Method for producing plastic-degrading oil

Abstract

Provided is a method for producing a plastic decomposition oil enabling reduction of an organic nitrogen-containing component other than ammonia contained in the obtained plastic decomposition oil in chemical recycling. A method for producing a plastic decomposition oil according to the present invention comprises: decomposing a waste plastic raw material to obtain a plastic decomposition oil; determining whether or not a content ratio of a specific nitrogen-containing compound (A) contained in the waste plastic raw material (P1) exceeds a predetermined value with respect to a total mass of the waste plastic raw material (P1); and, when the content ratio exceeds the predetermined value in the determination, performing a specific operation on the waste plastic raw material (P1), to carry out decomposition processing with the content ratio of the nitrogen-containing compound (A) contained in the waste plastic raw material to be subjected to the decomposition processing being the predetermined value or less with respect to the total mass of the waste plastic raw material to be subjected to the decomposition processing, and, when the content ratio does not exceed the predetermined value in the determination, the waste plastic raw material (P1) is subjected to the decomposition processing.

Description

Technical Field

[0001] The present invention relates to a method for producing plastic decomposition oil. This application claims priority based on Japanese Patent Application No. 2024-040338 filed on March 14, 2024, and incorporates its content herein.

Background Art

[0002] In recent years, from the viewpoints of environmental protection and sustainability, reprocessing waste plastics including polyolefin polymers such as high-density polyethylene (HDPE) and polypropylene (PP), and recycling them as new products or materials has become an important issue. By doing so, it is expected to reduce the impact on the environment and waste of resources. As methods for recycling waste plastics, a material recycling method and a chemical recycling method are known.

[0003] In the material recycling method, a thermoplastic resin is heated to soften it and then remolded. The process of the material recycling method is generally simple, but it is difficult to physically separate heterogeneous materials such as metals and chlorine-containing compounds, and the obtained remolded products have limited uses because their physical properties are insufficient.

[0004] On the other hand, in the chemical recycling method, a thermoplastic resin is chemically converted, returned to a raw material compound, and then purified and resynthesized. The process of the chemical recycling method generally becomes complicated, and the cost for obtaining recycled products is high if viewed only once, but the physical properties of the recycled products are excellent.

[0005] As a method for recovering waste polyolefin resin from various molded products such as containers and packaging materials mainly composed of polyolefin polymers such as high-density polyethylene (HDPE) and chemically recycling the recovered waste polyolefin resin, specifically, a method of reusing the decomposition oil obtained by decomposing the polyolefin polymer and the fraction separated and purified from the decomposition oil by a distillation purification method as a raw material for new chemical products is known.

[0006] As a method for chemically recycling polyolefin resins to obtain decomposed oil, for example, Patent Document 1 discloses a technology in which polyolefin resins are melted and thermally decomposed using a pyrolysis tank, and the resulting light oil components are reused. Furthermore, Patent Documents 2 and 3 disclose a technology for catalytic thermal decomposition of polyolefin resins in the presence of a catalyst, and for refining and reusing the resulting decomposition oil. Furthermore, Patent Document 4 and Non-Patent Document 1 disclose a technology for hydrothermally decomposing waste polyolefin resins such as polyethylene and polypropylene using supercritical water as a reaction medium, and then refining and reusing the resulting decomposition oil.

[0007] However, in the sorting process for waste plastics intended for chemical recycling, due to the limitations of sorting technology, it may not be possible to completely remove acrylonitrile polymers such as acrylonitrile-styrene resins (AS resins), acrylonitrile-ethylene-propylene-diene-styrene resins (AES resins), and acrylonitrile-butadiene-styrene resins (ABS resins), as well as resins containing nitrogen atoms in their structure, such as polyurethane resins, and additives containing nitrogen atoms in their molecules, such as imidazole compounds, amine compounds, amide compounds, nitrile compounds, imine compounds, and nitrile compounds used as plasticizers and heat stabilizers. As a result, waste polyolefin resins containing trace amounts of these nitrogen-containing compounds (hereinafter referred to as "nitrogen-containing compounds") may be used for chemical recycling.

[0008] According to Non-Patent Documents 2 and 3, when nitrogen-containing compounds are decomposed using the chemical recycling method, they are broken down into ammonia or other organic nitrogen-containing components. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2005-154510 [Patent Document 2] Japanese Patent Publication No. 9-302358 [Patent Document 3] Japanese Patent Publication No. 2014-37518 [Patent Document 4] Japanese Patent Application Publication No. 10-67991 [Non-patent literature]

[0010] [Non-Patent Document 1] "Decomposition of polyethylene, polypropylene, and polystyrene by supercritical water," Environmental Resource Engineering, Vol. 52, pp. 5-13 (2005) [Non-Patent Document 2] "Monomerization of Nylon 6 by Subcritical and Supercritical Water," Journal of Polymer Science, Vol. 58(10), pp. 548-551 (2001) [Non-Patent Document 3] “The resource utilization of ABS plastic waste with subcritical and supercritical water treatment”, International Journal of Hydrogen Energy, Vol.44(30), p15758-15765(2019) [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Our investigations have revealed that the decomposition oil obtained from waste polyolefin resin containing nitrogen-containing compounds contains ammonia and other organic nitrogen-containing components that are produced when the nitrogen-containing compounds are decomposed. Furthermore, we found that while ammonia can be removed relatively easily from the decomposition oil using decomposition and purification methods such as distillation, some other organic nitrogen-containing components are difficult to remove efficiently using decomposition and purification methods. As a result, we found that these unremoved organic nitrogen-containing components can be mixed into the decomposition oil or products obtained from the decomposition oil, leading to a decrease in product quality. In addition, if a considerable amount of organic nitrogen-containing components are mixed into the process wastewater, it becomes necessary to decompose the process wastewater using known wastewater treatment methods such as coagulation and sedimentation or activated sludge methods, thereby increasing the load on the wastewater treatment process. It should be noted that Non-Patent Documents 2 and 3 do not mention anything about suppressing the generation of organic nitrogen-containing components other than ammonia when chemically recycling waste polyolefin resin containing nitrogen-containing compounds.

[0012] The present invention aims to solve these problems. In other words, the present invention aims to provide a method for producing plastic decomposition oil that can reduce organic nitrogen-containing components other than ammonia in the resulting plastic decomposition oil during chemical recycling, such as the chemical recycling of polyolefin polymers or polyolefin polymers containing nitrogen-containing compounds. [Means for solving the problem]

[0013] As a result of repeated studies to solve the above problems, the inventors of the present invention have found that the above problems can be solved by setting the content ratio of nitrogen-containing compounds having a specific structure in waste plastic raw materials to below a threshold.

