Method for producing pyrolysis oil from waste plastics

Abstract

The present invention provides a method for producing waste plastic pyrolysis oil, comprising the steps of: (S1) supplying waste plastic raw material and a process oil stream to a first melting tank and mixing them to obtain a primary molten material; (S2) passing the primary molten material through a first filter to remove unmelted solid material; (S3) supplying the primary molten material from which the unmelted solid material has been removed to a second melting tank and heating it to obtain a secondary molten material; (S4) pyrolyzing the secondary molten material to obtain a pyrolysis product comprising a gas phase fraction and a liquid phase fraction; and (S5) supplying the pyrolysis product to a distillation column and purifying it.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0157804 filed November 15, 2023 and Korean Patent Application No. 10-2024-0119622 filed September 3, 2024, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for producing pyrolysis oil from waste plastics, and more particularly to a method for producing pyrolysis oil in high yield by removing foreign matter and impurities from waste plastics to ensure process stability. [Background technology]

[0003] Recently, the development and use of plastics with properties required for various uses and purposes has been increasing. Plastics require a large amount of energy from the extraction of crude oil to their production, and a large amount of carbon is emitted in the process. Furthermore, when plastics used in various products are discarded, environmental pollution and huge disposal costs occur, making the recycling of waste plastics an important social issue.

[0004] Generally, methods for recycling waste plastics (resins) include mechanical recycling and chemical recycling. Mechanical recycling involves crushing and sorting collected waste plastics, separating them by type, and then melting and pelletizing them. The resulting material is then mixed with new materials in a specified ratio or reinforced with functional additives to produce resin products. Chemical recycling involves using various chemical means to extract only specific polymers, or recovering them as pure single molecules and repolymerizing them.

[0005] Chemical recycling can reduce greenhouse gas emissions compared to incineration of waste plastics and is attracting attention in terms of the development of alternative fuels. For example, waste plastics such as polyethylene or polypropyl are collected and sorted, and then pre-processed, including crushing, washing, drying, and melting, to obtain molten plastics. The molten plastics can then be pyrolyzed to produce liquid hydrocarbon oil, which can be used as fuel oil for the production of petrochemical products.

[0006] 1 shows a typical waste plastic pyrolysis process. The waste plastic is fed into a screw-type extruder 100 equipped with a heater and melted. The melt discharged from the extruder 100 is then pyrolyzed in a reactor 200. A gaseous stream containing light oil (LO) components is discharged to the top of the reactor, while an unvaporized liquid stream is discharged to the bottom. Additionally, highly viscous wax residues, such as char, remain at the bottom of the reactor.

[0007] The extruder used to melt the waste plastics has the function of melting and kneading the crushed waste plastics that have been washed and dried by applying electrical energy and shear. However, the process requires a large amount of electricity, resulting in high energy consumption and limiting the scale-up of the process.

[0008] The main component that can be converted into useful hydrocarbon oil from waste plastic feedstock is polyolefin. However, the presence of other impurities, such as foreign matter, polyethylene terephthalate (PET)-derived materials, and chlorine (Cl) compounds, can cause operational abnormalities such as plugging in process equipment, including the pyrolysis reactor, impairing process stability and resulting in reduced yield and purity of the pyrolysis oil. For example, if the waste plastic feedstock contains polyethylene terephthalate (PET), the sublimable substances terephthalic acid and benzoic acid are produced during the pyrolysis process. These substances accumulate in the reactor and downstream process equipment, causing blockages. Furthermore, if combustible waste such as polyvinyl chloride is included, chlorine (Cl) compounds are released into the liquid and gaseous pyrolysis products during the pyrolysis process, which can cause severe corrosion of the process equipment. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention is intended to solve the problems mentioned in the Background of the Invention section above, and provides a method for producing pyrolysis oil with high yield by removing impurities such as foreign matter and chlorine compounds from waste plastic raw materials to ensure process stability. [Means for solving the problem]

[0010] According to one embodiment of the present invention for solving the above problems, there is provided a method for producing waste plastic pyrolysis oil, comprising the steps of: (S1) supplying waste plastic raw material and a process oil stream to a first melting tank and mixing them to obtain a primary molten material; (S2) passing the primary molten material through a first filter to remove unmelted solid materials; (S3) supplying the primary molten material from which the unmelted solid materials have been removed to a second melting tank and heating it to obtain a secondary molten material; (S4) pyrolyzing the secondary molten material to obtain a pyrolysis product including a gas phase fraction and a liquid phase fraction; and (S5) supplying the pyrolysis product to a distillation column and purifying it.

