Method for preparing pyrolytic oil from waste plastics

Abstract

The invention provides a method for preparing pyrolytic oil from waste plastic, the method comprising: (S1) supplying a waste plastic raw material and a process oil stream to a first melting tank and mixing the waste plastic raw material with the process oil stream to obtain a primary melt; (S2) passing the primary melt through a first filter to remove unmelted solid material; (S3) supplying the primary melt from which the unmelted material is removed to a second melting tank, and raising the temperature of the primary melt to obtain a secondary melt; (S4) pyrolyzing the secondary melt to obtain a pyrolysis product containing a gaseous fraction and a liquid fraction; and (S5) supplying the pyrolysis product to a distillation column and refining the pyrolysis product.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2023 - 0157804, filed on November 15, 2023, and Korean Patent Application No. 10 - 2024 - 0119622, filed on September 3, 2024, the entire contents of which are incorporated herein by reference. Technical field

[0003] The present invention relates to a method for preparing pyrolysis oil from waste plastics, and more particularly, to a method for preparing pyrolysis oil with a high yield by removing foreign substances and impurities from waste plastic raw materials and ensuring process stability. Background art

[0004] Recently, the development and use of plastics having physical properties required for various applications and purposes have increased. From crude oil extraction to preparation, plastics require a large amount of energy, and a large amount of carbon is emitted during this process. In addition, even when plastics used in various products are discarded, environmental pollution and huge disposal costs are generated. Therefore, the recycling of waste plastics has become an important social issue.

[0005] Generally, methods for recycling waste plastics (resins) include mechanical recycling and chemical recycling. Mechanical recycling is a method of crushing and sorting collected waste plastics, separating waste plastics by type, melting the waste plastics, and mixing the waste plastics with new materials in a certain ratio or adding functional additives when granulating the waste plastics to produce resin products. Chemical recycling is a method of using various chemical means to extract only specific polymers or to recover and repolymerize pure single molecules.

[0006] Compared with incinerating waste plastics, chemical recycling can reduce greenhouse gases and has attracted attention in alternative fuel development. For example, molten plastics obtained by collecting and sorting waste plastics such as polyethylene or polypropylene and then subjecting them to a pretreatment process including crushing, washing, drying, and melting can be pyrolyzed to prepare liquid hydrocarbon oil, and the liquid hydrocarbon oil can be used as fuel oil for manufacturing petrochemical products.

[0007] Figure 1 A conventional waste plastic pyrolysis process is shown, in which waste plastic raw materials are introduced into a screw - type extruder 100 equipped with a heating device to melt the waste plastic raw materials, and the melt discharged from the extruder 100 is pyrolyzed in a reactor 200. A gaseous stream containing light oil (LO) components is discharged from the upper part of the reactor, and an unevaporated liquid stream is discharged from the lower part of the reactor. In addition, high - viscosity residual wax (such as coke) remains at the bottom of the reactor.

[0008] An extruder for melting waste plastics has the function of melting and mixing by applying electric energy and shear force to the washed and dried waste plastic crushing products. However, due to the high electricity consumption in the process, the energy consumption is high, and there are limitations in expanding the scale of the process.

[0009] The main component that can be converted from waste plastic raw materials into useful hydrocarbon oil is polyolefin. When foreign substances and impurities such as polyethylene terephthalate (PET) derivatives and chlorine (Cl) components are contained, operating abnormalities such as blockages occur in the process equipment including a pyrolysis reactor, which may damage the process stability and ultimately may reduce the yield and purity of pyrolysis oil. For example, when the waste plastic raw material contains polyethylene terephthalate (PET), sublimable substances such as terephthalic acid and benzoic acid are generated in the pyrolysis process, and these substances may accumulate in the reactor and downstream process equipment, which may cause blockages. In addition, when combustible waste such as polyvinyl chloride is contained, chlorine (Cl) compounds may be contained in the liquid and gaseous pyrolysis products in the pyrolysis process, which may cause severe corrosion of the process equipment. Summary of the Invention

[0010] Technical Problem

[0011] In order to solve the problems mentioned in the background art, the object of the present invention is to provide a method for preparing pyrolysis oil with a high yield by removing foreign substances and impurities such as chlorine compounds from waste plastic raw materials and ensuring process stability.

