Method of preparing pyrolysis oil from waste plastics

Abstract

The present invention provides a method for preparing pyrolysis oil from waste plastics, the method comprising the steps of: (S1) supplying waste plastic feedstock to a first reactor, performing primary pyrolysis, and discharging the resulting gaseous stream from the top of the reactor; (S2) supplying the gaseous stream from the top of the first reactor to one or more distillation columns, and separating same according to boiling points to obtain a stream containing light oil (LO) of C5-12, a stream containing middle oil (MO) of C13-22, and a stream containing heavy oil (HO) of C23 or higher; (S3) supplying a portion of the stream containing middle oil (MO) separated in the distillation column to a second reactor, performing secondary pyrolysis, and supplying the gaseous stream generated by the pyrosis to the distillation column; and (S4) recirculating the stream containing heavy oil (HO) separated in the distillation column back to the first reactor.

Description

Method for producing pyrolysis oil from waste plastic

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0110204, filed August 23, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a method for producing pyrolysis oil from waste plastic, and more specifically, to a method for producing light hydrocarbon oil from waste plastic raw materials at a high yield.

[0005] Recently, the development and use of plastics with properties required for various applications and purposes is increasing. Plastics consume significant energy from crude oil extraction to manufacturing, and the process emits significant carbon emissions. Furthermore, when plastics used in various products are discarded, environmental pollution and enormous disposal costs occur, making recycling of waste plastics a critical social issue.

[0006] Generally, recycling methods for waste plastic (resin) include mechanical, chemical, and thermal recycling. Mechanical recycling involves crushing and sorting collected waste plastic, separating it by type, melting it using an extruder, and pelletizing it. This process involves mixing it with virgin plastic at a specific ratio or reinforcing it with functional additives to create resin products. Chemical recycling utilizes various chemical means to extract specific polymers or recover pure single molecules for repolymerization. Thermal recycling involves incinerating waste plastic to recover heat energy.

[0007] In particular, the above chemical recycling can reduce greenhouse gases compared to incineration of waste plastics and has recently been attracting attention in terms of developing alternative fuels.

[0008] For example, when waste plastics such as polyethylene or polypropylene are heated and pyrolyzed at a specific temperature, a gaseous stream containing a mixture of non-condensable gases and liquid oils is generated, and highly viscous residual wax that is not completely decomposed may be discharged. Among the pyrolysis products, the liquid oil is increasingly important as a raw material for the production of petrochemical products, and thus active research is being conducted to increase the yield of the liquid oil.

[0009] The liquid oil produced from the pyrolysis of the above waste plastic, i.e. pyrolysis oil, is usually C such as naphtha. 5-12 It is a blended oil containing light hydrocarbon oil and hydrocarbon oils with longer chains. If the blended 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 such as excessive production of heavy oil components and discharge of wax residue.

[0010] To address these issues, methods have been proposed that involve performing a contact cracking reaction via catalytic cracking during the pyrolysis of waste plastics, or using a contactor, a contact heat exchanger, to condense the heavy hydrocarbon (i.e., long-chain hydrocarbon) components in the pyrolysis products of waste plastics and then recirculate them to the pyrolysis reactor for further pyrolysis. However, these methods have limitations in increasing the pyrolysis efficiency of waste plastics, and are limited to recycling them as mixed oil.

[0011] In particular, the contactor is positioned at the top of the pyrolysis reactor to enable improved selectivity only for pyrolysis oil components having a specific boiling point range (e.g., long-chain hydrocarbons having a boiling point of 240 to 280°C).

[0012] Therefore, there is a need for a technology that can improve the pyrolysis process of waste plastics to increase the yield of high-grade light hydrocarbon oil.

[0013] The problem to be solved in the present invention is to solve the problems mentioned in the background technology of the above invention, and relates to a method for improving the yield of light hydrocarbon oil by connecting one or more distillation columns in series instead of a contactor (heat exchanger) at the top of a reactor for pyrolyzing waste plastic to separate high-boiling-point components in the pyrolysis product into medium oil (MO) and heavy oil (HO) and then performing additional pyrolysis.