[0011] In the present invention, the first melting tank may be maintained at a temperature of 150°C to 220°C, and the temperature of the primary melt in the second melting tank may be increased to 250°C to 400°C. [Effects of the Invention]

[0012] According to the present invention, waste plastics are melted in a process oil stream in a first melting tank that can supply heat using a heat transfer fluid rather than electricity, and solid non-melt materials are removed from the resulting primary melt. The primary melt is then supplied to a second melting tank, where it is heated to decompose and remove chlorine (Cl) compounds contained in the waste plastics, thereby obtaining a secondary melt that has been heated to a temperature just before thermal decomposition.

[0013] This secondary melt is introduced into the subsequent pyrolysis reactor in a state where impurities such as solid foreign matter, PET-derived materials, and chlorine compounds have been removed, thereby ensuring process stability by minimizing operational abnormalities that may be caused by the impurities, and enabling the production of pyrolysis oil converted from the waste plastic at a high yield.

[0014] Furthermore, the use of light hydrocarbon oil obtained from the thermal decomposition of waste plastics can reduce greenhouse gas emissions caused by the supply of raw materials to petrochemical processes, and not only improves process efficiency by reducing energy consumption, but also has environmental benefits as no harmful gases are generated during the treatment of waste plastics. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a typical thermal decomposition process for waste plastics. [Figure 2] FIG. 1 is a diagram illustrating a process for producing pyrolysis oil from waste plastic according to one embodiment of the present invention. [Figure 3] FIG. 1 is a diagram illustrating a process for producing pyrolysis oil from waste plastics according to a comparative example. [Figure 4] The melt of Reference Example 1 (melting temperature 200°C) is shown. [Figure 5] The melt of Reference Example 2 (melting temperature 220°C) is shown. [Figure 6] The melt of Reference Example 3 (melting temperature 230°C) is shown. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0017] As used herein, the meaning of "comprise" or "contain" is to embody a particular property, region, constant, step, operation, element, or component, and does not exclude the addition of other particular properties, regions, constants, steps, operations, elements, or components.

[0018] The term "stream" as used herein can refer to the flow of fluid within a process, or the fluid itself flowing in a pipe. Specifically, the stream can refer to both the fluid itself flowing in the pipe connecting each device and the flow of the fluid. The fluid can contain one or more components of gas, liquid, and solid.

[0019] As used herein, the term "C n " denotes all hydrocarbons having n carbon atoms, e.g., "C 5-12 " refers to all hydrocarbon molecules containing 5 to 12 carbon atoms.

[0020] The term "liquid oil" as used herein means the product of the gaseous stream obtained in the pyrolysis step that is converted to the liquid phase by condensation, and may alternatively be referred to as "liquid distilled oil."

[0021] Also, "pressure" as referred to in this application means absolute pressure measured relative to a perfect vacuum.

[0022] The present invention will now be described in detail with reference to the accompanying drawings.

[0023] One embodiment of the present invention relates to a method for producing pyrolysis oil in high yield by removing impurities such as foreign matter and chlorine compounds from waste plastic raw materials to ensure process stability.

[0024] FIG. 2 illustrates a method for producing pyrolysis oil from waste plastic according to one embodiment of the present invention. The method can be carried out using a process system including a first melting tank 110 and a second melting tank 120 into which waste plastic raw material is introduced, a reactor 200 for pyrolyzing the molten plastic, a first filter 10 and a second filter 20 for removing impurities, a selective heating means H, and a distillation column (not shown) for purifying the pyrolysis product.

[0025] The waste plastic may be a composite film, multi-layer film, or other material recovered from urban residential waste, including natural polymers, synthetic polymers, or mixtures thereof. The synthetic polymer may include thermoplastic resins such as polyethylene, polypropylene, and polystyrene. The thermoplastic resin may also be a mixture with other resins, such as PVC (polyvinyl chloride), PET (polyethylene terephthalate), and PVDF (polyvinylidene fluoride), or a thermosetting resin. For example, the waste plastic raw material may be a thermoplastic resin containing less than 20 wt %, e.g., 1 to 16 wt %, of PET or PVC based on its total weight.

[0026] After being collected, waste plastics of such materials may be subjected to a pretreatment process including sorting, crushing, washing, and drying. The pretreatment process is not particularly limited and may be carried out in a manner commonly used in the art.

[0027] 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.

[0028] Specifically, 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).

