Method of preparing pyrolysis oil from waste plastics

Abstract

The present invention provides a method of preparing a pyrolysis oil from waste plastics, the method comprising the steps of: (S1) supplying a waste plastic raw material to a first reactor to perform primary pyrolysis, and upwardly discharging a gaseous stream generated by the pyrolysis; (S2) supplying the overhead gaseous stream of the first reactor to at least one distillation column and separating the overhead gaseous stream by boiling point to obtain a stream containing a C5-12 light oil (LO), a stream containing a C13-22 middle oil (MO), and a stream containing a C23 or higher heavy oil (HO); and (S3) supplying a portion of the middle oil (MO)-containing stream separated in the distillation column to a second reactor to perform secondary pyrolysis, and supplying a gaseous stream generated by the secondary pyrolysis to the distillation column, wherein the primary pyrolysis and the secondary pyrolysis are each performed under high pressure conditions of 2-40 bar.

Description

Method for producing pyrolysis oil from waste plastic

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0083799, filed June 26, 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 light hydrocarbon oil from waste plastic raw materials at a high yield.

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

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

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

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

[0009] The liquid oil produced from the pyrolysis of the above waste plastic, i.e. pyrolysis oil, is usually C such as naphtha. 5-12 It is a blended oil containing light hydrocarbon oil and longer-chain hydrocarbon oil.

[0010] Previously, methods have been proposed to promote the pyrolysis of waste plastics. These include performing a contact cracking reaction through catalytic cracking, or using a contactor, a contact heat exchanger, to condense the heavy hydrocarbons (i.e., long-chain hydrocarbons) in the pyrolysis products of waste plastics and then recirculating them to a pyrolysis reactor for further pyrolysis. However, these methods have limitations in increasing the pyrolysis efficiency of waste plastics.

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

[0012] Furthermore, existing waste plastic pyrolysis processes have typically been conducted under atmospheric pressure. These pyrolysis processes under these conditions often contain high-boiling-point components in the reactor top effluent, limiting the yield of high-value-added light hydrocarbon oils. Furthermore, they also generate excessive amounts of heavy oil components and wax residues.

[0013] Therefore, there is a need for a technology that can improve the pyrolysis process of waste plastics to increase the yield of high-grade light hydrocarbon oil.

[0014] The problem to be solved in the present invention is to solve the problems mentioned in the background technology of the above invention, by connecting one or more distillation columns in series instead of a contactor (heat exchanger) at the top of a reactor for pyrolyzing waste plastics to separate high-boiling-point components in the pyrolysis product into medium oil (MO) and heavy oil (HO) and then performing additional pyrolysis, while controlling the reaction pressure during pyrolysis to suppress vaporization of high-boiling-point components and selectively increase the residence time of the liquid phase reaction, thereby producing light hydrocarbon oil at a high yield.

[0015] According to one embodiment of the present invention for solving the above problem, (S1) a step of supplying waste plastic raw material to a first reactor to perform primary pyrolysis and discharging a gaseous stream generated by the pyrolysis to the upper portion; (S2) supplying the upper gaseous stream of the first reactor to one or more distillation columns and separating it according to boiling point to obtain C 5-12 Stream containing light oil (LO), C 13-22 Stream containing middle oil (MO) and C 23 A method for producing waste plastic pyrolysis oil is provided, comprising: obtaining a stream including heavy oil (HO); and (S3) supplying a portion of the stream including intermediate oil (MO) separated from the distillation column to a second reactor to perform secondary pyrolysis, and supplying a gaseous stream produced by the pyrolysis to the distillation column; wherein the first pyrolysis and the second pyrolysis are each performed under high pressure conditions of 2 to 40 bar.

[0016] According to the present invention, waste plastic is first pyrolyzed as a raw material in a first reactor under a high pressure condition higher than atmospheric pressure, an upper gaseous stream discharged from the first reactor is separated according to boiling point in one or more distillation columns, and then a portion of the middle oil (MO) among the separated components is secondarily pyrolyzed in a second reactor under a high pressure condition higher than atmospheric pressure, thereby improving the yield of high-grade light oil (LO). In particular, the high pressure condition during the first and second pyrolysis suppresses vaporization of high-boiling-point components, thereby selectively increasing the residence time of liquid components in the reactor, thereby improving the decomposition efficiency of waste plastic, and thereby further increasing the selectivity and production of light hydrocarbon oil among the pyrolysis products.