[0014] In other words, the gist of the present invention is as follows: [1] A method for producing plastic decomposition oil, comprising decomposing waste plastic raw materials to obtain plastic decomposition oil, Determine whether the content ratio of the nitrogen-containing compound (A) having a conjugated structure in which a nitrogen atom bonded to an aromatic ring is conjugated with the aromatic ring and contained in the waste plastic raw material (P1) exceeds a predetermined value with respect to the total mass of the waste plastic raw material (P1), In the determination, when the value exceeds the predetermined value, (i) Mix another plastic (P3) with the waste plastic raw material (P1), and after making the content ratio of the nitrogen-containing compound (A) contained in the obtained waste plastic raw material (P4) not more than the predetermined value with respect to the total mass of the waste plastic raw material (P4), decompose the waste plastic raw material (P4), or (ii) Remove a part of the waste plastic raw material (P1), and after making the content ratio of the nitrogen-containing compound (A) contained in the obtained waste plastic raw material (P2) not more than the predetermined value with respect to the total mass of the waste plastic raw material (P2), decompose the waste plastic raw material (P2), including, or In the determination, when the value does not exceed the predetermined value, (iii) including decomposing the waste plastic raw material (P1), A method for producing plastic decomposition oil. [2] The method for producing plastic decomposition oil according to [1], wherein the predetermined value is 0.18% by mass in terms of nitrogen atom. [3] The method for producing plastic decomposition oil according to [1] or [2], wherein the nitrogen-containing compound (A) includes a polyurethane-based polymer having a structural unit represented by the following general formula (1). -Ar-NH-C(=O)- (1) (In formula (1), Ar represents an aryl group which may have a substituent.) [4] The method for producing plastic decomposition oil according to any one of [1] to [3], wherein the nitrogen-containing compound (A) contains a structural unit derived from at least one selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate. [5] The method for producing plastic decomposition oil according to any one of [1] to [4], wherein the nitrogen-containing compound (A) has at least one chemical structure selected from the group consisting of an aromatic hetero five-membered ring structure in which the hetero atom is nitrogen, an aromatic hetero six-membered ring structure in which the hetero atom is nitrogen, and aniline structure and aniline derivative structure. [6] The method for producing plastic decomposition oil according to any one of [1] to [5], wherein the waste plastic raw material (P1) contains a nitrogen component. [7] The method for producing plastic decomposition oil according to any one of [1] to [6], wherein the waste plastic raw material (P1) contains 60% by mass or more of a polyolefin-based polymer based on the total mass of the waste plastic raw material (P1). [8] The method for producing plastic decomposition oil according to any one of [1] to [6], wherein the waste plastic raw material (P4) contains 60% by mass or more of a polyolefin-based polymer based on the total mass of the waste plastic raw material (P4). [9] The method for producing plastic decomposition oil according to any one of [1] to [6], wherein the waste plastic raw material (P2) contains 60% by mass or more of a polyolefin-based polymer based on the total mass of the waste plastic raw material (P2). [Effect of the Invention]

[0015] According to the present invention, in chemical recycling, for example, chemical recycling of a polyolefin-based polymer or chemical recycling of a polyolefin-based polymer containing a nitrogen-containing compound, it is possible to provide a method for producing plastic decomposition oil capable of reducing organic nitrogen components other than ammonia contained in the obtained plastic decomposition oil. [Brief Description of the Drawings]

[0016] [Figure 1] The graphs show the relationship between the content ratio (unit: mass%) of nitrogen-containing compounds (A) in waste plastic raw materials and the generation ratio of organic nitrogen-containing components in the decomposed oil and aqueous phase for Experimental Examples 1-8 and Comparative Experimental Examples 1-3. [Figure 2] This flowchart shows an example of the procedure for producing plastic decomposition oil according to the present invention. [Modes for carrying out the invention]

[0017] The present invention will be described in detail below, but the present invention is not limited to the following description and can be modified and implemented as such without departing from the spirit of the invention.

[0018] Unless otherwise specified, numerical ranges represented using "~" in this specification mean a range that includes the numbers before and after "~" as the lower and upper limits, respectively, and "A~B" means A or greater and B or less. In this specification, "A or B" means "A," "B," and "A and B" unless otherwise specified. For example, "including A or B" means "including A," "including B," and "including A and B" unless otherwise specified. In this specification, "mass%" indicates the percentage of a given component contained in 100% of the total amount. "Mass%" and "weight%" are synonymous. "Optional" or "optional" means that the situation described below may or may not occur, and this includes both cases in which the situation occurs and cases in which it does not occur. In this specification, the content of nitrogen-containing compound (A) in waste plastic raw materials is expressed in terms of nitrogen atoms conjugated to aromatic rings. The method for calculating this will be described later.

[0019] In the present invention, "waste plastic" refers to used plastic products or plastic materials, specifically materials that have been used once, discarded, and then have the potential to be reused, recycled, or disposed of.

[0020] All steps described herein may be carried out in any preferred order, unless otherwise specified herein or unless the context clearly contradicts it.

[0021] The present invention provides a method for producing plastic decomposition oil, which includes decomposing waste plastic raw materials to obtain plastic decomposition oil. Figure 2 shows a flowchart illustrating an example of the procedure for producing plastic-degrading oil according to the present invention. Each step will be described below. Specifically, this includes the following operations (1) and (2-a), or (1) and (2-b). (1) Determine whether the proportion of nitrogen-containing compounds (A) having a conjugated structure in which nitrogen atoms bonded to an aromatic ring are conjugated with the aromatic ring, contained in the waste plastic raw material (P1) to be decomposed, exceeds a predetermined value relative to the total mass of the waste plastic raw material (P1). In the determination of (2-a)(1), if the result exceeds the predetermined value mentioned above, (i) After mixing another plastic (P3) with the waste plastic raw material (P1) and ensuring that the nitrogen-containing compound (A) content in the resulting waste plastic raw material (P4) is less than or equal to the predetermined value mentioned above relative to the total mass of the waste plastic raw material (P4), the waste plastic raw material (P4) is subjected to decomposition treatment, or (ii) Remove a portion of the waste plastic raw material (P1), and after the content ratio of nitrogen-containing compound (A) in the obtained waste plastic raw material (P2) is set to be less than or equal to the predetermined value above relative to the total mass of the waste plastic raw material (P2), the waste plastic raw material (P2) is subjected to decomposition treatment. or, In the determination of (2-b)(1), if the result does not exceed the predetermined value mentioned above, (iii) Decompose the waste plastic raw material (P1).

[0022] Furthermore, when making the determination in (1) or before the decomposition treatment in (2-a), the sampling method for the waste plastic raw material is not particularly limited, and a person skilled in the art can appropriately select and use a known statistical sampling method in accordance with common technical knowledge. For example, analytical samples can be collected from a large amount of waste plastic (or the bale in the case of baled material) by random sampling or two-stage sampling in accordance with JIS Z 7302-1. The specific embodiments of the random sampling method are not limited, and those skilled in the art can use known random sampling methods by appropriately optimizing the conditions in accordance with common technical knowledge. For example, if the waste plastic raw material is about 200-300 kg, one method is to reduce it to about 20 kg using the quartering method and collect this as an analytical sample. Furthermore, the collected analytical sample (approximately 20 kg) can be pulverized by a person skilled in the art, according to common technical knowledge, by selecting a known pulverizer as appropriate, depending on the shape, dimensions, hardness, etc. of the sample. If necessary, the analytical sample can be pulverized while being cooled with liquid nitrogen. Furthermore, the pulverized analytical sample can be reduced to approximately 1 g using the incremental reduction method in accordance with JIS Z 8833:2011, and then analyzed.