[0029] The first melting tank 110 supplies heat to the supplied waste plastic to melt it, and a process oil stream as a heat source may be supplied to a supply line separate from the supply line for the waste plastic raw material. The first melting tank 110 may be equipped with an agitator to uniformly mix the waste plastic raw material and the process oil.

[0030] The process oil stream may be a liquid oil obtained in the thermal decomposition process of waste plastics. For example, the process oil stream may be a liquid oil generated in the process or an oil discharged from a distillation column for refining the liquid oil. In addition, fuel oil obtained in other oil refining processes or petrochemical processes may be used as the process oil stream.

[0031] If necessary, the process oil stream can be passed through a second filter 20 to remove impurities before being supplied to the first melting tank. Also, depending on the temperature of the process oil stream, an auxiliary heating means H can be installed in the supply line of the process oil stream to supply additional heat.

[0032] Such a process oil stream is stirred and mixed with the solid waste plastic in the first melting tank 110, and in the process acts as a heat transfer fluid, which can melt or dissolve the waste plastic depending on its temperature.

[0033] The process oil stream may be used in an amount of 5 to 40 times or 8 to 20 times by weight relative to the waste plastic raw material.

[0034] In one embodiment of the present invention, the first melting tank 110 is advantageously maintained at a temperature of 150°C to 220°C, more specifically, 170°C to 220°C. This temperature range allows selective melting, in which active components of resins contained in waste plastics that can be converted into hydrocarbon oil melt into a liquid phase while leaving solid contaminants such as paper, soil, and other components attached to the resins unmelted. Furthermore, PET, which can reduce the yield of hydrocarbon oil during pyrolysis and cause malfunctions in process equipment, remains unmelted at temperatures of 150°C to 220°C. More specifically, if the temperature of the first melting tank 110 is below 150°C, the resins contained in the waste plastic may not melt sufficiently. On the other hand, if the temperature of the first melting tank 110 exceeds 220°C, PET may melt along with the resins that can be converted into pyrolysis oil, making effective selective melting difficult. Furthermore, additives contained in the resins may melt, and contaminants such as heteroatoms and metal impurities may be included in the melt.

[0035] In addition, the selective melting of the waste plastic raw material in the first melting tank 110 may be carried out for 0.1 to 2 hours, specifically 0.15 to 1 hour.

[0036] After the selective melting, the primary melt obtained in the first melting tank 110 is passed through a first filter 10 to remove unmelted solid materials (S2).

[0037] The first filter is a means for separating solid foreign matter other than the liquid resins contained in the primary molten material, and any filter may be used without particular limitation as long as it is capable of separating solids and liquids.

[0038] In addition, the filtration through the first filter can be performed without heating in order to effectively separate unmelted solid foreign matter contained in the primary melt, i.e., the filtration can be performed at a temperature lower than or equal to the primary melting temperature.

[0039] The primary melt from which the unmelted solid material has been removed through the first filter 10 is supplied to the second melting tank 120 and heated to obtain a secondary melt (S3).

[0040] In the second melting tank 120, a higher heat quantity is supplied to the primary melt to perform additional melting, which further reduces the viscosity of the liquid components and raises the temperature to just before pyrolysis. In addition, during the additional melting process, a dechlorination process can be performed to decompose and remove chlorine (Cl) components from flammable materials such as PVC (polyvinyl chloride) in the waste plastic.

[0041] The temperature of the primary melt can be increased by any means capable of transferring high-temperature heat, without any particular limitation. For example, heat can be transferred by passing a heat medium flow, such as high-temperature / high-pressure steam, hot water, or a process oil stream, through a jacket provided outside the second melting tank 120. Alternatively, the melt in the second melting tank 120 can be divided into a certain amount, heated using an electric heater or a heating furnace, and then introduced into the second melting tank 120 to transfer high-temperature heat.

[0042] Specifically, the primary melt supplied from the second melting tank 120 can be heated to 250°C to 400°C, more specifically, 270°C to 400°C. If the temperature is lower than 250°C, the desalination efficiency may be insufficient, and if the temperature exceeds 400°C, a thermal decomposition reaction may occur in the second melting tank, reducing the oil yield.

[0043] The residence time for the primary melt to increase in temperature in the second melting tank 120 may be in the range of 0.1 to 3 hours, and more specifically, 0.5 to 1 hour.

[0044] Furthermore, a desalination agent capable of absorbing chlorine may be added to the second melting tank 120 to perform a more effective desalination process.