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

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

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

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

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

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

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

[0024] The term 'upper' as used herein, unless otherwise specified, means a point 0 to 20% in height downward from the top of the device, and may specifically mean the top (top). In addition, the term 'lower' means a point 80 to 100% in height downward from the top of the device, and may specifically mean the bottom (bottom). In addition, the term 'side cut' means a middle portion located on the side of the device. That is, the component flowing out through the side cut may indicate that it flows out from the middle portion excluding the top and bottom portions of the device.

[0025] 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.

[0026] The terms "first," "second," "primary," and "secondary" used herein may be used simply to distinguish the corresponding component from other corresponding components and do not limit the corresponding components in any other respect (e.g., importance or order).

[0027] 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'.

[0028] “Pressure” as referred to herein means absolute pressure measured relative to a perfect vacuum.

[0029] The “boiling point” referred to herein means the boiling point at atmospheric pressure (1 bar).

[0030] A method for producing waste plastic pyrolysis oil according to one embodiment of the present invention comprises (S1) a first pyrolysis step of waste plastic raw material, (S2) a separation step according to the boiling point of a pyrolyzed gaseous stream, and (S3) a second pyrolysis step of a portion of separated intermediate oil.

[0031] The above method can be performed using a process system including a first reactor (10) into which waste plastic raw material is supplied, one or more distillation columns (20) connected in series with the first reactor, a second reactor (30) connected to the distillation column (20), and an additionally connected residue treatment reactor (40), as shown in FIG. 1.

[0032] Hereinafter, a method for producing waste plastic pyrolysis oil according to the present invention will be described in detail step by step with reference to the drawings.

[0033] First, waste plastic raw material is supplied to the first reactor (10) to perform primary pyrolysis, and the gaseous stream generated by the pyrolysis is discharged upward (S1).

[0034] The above-mentioned waste plastic may include natural polymers, synthetic polymers, or mixtures thereof, and the synthetic polymer may include thermoplastic resins such as polyethylene, polypropylene, polystyrene, etc. In addition, the thermoplastic resin may be mixed with other types of resins such as PVC, PET, thermosetting resins, etc.

[0035] After being collected and sorted, waste plastics of this type may undergo a pretreatment process, including shredding, washing, drying, and melting. The pretreatment process may be performed using methods conventional in the art.

[0036] For example, the size of the shredded waste plastic is not particularly limited, but can typically be performed in the range of 0.5 to 6.0 cm, and the shredded waste plastic that has been washed and dried can be fed into a tubular melter such as an extruder to be melted. The extruder has a function of melting and kneading and extruding, and can be, for example, a twin-screw extruder. When the waste plastic is a thermoplastic resin such as polyethylene, polypropylene, or a mixture thereof, the melting temperature can be, but is not limited to, 120 to 350°C or 150 to 250°C.

[0037] The waste plastic melt obtained through the above pretreatment process is supplied to the first reactor for thermal decomposition.

[0038] 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 subjected to a nitrogen purge to maintain an oxygen-free or low-oxygen atmosphere while performing the pyrolysis reaction of the waste plastic melt.

[0039] The waste plastic melt is supplied to the first reactor equipped with such a stirrer, and the waste plastic melt is heated while the stirrer is operated to perform thermal decomposition of the waste plastic melt.

[0040] The heating of the above waste plastic can be performed by passing high temperature / high pressure steam, hot water, or heat transfer fluid through a jacket provided on the outside of the reactor to transfer high temperature heat to the waste plastic, and there are no special limitations thereon.

[0041] In one embodiment of the present invention, the primary thermal decomposition in the first reactor can be performed under high pressure conditions of 2 to 40 bar.