[0023] Furthermore, the content ratio (in terms of nitrogen atoms conjugated to the aromatic ring) of nitrogen-containing compounds (A) having a conjugated structure in which nitrogen atoms bonded to an aromatic ring are conjugated with the aromatic ring, contained in the aforementioned waste plastic raw materials (P1) to (P4) (hereinafter simply referred to as "waste plastic raw materials") can be measured using pyrolysis gas chromatography / mass spectrometry (pyrolysis GC / MS method) and elemental analysis by the following procedure.

[0024] First, the nitrogen atom content in the waste plastic raw material is measured using elemental analysis.

[0025] Next, the molecular structure of nitrogen-containing compound (A) contained in the waste plastic raw material is identified using pyrolysis gas chromatography / mass spectrometry (pyrolysis GC / MS). Furthermore, the content ratio of nitrogen-containing compound (A) contained in the waste plastic raw material is measured. Specifically, in structural analysis by pyrolysis GC / MS, the conjugated structure portion in the nitrogen-containing compound (A) is not pyrolyzed, and the component (fragment) having the conjugated structure is detected on the mass spectrum, confirming that the nitrogen-containing compound (A) is present in the waste plastic raw material. For example, the presence of the nitrogen-containing compound (A) can be confirmed by detecting peaks of specific pyrolysis products derived from the nitrogen-containing compound (A) in the MS spectrum (for example, isocyanates or polyalcohols if the nitrogen-containing compound (A) is polyurethane).

[0026] Furthermore, the proportion of nitrogen-containing compound (A) in the waste plastic raw material is measured using a gas chromatogram obtained by pyrolysis GC / MS, and the proportion of nitrogen-containing compound (A) in the waste plastic raw material is calculated based on this proportion. Specifically, for the nitrogen compound (A), the content ratio of the nitrogen-containing compound (A) contained in the waste plastic raw material is calculated using a calibration curve of the nitrogen compound (A) prepared in advance using the gas chromatogram obtained by the pyrolysis GC / MS method. When preparing the calibration curve, a mixture in which silica (SiO2) and / or calcium carbonate (CaCO3) is blended in the nitrogen-containing compound (A) to a content of 0.01 to 0.04% by mass is used as a standard sample. After setting the heating furnace temperature of the pyrolysis apparatus to a temperature at which the nitrogen-containing compound (A) is sufficiently pyrolyzed (for example, about 600 °C when the nitrogen-containing compound (A) is a polyurethane-based polymer, a nylon 6-based polymer, a nylon 66-based polymer, or an ABS resin), a calibration curve is prepared based on the peak area of the pyrolyzate characteristic of the nitrogen-containing compound (A). As the "pyrolyzate characteristic of the nitrogen-containing compound (A)", for example, when the nitrogen-containing compound (A) is a polyurethane-based polymer, an isocyanate-based compound; when it is a nylon 6-based polymer, caprolactam; when it is a nylon 66-based polymer, cyclopentanone; and when it is an ABS resin, a calibration curve can be prepared using the peak of a benzonitrile-based compound. As the main components of the waste plastic raw material other than the nitrogen-containing compound (A), when it is a polyethylene resin, 1-hexene; and when it is a polypropylene resin, 2,4-dimethyl-1-heptene can be used to prepare a calibration curve using the peak.

[0027] Note that an example of the measurement conditions for the pyrolysis GC / MS method is shown below. The following measurement conditions can be appropriately optimized by those skilled in the art according to well-known techniques.

[0028] <Pyrolysis Conditions> Pyrolysis apparatus: Multi-shot Pyrolyzer EGA / PY-3030D (manufactured by Frontier Lab Co., Ltd.) Thermal extraction temperature: 350 °C Pyrolysis temperature: 600 °C Sample amount: Approximately 0.4 mg <GC / MS Measurement Conditions> Gas chromatography mass spectrometry measurement apparatus (GC / MS apparatus): GC section: Agilent 7890B (manufactured by Agilent Technologies, Inc.) Single quadrupole mass spectrometer: Agilent 5977B (manufactured by Agilent Technologies) (GC conditions) Ionization method: Electron ionization (EI method) Column: GC capillary column BPX-5 (manufactured by SGE, inner diameter 0.25 mm x length 30 m x film thickness 0.25 μm) Carrier gas: Helium, flow rate 1.0 mL / min (constant flow) Heating conditions (350°C heat extraction): 40°C (holding time 2 minutes) → heating at 20°C / min → 320°C (holding time 14 minutes) Heating conditions (600°C thermal decomposition): 40°C (holding time 2 minutes) → heating at 20°C / min → 320°C (holding time 44 minutes) Inlet temperature: 320℃ Split ratio: 1:100 (MS conditions) Transfer line temperature: 250℃ Ion source temperature: 230℃ Quadrupole temperature: 150℃ Scan mode: m / z = 29~800 Measurement mode: SIM (m / z = 64, 113, 122, 128)

[0029] Next, based on the nitrogen content of nitrogen-containing compound (A) in the waste plastic raw material and the nitrogen atom content in the waste plastic raw material measured by elemental analysis, the nitrogen atom content of nitrogen-containing compound (A) can be calculated. Specifically, if a conjugated structure component (fragment) is detected by pyrolysis GC / MS, the nitrogen atom content measured using the above elemental analysis method can be evaluated as originating from a component having a conjugated structure in which nitrogen atoms bonded to an aromatic ring are conjugated with that aromatic ring. Based on this evaluation, the nitrogen atom content of nitrogen-containing compound (A) can be calculated.

[0030] If the waste plastic raw material contains multiple types of nitrogen-containing compounds (A) and other polymers, the content ratio of these components can be calculated using the pyrolysis GC / MS method. Specifically, the content ratio of the polymer can be calculated from the peak intensity ratio derived from each component on the gas chromatogram obtained by the pyrolysis GC / MS method.

[0031] The pyrolysis GC / MS spectra derived from each polymer can be found in publicly available literature and publicly known MS spectrum databases.

[0032] <Waste plastic raw materials> In the manufacturing method of the present invention, waste plastic raw materials are decomposed to obtain plastic decomposition oil. In the manufacturing method of the present invention, the waste plastic raw materials subject to decomposition treatment are the waste plastic raw material (P4) in (2-a)(i) above, the waste plastic raw material (P2) in (2-a)(ii) above, and the waste plastic raw material (P1) in (2-b) above. Hereinafter, these waste plastic raw materials subject to decomposition treatment will be collectively referred to as "waste plastic raw material (P)".