[0014] According to one embodiment of the present invention for solving the above problem, (S1) a step of supplying waste plastic raw material to a first reactor to perform primary pyrolysis and discharging a gaseous stream generated by the pyrolysis to the upper portion; (S2) supplying the upper gaseous stream of the first reactor to one or more distillation columns and separating it according to boiling point to obtain C 5-12 Stream containing light oil (LO), C 13-22 Stream containing middle oil (MO) and C 23 A method for producing waste plastic pyrolysis oil is provided, comprising: (S3) a step of obtaining a stream including heavy oil (HO); (S4) a step of supplying a portion of a stream including intermediate oil (MO) separated from the distillation column to a second reactor to perform secondary pyrolysis, and supplying a gaseous stream produced by the pyrolysis to the distillation column; and (S4) a step of recycling a stream including heavy oil (HO) separated from the distillation column to the first reactor.

[0015] According to the present invention, after separating a pyrolyzed gaseous stream according to boiling point in one or more distillation columns connected in series to a first reactor for pyrolyzing waste plastic raw materials, a portion of the middle oil (MO) among the separated components is subjected to secondary pyrolysis in a second reactor, while the heavy oil (HO) is recycled to the first reactor, thereby improving the yield of high-grade light oil (LO).

[0016] In addition, by performing the thermal decomposition of the first and second reactors under stepwise temperature increase conditions, the decomposition efficiency of waste plastic can be improved, thereby increasing the yield of high-grade light hydrocarbon oil while minimizing the discharge of residual wax with low utilization.

[0017] Additionally, by controlling the upper operating temperature of the distillation column to a predetermined range, the fraction of light oil (LO) components in the gaseous stream separated from the distillation column can be increased, and in the process in which the gaseous stream is obtained in a liquid phase by heat exchange with water in a condenser connected to the upper portion of the distillation column, the water supplied to the condenser can be converted into steam by recovering the waste heat of the gaseous stream.

[0018] Furthermore, the utilization of light hydrocarbon oil obtained from the pyrolysis of waste plastic can reduce greenhouse gas emissions generated when supplying raw materials for petrochemical processes, and improve process efficiency such as reducing energy consumption. In addition, it is also environmentally beneficial as no harmful gases are generated during the processing of waste plastic.

[0019] Figure 1 illustrates a thermal decomposition process of waste plastic according to an embodiment of the present invention.

[0020] Figure 2 shows the thermal decomposition process of waste plastic according to a comparative example.

[0021] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0022] As used herein, the terms “include” or “contain” specify a particular characteristic, area, integer, step, operation, element, or component, but do not exclude the addition of other particular characteristics, areas, integers, steps, operations, elements, or components.

[0023] The term "stream" as used herein may refer to the flow of fluid within a process, or may refer to the fluid itself flowing within a pipe. Specifically, the stream may refer to both the fluid itself flowing within the pipe connecting each device and the flow of the fluid. Furthermore, the fluid may include one or more components of gas, liquid, and solid.

[0024] The term "C" used herein n " represents all hydrocarbons with n carbon atoms, for example, "C 5-12 " represents all hydrocarbon molecules having 5 to 12 carbon atoms.

[0025] The term 'liquid oil' as used herein means the product obtained by converting the gaseous stream obtained in the pyrolysis step into a liquid phase by condensation, and may also be referred to as 'liquid distilled oil'.

[0026] Additionally, the “pressure” referred to herein means absolute pressure measured relative to a complete vacuum.

[0027]

[0028] A method for producing waste plastic pyrolysis oil according to one embodiment of the present invention comprises (S1) a first pyrolysis step of waste plastic raw material, (S2) a separation step according to the boiling point of a pyrolyzed gaseous stream, (S3) a second pyrolysis step of a portion of separated intermediate oil, and (S4) a step of recycling the separated heavy oil to the raw material pyrolysis.

[0029] The above method can be performed using a process system including a first reactor (10) into which waste plastic raw material is supplied, one or more distillation columns (20) in series with the first reactor, a second reactor (11) connected to the distillation column (20), and a residue treatment reactor (30), as shown in FIG. 1.