[0042] The existing waste plastic pyrolysis process is usually carried out under atmospheric pressure conditions, C 1-4 Gas components such as naphtha, C 5-12Light hydrocarbons and longer-chain hydrocarbons are vaporized and discharged to the top of the reactor, and the wax residue that was not vaporized remains at the bottom of the reactor. In this thermal cracking process under atmospheric pressure, the reactor top discharge contains a lot of high-boiling-point components, which limits the yield of high-value-added light hydrocarbon oil, and there are problems such as excessive production of heavy oil components and discharge of wax residue.

[0043] Accordingly, in the present invention, in order to increase the selectivity for conversion into light hydrocarbons during the pyrolysis of waste plastic, the pressure of the reactor in which the pyrolysis is performed is adjusted to a pressure higher than atmospheric pressure, for example, 2 to 40 bar, specifically 2 to 30 bar, and more specifically 2 to 10 bar. Unlike the conventional method of maintaining atmospheric pressure by opening the pyrolysis reactor, the present invention can adjust the reaction pressure to high pressure during the pyrolysis by installing a pressure control valve (PCV) at the top of the first reactor and performing a vapor vent by the PCV. For example, when a gas having a pressure higher than a certain level is generated during the pyrolysis reaction of waste plastic, the amount of exhaust gas by the PCV is adjusted so that the internal pressure of the reactor is maintained at 2 to 40 bar, while the gaseous stream generated during the pyrolysis reaction can be continuously discharged to the top of the reactor.

[0044] Maintaining high pressure within the reactor suppresses the vaporization of high-boiling-point components during the thermal decomposition of waste plastic, thereby increasing the liquid-phase residence time of these high-boiling-point components within the reactor. This increase in liquid-phase residence time enhances the efficiency of the waste plastic decomposition reaction, thereby increasing the selectivity for conversion to light hydrocarbons, thereby enabling the production of high-value-added light hydrocarbon oils at high yields.

[0045] That is, when the pressure of the first reactor is adjusted to be higher than the atmospheric pressure, the thermal decomposition reaction of waste plastic can be performed for 1 to 8 hours, specifically 2 to 6 hours, due to the increase in the liquid residence time, and in this process, light hydrocarbons, such as C, are converted from polymers. 5-12 can increase the rate at which it is converted into hydrocarbons.

[0046] If the pressure during the first pyrolysis in the first reactor is less than 2 bar, the vaporization of high-boiling-point components in the first reactor may not be effectively suppressed, and thus the proportion of high-boiling-point components having more than 12 carbon atoms in the upper discharge stream of the first reactor may increase. On the other hand, if the pressure during the first pyrolysis exceeds 40 bar, C 12 The hydrocarbons below may not be discharged to the top of the reactor and may remain inside the reactor for a long time, resulting in the formation of non-condensable, pyrolysis by-product gases that cannot be liquefied at room temperature (e.g., C 1-4 Gas) may be produced in excess.

[0047] In one embodiment of the present invention, the first pyrolysis in the first reactor may be performed at 400 to 450°C. Considering that the raw material of the waste plastic is mainly a thermoplastic resin, and may be a mixture including, for example, polyethylene having a number average molecular weight of 10,000 to 500,000, specifically 100,000 to 300,000, or polypropylene having a number average molecular weight of 5,000 to 300,000, specifically 10,000 to 200,000, the pyrolysis reaction is advantageously performed at a temperature in the range of 400 to 450°C, specifically 420 to 430°C. If the above first thermal decomposition temperature is less than 400℃, the thermal decomposition rate may be slow, and if it exceeds 450℃, the thermal decomposition rate is fast, but due to the high heat, an excessive amount of solid carbide such as char may be generated.

[0048] In addition, the first thermal decomposition reaction time in the first reactor can be determined by considering the point in time at which the production rate of light hydrocarbons having 12 or fewer carbon atoms increases in the temperature range of 400 to 450°C after the start of the decomposition reaction of waste plastic.

[0049] When the waste plastic raw material is thermally decomposed in the first reactor (10), C 1-4 Gas components such as naphtha, C 5-12 Light hydrocarbons and longer chain C 13-22 Hydrocarbons and C 23 A gaseous stream containing the above hydrocarbon components is discharged to the upper part of the reactor, and the highly viscous residual wax is not vaporized and remains at the lower part of the reactor. For example, based on the weight of the waste plastic raw material supplied to the first reactor (10), 20 to 95 wt% or 60 to 95 wt% may be generated as pyrolysis gas and discharged to the upper part of the reactor, and the remainder may remain as wax residue.

