Method for producing pyrolysis oil from waste plastics

Abstract

The present invention provides a method for producing pyrolysis oil from waste plastics, the method comprising the steps of: (S1) supplying waste plastic feedstock and process oil stream into a first melting tank and mixing same to obtain a first molten material; (S2) passing the first molten material through a first filter to remove non-molten solid materials; (S3) supplying the first molten material, from which the non-molten materials have been removed, into a second melting tank and raising the temperature to obtain a second molten material; (S4) pyrolyzing the second molten material to obtain a pyrolysis product including a gas phase fraction and a liquid phase fraction; and (S5) purifying the pyrolysis product by supplying the pyrolysis product to a distillation column.

Description

Method for producing pyrolysis oil from waste plastic

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0157804, filed November 15, 2023, and Korean Patent Application No. 10-2024-0119622, filed September 3, 2024, 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 pyrolysis oil with a high yield by removing foreign substances and impurities from waste plastic raw materials to ensure process stability.

[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, methods for recycling waste plastic (resin) include mechanical recycling and chemical recycling. Mechanical recycling involves crushing and sorting collected waste plastic, separating it by type, and then melting and pelletizing it. This process involves mixing it with virgin plastic at a certain ratio or reinforcing it with functional additives to create resin products. Chemical recycling utilizes various chemical means to extract specific polymers or recover them as pure single molecules, which are then repolymerized.

[0007] The chemical recycling described above can reduce greenhouse gas emissions compared to incineration of waste plastics and is attracting attention for its potential as an alternative fuel. For example, waste plastics made of materials such as polyethylene or polypropylene can be collected and sorted, followed by preprocessing processes including crushing, washing, drying, and melting. The resulting molten plastic can then be pyrolyzed to produce liquid hydrocarbon oil. This liquid hydrocarbon oil can then be used as fuel oil for the production of petrochemical products.

[0008] Figure 1 illustrates a typical thermal decomposition process of waste plastic. Waste plastic raw material is fed into a screw-type extruder (100) equipped with a heating device to be melted, and the molten material discharged from the extruder (100) is thermally decomposed in a reactor (200) to discharge a gaseous stream containing a light oil (LO) component to the upper portion of the reactor, and a liquid stream that has not yet been vaporized is discharged to the lower portion of the reactor. In addition, a highly viscous wax residue such as char remains at the lower portion of the reactor.

[0009] The extruder used for melting the above waste plastic has the function of melting and kneading by applying electric energy and shear to the washed and dried waste plastic shreds, but the high electricity usage in the process results in high energy consumption and limits the scale-up of the process.

[0010] The main component that can be converted into useful hydrocarbon oil from the above waste plastic raw material is polyolefin. In addition, if impurities such as foreign substances, polyethylene terephthalate (PET)-derived substances, and chlorine (Cl) components are included, it can cause operational abnormalities such as plugging in the process equipment including the pyrolysis reactor, which can hinder the process stability, and ultimately reduce the yield and purity of the pyrolysis oil. For example, if polyethylene terephthalate (PET) is included in the waste plastic raw material, sublimable substances such as terephthalic acid and benzoic acid are generated during the pyrolysis process, and these substances can accumulate in the reactor and subsequent process equipment, causing clogging. In addition, if combustible waste such as polyvinyl chloride is included, chlorine (Cl) compounds can be included in the liquid and gaseous pyrolysis products during the pyrolysis process, which can cause serious corrosion of the process equipment.

[0011] The present invention is intended to solve the problems mentioned in the background technology of the above invention, and provides a method for producing pyrolysis oil with a high yield by removing impurities such as foreign substances and chlorine compounds from waste plastic raw materials to ensure process stability.

[0012] According to one embodiment of the present invention for solving the above problems, a method for producing waste plastic pyrolysis oil is provided, comprising the steps of: (S1) supplying waste plastic raw material and process oil stream to a first melting tank and mixing them to obtain a first melt; (S2) passing the first melt through a first filter to remove unmelted solid materials; (S3) supplying the first melt from which the unmelted materials have been removed to a second melting tank and increasing the temperature to obtain a second melt; (S4) pyrolyzing the second melt to obtain a pyrolysis product including a gaseous fraction and a liquid fraction; and (S5) supplying the pyrolysis product to a distillation column to purify it.

[0013] In the present invention, the first melting tank can be maintained at a temperature of 150°C to 220°C, and the temperature of the primary melt in the second melting tank can be increased to 250°C to 400°C.