[0012] Technical Solution

[0013] In a general aspect, a method for preparing pyrolysis oil from waste plastics includes: (S1) supplying a waste plastic raw material and a process oil stream to a first melting tank, and mixing the waste plastic raw material with the process oil stream to obtain a primary melt; (S2) passing the primary melt through a first filter to remove unmolten solid materials; (S3) supplying the primary melt from which the unmolten materials have been removed to a second melting tank, and raising the temperature of the primary melt to obtain a secondary melt; (S4) pyrolyzing the secondary melt to obtain a pyrolysis product containing a gaseous fraction and a liquid fraction; and (S5) supplying the pyrolysis product to a distillation column and refining the pyrolysis product.

[0014] In the present invention, the first melting tank can be maintained at a temperature of 150°C to 220°C, and in the second melting tank, the temperature rise of the primary melt can be carried out at 250°C to 400°C.

[0015] Advantageous Effects

[0016] According to the present invention, in a first melting tank capable of supplying heat through a heat transfer fluid other than electricity, unmolten solid materials are removed from a primary melt obtained by dissolving waste plastics in a process oil stream, and then the primary melt is supplied to a second melting tank and the temperature of the primary melt is raised to decompose and remove chlorine (Cl) compounds contained in the waste plastics, so that a secondary melt heated to a temperature just before pyrolysis can be obtained.

[0017] Since the secondary melt is introduced into a downstream pyrolysis reactor in a state where solid foreign matters and impurities such as PET derivatives and chlorine compounds are removed, process stability is ensured, minimizing operating abnormalities that may be caused by impurities, and thus pyrolysis oil converted from waste plastics can be prepared with high yield.

[0018] In addition, using light hydrocarbon oil obtained from the pyrolysis of waste plastics can reduce greenhouse gas emissions caused when supplying raw materials in petrochemical processes, improve process efficiency (such as saving energy consumption), and is environmentally friendly because no harmful gases are generated when treating waste plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shows a conventional waste plastic pyrolysis process.

[0020] Figure 2 Shows a process for preparing pyrolysis oil from waste plastics according to an embodiment of the present invention.

[0021] Figure 3 Shows a process for preparing pyrolysis oil from waste plastics in a comparative example.

[0022] Figure 4 Shows the melt of Reference Example 1 (melting temperature 200 °C).

[0023] Figure 5 Shows the melt of Reference Example 2 (melting temperature 220 °C).

[0024] Figure 6 Shows the melt of Reference Example 3 (melting temperature 230 °C). DETAILED DESCRIPTION

[0025] The terms and words used in the specification and claims of the present invention should not be construed limitedly to have a conventional meaning or a dictionary meaning, but should be construed to have a meaning and concept that satisfy the technical idea of the present invention based on the principle that the inventor can appropriately define the terms in order to best describe his invention.

[0026] As used in this application, the meaning of "including" or "comprising" specifically designates a specific property, region, integer, step, operation, element, and / or component, and does not exclude the addition of another specific property, region, integer, step, operation, element, and / or component.

[0027] The term "stream" as used in this application may refer to a fluid stream in a process and may also refer to the fluid itself flowing through a pipeline. Specifically, the stream may refer to both the fluid itself and the fluid stream flowing through the pipeline connecting the corresponding devices to each other. In addition, the fluid may include any one or more components of gas, liquid, and solid.

[0028] The term "C n " in this application refers to all hydrocarbons having n carbon atoms. For example, "C 5-12 " refers to all hydrocarbon molecules having 5 to 12 carbon atoms.

[0029] The term "liquid oil" as used in this application refers to the product obtained by converting the gas stream obtained in the pyrolysis step into a liquid phase by condensation, and may also be referred to as "liquid distillate oil".

[0030] In addition, the "pressure" mentioned in this application refers to the absolute pressure measured based on a complete vacuum.

[0031] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0032] One embodiment of the present invention relates to a method for producing pyrolysis oil with high yield by removing foreign substances and impurities such as chlorine compounds from waste plastic raw materials and ensuring process stability.