[0050] Next, the gaseous stream discharged from the upper portion of the first reactor (10) is supplied to one or more distillation columns (20) and separated according to boiling point (S2).

[0051] The one or more distillation columns (20) are arranged in series on the upper portion of the first reactor (10), and can separate the pyrolysis products transferred from the first reactor into components according to their boiling points by selective heating and condensation. For example, the stream supplied to each distillation column is heated by heat provided from a reactor connected to the lower portion of the column, and the vapor generated by the heating moves to the upper portion of the column and is discharged, and the discharged vapor can be partially or completely condensed in a condenser connected to the upper portion of the column. A portion of the condensate can be circulated back into the column. More specifically, the one or more distillation columns (20) can have a multi-stage structure of 20 to 50 trays, and the temperature gradually decreases toward the upper portion, so that hydrocarbon components having relatively high boiling points can be separated in the lower portions, carbon-hydrogen components having relatively low boiling points can be separated in the upper portions, and hydrocarbon components having relatively medium boiling points can be separated in the portions of the trays therebetween.

[0052] Therefore, in the present invention, by arranging one or more distillation columns on the upper part of the first reactor to separate thermal decomposition products according to boiling points, and supplying oil having an intermediate boiling point (e.g., 210 to 360° C.) discharged from a side cut in the middle stage of the distillation column to a second reactor (30) for secondary thermal decomposition, the yield of light oil (LO) can be improved.

[0053] Furthermore, the present invention allows for varying the carbon range of the desired pyrolysis oil (distillate) by controlling the operating temperature at the top of the distillation column. This overcomes the limitations of conventional waste plastic pyrolysis processes, which employed a contactor (heat exchanger) in the pyrolysis reactor to selectively discharge only hydrocarbon components within a specific boiling point range.

[0054] Specifically, when the upper operating temperature of the distillation column is increased, the carbon range of the pyrolysis oil moves to a high boiling point, and when the upper operating temperature of the distillation column is decreased, the carbon range of the pyrolysis oil moves to a low boiling point, thereby increasing the yield of light oil such as naphtha.

[0055] For example, when the upper temperature of the distillation column is controlled to 220°C to 300°C, C 5-12 Low boiling point hydrocarbons and C 13-22 A gaseous stream containing more than 80% of intermediate boiling point hydrocarbons can be discharged. Meanwhile, when the upper temperature of the distillation column is controlled to less than 150°C to 220°C, C 5-12 A gaseous stream containing more than 70% of low-boiling-point hydrocarbons can be discharged. The gaseous stream can be cooled and condensed by heat exchange with water connected to the top of the distillation column and converted into liquid oil, and the gaseous components that are not condensed in the heat exchange (e.g., C 1-4 ) can be discharged to the top. At this time, some components contained in the condensed liquid oil, i.e., intermediate boiling point or high boiling point components, can be refluxed to the top of the distillation column and moved toward the bottom of the distillation column. As a result, in the upper stage of the column, C 5-12 Light oil (LO) is discharged from the column, and C is discharged from the middle stage of the column. 13-22 Middle oil (MO) is discharged, and C is discharged from the lower stage of the column. 23 Ideally, for example, C 23-40 Heavy oil (HO) may be discharged.

[0056] In addition, a dividing wall type distillation column (DWC) having two regions separated by a central dividing wall may be used as the distillation column (20), and C is introduced into the upper part of the DWC. 5-12 Stream containing light hydrocarbons, C to the side of the DWC 13-22Stream containing intermediate hydrocarbons, C to the bottom of DWC 23 A stream containing the above high boiling point hydrocarbons can be separated.

[0057] In addition, when the distillation columns (20) are arranged in multiples, the temperature of the condenser connected to the upper part of each column can be operated differently. That is, by setting the upper temperature of the front column relatively high and setting the upper temperature of the rear column relatively low, the carbon range of the pyrolysis oil (distillate oil) can be changed. For example, the upper temperature of the front column can be adjusted to 220°C to 300°C, and the upper temperature of the rear column can be adjusted to 150°C to less than 220°C. The upper gaseous stream discharged from each of the front and rear columns can be discharged as liquid oil after condensation as described above, or a portion thereof can be recirculated back to the upper part of each column. In addition, in the middle and lower part of each column, C 13-22 Medium oil (MO) or C 23 The above heavy oil (HO) can be selectively discharged.