[0033] In the waste plastic raw material (P) of the present invention, from the viewpoint of reducing the content of organic nitrogen-containing components other than ammonia in the resulting plastic decomposition oil, it is necessary that the content ratio of the nitrogen-containing compound (A), described later, does not exceed a predetermined value. This value can be appropriately set depending on the quality required for the resulting plastic decomposition oil. This invention has for the first time discovered that at least a portion of the organic nitrogen-containing components remaining in plastic decomposition oil obtained by the decomposition treatment of waste plastics originates from a specific nitrogen-containing compound (A) in the waste plastic raw material. This makes it possible to set the conditions required for the waste plastic raw material used in the production of plastic decomposition oil with desired quality.

[0034] The predetermined value relating to the nitrogen-containing compound (A) content in waste plastic raw materials can be determined experimentally or calculated through simulation, depending on the combination of manufacturing conditions adopted during the decomposition treatment of waste plastic raw materials.

[0035] The upper limit of the nitrogen atom content of nitrogen-containing compounds (A) contained in the waste plastic raw material (P) is preferably 0.18% by mass or less, more preferably 0.16% by mass or less, even more preferably 0.13% by mass or less, particularly preferably 0.10% by mass or less, and especially preferably 0.05% by mass or less, based on the total mass of the waste plastic raw material (P), from the viewpoint of reducing the amount of organic nitrogen-containing components other than ammonia generated in the resulting plastic decomposition oil. On the other hand, the lower limit of the nitrogen content of nitrogen-containing compound (A) in terms of nitrogen atoms is not particularly limited, and it may be substantially absent (0% by mass). However, from the viewpoint of economics, such as the manufacturing costs required to reduce nitrogen atoms, it is usually possible to set it to 0.001% by mass or more, preferably 0.005% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.02% by mass or more, and particularly preferably 0.03% by mass or more.

[0036] The above upper and lower limits can be combined arbitrarily. As stated above, the nitrogen atom content of nitrogen-containing compounds (A) contained in the waste plastic raw material (P) is not particularly limited, as it can be set according to the desired quality of the plastic decomposition oil, and may be 0% by mass, or for example, 0.001% by mass or more and 0.18% by mass or less, 0.005% by mass or more and 0.16% by mass or less, 0.01% by mass or more and 0.13% by mass or less, 0.02% by mass or more and 0.10% by mass or less, or 0.03% by mass or more and 0.05% by mass or less.

[0037] The method for measuring the content ratio (in terms of nitrogen atoms conjugated to aromatic rings) of nitrogen-containing compound (A) contained in the waste plastic raw material of the present invention will be described later.

[0038] In carrying out the manufacturing method of the present invention, it is necessary that the waste plastic raw material (P) to be decomposed does not exceed a predetermined value in terms of the nitrogen-containing compound (A) content. If the nitrogen-containing compound (A) content in a certain waste plastic raw material (P1) does not exceed a predetermined value, a plastic decomposition oil of the desired quality can be produced by decomposing that waste plastic raw material (P1) (see (2-b) above).

[0039] On the other hand, if the nitrogen-containing compound (A) content in a certain waste plastic raw material (P1) exceeds a predetermined value, then using that waste plastic raw material (P1) for decomposition treatment will not produce plastic decomposition oil with the desired quality. Therefore, it is necessary to adjust the nitrogen-containing compound (A) content in the waste plastic raw material (P1). The following are examples of methods for adjusting the content ratio of nitrogen-containing compound (A) in waste plastic raw materials, particularly methods for adjusting the content ratio of nitrogen-containing compound (A) so that it does not exceed a predetermined value. (i) A method of further mixing another plastic (P3) with waste plastic raw material (as (i) in (2-a) above). (ii) A method for removing part of the waste plastic raw material (as in (ii) of (2-a) above).

[0040] (i) A method of further mixing another plastic (P3) with waste plastic raw material. One method for reducing the nitrogen-containing compound (A) content in waste plastic raw materials (waste plastic raw materials (P1)) is to mix in another plastic (P3) which has a lower nitrogen-containing compound (A) content than waste plastic raw materials (P1), in particular, a nitrogen-containing compound (A) content lower than a predetermined value, thereby reducing the nitrogen-containing compound (A) content in the overall waste plastic raw materials. As for the plastic (P3), any plastic with a lower nitrogen-containing compound (A) content than the waste plastic raw material (P1), and especially one with a nitrogen-containing compound (A) content lower than a predetermined value, may be used, or unused plastic products or plastic materials may be used. Alternatively, waste plastic raw materials, unused plastic products or plastic materials that substantially do not contain nitrogen-containing compound (A) may be used. From the perspective of chemical recycling, it is preferable to use waste plastic raw materials in which the content of nitrogen-containing compound (A) is less than a predetermined value, or waste plastic raw materials that substantially do not contain nitrogen-containing compound (A).

[0041] (ii) Method for removing part of the waste plastic raw material One method for reducing the nitrogen-containing compound (A) content in waste plastic raw materials (waste plastic raw materials (P1)) is to remove a portion of the waste plastic raw materials (P1) that has a high nitrogen-containing compound (A) content, particularly a portion where the nitrogen-containing compound (A) content is greater than a predetermined value. The distribution of components in waste plastic raw materials is often not uniform. In such cases, some parts of the waste plastic raw material may have a high proportion of nitrogen-containing compound (A), while other parts may have a low proportion of nitrogen-containing compound (A). In such cases, by removing the portion with a high proportion of nitrogen-containing compound (A), the overall proportion of nitrogen-containing compound (A) in the waste plastic raw material can be reduced and adjusted so that it does not exceed a predetermined value.

[0042] <Organic nitrogen-containing components other than ammonia> In the present invention, organic nitrogen-containing components other than ammonia contained in the plastic decomposition oil (hereinafter also simply referred to as "organic nitrogen-containing components") are decomposition products derived from nitrogen-containing compounds (A) contained in the waste plastic raw material. In the present invention, nitrogen-containing compound (A) is a compound having a conjugated structure in which a nitrogen atom bonded to an aromatic ring is conjugated with the aromatic ring. Examples include compounds having an aromatic hetero five-membered ring structure in which the heteroatom is nitrogen, compounds having an aromatic hetero six-membered ring structure in which the heteroatom is nitrogen, and compounds having an aniline structure or an aniline derivative structure. Some organic nitrogen-containing components other than ammonia in plastic decomposition oil are difficult to remove efficiently using known decomposition and purification methods. As a result, these unremoved organic nitrogen-containing components can contaminate the decomposition oil or products obtained from it, leading to a decline in product quality. Furthermore, a considerable amount of organic nitrogen-containing components may be mixed into the process wastewater, requiring decomposition treatment of the process wastewater using known wastewater treatment methods such as coagulation and sedimentation or activated sludge methods, which increases the burden on the wastewater treatment process.

[0043] <Nitrogen-containing compounds (A)> In the present invention, nitrogen-containing compound (A) is a compound having a conjugated structure in which a nitrogen atom bonded to an aromatic ring is conjugated with that aromatic ring. According to the inventors' studies, nitrogen-containing compound (A) having such a structure is not easily decomposed into ammonia when decomposed using a chemical recycling method, but is decomposed into organic nitrogen-containing components other than ammonia that maintain a conjugated structure. Therefore, the lower the content of nitrogen-containing compound (A) in the waste plastic raw material, the less likely it is that the amount of organic nitrogen-containing components other than ammonia will be generated in the resulting plastic decomposition oil. Accordingly, by keeping the content of nitrogen-containing compound (A) in the waste plastic raw material below a predetermined value, the content of organic nitrogen-containing components other than ammonia in the plastic decomposition oil can be reduced.