[0045] The dechlorinating agent can be any material capable of absorbing chlorine, and examples thereof include CaO, CaCO3, Ca(OH)2, NaOH, Na2CO3, NaHCO3, Fe2O3, Fe3O4, and mixtures thereof.

[0046] Through the above-mentioned additional melting, chlorine (Cl) contained in the waste plastic can be removed, and a secondary melt can be obtained whose temperature has risen to just before the pyrolysis. This secondary melt can be fed into the subsequent pyrolysis reactor to minimize operational abnormalities that may be caused by impurities and improve the cracking efficiency, thereby enabling the stable production of high-yield pyrolysis oil.

[0047] If additional melting is not performed in the second melting tank 120, desalination will not be sufficient, which may cause corrosion of process equipment including the pyrolysis reactor or cause process instability.

[0048] Meanwhile, gas containing chlorine (Cl) may be discharged from the top of the first melting tank and the second melting tank, and the discharged gas may be removed by a neutralization process. The neutralization process may be carried out by a method commonly used in the art, such as, but not limited to, a water washing tower or an adsorption tower.

[0049] The secondary melt obtained in the second melting tank 120 is supplied to a reactor 200 and pyrolyzed to obtain a pyrolysis product including a gas phase fraction and a liquid phase fraction (S4).

[0050] 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 agitate the waste plastic melt supplied as a raw material. For example, it may be a helical ribbon type or an anchor type. Maintaining a gap of about 5 mm to 1 cm between the agitator and the inner wall of the reactor is advantageous for maximizing the agitation of the waste plastic and heat transfer through the reactor wall. The reactor may be operated in either a batch or continuous mode. Furthermore, the reactor may be purged with nitrogen to maintain an oxygen-free or low-oxygen atmosphere during the pyrolysis reaction of the waste plastic melt.

[0051] The molten waste plastic is supplied to a reactor equipped with such an agitator, and is heated while the agitator is operated to thermally decompose the molten waste plastic.

[0052] The secondary melt supplied to the reactor 200 can be heated by a heating means provided outside the reactor. For example, the heating means can be achieved by passing a heat medium flow such as high-temperature / high-pressure steam, hot water, or a process oil stream through a jacket to transfer heat, or the melt can be divided into a certain amount, heated using an electric heater or a heating furnace, and then introduced back into the reactor 200 to transfer high-temperature heat. Other heating means can also be used without any particular limitations.

[0053] In one embodiment of the present invention, the pyrolysis of the secondary melt may be carried out at a temperature of greater than 400°C to 500°C. Considering that the waste plastic raw material is primarily composed of a thermoplastic resin, such as 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, the pyrolysis reaction is advantageously carried out at a temperature of greater than 400°C to 500°C, specifically 410 to 450°C. If the pyrolysis temperature is 400°C or less, the pyrolysis rate may be slow, whereas if the temperature exceeds 500°C, the pyrolysis rate is fast but excessive amounts of solid carbonized materials such as char may be produced due to the high heat.

[0054] In the thermal decomposition step, the waste plastic melt is decomposed into uncondensed C 1-4 Components, such as naphtha, which can be converted to liquid oil by condensation 5-12 Light components of C 13-22 The middle components of C 23-40 The heavy components are cracked into low molecular weight hydrocarbons and then vaporized and discharged as the top stream from the reactor, while the liquid phase stream that has not yet vaporized is discharged as the bottom stream from the reactor. Also, highly viscous wax residues such as char remain at the bottom of the reactor.

[0055] A portion of the liquid-phase oil obtained in the pyrolysis step can be used as the process oil stream mentioned above. If necessary, the process oil stream can be passed through a second filter 20 to remove impurities, such as highly viscous residues such as char remaining during pyrolysis, before being supplied to the first melting tank. An auxiliary heating means H can 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 can be any type that can separate highly viscous components and liquids.

[0056] The top discharge stream of the reactor 200 is converted into a liquid gas oil through a condensation process, and then supplied to a distillation column for purification, thereby obtaining a pyrolysis oil (S5).

[0057] The condensation is a process of cooling the pyrolysis gas, which suppresses the polymerization reaction of hydrocarbons in the high-temperature pyrolysis gas discharged from the pyrolysis reactor and reduces the heat load of the subsequent process (refining process). For example, the gas phase stream discharged from the top of the pyrolysis reactor is supplied to a condenser and subjected to heat exchange with quench oil or quench water, whereby the gas is cooled and condensed to obtain a liquid gas oil. Meanwhile, gas components (e.g., C) that are not condensed in the heat exchange are condensed. 1-4 The hydrocarbons can be discharged from the top of the condenser and can be used as a heat source for a petrochemical process or a thermal cracking process after undergoing a subsequent process such as compression.