[0014] According to the present invention, in a first melting tank capable of supplying heat by a heat transfer fluid other than electricity, waste plastic is melted into a process oil stream, and solid unmelted substances are removed from the obtained primary melt, and then the primary melt is supplied to a second melting tank and heated to decompose and remove chlorine (Cl) compounds contained in the waste plastic, thereby obtaining a secondary melt whose temperature has been raised to a temperature immediately before thermal decomposition.

[0015] Since this secondary melt is fed into a post-stage pyrolysis reactor with impurities such as solid foreign substances, PET-derived substances, and chlorine compounds removed, process stability is secured to minimize operational abnormalities that may be caused by the impurities, thereby enabling the production of pyrolysis oil converted from the waste plastic at a high yield.

[0016] 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.

[0017] Figure 1 illustrates a typical thermal decomposition process of waste plastic.

[0018] Figure 2 illustrates a process for producing pyrolysis oil from waste plastic according to one embodiment of the present invention.

[0019] [Revised 17.12.2024 under Rule 91] Figure 3 illustrates a process for manufacturing pyrolysis oil from waste plastic according to comparative examples. Figure 4 shows the melt of Reference Example 1 (melting temperature 200ºC). Figure 5 shows the melt of Reference Example 2 (melting temperature 220ºC). Figure 6 shows the melt of Reference Example 3 (melting temperature 230ºC).

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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'.

[0025] Additionally, the “pressure” referred to herein means absolute pressure measured relative to a complete vacuum.

[0026]

[0027] Hereinafter, the present invention will be described in detail with reference to the attached drawings.

[0028] One embodiment of the present invention relates to a method for producing pyrolysis oil with a high yield by removing impurities such as foreign substances and chlorine compounds from waste plastic raw materials to ensure process stability.

[0029] FIG. 2 illustrates a method for producing pyrolysis oil from waste plastic according to one embodiment of the present invention, and the method can be performed using a process system including a first melting tank (110) and a second melting tank (120) into which waste plastic raw materials are introduced, a reactor (200) for performing pyrolysis of molten plastic, a first filter (10) and a second filter (20) for removing impurities, an optional heating means (H), and a distillation tower (not shown) for purifying pyrolysis products.

[0030] The waste plastic may be recovered from composite films, multi-films, and other urban waste containing natural polymers, synthetic polymers, or mixtures thereof. The synthetic polymer may include thermoplastic resins such as polyethylene, polypropylene, and polystyrene. In addition, the thermoplastic resin may be mixed with other types of resins such as polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polyvinylidene fluoride (PVDF), thermosetting resins, etc. For example, the waste plastic raw material may be a thermoplastic resin containing less than 20 wt%, for example, 1 to 16 wt%, of PET or PVC based on the total weight thereof.

[0031] After collection, waste plastics of this type may undergo a pretreatment process, including sorting, shredding, washing, and drying. The pretreatment process can be performed using any method commonly used in the field, without any specific limitations.

[0032] According to one embodiment of the present invention, a dissolver capable of supplying heat by a high-temperature heat transfer fluid is used to melt the waste plastic.

[0033] Specifically, waste plastic raw material and process oil stream are supplied to the first melting tank (110) and mixed to obtain a primary melt (S1).

[0034] The first melting tank (110) supplies heat to the supplied waste plastic to melt it, and at this time, a process oil stream as a heat source can be supplied through a different supply line from the waste plastic raw material. An agitator can be installed in the first melting tank (110) to ensure uniform mixing of the waste plastic raw material and the process oil.

[0035] The above process oil stream may be a liquid oil obtained from a pyrolysis process for waste plastic. For example, the process oil stream may include pyrolysis liquid oil generated within the process and oil discharged from a distillation tower for refining the pyrolysis liquid oil. Additionally, fuel oil obtained from other oil refining or petrochemical processes may be used as the process oil stream.

[0036] If necessary, the process oil stream may be supplied to the first melting tank after passing through a filter (20) to remove impurities. In addition, an auxiliary heating means (H) may be installed in the supply line of the process oil stream to supply additional heat depending on the temperature of the process oil stream.

[0037] This process oil stream is stirred and mixed with solid waste plastic in the first melting tank (110), and in this process, it acts as a heat transfer fluid and can melt or dissolve the waste plastic depending on its temperature.

[0038] The above process oil stream can be used in amounts of 5 to 40 times or 8 to 20 times the weight of the waste plastic raw material.