[0044] A first embodiment of the nitrogen-containing compound (A) is a polyurethane polymer having a structural unit represented by the following general formula (1). -Ar-NH-C(=O)- (1) (In formula (1), Ar represents an aryl group which may have substituents.)

[0045] In formula (1), the substituents on Ar include linear, branched, or cyclic hydrocarbon groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, t-butyl, n-butyl, hexyl, cyclohexyl, and phenyl groups. Specifically, examples of the aryl group include phenylene groups such as o-phenylene groups, m-phenylene groups, and p-phenylene groups.

[0046] The structural unit represented by the general formula (1) mentioned above is a structural unit derived from an aromatic isocyanate in which an isocyanate group (-N=C=O) is bonded to an aryl group which may have substituents. Examples of such aromatic isocyanates include 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate.

[0047] A second embodiment of the nitrogen-containing compound (A) is a polyurethane polymer containing a structural unit derived from an aromatic isocyanate in which an isocyanate group (-N=C=O) is bonded to an aryl group which may have substituents. Examples of such aromatic isocyanates include at least one selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate.

[0048] A third embodiment of nitrogen-containing compound (A) includes compounds having an aromatic hetero five-membered ring structure in which the heteroatom is nitrogen, an aromatic hetero six-membered ring structure in which the heteroatom is nitrogen, or an aniline or aniline derivative structure. By selecting such nitrogen-containing compounds and setting their content below a predetermined value, the content of organic nitrogen-containing components other than ammonia in the plastic decomposition oil can be reduced more efficiently.

[0049] Compounds having an aromatic heterofive-membered ring structure in which the heteroatom is nitrogen are not particularly limited, and examples include compounds having an imidazole ring, pyrrole ring, pyrazole ring, triazole ring, tetrazole ring, indole ring, isoindole ring, indoridine ring, purine ring, carbazole skeleton, porphyrin skeleton, or phthalocyanine skeleton.

[0050] Compounds having an aromatic heterosix-membered ring structure in which the heteroatom is nitrogen are not particularly limited, and examples include compounds having a pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring, triazine ring, tetrazine ring, pentazine ring, quinoline ring, isoquinoline ring, quinoxaline ring, sinnoline ring, quinazoline ring, phthalazine ring, naphthidiline ring, pteridine ring, phenanthroline skeleton, acridine skeleton, naftazine skeleton, or phenazine skeleton.

[0051] The aniline or aniline derivative structure is not particularly limited, and examples include aromatic compounds having an isocyanate group, an amino group, an imino group, an amide group, or an imide group, and in particular, phenyl substituted with an isocyanate group, an amino group, an imino group, an amide group, or an imide group.

[0052] The waste plastic raw material in the present invention may include polyolefin polymers as described later. In particular, the lower limit of the content of polyolefin polymers in the waste plastic raw material (P) to be decomposed is not particularly limited, but is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, especially preferably 85% by mass or more, and particularly preferably 90% by mass or more, based on 100% of the total mass of the waste plastic raw material (P). On the other hand, the lower limit of the polyolefin polymer content is not particularly limited. From the viewpoint of economics, such as the manufacturing costs required to purify the waste plastic raw material, it is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 96% by mass or less, especially preferably 94% by mass or less, and particularly preferably 92% by mass or less, based on 100% of the total mass of the waste plastic raw material (P). The above upper and lower limits can be combined in any way. For example, they may be 60-99% by mass, 70-98% by mass, 80-96% by mass, 85-94% by mass, or 90-92% by mass.

[0053] (Polyolefin polymers) The waste plastic raw material of the present invention may contain polyolefin polymers. Examples of polyolefin polymers include high-density polyethylene, low-density polyethylene, linear ultra-low-density polyethylene, polypropylene (homopolypropylene, block copolymer polypropylene, random copolymer polypropylene, etc.), polybutene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-maleic anhydride copolymer, and other ethylene-based resins, as well as ionomer resins (e.g., ethylene-methacrylic acid copolymer ionomer resin). These may be used individually or in combination. Polyethylenes are particularly preferred as polyolefin polymers included in waste plastic raw materials. The origin of these polymers is not particularly limited, and examples include polyolefin films or polyolefin sheets, such as those used in recyclable bottles, transparent packaging like Saran Wrap (registered trademark), and shopping bags, as well as polyolefin fibers. The shape of these polymers is not particularly limited, and prior to the decomposition treatment of the present invention, they can be pre-treated by conventional methods, such as separation from other materials and washing, to form granules, threads, or flakes, or commercially available products can be used as is, or processed into any shape suitable for handling, such as by compression or cutting.

[0054] <Plastic Decomposition Oil> In this invention, "plastic decomposition oil" refers to an oil or oily substance that is a decomposition product of waste plastic raw material (P).

[0055] <Method for decomposing waste plastic raw materials> The embodiments of the waste plastic decomposition treatment in the present invention are not particularly limited as long as they are methods that decompose waste plastic raw materials to obtain plastic decomposition oil. For example, known decomposition treatments using known supercritical or subcritical fluids such as thermal decomposition treatment and hydrothermal decomposition treatment, and known catalytic thermal decomposition treatments can be used.

[0056] "Thermal decomposition treatment" refers to the thermochemical decomposition of organic substances by temperature alone, under conditions that are virtually oxygen-free and without the supply of oxygen from an external source. The pressure used in the pyrolysis treatment is a gauge pressure, typically ranging from -0.1 to 10 MPaG, preferably in the range of -0.05 to 1.0 MPa, as this provides excellent operability and results in a good color for the resulting decomposed oil. Furthermore, the pyrolysis treatment temperature, residence time within the pyrolysis apparatus, and type of pyrolysis apparatus can be appropriately optimized by those skilled in this field to perform the pyrolysis treatment.

[0057] The apparatus for carrying out the pyrolysis treatment is not particularly limited, and known pyrolysis treatment apparatuses can be used. Examples of reactors include single-screw or twin-screw extruder type reactors; kiln-type reactors such as gas-heated kilns and electric-heated kilns; tank-type reactors with agitators; tank-type reactors; tubular reactors; fluidized bed reactors; and fixed-bed reactors. Steam, heat transfer oil / gas, electricity, microwaves, and combustion gases can be used as heat sources. Twin-screw extruder type reactors and kiln-type reactors are preferred due to their superior productivity.

[0058] "Decomposition treatment using supercritical or subcritical fluid" refers to the thermochemical decomposition of organic substances by utilizing the high reactivity of supercritical fluids or subcritical fluids that are in a state that is neither liquid nor gaseous, achieved by adjusting the temperature and pressure. When water is used as the fluid, it becomes thermal decomposition in the presence of water (hydrothermal decomposition). Specifically, when using water, the temperature and pressure may be controlled to heat it to 100-700°C, preferably 150-500°C, and the hydrothermal decomposition treatment may be performed using the high reactivity of supercritical or subcritical water.