[0058] The refining process can be carried out in a manner commonly used in the art and is not particularly limited. For example, the feed stream supplied to the distillation column can contain all oil components obtained from the pyrolysis gas of waste plastics, and low-boiling light oil (LO) can be discharged from the top of the distillation column, and high-boiling heavy oil (HO) can be discharged from the bottom of the distillation column.

[0059] The heavy oil discharged from the distillation column may have a boiling point of 200 to 550° C. at atmospheric pressure, and may be recovered and used as a process oil stream.

[0060] According to the present invention as described above, waste plastics are melted with a process oil stream in a first melting tank capable of supplying heat by a heat transfer fluid rather than electricity, and solid non-melted materials including PET are removed from the primary melt. The primary melt is then supplied to a second melting tank and heated to decompose and remove chlorine (Cl) compounds contained in the waste plastics, thereby obtaining a secondary melt whose temperature has risen to just before the thermal decomposition temperature.

[0061] This secondary melt is introduced into the downstream pyrolysis reactor in a state where impurities such as solid foreign matter, PET-derived materials, and chlorine compounds have been removed, thereby ensuring process stability by minimizing operational abnormalities that may be caused by the impurities, and enabling the production of pyrolysis oil converted from the waste plastic at a high yield.

[0062] Furthermore, the use of light hydrocarbon oil obtained from the thermal decomposition of waste plastics can reduce greenhouse gas emissions caused when supplying raw materials to petrochemical processes, and not only improves process efficiency by reducing energy consumption, but also has environmental benefits as no harmful gases are generated during the treatment of waste plastics.

[0063] The present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention, and the scope of the present invention is not limited to these examples.

[0064] Example 1: The waste plastic was pyrolyzed in the order shown in Figure 2.

[0065] First, crushed waste plastics 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 phase stream discharged from the bottom of the downstream pyrolysis reactor 200 as a process oil stream were supplied to the first melting tank 110 and mixed to obtain a primary melt. Here, the crushed waste plastics and process oil were used in a weight ratio of 1:5, and melting was carried out while maintaining the temperature of the first melting tank 110 at 200°C.

[0066] The 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, to which a mixture of CaO and CaCO3 was added as a desalting agent. The liquid melt supplied to the second melting tank 120 was heated to 250°C to obtain a secondary melt.

[0067] The secondary melt was fed to reactor 200 and pyrolyzed at 430°C for 1 hour. The upper vapor stream produced by the pyrolysis was condensed and then fed to a distillation column where it was distilled up to 350°C to obtain light / medium pyrolysis oil, and the remaining liquid heavy oil and solid char were separated.

[0068] Example 2: A pyrolysis oil was obtained by the same process as in Example 1, except that the molten material supplied to the second melting tank 120 was heated to 400°C.

[0069] Comparative Example 1: The waste plastic was pyrolyzed in the order shown in Figure 3.

[0070] First, crushed 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 desalting agent, and a portion of the liquid phase stream discharged from the bottom of the downstream pyrolysis reactor 200 as a process oil stream were supplied to the first melting tank 110 and mixed to obtain a molten material. Here, the temperature of the first melting tank 110 was maintained at 350°C.

[0071] The melt was fed to reactor 200 and pyrolyzed at 430°C for 1 hour. The upper vapor stream produced by the pyrolysis was condensed and then fed to a distillation column where it was distilled up to 350°C to obtain light / medium pyrolysis oil and separate the remaining liquid heavy oil and solid char.

[0072] Comparative Example 2: The pyrolysis oil was obtained by the same process as in Example 1, except that the temperature of the first melting tank 110 was maintained at 400° C. for melting.

[0073] Table 1 below shows the process conditions applied in the examples and comparative examples, the composition of the pyrolysis oil confirmed by simple distillation, and the presence or absence of abnormalities due to abnormalities in the equipment operation (pyrolysis reactor, distillation column, etc.).

[0074] [Table 1]

[0075] As shown in Table 1, in Examples 1 and 2, primary melting was performed in the first melting tank at a low temperature of 200°C, and unmelted foreign matter including PET was removed. Thereafter, secondary melting was performed in the second melting tank at a higher temperature, and the material was then fed into the pyrolysis reactor. As a result, no operational abnormalities that may have been caused by the foreign matter occurred.