[0030]

[0031] Hereinafter, a method for producing waste plastic pyrolysis oil according to the present invention will be described in detail step by step with reference to the drawings.

[0032] First, waste plastic raw material is supplied to the first reactor (10) to perform primary pyrolysis, and the gaseous stream generated by the pyrolysis is discharged upward (S1).

[0033] The above-mentioned waste plastic may include natural polymers, synthetic polymers, or mixtures thereof, and the synthetic polymer may include thermoplastic resins such as polyethylene, polypropylene, polystyrene, etc. In addition, the thermoplastic resin may be mixed with other types of resins such as PVC, PET, thermosetting resins, etc.

[0034] After being collected and sorted, waste plastics of this type may undergo a pretreatment process, including shredding, washing, drying, and melting. The pretreatment process may be performed using methods conventional in the art.

[0035] For example, the size of the shredded waste plastic is not particularly limited, but can typically be performed in the range of 0.5 to 6.0 cm, and the shredded waste plastic that has been washed and dried can be fed into a tubular melter such as an extruder to be melted. The extruder has a function of melting and kneading and extruding, and can 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 can be, but is not limited to, 120 to 350°C or 150 to 250°C.

[0036] The waste plastic melt obtained through the above pretreatment process is supplied to the first reactor for thermal decomposition.

[0037] The pyrolysis reactor usable in the present invention may be a stirred tank reactor equipped with an agitator. The agitator is not particularly limited as long as it can sufficiently stir the waste plastic melt supplied as a raw material, and may be, for example, a helical ribbon type or an anchor type. Maintaining a gap of about 5 mm to 1 cm from the inner wall of the reactor is advantageous in maximizing the stirring of the waste plastic and heat transfer through the wall of the reactor. In addition, the reactor may be operated in either a batch type or a continuous type. In addition, the reactor may be purged with nitrogen to maintain an oxygen-free or low-oxygen atmosphere while performing the pyrolysis reaction of the waste plastic melt.

[0038] The waste plastic melt is supplied to the first reactor equipped with such a stirrer, and the waste plastic melt is heated while the stirrer is operated to perform thermal decomposition of the waste plastic melt.

[0039] The heating of the waste plastic can be performed by passing high-temperature / high-pressure steam, hot water, or heat transfer fluid through a jacket provided on the outside of the reactor to transfer high-temperature heat to the waste plastic, and there are no special limitations thereon.

[0040] In one embodiment of the present invention, the first pyrolysis in the first reactor may be performed at 400 to 450°C. Considering that the raw material of the waste plastic is mainly a thermoplastic resin, and may be a mixture including, for example, 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 performed at a temperature in the range of 400 to 450°C, specifically 420 to 430°C. If the above first thermal decomposition temperature is less than 400℃, the thermal decomposition rate may be slow, and if it exceeds 450℃, the thermal decomposition rate is fast, but due to the high heat, an excessive amount of solid carbide such as char may be generated.

[0041] In addition, the first pyrolysis in the first reactor may be performed at a pressure of 0.9 to 1.1 bar for 1 to 5 hours, specifically 2 to 4 hours. The first pyrolysis reaction time may be determined by considering the point in time at which the production rate of light hydrocarbons having 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.

[0042] When the waste plastic raw material is thermally decomposed in the first reactor (10), C 1-4 Gas components such as naphtha, C 5-12 Light hydrocarbons and longer chain C 13-22 Hydrocarbons and C 23A gaseous stream containing the above hydrocarbon components is discharged to the top of the reactor, and the highly viscous residual wax is not vaporized and remains at the bottom of the reactor.

[0043]

[0044] Next, the gaseous stream discharged from the upper portion of the first reactor (10) is supplied to one or more distillation columns (20) and separated according to boiling point (S2).

[0045] The above one or more distillation columns (20) are arranged in series on the upper part of the first reactor (10), and can separate the thermal decomposition products transferred from the first reactor into components according to their boiling points by selective heating and condensation. For example, the stream supplied to each distillation column is heated by heat provided from a reactor connected to the lower part of the column, and the vapor generated by the heating moves to the upper part of the column and is discharged, and the discharged vapor can be partially or completely condensed in a condenser connected to the upper part of the column. A portion of the condensate can be circulated back into the column.