[0059] A "supercritical fluid" refers to a fluid in which a solvent such as methanol or water, or a gas such as CO2, is subjected to temperatures and pressures higher than its critical point. Its density is higher than that of a normal gas, and the momentum of its molecules is similar to that of a gas. A "subcritical fluid" is a fluid that exists in a temperature range near its critical point but below its critical temperature, and its reactivity is similar to that of a supercritical fluid. As the supercritical or subsupercritical fluid, it is preferable to use water in a supercritical or subcritical state from the viewpoint of economy and efficiency of the decomposition process.

[0060] "Contact pyrolysis treatment" refers to the thermochemical decomposition of organic substances in a high-temperature range under conditions that are substantially oxygen-free, without supplying oxygen from the outside, in the presence of a known pyrolysis catalyst, and influenced by the pyrolysis catalyst and temperature. For example, waste plastics are melted and pyrolyzed using a known heating means such as an extruder, and the molten material, vapor, or both are brought into contact with a pyrolysis catalyst to lighten them. Examples of pyrolysis catalysts include inorganic solid acid oxide particles such as silica-alumina, silica-titania, silica-zirconia, alumina-magnesia, alumina-zirconia, alumina-titania, bentonite, kaolinite, and theolite.

[0061] The method for thermally decomposing waste plastic raw materials in the present invention is not particularly limited, and examples include the following methods (1-1) or (1-2). Method (1-1): A method of decomposing the waste plastic raw material of the present invention while melting and kneading it using known melting means such as a single-screw extruder or a twin-screw extruder. Method (1-2): A method for decomposing waste plastic raw materials according to the present invention by melting and mixing them using known reactors such as kiln reactors, tank reactors, tubular reactors, fluidized bed reactors, and fixed bed reactors.

[0062] The method for decomposing waste plastic raw materials in the present invention by applying a supercritical or subcritical fluid is not particularly limited, and examples include the following methods (2-1) to (2-3). Method (2-1): A method in which the waste plastic raw material of the present invention is melted using known melting means such as a single-screw extruder or a twin-screw extruder, and then a solvent such as methanol or water, or a gas such as CO2 is applied to the waste plastic raw material using a reactor for decomposition treatment, under high temperature and high pressure conditions in which the solvent or gas forms a supercritical or subcritical fluid. Method (2-2): A method of reacting the waste plastic raw material of the present invention with a solvent such as methanol or water, or a gas such as CO2, which is capable of forming a supercritical or subcritical fluid, using a known melt-mixing means of a single-screw extruder or twin-screw extruder, under high temperature and high pressure conditions in which the solvent or gas forms a supercritical or subcritical fluid. Method (2-3): A method in which waste plastic raw materials according to the present invention and solvents such as methanol, water, or gases such as CO2 capable of forming supercritical or subsupercritical fluids are charged into a reactor for decomposition treatment, and the supercritical or subsupercritical fluid is applied to the waste plastic raw materials under high temperature and high pressure conditions in which the solvent or gas forms a supercritical or subsupercritical state.

[0063] In method (2-1) or (2-3), the reactor used for the decomposition process may be batch or continuous. The reactor can be, for example, pipe-type, cylindrical vertical, or horizontal. The means for achieving the dispersion of waste plastic raw materials in a molten state in high-temperature, high-pressure water according to the present invention are not particularly limited, but for example, static dispersion means using packing materials such as partitions and stationary mixers, and / or forced dispersion means using agitators, mixers, and inserts that perform reciprocating or rotating movements can be used, either one or more of a single type of dispersion means, or a combination of multiple types of dispersion means.

[0064] In this invention, the reaction temperature for decomposing waste plastic raw materials varies depending on the type and proportion of polyolefin polymers contained in the waste plastic raw materials, but is usually between 250°C and 450°C, preferably between 250°C and 370°C. Below 250°C, a considerable reaction time is required to ensure monomer recovery, leading to larger equipment and reduced productivity. Above 450°C, the monomer recovery rate decreases significantly. Furthermore, the reaction pressure required for the decomposition process is, • A pressure at which a solvent such as methanol or water, or a gas such as CO2, can maintain a liquid state, capable of forming a supercritical or subsupercritical fluid. • In order to ensure the solubility of the decomposed oil obtained by decomposing polyolefin polymers and polyolefin polymers in the waste plastic raw material of the present invention in a supercritical fluid or subsupercritical fluid, the density of the supercritical fluid or subsupercritical fluid must be 0.2 g / cm³. 3 The pressure should preferably be above this level, and higher reaction temperatures require higher pressure. While there are no reaction-side restrictions on the upper limit of the reaction pressure for the decomposition process, a pressure of 50 MPa or less is practical from an equipment standpoint.

[0065] In the present invention, the weight ratio of solvents such as methanol and water, or gases such as CO2, that can form a supercritical or subsupercritical fluid and are supplied to the reactor, to the polyolefin polymer in the waste plastic raw material is preferably in the range of 2 to 10, more preferably in the range of 3 to 7. If the weight ratio is above the lower limit, the amount of solvent or gas required for the hydrolysis of the polyolefin polymer is likely to be sufficient to completely dissolve the decomposed oil produced by the decomposition process. For example, if the polyolefin polymer is polypropylene, if the weight ratio is 2 or higher, the resulting monomer, propylene, can be completely dissolved in the supercritical or subsupercritical fluid. On the other hand, if the weight ratio is 10 or lower, the decomposition process occurs sufficiently quickly, which does not lead to an increase in the size of the reactor, the equipment for producing high-temperature, high-pressure supercritical or subsupercritical fluids, or the wastewater treatment equipment, nor does it lead to an increase in the energy required for the process.

[0066] In the present invention, the residence time in the reactor is determined to be optimal by the type of polyolefin polymer in the waste plastic raw material and the reaction temperature. As the size of the reactor increases in proportion to the residence time, the reaction is usually carried out for 20 minutes or less, and for 1 second or more due to the difficulty of adjusting the reaction equipment. From the viewpoint of the yield of raw material olefin, it is preferably carried out for 10 minutes or less, 10 seconds or more, and more preferably for 5 minutes or less, 20 seconds or more. The plastic decomposition oil obtained by the method of the present invention can be recovered by passing it through a solid-liquid separation unit to separate and remove solids or insoluble matter from the aqueous solution after the reaction, as needed, then applying pressure and performing normal separation and purification operations such as crystallization and distillation. [Examples]

[0067] The present invention will be described in more detail below with reference to experimental examples that replace the embodiments, but the present invention is not limited to these experimental examples.