[0076] In contrast, in Comparative Examples 1 and 2, a single melting at a high temperature of 350-400°C resulted in the PET components present in the waste plastic raw material being contained in the melt and being fed into the pyrolysis reactor, which resulted in the production of sublimable substances such as terephthalic acid or benzoic acid from the PET during the pyrolysis process, resulting in the observation of a white solid at the top of the reactor or the occurrence of pipe blockage. Furthermore, char was formed during the pyrolysis process, the yield of liquid oil was lower than in the Examples, and the quality of the pyrolysis oil was reduced due to the inclusion of PET decomposition products in the oil.

[0077] Example 3: The pyrolysis oil was obtained by the same process as in Example 1, except that the temperature of the first melting tank 120 was maintained at 220°C and the molten material supplied to the second melting tank 120 was heated to 350°C.

[0078] Example 4: The same process as in Example 1 was carried out, except that the temperature of the first melting tank 120 was maintained at 230°C and the melt supplied to the second melting tank 120 was heated to 350°C.

[0079] The obtained pyrolysis oil was subjected to a component analysis to measure the contents of heteroatoms and metal impurities. The results are shown in Table 2.

[0080] [Table 2]

[0081] As shown in Table 2, in Example 3, the melting temperature of the first melting tank was maintained up to 220°C, so no metal impurities were detected in the final pyrolysis oil, and heteroatoms were detected at an acceptable level in trace amounts. On the other hand, in Example 4, the melting temperature of the first melting tank was increased to 230°C, so metal impurities were detected in the final pyrolysis oil, and the heteroatom content also increased. Therefore, it can be confirmed that it is preferable to maintain the melting temperature of the first melting tank at 220°C or less.

[0082] Reference Examples 1-3: In order to confirm the selective melting of polyolefin resins depending on the melting temperature, 4 g each of PE pellets, PP pellets, and PET pellets were placed in the first melting tank 110, 200 g of process oil was added, and melting was carried out for 1 hour at the melting temperatures shown in Figures 4 to 6.

[0083] The state of the melt obtained in the above-mentioned Reference Example is shown in FIGS.

[0084] 4 to 6, it can be seen that in the melts of Reference Example 1 (melting temperature 200°C) and Reference Example 2 (melting temperature 220°C), the PE and PP pellets are melted, but the PET pellets remain unmelted and maintain their pellet form, whereas in Reference Example 3 (melting temperature 230°C), the PET pellets are melted along with the PE / PP.

[0085] Therefore, it is preferable to maintain the temperature of the first melting tank at 150°C to 220°C in order to selectively melt the active ingredients of the resins contained in the waste plastic that can be converted into hydrocarbon oil, while leaving the PET, which may cause abnormalities in the processing equipment, in an unmelted state.

Claims

1. (S1) feeding waste plastic raw materials and a process oil stream into a first melting tank and mixing them 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 non-melted solid material has been removed to a second melting tank and heating it to obtain a secondary melt; (S4) feeding the secondary melt into a pyrolysis reactor and discharging an upper stream of a gas phase and a lower stream of a liquid phase; (S5) condensing the upper stream of the gas phase discharged from the pyrolysis reactor, and then supplying it to a distillation column for purification.

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

3. 2. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the process oil stream comprises one or more selected from the group consisting of pyrolysis liquid oil generated within the process, oil discharged from a distillation column for refining the pyrolysis liquid oil, and fuel oil obtained in other oil refining processes or petrochemical processes.

4. The method for producing waste plastic pyrolysis oil 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 for producing waste plastic pyrolysis oil 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 lines.

6. 2. The method for producing waste plastic pyrolysis oil according to claim 1, wherein a heating means for supplying additional heat is included in the supply line of the process oil stream.

7. 2. The method for producing waste plastic pyrolysis oil according to claim 1, wherein the temperature of the primary melt in the second melting tank is increased to 250°C to 400°C.

8. The method for producing waste plastic pyrolysis oil according to claim 1 , further comprising supplying a demineralizing agent to the second melting tank.

9. The dechlorinating agent is CaO, CaCO ３ , Ca(OH) ２ , NaOH, Na ２ CO ３ , NaHCO ３ , Fe ２ O ３ , Fe ３ O ４ The method for producing waste plastic pyrolysis oil according to claim 8, wherein the oil comprises a mixture of these.

10. The method for producing waste plastic pyrolysis oil according to any one of claims 1 to 9, wherein the thermal decomposition of the secondary melt is carried out at a temperature of greater than 400 ° C to 500 ° C.

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