[0046] Unlike the existing pyrolysis process of waste plastic in which a contactor (heat exchanger) is applied to a pyrolysis reactor, in the present invention, one or more distillation columns are arranged on the upper part of the first reactor to separate pyrolysis products according to boiling points, and high-boiling-point oil discharged from the middle or lower part of the distillation column can be selectively recycled to the first reactor or supplied to the second reactor to perform an additional pyrolysis reaction, thereby improving the yield of light oil (LO).

[0047] In addition, in the present invention, the carbon range of the desired pyrolysis oil (distillate oil) can be changed by controlling the upper operating temperature of the distillation column.

[0048] Specifically, when the upper operating temperature of the distillation column is increased, the carbon range of the pyrolysis oil moves to a high boiling point, and when the upper operating temperature of the distillation column is decreased, the carbon range of the pyrolysis oil moves to a low boiling point, thereby increasing the yield of light oil such as naphtha.

[0049] For example, when the upper temperature of the distillation column is controlled to 220°C to 300°C, C 5-12 Low boiling point hydrocarbons and C 13-22 A gaseous stream containing more than 80% of intermediate boiling point hydrocarbons can be discharged. Meanwhile, when the upper temperature of the distillation column is controlled to less than 150°C to 220°C, C 5-12 A gaseous stream containing more than 70% of low-boiling-point hydrocarbons can be discharged. The gaseous stream can be cooled and condensed by heat exchange with water connected to the top of the distillation column and converted into liquid oil, and the gaseous components that are not condensed in the heat exchange (e.g., C 1-4 Hydrocarbons) can be discharged to the top. At this time, some components contained in the condensed liquid oil, i.e., intermediate boiling point or high boiling point components, can be refluxed to the top of the distillation column and moved toward the bottom of the distillation column. As a result, C in the upper tray of the column 5-12 Light oil (LO) is discharged from the column, and C is discharged from the middle stage of the column. 13-22 Middle oil (MO) is discharged, and C is discharged from the lower stage of the column. 23 Ideally, for example, C 23-40 Heavy oil (HO) may be discharged.

[0050] In addition, a dividing wall type distillation column (DWC) having two regions separated by a central dividing wall may be used as the distillation column (10), and C is introduced into the upper part of the DWC. 5-12 Stream containing light hydrocarbons, C to the side of the DWC 13-22Stream containing intermediate hydrocarbons, C to the bottom of DWC 23 A stream containing the above high boiling point hydrocarbons can be separated.

[0051] Meanwhile, when the distillation columns (10) are arranged in multiple numbers, the temperature of the condenser connected to the upper part of each column can be operated differently. That is, by setting the upper temperature of the front column relatively high and setting the upper temperature of the rear column relatively low, the carbon range of the pyrolysis oil (distillate oil) can be changed. For example, the upper temperature of the front column can be adjusted to 220°C to 300°C, and the upper temperature of the rear column can be adjusted to 150°C to less than 220°C. The upper gaseous stream discharged from each of the front and rear columns can be discharged as liquid oil after condensation, as described above, or a portion thereof can be recirculated back to the upper part of each column. In addition, in the middle and lower part of each column, C 13-22 Medium oil (MO) or C 23 The above heavy oil (HO) can be selectively discharged.

[0052] In this way, the gaseous stream generated by the primary pyrolysis of waste plastic raw materials in the above one or more distillation columns is separated according to boiling point to C 5-12 Stream containing light oil (LO), C 13-22 Stream containing intermediate oil (MO) and C 23 A stream containing the above heavy oil (HO) can be obtained.

[0053] Additionally, in the process of obtaining a liquid phase by heat exchange with water in a gaseous stream in a condenser connected to the upper portion of the distillation column, the water supplied to the condenser can be converted into steam by recovering the waste heat of the gaseous stream.