[0033] Figure 2 A method for producing pyrolysis oil from waste plastics according to one embodiment of the present invention is shown. This method can be carried out through a process system including a first melting tank 110 and a second melting tank 120 for introducing waste plastic raw materials therein, a reactor 200 for pyrolyzing molten plastics, a first filter 10 and a second filter 20 for removing impurities, an optional heating device H, and a distillation tower (not shown) for refining pyrolysis products.

[0034] Waste plastics can be recovered from composite films, multilayer films, and other municipal wastes containing natural polymers, synthetic polymers, or mixtures thereof. Synthetic polymers may include thermoplastic resins such as polyethylene, polypropylene, and polystyrene. In addition, the thermoplastic resin may be a mixture of 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% by weight, such as 1 to 16% by weight of PET or PVC, based on its total weight.

[0035] After collection, pre-treatment processes including sorting, crushing, washing, and drying can be performed on waste plastics such as these materials. The pre-treatment processes can be carried out by conventional methods in the art without any particular limitation.

[0036] According to one embodiment of the present invention, a melting tank (dissolver) capable of supplying heat through a high-temperature heat transfer fluid is used to melt the waste plastics.

[0037] Specifically, a waste plastic raw material and a process oil stream are supplied to a first melting tank 110 and mixed to obtain a primary melt (S1).

[0038] The first melting tank 110 supplies heat to the supplied waste plastics to melt them. At this time, the process oil stream as a heat source can be supplied through a supply line different from the supply line of the waste plastic raw material. A stirrer can be installed in the first melting tank 110 to uniformly mix the waste plastic raw material and the process oil.

[0039] As the process oil stream, a liquid oil obtained in the pyrolysis process of waste plastics can be used. For example, as the process oil stream, pyrolysis liquid oil generated in the process and oil discharged from a distillation tower for refining the pyrolysis liquid oil can be used. In addition, fuel oil obtained in other refining processes or petrochemical processes can be used as the process oil stream.

[0040] When necessary, the process oil stream can be supplied to the first melting tank after passing through a filter 20 to remove impurities. In addition, in order to supply additional heat according to the temperature of the process oil stream, an auxiliary heating device H can be installed in the supply line of the process oil stream.

[0041] The process oil stream is stirred and mixed with the solid waste plastics in the first melting tank 110. During this process, the process oil stream can act as a heat transfer fluid and can melt or dissolve the waste plastics according to its temperature.

[0042] The amount of the process oil stream can be 5 to 40 times, or 8 to 20 times, the weight of the waste plastic raw material.

[0043] In one embodiment of the present invention, advantageously, the first melting tank 110 is maintained at a temperature of 150°C to 220°C, specifically 170°C to 220°C. When the above temperature range is satisfied, the following selective melting can be carried out: the effective components in the resin contained in the waste plastic that can be converted into hydrocarbon oil are melted into a liquid state, while leaving solid foreign matters such as paper, dirt, and other components attached to the resin in a non-molten state. In addition, PET that may reduce the yield of hydrocarbon oil in the pyrolysis process and may cause abnormalities in the process equipment remains non-molten at a temperature of 150°C to 220°C. More specifically, when the temperature of the first melting tank 110 is lower than 150°C, the resin contained in the waste plastic may not be fully melted. At the same time, when the temperature of the first melting tank 100 is higher than 220°C, PET may be melted together with the resin that can be converted into pyrolysis oil, making it difficult to carry out effective selective melting, and the additives contained in the resin may be melted, resulting in foreign matters such as heteroatoms and metal impurities in the melt.

[0044] In addition, the selective melting of the waste plastic raw material in the first melting tank 110 can be carried out for 0.1 to 2 hours, specifically 0.15 to 1 hour.

[0045] After the selective melting, the primary melt obtained in the first melting tank 110 is passed through the first filter 10 to remove the unmelted solid materials (S2).

[0046] The first filter is a device for separating solid foreign matters other than the liquid resin contained in the primary melt, and can be used without particular limitation as long as it has a form capable of separating solids and liquids.

[0047] In addition, the filtration in the first filter can be carried out without heating in order to effectively separate the unmelted solid foreign matters contained in the primary melt. That is, the filtration can be carried out at a temperature lower than or equal to the primary melting temperature.