[0068] The compounds used in the experimental example are as follows: PE: High-density polyethylene (Product name: Cat. No. 547999, manufactured by Sigma-Aldrich) Nitrogen-containing plastic (1): Polyurethane having a phenyl isocyanate structural unit represented by the following general formula (product name: Elastoran® C95A10, manufactured by BASF)

[0069] [ka]

[0070] Nitrogen-containing plastic (2): Nylon 66 resin (product name: Cat. No. 181110, manufactured by Sigma-Aldrich) Nitrogen-containing plastic (3): ABS resin (product name: Denka ABS GR-2000, manufactured by Denka Co., Ltd.) Nitrogen-containing resin additive (1): 2-mercaptobenzimidazole (product name: B0055, manufactured by Tokyo Chemical Industry Co., Ltd.) Nitrogen-containing resin additive (2): 2-(5-tert-butyl-2-hydroxyphenyl)benzotriazole (product name: H0719, manufactured by Tokyo Chemical Industry Co., Ltd.) Nitrogen-containing resin additive (3): Stearic acid amide (product name: S0075, manufactured by Tokyo Chemical Industry Co., Ltd.) Nitrogen-containing resin additive (4): Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (product name: B3924, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0071] <Evaluation Method> (1) Evaluation of waste plastic raw materials (1-1) Method for measuring the content ratio of nitrogen-containing compounds in waste plastic raw materials (equivalent to the amount of nitrogen atoms bonded to aromatic rings) For the nitrogen-containing plastics (1) to (3) and nitrogen-containing resin additives (1) to (4) used in the experimental and comparative experimental examples, since their molecular structures are known, the proportion of nitrogen-containing compound (A) in the waste plastic raw material (equivalent to the amount of nitrogen atoms bonded to the aromatic ring) was calculated using the nitrogen atom concentration in the waste plastic calculated using the nitrogen atom concentration in the waste plastic calculated using "(1-2) Method for measuring nitrogen atom concentration in waste plastic raw materials" described later, and the following formula (I).

[0072]

number

[0073] Furthermore, if the molecular structure of nitrogen-containing plastics and nitrogen-containing resin additives in waste plastics is unknown, their molecular structure can be determined by pyrolysis GC / MS analysis.

[0074] (1-2) Method for measuring nitrogen atom concentration in waste plastic raw materials (1-2-1) Nitrogen-containing plastics First, nitrogen analysis was performed on the nitrogen-containing plastics (1) to (3) used in the experimental and comparative experiments using an elemental analyzer (instrument name: Vario EL cube, manufactured by Elemental), and the nitrogen atom content (unit: mass%) was measured. Next, the nitrogen atom content (in terms of mass %) in nitrogen-containing plastics was calculated from the obtained nitrogen atom content values. The measurement conditions were as follows: combustion tube temperature 1150°C, reduction tube temperature 850°C, and measurement mode CHNS. Sulfanilic acid was used as the standard substance. The analytical value was the average of three measurements. Next, the nitrogen atom concentration in the waste plastic raw material was calculated using the obtained nitrogen atom equivalent content and the following formula (II).

[0075]

number

[0076] (1-2-2) Nitrogen resin additive For the nitrogen-containing resin additives (1) to (4) used in the experimental and comparative experimental examples, the nitrogen atom content (in mass %) contained in the nitrogen-containing resin additive was calculated from the molecular formula of the additive component, and the nitrogen atom concentration in the waste plastic raw material was calculated using the following formula (III).

[0077]

number

[0078] (2) Evaluation of the cracked oil and aqueous phase The production rate of ammonia in the aqueous phase obtained in the experimental example and comparative experimental example, and the production rate of organic nitrogen-containing components in the decomposed oil and aqueous phase obtained in the experimental example and comparative experimental example were measured according to the following method.

[0079] (2-1) Method for measuring the rate of ammonia production in the aqueous phase First, the "number of nitrogen atoms in the raw materials" used in the experimental example and comparative experimental example was measured using "(3-1) Method for measuring the number of nitrogen atoms in the raw materials," which will be described later. Furthermore, the "number of nitrogen atoms in ammonia in the aqueous phase" obtained in the experimental example and comparative experimental example was measured using "(4) Method for measuring the number of nitrogen atoms in ammonia in the aqueous phase," which will be described later. Next, the ammonia generation rate in the aqueous phase obtained in the experimental example and the comparative experimental example was calculated using the following formula (IV).

[0080]

number

[0081] (2-2) Method for measuring the generation ratio of organic nitrogen-containing components in the decomposed oil and aqueous phase The "number of nitrogen atoms in the raw materials" used in the experimental example and comparative experimental example was measured using the method described later in "(3-1) Method for measuring the number of nitrogen atoms in the raw materials". Furthermore, the "number of nitrogen atoms in organic nitrogen-containing components in the decomposed oil and aqueous phase" obtained in the experimental example and comparative experimental example was measured using "(3-2) Method for measuring the number of nitrogen atoms in organic nitrogen-containing components in the decomposed oil and aqueous phase". Next, the "proportion of organic nitrogen-containing components produced in the decomposed oil and aqueous phase" obtained in the experimental example and comparative experimental example was calculated using the following formula (V).

[0082]

number

[0083] In other words, if the ammonia production rate is 1.00, it means that all the nitrogen components in the raw material have been quantified as ammonia.

[0084] (3) Method for measuring the amount of organic nitrogen components (3-1) Method for measuring the number of nitrogen atoms in raw materials (3-1-1) Nitrogen-containing plastics For the nitrogen-containing plastics (1) to (3) used in the experimental and comparative experiments, nitrogen analysis was performed using an elemental analyzer (instrument name: Vario EL cube, manufactured by Elemental), and the nitrogen atom content (unit: mass%) was measured. Next, the nitrogen atom content (in terms of mass %) in nitrogen-containing plastics was calculated from the obtained nitrogen atom content values. The measurement conditions were as follows: combustion tube temperature 1150°C, reduction tube temperature 850°C, and measurement mode CHNS. Sulfanilic acid was used as the standard substance. The analytical value was the average of three measurements.

[0085] Next, the number of nitrogen atoms in the raw material was calculated using the obtained nitrogen atom content and the following formula (VI).

[0086]

number

[0087] (3-1-2) Nitrogen-containing resin additives For the nitrogen-containing resin additives (1) to (4) used in the experimental and comparative experimental examples, the nitrogen atom content (in mass %) in the nitrogen-containing resin additive was calculated from the molecular formula of the additive component, and the number of nitrogen atoms in the raw material was calculated using the following formula (VII).

[0088]

number

[0089] (3-2) Method for measuring the number of nitrogen atoms in organic nitrogen-containing components in decomposed oil and aqueous phase The total nitrogen content (unit: mass ppm) of the cracked oil and aqueous phase obtained in the experimental and comparative experimental examples was measured using a trace total nitrogen analyzer under the following measurement conditions. From this value, the nitrogen atom content (unit: mass ppm) in the cracked oil and aqueous phase was calculated. The cracked oil and aqueous phase were diluted with toluene and used as the measurement samples. (Measurement conditions) Equipment: Trace Total Nitrogen Analyzer (Model Name: TN-2100V, manufactured by Nitto Seikou Analytech Co., Ltd.) Measurement modes: Oil-based mode, Water-based mode Sample injection temperature: 600°C (aqueous system mode), 800°C (oil system mode) Outlet temperature: 800°C (water-based mode), 900°C (oil-based mode)

[0090] Next, using the obtained "nitrogen atom content in the cracked oil" and "nitrogen atom content in the aqueous phase," along with the following formulas (VIII) and (IX), the "number of nitrogen atoms in the organic nitrogen-containing components in the cracked oil" and "number of nitrogen atoms in the organic nitrogen-containing components in the aqueous phase" were calculated, and the sum of these values ​​was taken as the "number of nitrogen atoms in the organic nitrogen-containing components in the cracked oil and aqueous phase."