[0054] To generate steam through waste heat recovery, the present invention uses hot water of 60 to 100°C as heat-exchanged water in the upper condenser of the distillation column. The temperature of the water can be adjusted according to the desired pyrolysis oil composition.

[0055] In particular, when the distillation columns are arranged in multiple numbers, as described above, steam of different pressures can be generated by operating the condenser temperature of the front column high and the condenser temperature of the rear column low. For example, when the upper operating temperature of the distillation column is set high so that the carbon range of the pyrolysis oil moves to a high boiling point, high-pressure steam can be generated through the heat of absorption of the condenser connected to the upper part of the column. On the other hand, when the upper operating temperature of the distillation column is set low so that the carbon range of the pyrolysis oil moves to a low boiling point, low-pressure steam can be generated.

[0056]

[0057] Afterwards, C separated from the distillation column (20) 13-22 A portion of the stream containing intermediate oil (MO) is supplied to a second reactor (11) to perform secondary pyrolysis, and the gaseous stream produced by the pyrolysis is supplied to the distillation column (20) (S3).

[0058] The second reactor (11) may be arranged in series with the distillation column (20). That is, the first reactor (10) may be arranged on one side of the distillation column (20) and the second reactor (11) may be arranged on the other side of the distillation column (20), so that the first reactor, the distillation column, and the second reactor may be arranged in series in that order.

[0059] In the second reactor, the thermal decomposition of a portion of the intermediate oil (MO) can be performed at a higher temperature than the thermal decomposition of the waste plastic raw material performed in the first reactor. That is, in the present invention, it is advantageous to perform the thermal decomposition of the first reactor and the second reactor under stepwise temperature elevation conditions to increase the decomposition efficiency of the waste plastic.

[0060] In one embodiment of the present invention, the temperature of the secondary pyrolysis of the second reactor (11) may be in the range of 420°C to 450°C, and when performed at a higher temperature than the primary pyrolysis, the production of light oil (LO) due to the decomposition of intermediate oil (MO) may 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.

[0061] In addition, the secondary pyrolysis may be performed at a pressure of 0.9 to 1.1 bar for 1 to 3 hours, specifically 1.5 to 2.5 hours. The secondary pyrolysis reaction time may be determined by considering the point in time at which the production rate of light hydrocarbons having 12 or fewer carbon atoms increases after the start of the decomposition reaction of the middle oil (MO).

[0062] Through this secondary pyrolysis, C obtained from waste plastic raw materials 13-22 Sufficient thermal decomposition of middle oil (MO) can be induced to convert it into a lower carbon number, thereby obtaining the final C 5-12 can increase the yield of light oil (LO).

[0063]

[0064] Meanwhile, C separated from the distillation column (20) 23 The stream containing the above heavy oil (HO) is recycled to the first reactor (10) (S4).

[0065] Heavy oil (HO) included in the gaseous products obtained by the first pyrolysis of the above waste plastic raw material is a high-boiling hydrocarbon with a boiling point of 360°C or higher and can be discharged to the bottom of the distillation column. The stream containing this high-boiling heavy oil is transferred to the first reactor and pyrolyzed again to produce C 5-12 Light oil (LO) and C 13-22can be converted into intermediate oil (MO).

[0066]

[0067] Additionally, the bottom residue of the first reactor (10) and the bottom residue of the second reactor (11) can be supplied to the residue treatment reactor (30) to perform additional pyrolysis.

[0068] The above residue treatment reactor (30) may include an upper zone where a thermal decomposition reaction is performed and a lower zone where high viscosity wax residue is discharged.

[0069] In the upper section of the residue treatment reactor, the lower residue of the first reactor and the lower residue of the second reactor may be supplied to perform additional pyrolysis, and it is preferable that the additional pyrolysis be performed at a higher temperature than the pyrolysis of the first reactor or the second reactor.

[0070] Additionally, the additional pyrolysis of the residue treatment reactor may be performed at a pressure of 0.9 to 1.1 bar for 1 to 3 hours, specifically 1.5 to 2.5 hours. The additional pyrolysis reaction time may be determined by considering the point in time at which the production rate of low-boiling-point hydrocarbons increases after the start of the decomposition reaction of the residue.

