3. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the stream containing the light oil (LO) is separated as a gas phase at the top of the distillation column and then recovered as liquid light oil (LO) by heat exchange with water in a condenser.

4. The method for producing waste plastic pyrolysis oil according to claim 3, wherein the water supplied to the condenser is hot water at 60 to 100°C, and the waste heat from the gas phase stream is recovered by the heat exchange and converted into steam.

5. The temperature at the top of the distillation column is adjusted to 150°C to less than 220°C, C ５－１２ A method for producing waste plastic pyrolysis oil according to claim 1, wherein the upper gas phase stream containing 70% or more of light hydrocarbons is discharged.

6. A method for producing waste plastic pyrolysis oil according to claim 1, wherein the pyrolysis of the first reactor and the second reactor is carried out under stepwise heating conditions.

7. The method for producing waste plastic pyrolysis oil according to claim 6, wherein the pyrolysis of the first reactor is carried out at 400°C to 450°C.

8. The method for producing waste plastic pyrolysis oil according to claim 6, wherein the pyrolysis of the second reactor is carried out in the range of 420°C to 450°C.

9. A method for producing waste plastic pyrolysis oil according to claim 1, wherein the lower residue of the first reactor and the lower residue of the second reactor are supplied to a residue treatment reactor for additional pyrolysis, and the gas phase stream generated by the additional pyrolysis is recirculated to the distillation column.

10. The method for producing waste plastic pyrolysis oil according to claim 9, wherein the additional pyrolysis of the residue treatment reactor is carried out at a temperature higher than the pyrolysis temperature of the first reactor or the second reactor.

11. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the content of the light oil (LO) is 50 to 70% by weight based on the weight of the waste plastic raw material.

12. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the waste plastic raw material is a mixture containing polyethylene (PE) or polypropylene (PP).

13. A method for producing waste plastic pyrolysis oil according to any one of claims 1 to 12, wherein the waste plastic raw material is supplied to a first reactor after undergoing a pretreatment process including crushing, washing, drying, and melting.

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