[0058] In this way, the gaseous stream generated by the primary pyrolysis of waste plastic raw materials in the above one or more distillation columns is separated according to boiling point to C 5-12 Stream containing light oil (LO), C 13-22 Stream containing intermediate oil (MO) and C 23 A stream containing the above heavy oil (HO) can be obtained.

[0059] Additionally, in the process of obtaining a liquid phase by heat exchange with water in a gaseous stream in a condenser connected to the upper portion of the distillation column, the water supplied to the condenser can be converted into steam by recovering the waste heat of the gaseous stream.

[0060] To generate steam through waste heat recovery, the present invention uses hot water of 60 to 100°C as heat-exchanged water in the upper condenser of the distillation column. The temperature of the water can be adjusted according to the desired pyrolysis oil composition.

[0061] In particular, when the distillation columns are arranged in multiple numbers, as described above, steam of different pressures can be generated by operating the condenser temperature of the front column high and the condenser temperature of the rear column low. For example, when the upper operating temperature of the distillation column is set high so that the carbon range of the pyrolysis oil moves to a high boiling point, high-pressure steam can be generated through the heat of absorption of the condenser connected to the upper part of the column. On the other hand, when the upper operating temperature of the distillation column is set low so that the carbon range of the pyrolysis oil moves to a low boiling point, low-pressure steam can be generated.

[0062]

[0063] Afterwards, C separated from the distillation column (20) 13-22 A portion of the stream containing intermediate oil (MO) is supplied to a second reactor (30) to perform secondary pyrolysis, and the gaseous stream produced by the secondary pyrolysis is supplied to the distillation column (20) (S3).

[0064] Specifically, C separated from the distillation column (20) 13-22 The middle oil (MO) may be 30 to 85 wt% or 40 to 60 wt% based on the total weight of the stream, and such C 13-22 The intermediate oil (MO) is supplied to the second reactor (30), and the remaining stream can be discharged and used as fuel oil.

[0065] The second reactor (30) may be arranged in series with the distillation column (20). That is, the first reactor (10) may be arranged on one side of the distillation column (20), and the second reactor (30) may be arranged on the other side of the distillation column (20), so that the first reactor, the distillation column, and the second reactor may be arranged in series in that order.

[0066] In one embodiment of the present invention, the secondary thermal cracking of the intermediate oil (MO) in the second reactor (30) can be performed at a high pressure of 2 to 40 bar, specifically 2 to 30 bar, and more specifically 2 to 10 bar.

[0067] Similar to the first reactor described above, a pressure control valve (PCV) can be installed at the top of the second reactor to control the reaction pressure during the second pyrolysis to a high pressure, thereby promoting additional pyrolysis of middle oil (MO) and increasing the production of light oil (LO).

[0068] If the pressure of the secondary pyrolysis in the second reactor is less than 2 bar, the additional pyrolysis of the middle oil (MO) in the second reactor may not be sufficient, and if the pressure of the secondary pyrolysis exceeds 40 bar, C 12 The hydrocarbons below may not be discharged to the top of the reactor and may remain inside the reactor for a long time, resulting in the formation of non-condensable, pyrolysis by-product gases that cannot be liquefied at room temperature (e.g., C 1-4 Gas) may be produced in excess.

[0069] The secondary pyrolysis under these high-pressure conditions can be performed for 1 to 3 hours, specifically 1.5 to 2.5 hours. The secondary pyrolysis reaction time can be determined by considering the point in time at which the production rate of light hydrocarbons having 12 or fewer carbon atoms increases after the start of the decomposition reaction of the middle oil (MO).