[0071] The pyrolysis oil obtained from the above pyrolysis process is a high value-added C 5-12 It can contain a high fraction of light oil (LO). For example, the final obtained C 5-12 The content of light oil (LO) may be 50 to 70 wt%, specifically 50 to 60 wt%, based on the weight of the waste plastic raw material. C obtained in such a high yield 5-12 Light hydrocarbons can be condensed and used as high-grade fuel oil.

[0072] In particular, the C finally obtained in the present invention 5-12The 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 thus can be usefully used as a petrochemical raw material.

[0073]

[0074] According to the present invention as described above, after separating a gaseous stream pyrolyzed in one or more distillation columns connected in series to a first reactor for pyrolyzing waste plastic raw materials according to boiling point, a portion of the middle oil (MO) among the separated components is subjected to secondary pyrolysis in a second reactor, while the heavy oil (HO) is recycled to the first reactor, thereby improving the yield of high-grade light oil (LO).

[0075] In addition, by performing the thermal decomposition of the first and second reactors under stepwise temperature increase conditions, the decomposition efficiency of waste plastic can be improved, thereby increasing the yield of high-grade light hydrocarbon oil while minimizing the discharge of residual wax with low utilization.

[0076] Additionally, by controlling the upper operating temperature of the distillation column to a predetermined range, the fraction of light oil (LO) components in the gaseous stream separated from the distillation column can be increased, and in the process in which the gaseous stream is obtained in a liquid phase by heat exchange with water in a condenser connected to the upper portion of the distillation column, the water supplied to the condenser can be converted into steam by recovering the waste heat of the gaseous stream.

[0077] Furthermore, the utilization of light hydrocarbon oil obtained from the pyrolysis of waste plastic can reduce greenhouse gas emissions generated when supplying raw materials for petrochemical processes, and improve process efficiency such as reducing energy consumption. In addition, it is also environmentally beneficial as no harmful gases are generated during the processing of waste plastic.

[0078] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention, and the scope of the present invention is not limited to these examples alone.

[0079] Example 1:

[0080] As shown in Fig. 1, thermal decomposition of waste plastic was performed using a process system including a first reactor (10), a distillation column (20), a second reactor (11), and a residue treatment reactor (30).

[0081] First, 100 parts by weight of a waste plastic melt containing polyethylene (PE) and polypropylene (PP) in a weight ratio of 6:4 was supplied to a first reactor (10) of a stirring type, and after the reactor (10) was heated by an external heating means and reached 430°C, a first thermal decomposition reaction was performed for 4 hours while maintaining a constant temperature.

[0082] The gaseous stream discharged from the top of the first reactor (10) was supplied to a distillation column (20) and separated into components according to boiling points. Specifically, the upper temperature of the column was operated at 210°C to discharge the gaseous stream to the top and cooled to 25°C in a condenser to condense the liquid C 5-12 Light oil (LO) was obtained and the non-condensed gas component was discharged. Then, C was extracted from the middle tray of the column. 13-22 A stream containing intermediate oil (MO) is obtained, and C is extracted from the lower stage of the column. 23-40 The bottom stream containing heavy oil (HO) was discharged.

[0083] A portion of the intermediate oil (MO) separated from the distillation column (20) was supplied to the second reactor (11) to perform secondary pyrolysis at 430°C for 2 hours, and the gaseous stream generated by the secondary pyrolysis was recycled to the distillation column (20).

[0084] Meanwhile, the bottom discharge stream of the distillation column (20) was recycled to the first reactor (10) for thermal decomposition again.

[0085] In addition, the bottom residue of the first reactor (10) and the bottom residue of the second reactor (11) were each supplied to a residue treatment reactor (30) and further thermal decomposition was performed at 450°C for 2 hours, and the upper gaseous stream produced was recycled to the bottom of the distillation column (20), and the residue remaining at the bottom was discharged.

[0086] Example 2:

[0087] The same process as Example 1 was performed except that secondary thermal decomposition of a portion of the intermediate oil (MO) in the second reactor (11) was performed at 440°C for 2 hours.