[0048] The primary melt from which the unmelted solid materials have been removed through the first filter 10 is supplied to the second melting tank 120, and the temperature of the primary melt is raised to obtain a secondary melt (S3).

[0049] In the second melting tank 120, additional melting is carried out by supplying heat at a higher temperature to the primary melt, and the temperature can be raised to the temperature just before pyrolysis while further reducing the viscosity of the liquid components. In addition, in the additional melting process, a dechlorination process can be carried out to decompose and remove the chlorine (Cl) component of combustible materials such as polyvinyl chloride (PVC) in the waste plastic.

[0050] The temperature rise of the primary melt can be carried out using a device capable of transferring high-temperature heat, without any particular limitation. For example, the temperature rise of the primary melt can be carried out by passing a heat transfer fluid such as high-temperature / high-pressure steam, hot water, or process oil through a jacket provided outside the second melting tank 120 to transfer heat, or by dividing the melt in the second melting tank 120 into a certain amount, heating the melt using an electric heater or a heating furnace, and then introducing the melt into the second melting tank 120 again to transfer high-temperature heat.

[0051] Specifically, the temperature of the primary melt supplied to the second melting tank 120 can be raised to 250°C to 400°C, and specifically 270°C to 400°C. When the elevated temperature is lower than 250°C, the dechlorination efficiency may be insufficient, and when the elevated temperature is higher than 400°C, a pyrolysis reaction may occur in the second melting tank, resulting in a decrease in the oil yield.

[0052] In addition, in the second melting tank 120, the residence time for the temperature rise of the primary melt can be 0.1 to 3 hours, and specifically 0.5 to 1 hour.

[0053] In addition, a dechlorinating agent capable of absorbing chlorine can be added to the second melting tank 120 to carry out a more effective dechlorination process.

[0054] The dechlorinating agent can be used without limitation as long as it is a material capable of absorbing chlorine. For example, CaO, CaCO3, Ca(OH)2, NaOH, Na2CO3, NaHCO3, Fe2O3, Fe3O4, or a mixture thereof can be used.

[0055] Through the additional melting as described above, a secondary melt heated to a temperature just before pyrolysis can be obtained while removing chlorine (Cl) contained in the waste plastic, and by introducing the secondary melt into a downstream pyrolysis reactor, operation abnormalities that may be caused by impurities can be minimized, and the decomposition efficiency can be improved, so that pyrolysis oil can be stably prepared at a high yield.

[0056] When the additional melting is not carried out in the second melting tank 120, dechlorination is not sufficiently carried out, which may lead to corrosion of process equipment including the pyrolysis reactor or cause process instability.

[0057] At the same time, a gas containing chlorine (Cl) can be discharged from the upper parts of the first melting tank and the second melting tank, and the discharged gas can be removed through a neutralization process. The neutralization process can be carried out by a conventional method in the art. For example, a scrubber, an absorption tower, etc. can be used, but it is not limited thereto.

[0058] The secondary melt obtained in the second melting tank 120 is supplied to the reactor 200, and the secondary melt is pyrolyzed to obtain a pyrolysis product containing a gaseous fraction and a liquid fraction (S4).

[0059] The pyrolysis reactor that can be used in the present invention can be a stirred tank reactor equipped with a stirrer. The stirrer is not particularly limited as long as it can sufficiently stir the waste plastic melt supplied as a raw material. For example, it can be a spiral ribbon type or an anchor type, and it is advantageous to maintain a gap of about 5 mm to 1 cm from the inner wall of the reactor to maximize the stirring of the waste plastic and heat transfer through the reactor wall. In addition, the reactor can operate in either a batch mode or a continuous mode. Furthermore, the reactor can be purged with nitrogen to maintain an anaerobic or low-oxygen atmosphere while performing the pyrolysis reaction of the waste plastic melt.

[0060] The waste plastic melt is supplied to a reactor equipped with a stirrer and heated while operating the stirrer to perform pyrolysis of the waste plastic melt.