[0070] In addition, the secondary pyrolysis may be performed in the range of 420°C to 450°C. If the secondary pyrolysis temperature is 420°C or lower, it is difficult to induce sufficient pyrolysis of the intermediate oil (MO), and if it exceeds 450°C, the formation of solid carbides such as char may be accelerated. In addition, if the secondary pyrolysis temperature is higher than the primary pyrolysis temperature, it may be more advantageous for the conversion of light oil (LO) through the decomposition of intermediate oil (MO).

[0071] Through this secondary pyrolysis, C obtained from waste plastic raw materials 13-22 Further thermal cracking of middle oil (MO) can be efficiently performed to convert it into a lower carbon number, thereby obtaining the final C 5-12 can increase the yield of light oil (LO).

[0072] Meanwhile, the lower residue of the first reactor (10) remaining after the first pyrolysis of the waste plastic raw material, the heavy oil (HO) separated at the lower portion of the distillation column (20), and the lower residue of the second reactor (30) remaining after the second pyrolysis of the middle oil (MO) may all contain high boiling point components of 360°C or higher, and these may cause obstacles in process operation or deterioration in the quality of the final product, so their utilization is low.

[0073] Accordingly, the bottom residue of the first reactor (10), the stream including heavy oil (HO) separated in the distillation column (20), and the bottom residue of the second reactor (30) can each be supplied to a residue treatment reactor to perform additional pyrolysis, and the gaseous stream produced by the additional pyrolysis can be recycled to the distillation column.

[0074] The above residue treatment reactor (40) may include an upper zone where a thermal decomposition reaction is performed and a lower zone where high viscosity wax residue is discharged.

[0075] Specifically, the high boiling point components supplied to the residue treatment reactor (40) can be further thermally decomposed in the upper region of the residue treatment reactor (40), and it may be advantageous for the further thermal decomposition to be performed at a higher temperature than the thermal decomposition in the first reactor or the second reactor. Meanwhile, the high viscosity wax residue that has not been thermally decomposed can remain in the lower region of the residue treatment reactor (40) and then be discharged.

[0076] Additionally, the additional pyrolysis of the residue treatment reactor may be performed at a pressure of 0.9 to 1.1 bar for 1 to 3 hours, specifically 1.5 to 2.5 hours. The additional pyrolysis reaction time may be determined by considering the point in time at which the production rate of low-boiling-point hydrocarbons increases after the start of the decomposition reaction of the residue.

[0077] As described above, the present invention can improve the yield of high-grade light oil (LO) by first pyrolyzing waste plastic as a raw material in a first reactor under high pressure conditions higher than atmospheric pressure, separating the upper gaseous stream discharged from the first reactor according to boiling point in one or more distillation columns, and then secondarily pyrolyzing a portion of the middle oil (MO) among the separated components in a second reactor under high pressure conditions higher than atmospheric pressure. In particular, the high pressure conditions during the first and second pyrolysis suppress vaporization of high-boiling-point components, thereby selectively increasing the residence time of the liquid components in the reactor, thereby improving the decomposition efficiency of waste plastic, and thereby further increasing the selectivity and production of light hydrocarbon oil among the pyrolysis products.

[0078] Therefore, the final pyrolysis oil obtained through the pyrolysis process according to the present invention is a high value-added C 5-12 It may contain a high fraction of light oil (LO), for example, the final obtained C 5-12The content of light oil (LO) may be 50 to 70 wt%, specifically 50 to 60 wt%, based on the weight of the waste plastic raw material. C obtained in such a high yield 5-12 Light hydrocarbons can be condensed and used as high-grade fuel oil.

[0079] In particular, the C finally obtained in the present invention 5-12 The light hydrocarbon fuel oil has a boiling point of 0 to 230°C, specifically 30 to 216°C, a kinematic viscosity at 40°C of 0.3 to 1.0 cSt, specifically 0.4 to 0.9 cSt, and a flash point of -80°C or higher (e.g., -40°C), and thus can be usefully used as a petrochemical raw material.

[0080] Additionally, by controlling the upper operating temperature of the distillation column to a predetermined range, the fraction of light oil (LO) components in the gaseous stream separated from the distillation column can be increased, and in the process in which the gaseous stream is obtained in a liquid phase by heat exchange with water in a condenser connected to the upper portion of the distillation column, the water supplied to the condenser can be converted into steam by recovering the waste heat of the gaseous stream.