[0088] Example 3:

[0089] The same process as Example 1 was performed except that secondary thermal decomposition of a portion of the intermediate oil (MO) in the second reactor (11) was performed at 450°C for 2 hours.

[0090] Comparative Example 1:

[0091] As shown in Fig. 2, pyrolysis of waste plastic was performed using a process system including a first reactor (10), a distillation column (20), and a residue treatment reactor (30). Specifically, the same process as Example 1 was performed except that secondary pyrolysis was not performed on a portion of the intermediate oil (MO) separated in the distillation column (20).

[0092]

[0093] Table 1 below shows the composition (weight% based on raw material supply amount) of the pyrolysis products obtained based on the feed in the above examples and comparative examples, as analyzed by GC-MS.

[0094] 1st pyrolysis product 2nd pyrolysis product Final pyrolysis oil composition Example 1 (430°C, 4h / 430°C, 2h) Gas 9 Gas 2 Gas 11 LO 48 LO 6 LO 5437 (30 fed to the second reactor) MO 22 MO 29 Residue 6-Residue 6 Example 2 (430°C, 4h / 440°C, 2h) Gas 9 Gas 3 Gas 12 LO 48 LO 8 LO 5637 (30 fed to the second reactor) MO 19 MO 26 Residue 6-Residue 6 Example 3 (430°C, 4h / 450°C, 2h) Gas 9 Gas 4 Gas 16 LO 48 LO 10 LO 5837 (30 fed to the second reactor) MO 16 MO 23Residue 6-Residue 6Comparative Example 1 (430℃ 4h)Gas 9Gas 9LO 48LO 4837MO 37Residue 6Residue 6

[0095] As can be seen from Table 1 above, Examples 1 to 3, in which a pyrolyzed gaseous stream was separated according to boiling point in one or more distillation columns connected in series to a first reactor for pyrolyzing waste plastic raw materials, and then a portion of the middle oil (MO) among the separated components was subjected to secondary pyrolysis in a second reactor, showed an improved yield of low-boiling-point light oil (LO) compared to Comparative Example 1, in which secondary pyrolysis was not performed.

[0096] In addition, examples 2 and 3, in which the first and second pyrolysis were performed under stepwise temperature increasing conditions, obtained light oils with a yield that was improved more than example 1 performed at the same temperature.

Claims

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

2. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the first reactor, distillation column, and second reactor are connected in series.

3. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein a stream containing the above light oil (LO) is separated into a gas phase at the top of the distillation column and then heat-exchanged with water in a condenser to recover the liquid light oil (LO).

4. In paragraph 3, A method for producing waste plastic pyrolysis oil in which the water supplied to the above condenser is hot water of 60 to 100°C, and waste heat of the gaseous stream is recovered through the heat exchange and converted into steam.

5. In paragraph 1, The upper temperature of the distillation column is controlled to be less than 150°C to 220°C. 5-12 A method for producing waste plastic pyrolysis oil, which discharges an upper gaseous stream containing 70% or more of light hydrocarbons.

6. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the pyrolysis of the first reactor and the second reactor is performed under stepwise temperature increase conditions.

7. In paragraph 6, A method for producing waste plastic pyrolysis oil, wherein pyrolysis of the first reactor is performed at 400 to 450°C.

8. In paragraph 6, A method for producing waste plastic pyrolysis oil, wherein pyrolysis of the second reactor is performed at a temperature ranging from 420°C to 450°C.

9. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the bottom residue of the first reactor and the bottom residue of the second reactor are each supplied to a residue treatment reactor to perform additional pyrolysis, and the gaseous stream produced by the pyrolysis is recycled to the distillation column.

10. In paragraph 9, A method for producing waste plastic pyrolysis oil, wherein pyrolysis of the above residue treatment reactor is performed at a temperature higher than the pyrolysis temperature of the first reactor or the second reactor.

11. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the content of the above light oil (LO) is 50 to 70 wt% based on the weight of the waste plastic raw material.

12. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the above waste plastic raw material is a mixture containing polyethylene (PE) or polypropylene (PP).

13. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the above 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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