[0061] The secondary melt supplied to the reactor 200 can be heated by a heating device provided outside the reactor. For example, the heating device can heat by passing a heat transfer fluid such as high-temperature / high-pressure steam, hot water, or process oil flow through a jacket and transferring heat, or the melt can be divided into a certain amount, heated using an electric heater or a heating furnace, and then the melt is introduced into the reactor 200 again to transfer high-temperature heat. In addition, another heating means can be used without particular limitation.

[0062] In one embodiment of the present invention, the pyrolysis of the secondary melt can be carried out at a temperature higher than 400°C to 500°C. The main component of the waste plastic raw material is a thermoplastic resin. And for example, considering that the waste plastic raw material can be a mixture containing polyethylene with a number average molecular weight of 10,000 to 500,000, specifically 100,000 to 300,000, or polypropylene with a number average molecular weight of 5,000 to 300,000, specifically 10,000 to 200,000, it is advantageous to carry out the pyrolysis reaction at a temperature higher than 400°C to 500°C, specifically 410°C to 450°C. When the pyrolysis temperature is below 400°C, the pyrolysis rate may be very slow, and when the pyrolysis temperature is higher than 500°C, the pyrolysis rate may be very fast, but excessive solid carbides such as coke may be generated due to the high temperature.

[0063] In the pyrolysis step of the waste plastic melt, non-condensable C 1-4 components and by-products such as naphtha C 5-12 light components (which can be converted into liquid oil by condensation), C 13-22 medium components and C 23-40The vaporized low-molecular-weight hydrocarbons obtained from the decomposition of the heavy components can be discharged as the upper stream of the reactor, and the unvaporized liquid stream can be discharged as the lower stream of the reactor. In addition, high-viscosity residual wax (such as coke) remains at the bottom of the reactor.

[0064] A part of the liquid oil obtained in the pyrolysis step can be used as the process oil stream as described above. If necessary, the process oil stream can be passed through a second filter 20 before being supplied to the first melting tank to remove impurities (for example, high-viscosity residues such as coke remaining during the pyrolysis process). In addition, in order to supply additional heat according to the temperature of the process oil stream, an auxiliary heating device H can be installed in the supply pipeline of the process oil stream. The second filter can be used without any particular limitation as long as it has a form capable of separating high-viscosity components and liquids.

[0065] The upper discharge stream of the reactor 200 can be converted into liquid gas oil through a condensation process and then supplied to a distillation tower for refining to obtain pyrolysis oil (S5).

[0066] Condensation is a process of cooling the pyrolysis gas. Thereby, the polymerization reaction of hydrocarbons in the high-temperature pyrolysis gas discharged from the pyrolysis reactor can be inhibited, and the heat load of the subsequent process (refining process) can be reduced. For example, 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. At this time, the gaseous stream can be cooled and condensed to obtain liquid gas oil. At the same time, the uncondensed gas components (for example, C 1-4 hydrocarbons) can be discharged from the upper part of the condenser and can be used as a heat source for petrochemical processes or a heat source for pyrolysis processes through subsequent processes such as compression.

[0067] The refining process can be carried out in a conventional manner in the art and is not particularly limited. For example, the supply stream supplied to the distillation tower can contain all the oil components obtained from the pyrolysis gas of waste plastics. The light oil (LO) with a low boiling point can be discharged from the upper part of the distillation tower, and the heavy oil (HO) with a high boiling point can be discharged from the lower part of the distillation tower.

[0068] The boiling point of the heavy oil discharged from the distillation tower at atmospheric pressure can be 200°C to 550°C, and it can be recovered and used as the process oil stream.

[0069] According to the present invention described above, in the first melting tank capable of supplying heat through a heat transfer fluid other than electricity, the unmolten solid material containing PET is removed from the primary melt obtained by melting waste plastics with the process oil stream, and then the primary melt is supplied to the second melting tank and the temperature of the primary melt is raised to decompose and remove the chlorine (Cl) compounds contained in the waste plastics, thereby obtaining a secondary melt heated to a temperature just before pyrolysis.

[0070] Since the secondary melt is introduced into the downstream pyrolysis reactor in a state where solid foreign matters and impurities such as PET derivatives and chlorine compounds are removed, process stability is ensured, operation abnormalities that may be caused by impurities are minimized, and thus pyrolysis oil converted from waste plastics can be prepared at a high yield.