[0039] In one embodiment of the present invention, it is advantageous to maintain the first melting tank (110) at a temperature of 150°C to 220°C, specifically, 170°C to 220°C. When the temperature range is satisfied, selective melting can be performed in which the effective component that can be converted into hydrocarbon oil among the resins contained in the waste plastic is melted in a liquid phase, while solid foreign substances such as paper, soil, and other components attached to the resins remain in an unmelted state. In addition, PET, which can reduce the yield of hydrocarbon oil during pyrolysis and cause abnormalities in process equipment, remains in an unmelted state at a temperature of 150°C to 220°C. More specifically, when the temperature of the first melting tank (110) is less than 150°C, the resins contained in the waste plastic may not be sufficiently melted. On the other hand, when the temperature of the first melting tank (110) exceeds 220°C, PET is melted together with the resins that can be converted into pyrolysis oil, thereby effectively performing selective melting. Melting may be difficult, and additives included in the above resin may melt, resulting in the inclusion of foreign substances such as heteroatoms and metal impurities in the melt.

[0040] Additionally, selective melting of waste plastic raw materials in the first melting tank (110) can be performed for 0.1 to 2 hours, specifically 0.15 to 1 hour.

[0041] After this selective melting, the primary melt obtained from the first melting tank ((110)) is passed through the first filter (10) to remove unmelted solid materials (S2).

[0042] The above first filter is a means for separating solid foreign substances other than liquid resins contained in the primary melt, and can be used without special restrictions as long as it has a form capable of separating solids and liquids.

[0043] Additionally, filtration in the first filter can be performed without heating to effectively separate non-melted solid foreign substances contained in the primary melt. That is, filtration can be performed at a temperature lower than or equal to the primary melting temperature.

[0044] The first melt from which non-melted solid materials have been removed through the first filter (10) is supplied to the second melting tank (120) and the temperature is increased to obtain a second melt (S3).

[0045] In the second melting tank (120), additional melting is performed by supplying a higher temperature of heat to the primary melt, thereby further reducing the viscosity of the liquid component and raising the temperature to a temperature just before thermal decomposition. In addition, during the additional melting process, a dechlorination process may be performed to decompose and remove chlorine (Cl) components of combustible materials such as PVC (polyvinyl chloride) within the waste plastic.

[0046] The heating of the above-mentioned primary melt can be carried out using any means capable of transferring high-temperature heat without any particular limitation. For example, heat can be transferred by passing a heat medium such as high-temperature / high-pressure steam, hot water, or process oil stream through a jacket provided on the outside of the second melting tank (120), or the melt of the second melting tank (120) can be branched into a certain amount, heated using an electric heater or a heating furnace, and then injected back into the second melting tank (120) to transfer high-temperature heat.

[0047] Specifically, the primary molten material supplied from the second melting tank (120) may be heated to 250°C to 400°C, specifically 270°C to 400°C. If the heating temperature is lower than 250°C, the desalination efficiency may not be sufficient, and if it exceeds 400°C, a thermal decomposition reaction may occur in the second melting tank, reducing the oil yield.

[0048] Additionally, the residence time for the primary melt to be heated in the second melting tank (120) may be in the range of 0.1 to 3 hours, specifically 0.5 to 1 hour.

[0049] Additionally, a desalting agent capable of absorbing chlorine may be added to the second melting tank (120) to perform a more effective desalting process.

[0050] The above dechlorinating agent can be used without limitation as long as it is a substance capable of absorbing chlorine, and for example, CaO, CaCO3, Ca(OH)2, NaOH, Na2CO3, NaHCO3, Fe2O3, Fe3O4 or a mixture thereof can be used.

[0051] Through the additional melting as described above, a secondary melt that has been raised to a temperature just before pyrolysis while removing chlorine (Cl) contained in waste plastic can be obtained, and by introducing this secondary melt into a subsequent pyrolysis reactor, it is possible to stably produce a high-yield pyrolysis oil by minimizing operational abnormalities that may be caused by impurities and improving the decomposition efficiency.

[0052] If additional melting is not performed in the second melting tank (120), desalination is not sufficiently achieved, which may cause corrosion of process equipment including the pyrolysis reactor or cause process instability.

[0053] Meanwhile, a gas containing chlorine (Cl) may be discharged from the upper portions of the first and second melting tanks, and the discharged gas may be removed through a neutralization process. The neutralization process may be performed using a method conventional in the art, such as a washing tower or an adsorption tower, but is not limited thereto.

[0054]

[0055] The secondary melt obtained in the second melting tank ((120)) is supplied to the reactor (200) and thermally decomposed to obtain a thermal decomposition product including a gaseous fraction and a liquid fraction (S4).