[0081] 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.

[0082] 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.

[0083] Example 1:

[0084] As shown in Fig. 1, thermal decomposition of waste plastic was performed using a process system including a first reactor (10), a distillation column (20), a second reactor (30), and a residue treatment reactor (40).

[0085] First, 100 parts by weight of a waste plastic melt containing polyethylene (PE) and polypropylene (PP) in a weight ratio of 6:4 was supplied to a first reactor (10) of a stirring type, and after the reactor (10) was heated by an external heating means and reached 430°C, a first thermal decomposition reaction was performed for 2 hours while maintaining a constant temperature. At this time, the exhaust amount of steam generated during the thermal decomposition reaction was controlled using a pressure control valve (PCV) installed at the top of the first reactor, thereby maintaining the internal pressure of the first reactor at 10 bar.

[0086] The gaseous stream discharged from the top of the first reactor (10) was supplied to a distillation column (20) and separated into components according to boiling points by simple distillation. Specifically, the upper temperature of the column was operated at 210°C to discharge the gaseous stream to the top and cooled to 25°C in a condenser to condense the liquid C 5-12 Light oil (LO) was obtained and the non-condensed gas component was discharged. Then, C was extracted from the middle tray of the column. 13-22 A stream containing intermediate oil (MO) is obtained, and C is extracted from the lower stage of the column. 23-40 The bottom stream containing heavy oil (HO) was discharged.

[0087] A portion of the intermediate oil (MO) having a boiling point of 210 to 360°C separated from the distillation column (20) was supplied to a second reactor (30) and subjected to secondary pyrolysis at 430°C for 2 hours. At this time, the exhaust amount of steam generated during the pyrolysis reaction was controlled using a pressure control valve (PCV) installed at the top of the second reactor, thereby maintaining the internal pressure of the second reactor at 2 bar. The gaseous stream generated by the secondary pyrolysis was recycled to the distillation column (20).

[0088] Additionally, the bottom residue of the first reactor (10), the bottom stream including heavy oil (HO) separated from the bottom stage of the distillation column (20), and the bottom residue of the second reactor (30) were each supplied to a residue treatment reactor (40) and further thermally decomposed at 1 bar and 430° C. for 2 hours, and the generated upper gaseous stream was recycled to the bottom of the distillation column (20), and the residue remaining at the bottom was discharged.

[0089] Example 2:

[0090] The same process as Example 1 was performed except that secondary pyrolysis of a portion of the intermediate oil (MO) in the second reactor (30) was performed at a pressure of 5 bar.

[0091] Example 3:

[0092] The same process as Example 1 was performed except that secondary pyrolysis of a portion of the intermediate oil (MO) in the second reactor (30) was performed at a pressure of 10 bar.

[0093] Comparative Example 1:

[0094] As shown in Fig. 2, pyrolysis of waste plastic was performed using a process system including a first reactor (10), a distillation column (20), and a residue treatment reactor (40). Specifically, the same process as Example 1 was performed except that secondary pyrolysis was not performed on a portion of the intermediate oil (MO) separated in the distillation column (20).

[0095] Comparative Example 2:

[0096] The same process as Example 1 was performed except that the first thermal decomposition in the first reactor (10) was performed at atmospheric pressure (1 bar).

[0097] Comparative Example 3:

[0098] The same process as Example 1 was performed except that secondary thermal decomposition of a portion of the intermediate oil (MO) in the second reactor (30) was performed at atmospheric pressure (1 bar).

[0099] Table 1 below shows the composition of the pyrolysis products obtained based on the feed in the above examples and comparative examples, as analyzed by GC-MS.