[0071] In addition, using the light hydrocarbon oil obtained from the pyrolysis of waste plastics can reduce greenhouse gas emissions caused when supplying raw materials in petrochemical processes, improve process efficiency (such as energy consumption savings), and is environmentally friendly because no harmful gases are generated during the treatment of waste plastics.

[0072] Examples

[0073] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are provided to clarify the present invention. It will be apparent to those skilled in the art that various modifications and changes can be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0074] Example 1:

[0075] The pyrolysis of waste plastics is carried out according to Figure 2 the process sequence shown.

[0076] First, a waste plastic crushed product containing polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) in a weight ratio of 56:33:9:2 and a part of the liquid flow discharged from the lower part of the downstream pyrolysis reactor 200 as a process oil stream are supplied to the first melting tank 110 and mixed to obtain a primary melt. At this time, the waste plastic crushed product and the process oil are used in a weight ratio of 1:5, and melting is carried out while maintaining the temperature of the first melting tank 110 at 200°C.

[0077] The primary melt is passed through the first filter 10 at a temperature lower than the melting temperature to remove unmolten solid materials containing PET, the liquid melt is supplied to the second melting tank 120, and a mixture of CaO and CaCO3 is added to the second melting tank 120 as a dechlorination agent. The liquid melt supplied to the second melting tank 120 is heated to 250°C to obtain a secondary melt.

[0078] The secondary melt is supplied to the reactor 200 and pyrolyzed at 430°C for 1 hour. The upper gaseous stream generated by pyrolysis is condensed and then supplied to a distillation column, where distillation is carried out until 350°C to obtain light / medium pyrolysis oil, and the remaining liquid heavy oil and solid coke are separated.

[0079] Example 2:

[0080] The pyrolysis oil was obtained by performing the same procedures as in Example 1, except that the melt supplied to the second melting tank 120 was heated to 400 °C.

[0081] Comparative Example 1:

[0082] The pyrolysis of waste plastics was carried out according to Figure 3 the process sequence shown.

[0083] First, a crushed product of waste plastics 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 dechlorination agent, and a part of the liquid stream discharged from the lower part of the downstream pyrolysis reactor 200 as a process oil stream were supplied to the first melting tank 110 and mixed to obtain a melt. At this time, the temperature of the first melting tank 110 was maintained at 350 °C.

[0084] The melt was supplied to the reactor 200 and pyrolyzed at 430 °C for 1 hour. The upper gaseous stream generated by pyrolysis was condensed and then supplied to a distillation column for distillation until 350 °C to obtain light / medium pyrolysis oil, and the remaining liquid heavy oil and solid coke were separated.

[0085] Comparative Example 2:

[0086] The pyrolysis oil was obtained by performing the same procedures as in Example 1, except that melting was carried out by maintaining the temperature of the first melting tank 110 at 400 °C.

[0087] Table 1 shows the process conditions applied in the above examples and comparative examples, the composition of the pyrolysis oil confirmed by single distillation, and whether there were any operation abnormalities in the equipment (pyrolysis reactor, distillation column, etc.).

[0088] [Table 1]

[0089]

[0090] As can be seen from Table 1, in Examples 1 and 2, primary melting was carried out at a low temperature of 200 °C in the first melting tank to remove unmolten impurities containing PET, and then secondary melting was carried out at a higher temperature in the second melting tank and then supplied to the pyrolysis reactor, so that no operation abnormalities that might be caused by impurities occurred.

[0091] On the other hand, in Comparative Examples 1 and 2, as a result of single melting at a high temperature of 350°C to 400°C, the PET component present in the waste plastic raw material was contained in the melt and introduced into the pyrolysis reactor. Therefore, in the pyrolysis process, terephthalic acid or benzoic acid (which is a sublimable substance) was generated from PET, resulting in the observation of white solids in the upper part of the reactor or pipe blockage. In addition, coke was formed in the pyrolysis process. Therefore, the yield of liquid oil was lower than that in the examples, and since the oil contained PET decomposition products, the quality of the pyrolysis oil deteriorated.