[0056] 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.

[0057] A waste plastic melt is supplied to a reactor equipped with such a stirrer, and the melt is heated while the stirrer is operated to perform thermal decomposition of the waste plastic melt.

[0058] The secondary molten material supplied to the reactor (200) may be heated by a heating means provided outside the reactor. For example, the heating means may be implemented by passing heat through a jacket, such as a high-temperature / high-pressure steam, hot water, or process oil stream, to transfer heat, or the molten material may be divided into a certain amount, heated using an electric heater or a heating furnace, and then fed back into the reactor (200) to transfer high-temperature heat. In addition, another heating means may be used without any particular limitation.

[0059] In one embodiment of the present invention, the thermal decomposition of the secondary melt may be performed at a temperature of more than 400°C to 500°C. Considering that the main component of the waste plastic raw material is 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 thermal decomposition reaction is advantageously performed at a temperature of more than 400°C to 500°C, specifically 410 to 450°C. When the above thermal decomposition temperature is 400℃ or lower, the thermal decomposition rate may be slow, and when it exceeds 500℃, the thermal decomposition rate is fast, but due to the high heat, an excessive amount of solid carbide such as char may be generated.

[0060] In the above pyrolysis step, the waste plastic melt is non-condensable C 1-4 Components such as naphtha, which can be converted into liquid oil by condensation 5-12 Hard component of C 13-22 The intermediate components and C 23-40 The heavy components of the reactor can be vaporized after being broken down into low molecular weight hydrocarbons and discharged as an upper stream of the reactor, and the liquid stream that has not yet been vaporized can be discharged as a lower stream of the reactor. In addition, a high viscosity residual wax such as char remains at the bottom of the reactor.

[0061] A portion of the liquid oil obtained in the above pyrolysis step may be used as a process oil stream as mentioned above. If necessary, the process oil stream may be passed through a second filter (20) before being supplied to the first melting tank to remove impurities, such as high viscosity residues such as char remaining during pyrolysis. In addition, an auxiliary heating means (H) may be installed in the supply line of the process oil stream to supply additional heat depending on the temperature of the process oil stream. The second filter may be used without any special restrictions as long as it is of a type capable of separating high viscosity components and liquids.

[0062]

[0063] The upper discharge stream of the above reactor (200) can be converted into liquid gas oil through a condensation process, and then supplied to a distillation tower for purification, thereby obtaining pyrolysis oil (S5).

[0064] The above condensation is a process for cooling the pyrolysis gas, thereby suppressing the polymerization reaction of hydrocarbons in the high-temperature pyrolysis gas discharged from the pyrolysis reactor and reducing the heat load of the subsequent process (purification process). For example, if the gaseous stream discharged from the upper part of the pyrolysis reactor is supplied to a condenser and heat exchanged with quench oil or quench water is performed, it can be cooled and condensed to obtain liquid gas oil. Meanwhile, the gas components that are not condensed in the heat exchange (e.g., C 1-4 The hydrocarbons) can be discharged to the top of the condenser and can be used as a heat source for a petrochemical process or a heat source for a pyrolysis process after going through a subsequent process such as compression.

[0065] The above purification process can be performed in a manner conventional in the art and is not particularly limited. For example, the feed stream supplied to the distillation tower can include all oil components obtained from the pyrolysis gas of waste plastic, and low-boiling-point light oil (LO) can be discharged from the top of the distillation tower, and high-boiling-point heavy oil (HO) can be discharged from the bottom of the distillation tower.

[0066] The heavy oil discharged from the distillation tower may have a boiling point of 200 to 550°C at atmospheric pressure, and may be recovered and used as a process oil stream.

[0067]

[0068] According to the present invention as described above, in a first melting tank capable of supplying heat by heat transfer fluid rather than electricity, waste plastic is melted into a process oil stream, and solid non-melted substances including PET are removed from the obtained primary melt, and then the primary melt is supplied to a second melting tank and heated to decompose and remove chlorine (Cl) compounds contained in the waste plastic, thereby obtaining a secondary melt whose temperature has been raised to a temperature immediately before thermal decomposition.

[0069] Since this secondary melt is fed into a post-stage pyrolysis reactor with impurities such as solid foreign substances, PET-derived substances, and chlorine compounds removed, process stability is secured to minimize operational abnormalities that may be caused by the impurities, thereby enabling the production of pyrolysis oil converted from the waste plastic at a high yield.

[0070] 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.

[0071] 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.