[0100] 1st pyrolysis 2nd pyrolysis Final pyrolysis oil composition Condition Product (weight parts based on raw materials) Condition Product (weight parts based on raw materials) Example 1430℃10barC 1-4 Gas 11430℃2barC 1-4 Gas 3C 1-4 Gas 14C 5-12 LO 36C 5-12 LO 6C 5-12 LO 42C 13-22 MO 36 (of which MO 30 is fed to the second reactor)C 13-22 MO 21C 13-22 MO 27 Residue 17-Residue 17 Example 2430℃10barC 1-4 Gas 11430℃5barC 1-4 Gas 5C 1-4 Gas 16C 5-12 LO 36C 5-12 LO 9C 5-12 LO 45C 13-22MO 36 (of which MO 30 is fed to the second reactor)C 13-22 MO 16C 13-22 MO 22 Residue 17-Residue 17 Example 3430℃10barC 1-4 Gas 11430℃10barC 1-4 Gas 7C 1-4 Gas 18C 5-12 LO 36C 5-12 LO 11C 5-12 LO 47C 13-22 MO 36 (of which MO 30 is fed to the second reactor)C 13-22 MO 12C 13-22 MO 18 Residue 17-Residue 17 Comparative Example 1430℃10barC 1-4 Gas 11--C 1-4 Gas 11C 5-12 LO 36C 5-12 LO 36C 13-22 MO 36C 13-22 MO 36 Residue 17 Residue 17 Comparative Example 2430℃1barC 1-4 Gas 8430℃2barC 1-4 Gas 3C 1-4 Gas 11C 5-12 LO 21C 5-12 LO 6C 5-12 LO 27C 13-22 MO 40 (of which MO 34 is fed to the second reactor)C 13-22 MO 25C 13-22 MO 31 Residue 31-Residue 35 Comparative Example 3430℃10barC 1-4 Gas 11430℃1barC 1-4 Gas 1C 1-4 Gas 12C 5-12 LO 36C 5-12 LO 3C 5-12 LO 39C 13-22 MO 36 (of which MO 30 is fed to the second reactor)C 13-22 MO 26C 13-22 MO 32 Residue 17-Residue 17

[0101] From the above Table 1, it can be confirmed that when waste plastic is first thermally decomposed under a high pressure condition of 10 bar in the first reactor, the upper gaseous stream discharged from the first reactor is separated according to boiling point in a distillation column, and then 30 parts by weight of 36 parts by weight of middle oil (MO) among the separated components is secondarily thermally decomposed in the second reactor, the additional production of high-grade light oil (LO) is improved as the pressure increases under the same temperature condition. In contrast, in Comparative Example 1, the yield of light oil (LO) did not increase because the second thermal decomposition was not performed.

[0102] Comparative Example 2 showed that as the pressure of the first reactor was adjusted to atmospheric pressure, the yield of light oil (LO) in the first pyrolysis decreased while the residue increased, and even when the second pyrolysis was performed at a pressure higher than atmospheric pressure, the yield of light oil (LO) was the lowest.

[0103] In Comparative Example 3, as the pressure of the second reactor was adjusted to atmospheric pressure, the additional production of light oil (LO) and the resulting final yield decreased compared to Example 1.

Claims

1. (S1) A step of supplying waste plastic raw material to a first reactor to perform primary pyrolysis, and discharging a gaseous stream generated by the pyrolysis upward; (S2) The upper gaseous stream of the first reactor is supplied to one or more distillation columns and separated according to boiling point to produce C 5-12 Stream containing light oil (LO), C 13-22 Stream containing middle oil (MO) and C 23 A step of obtaining a stream containing the above heavy oil (HO); and (S3) A step of supplying a portion of a stream containing intermediate oil (MO) separated from the distillation column to a second reactor to perform secondary pyrolysis, and supplying a gaseous stream produced by the secondary pyrolysis to the distillation column; A method for producing waste plastic pyrolysis oil, wherein the first pyrolysis and second pyrolysis are each performed under high pressure conditions of 2 to 40 bar.

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

3. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the stream containing the intermediate oil (MO) separated from the distillation column has a boiling point of 210°C to 360°C.

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

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

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

7. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the first pyrolysis in the first reactor is performed at 400°C to 450°C.

8. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein secondary pyrolysis in the second reactor is performed at a temperature in the range of 420°C to 450°C.

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

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

11. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the waste plastic raw material is a mixture comprising a material selected from the group consisting of polyethylene (PE), polypropylene (PP) and combinations thereof.

12. In paragraph 1, A method for producing waste plastic pyrolysis oil, wherein the above waste plastic raw material is supplied to a pyrolysis reactor after undergoing a pretreatment process including crushing, washing, drying and melting.

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