[0092] Example 3:

[0093] Pyrolysis oil was obtained by performing the same process as in Example 1, except that melting was carried out by maintaining the temperature of the first melting tank 120 at 220°C, and the melt supplied to the second melting tank 120 was heated to 350°C.

[0094] Example 4:

[0095] The same process as in Example 1 was carried out, except that melting was carried out by maintaining the temperature of the first melting tank 120 at 230°C, and the melt supplied to the second melting tank 120 was heated to 350°C.

[0096] The components of the obtained pyrolysis oil were analyzed to measure the content of heteroatoms and metal impurities, and the results are shown in Table 2.

[0097] [Table 2]

[0098]

[0099] As can be seen from Table 2, in Example 3, since the melting temperature of the first melting tank was maintained at 220°C, no metal impurities were detected in the finally obtained pyrolysis oil, and a trace amount of heteroatoms at an acceptable level was detected. At the same time, in Example 4, since the melting temperature of the first melting tank was 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 advantageous to maintain the melting temperature of the first melting tank below 220°C.

[0100] Reference Examples 1 to 3:

[0101] To confirm the selective melting of polyolefin resins according to the melting temperature, 4 g of PE pellets, PP pellets, and PET pellets were respectively introduced into the first melting tank 110, 200 g of process oil was supplied to the first melting tank 110, and then melting was carried out at Figures 4 to 6 the indicated melting temperature for 1 hour.

[0102] The state of the melt obtained in the above reference examples is shown in Figures 4 to 6shown in

[0103] In Figures 4 to 6 it can be confirmed that the melt holding pellets of Reference Example 1 (melting temperature: 200 °C) and Reference Example 2 (melting temperature: 220 °C) are in pellet form, where the PE and PE pellets are melted but the PET pellets are not melted, while in Reference Example 3 (melting temperature: 230 °C), the PET pellets are melted together with the PE / PP.

[0104] Therefore, for selective melting in which the effective components convertible to hydrocarbon oil in the resin contained in the waste plastics are melted while keeping the PET that may cause abnormalities in the process equipment un-melted, it is preferable to maintain the temperature of the first melting tank at a temperature of 150 °C to 220 °C.

Claims

1. A method for preparing pyrolysis oil from waste plastics, the method comprising: (S1) Supplying a waste plastic raw material and a process oil stream to a first melting tank, and mixing the waste plastic raw material with the process oil stream to obtain a primary melt; (S2) Passing the primary melt through a first filter to remove unmolten solid materials; (S3) Supplying the primary melt from which unmolten materials have been removed to a second melting tank, and raising the temperature of the primary melt to obtain a secondary melt; (S4) Supplying the secondary melt to a pyrolysis reactor, and discharging a gaseous upper stream and a liquid lower stream; and (S5) Condensing the gaseous upper stream discharged from the pyrolysis reactor, and then supplying the condensed gaseous upper stream to a distillation column and refining the condensed gaseous upper stream.

2. The method according to claim 1, wherein The temperature of the first melting tank is maintained at a temperature of 150°C to 220°C.

3. The method according to claim 1, wherein, The process oil stream includes one or more selected from the following: pyrolysis liquid oil generated in the process, oil discharged from a distillation column for refining the pyrolysis liquid oil, and fuel oil obtained in other refining processes or petrochemical processes.

4. The method according to claim 1, wherein, The process oil stream is passed through a second filter to remove impurities before being supplied to the first melting tank.

5. The method according to claim 1, wherein, The waste plastic raw material and the process oil stream are supplied to the first melting tank through different supply pipelines.

6. The method according to claim 1, wherein, A heating device for supplying additional heat is included in the supply pipeline for the process oil stream.

7. The method according to claim 1, wherein The temperature rise of the primary melt in the second melting tank is carried out at 250°C to 400°C.

8. The method according to claim 1, wherein A dechlorinating agent is additionally supplied to the second melting tank.

9. The method according to claim 8, wherein, The dechlorinating agent includes CaO, CaCO3, Ca(OH)2, NaOH, Na2CO3, NaHCO3, Fe2O3, Fe3O4, or a mixture thereof.

10. The method according to claim 1, wherein, The pyrolysis of the secondary melt is carried out at a temperature higher than 400°C to 500°C.

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