[0072]

[0073] Example 1:

[0074] Thermal decomposition of waste plastic was performed according to the process sequence shown in Fig. 2.

[0075] First, waste plastic shredders containing polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) in a weight ratio of 56:33:9:2 and a portion of the liquid stream discharged from the lower portion of the post-stage pyrolysis reactor (200) were supplied to the first melting tank (110) and mixed with the process oil stream to obtain a primary melt. At this time, the waste plastic shredders and the process oil were used in a weight ratio of 1:5, and melting was performed by maintaining the temperature of the first melting tank (110) at 200°C.

[0076] The above primary melt was passed through a first filter (10) at a temperature lower than the melting temperature to remove unmelted solid materials including PET, and the liquid melt was supplied to a second melting tank (120), where a mixture of CaO and CaCO3 was added as a demineralizing agent. The liquid melt supplied to the second melting tank (120) was heated to 250°C to obtain a secondary melt.

[0077] The above secondary melt was supplied to a reactor (200) and thermally decomposed at 430°C for 1 hour. The upper gaseous stream generated by the thermal decomposition was condensed and supplied to a distillation tower and distilled to 350°C to obtain light / medium thermal decomposition oil, and the remaining liquid heavy oil and solid char were separated.

[0078]

[0079] Example 2:

[0080] Pyrolysis oil was obtained by performing the same process as Example 1, except that the melt supplied to the second melting tank (120) was heated to 400°C.

[0081]

[0082] Comparative Example 1:

[0083] Thermal decomposition of waste plastic was performed according to the process sequence shown in Fig. 3.

[0084] First, a waste plastic shredder containing polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) in a weight ratio of 56:33:9:2, a mixture of CaO and CaCO3 as a desalting agent, and a portion of a liquid stream discharged from the lower portion of a subsequent pyrolysis reactor (200) were supplied to a first melting tank (110) and mixed as a process oil stream to obtain a melt. At this time, the temperature of the first melting tank (110) was maintained at 350°C.

[0085] The above melt was supplied to a reactor (200) and thermally decomposed at 430°C for 1 hour. The upper gaseous stream generated by the thermal decomposition was condensed and supplied to a distillation tower and distilled to 350°C to obtain light / medium thermal decomposition oil, and the remaining liquid heavy oil and solid char were separated.

[0086]

[0087] Comparative Example 2:

[0088] Pyrolysis oil was obtained by performing the same process as Example 1, except that melting was performed by maintaining the temperature of the first melting tank (110) at 400°C.

[0089]

[0090] Table 1 below shows the process conditions applied in the above examples and comparative examples, the composition of pyrolysis oil confirmed through single distillation, and the presence or absence of abnormalities occurring in equipment operation (pyrolysis reactor, distillation tower, etc.).

[0091]

[0092] Process conditions Pyrolysis oil composition Equipment operation Abnormal melting tank Pyrolysis reactor Liquid oil (%) Solid (%) Gas (%) Primary Secondary Light / Intermediate Heavy Char Example 1200℃250℃430℃81.015.1-3.9- Example 2200℃400℃430℃79.715.6-4.7- Comparative example 1350℃-430℃74.918.11.06.0 White solid observed at the top of the reactor White sediment formation in the oil Comparative example 2400℃-430℃75.517.20.96.4 Pipe clogging White sediment formation in the oil

[0093] As can be seen in Table 1 above, Examples 1 and 2 performed primary melting at a low temperature of 200°C in the first melting tank to remove unmelted foreign substances including PET, and then performed secondary melting at a higher temperature in the second melting tank and fed into the pyrolysis reactor, so that no operational abnormalities that may be caused by the foreign substances occurred. In contrast, Comparative Examples 1 and 2 performed a single melting at a high temperature of 350°C to 400°C, and as a result, the PET component present in the waste plastic raw material was included in the melt and fed into the pyrolysis reactor, so that terephthalic acid or benzoic acid, which are sublimable substances from PET, were generated during the pyrolysis process, and a white solid was observed at the top of the reactor or pipe blockage occurred. In addition, char was formed during the pyrolysis process, so the yield of liquid oil was lower than that of the examples, and since PET decomposition products were included in the oil, the quality of the pyrolysis oil deteriorated.

[0094]

[0095] Example 3:

[0096] The temperature of the first melting tank (120) was maintained at 220°C to perform melting, and the same process as Example 1 was performed except that the melt supplied to the second melting tank (120) was heated to 350°C to obtain pyrolysis oil.

[0097]

[0098] Example 4:

[0099] The same process as Example 1 was performed, except that the temperature of the first melting tank (120) was maintained at 230°C to perform melting, and the melt supplied to the second melting tank (120) was heated to 350°C.

[0100] The obtained pyrolysis oil was subjected to component analysis to measure the content of heteroatoms and metal impurities, and the results are shown in Table 2.

[0101] Process conditions Pyrolysis oil composition Foreign matter Melting tank Pyrolysis reactor Liquid oil (%) Solid (%) Gas (%) Heteroatom (N) Metal impurity (Ca) 1st 2nd Example 3 220℃ 350℃ 430℃ 94.5-5.525ppm - Example 4 230℃ 350℃ 430℃ 93.9-6.188ppm 17ppm

[0102] As can be seen in Table 2 above, in Example 3, as the melting temperature of the first melting tank was maintained at 220°C, no metal impurities were detected in the final pyrolysis oil obtained, and heteroatoms were detected in trace amounts at an acceptable level. On the other hand, in Example 4, as the melting temperature of the first melting tank increased to 230°C, metal impurities were detected in the final pyrolysis oil, and the content of heteroatoms also increased. Therefore, it can be confirmed that it is desirable to maintain the melting temperature of the first melting tank at 220°C or lower.

[0103]

[0104] Reference examples 1 to 3:

[0105] [Revised 17.12.2024 under Rule 91] In order to confirm the selective melting of polyolefin resin according to melting temperature, 4 g each of PE pellets, PP pellets and PET pellets were charged into the first melting tank ((110) and 200 g of process oil was supplied, and then melting was performed for 1 hour at the melting temperatures shown in Figures 4 to 6 below.

[0106] [Correction under Rule 91 17.12.2024] The state of the melt obtained in the above reference example is shown in Figures 4 to 6.

[0107] [Correction pursuant to Rule 91, December 17, 2024]

[0108] [Correction under Rule 91 17.12.2024] In Figures 4 to 6, it can be confirmed that the melts of Reference Example 1 (melting temperature 200°C) and Reference Example 2 (melting temperature 220°C) maintain the pellet form in which PE and PE pellets are melted but PET pellets are not melted, while Reference Example 3 (melting temperature 230°C) shows that PET pellets are melted together with PE / PP.

[0109] Therefore, in order to perform selective melting, which melts the effective components among the resins contained in waste plastic that can be converted into hydrocarbon oil while leaving PET, which can cause abnormalities in the process equipment, in a non-melted state, it is preferable to maintain the temperature of the first melting tank at a temperature of 150°C to 220°C.

Claims

1. (S1) A step of supplying a waste plastic raw material and a process oil stream to a first melting tank and mixing them to obtain a primary melt; (S2) A step of passing the primary melt through a first filter to remove non-melted solid materials; (S3) A step of supplying the first melt from which the above non-melting material has been removed to a second melting tank and raising the temperature to obtain a second melt; (S4) a step of supplying the secondary melt to a pyrolysis reactor and discharging a gaseous upper stream and a liquid lower stream; and (S5) A method for producing waste plastic pyrolysis oil, comprising the step of condensing an upper stream of a gaseous phase discharged from the pyrolysis reactor and supplying it to a distillation tower for purification.

2. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the first melting tank is maintained at a temperature of 150°C to 220°C.

3. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the process oil stream comprises at least one selected from pyrolysis liquid oil generated within the process, oil discharged from a distillation tower for refining the pyrolysis liquid oil, and fuel oil obtained from another oil refining process or petrochemical process.

4. In paragraph 1, A method for producing waste plastic pyrolysis oil in which the above process oil stream is passed through a second filter to remove impurities before being supplied to the first melting tank.

5. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the above waste plastic raw material and processed oil streams are supplied to the first melting tank through different supply lines.

6. In paragraph 1, A method for producing waste plastic pyrolysis oil, comprising a heating means for supplying additional heat to the supply line of the above process oil stream.

7. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the temperature of the first melt in the second melting tank is raised to 250°C to 400°C.

8. In paragraph 1, A method for producing waste plastic pyrolysis oil by additionally supplying a desalting agent to the second melting tank.

9. In paragraph 8, The above demineralizers are CaO, CaCO 3 , Ca(OH) 2 , NaOH, Na 2 CO 3 , NaHCO 3 , Fe 2 O 3 , Fe 3 O 4 Or a method for producing waste plastic pyrolysis oil comprising a mixture thereof.

10. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein pyrolysis of the secondary melt is performed at a temperature of more than 400°C to 500°C.

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