[0091]

number

[0092] Furthermore, since all inorganic nitrogen components migrated to the aqueous phase and were not present in the cracked oil, it was assumed that all nitrogen atoms in the cracked oil originated from organic nitrogen components. In addition, since no inorganic nitrogen components other than ammonia were detected in the aqueous phase, it was assumed that nitrogen atoms other than ammonia in the aqueous phase originated from organic nitrogen components.

[0093] (4) Method for measuring the number of nitrogen atoms in ammonia in the aqueous phase The number of nitrogen atoms of ammonia in the aqueous phase obtained in the experimental and comparative experiments was quantified using capillary electrophoresis (CE) according to the measurement method 1 described below. Since the ammonia in the plastic decomposition gas is not present in the decomposition oil but is almost entirely dissolved in the aqueous phase, only the aqueous phase was evaluated. <Measurement method 1> The aqueous phases obtained in the experimental and comparative experiments were filtered using a PTFE membrane filter (pore size 0.20 μm). The resulting filtrate was diluted 10-fold with ultrapure water, and the ammonia content in the aqueous phase was measured by capillary electrophoresis under the following measurement conditions. Next, the number of nitrogen atoms in the ammonia in the aqueous phase was calculated using the following formula (X).

[0094]

number

[0095] (Measurement conditions) Equipment: Capillary electrophoresis system (System name: Agilent G7100B, manufactured by Agilent) Electrophoresis buffer: Anionic buffer containing 20 mM imidazole and 0.5 mM 18-crown-6-ether (pH=4.5) Preconditioning: The electrophoresis buffer was passed through the column for 5 minutes. Column: Inactive Fused Silica (Product name, manufactured by Agilent, Column size: Total length 112.5 cm, Effective length 104 cm, Inner diameter 50 μm) Column temperature: 20℃ Injection method: Pressurized injection method (inject under pressure of 50 mbar for 30 seconds) Applied voltage: 30kV (reversed polarity mode) Detection: UV indirect absorption spectroscopy (detecting the difference between 280nm (bandwidth 40nm) and 210nm (bandwidth 10nm)).

[0096] [Experimental Example 1] A batch-type autoclave with a capacity of 50 mL was charged with 2.8 g (100 parts by mass) of PE (high-density polyethylene), 0.1 g (3.6 parts by mass) of nitrogen-containing plastic (2), and 30 mL of water. After purging the inside of the autoclave with nitrogen, it was sealed tightly, and the temperature inside the autoclave was raised to 450 °C using an electric furnace, and the internal pressure was set to 25 MPa. The reaction was then continued for 25 minutes while maintaining this temperature and pressure. After that, the reactor was cooled to room temperature, the contents were collected, and the decomposed oil and aqueous phases were obtained. Table 1 shows the proportions of organic nitrogen-containing components and ammonia generated in the decomposed oil and aqueous phase, calculated according to the measurement method described above.

[0097] [Experimental Examples 2-8] In Experimental Example 1, the decomposition treatment was carried out under the same conditions as in Experimental Example 1, except that the type and amount of nitrogen-containing compound were changed from nitrogen-containing plastic (2) as shown in Table 1, to obtain decomposed oil and an aqueous phase. The evaluation results of the obtained decomposed oil and aqueous phase are shown in Table 1.

[0098] [Comparative Experiment Example 1] A batch-type autoclave with a capacity of 75 mL was charged with 4.3 g (100 parts by mass) of PE (high-density polyethylene), 0.04 g (0.93 parts by mass) of nitrogen-containing additive (1), and 33 mL of water. The decomposition treatment was carried out under the same conditions as in Experimental Example 1, and decomposed oil and aqueous phase were obtained. The evaluation results of the obtained decomposed oil and aqueous phase are shown in Table 1.

[0099] [Comparative Experiment Examples 2-3] In Comparative Experiment Example 1, the decomposition treatment was carried out under the same conditions as in Experiment Example 1, except that the type of nitrogen-containing additive was changed from nitrogen-containing additive (1) to the type shown in Table 1, and the decomposed oil and aqueous phase were obtained. The evaluation results of the obtained decomposed oil and aqueous phase are shown in Table 1.

[0100] [Table 1]

[0101] Figure 1 shows the relationship between the content ratio of nitrogen-containing compound (A) in the waste plastic raw material (equivalent to the amount of nitrogen atoms bonded to the aromatic ring) (unit: mass%) and the generation ratio of organic nitrogen-containing components in the decomposed oil and aqueous phase for Experimental Examples 1-8 and Comparative Experimental Examples 1-3.

[0102] Table 1 and Figure 1 show that in the waste plastic raw materials of Experimental Examples 1-8, the proportion of organic nitrogen-containing components generated in the decomposed oil and aqueous phase was small. On the other hand, in the waste plastic raw materials of comparative experimental examples 1 to 3, the nitrogen-containing compound (A), which has a conjugated structure in which nitrogen atoms bonded to an aromatic ring are conjugated with the aromatic ring, had a content ratio exceeding 0.18% by mass in terms of nitrogen atoms, resulting in a large generation ratio of organic nitrogen-containing components in the decomposed oil and aqueous phase.

[0103] Specifically, in the case of nylon 66 in Experimental Example 1, ABS resin in Experimental Examples 2-3, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate in Experimental Example 4, and stearic acid amide in Experimental Example 5, the nitrogen atom bonded to the aromatic ring does not have a conjugated structure in which it is conjugated with the aromatic ring, resulting in a small generation rate of decomposed oil and organic nitrogen-containing components in the aqueous phase. Furthermore, in the polyurethane with a phenyl isocyanate structure in Experimental Example 7, and in the mixture of polyurethane and ABS resin in Experimental Example 8, the nitrogen atoms bonded to the aromatic ring have a conjugated structure in which they are conjugated with the aromatic ring. However, because the content of nitrogen-containing compound (A) in the waste plastic raw material (equivalent to the amount of nitrogen atoms bonded to the aromatic ring) is 0.18% by mass or less, the generation rate of organic nitrogen-containing components in the decomposed oil and aqueous phase was smaller compared to comparative Experimental Examples 1 to 3.

[0104] On the other hand, in comparative experiment example 1 (2-mercaptobenzimidazole), comparative experiment example 2 (2-(5-tert-butyl-2-hydroxyphenyl)benzotriazole), and comparative experiment example 3 (polyurethane with a phenyl isocyanate structure), the nitrogen atoms bonded to the aromatic ring have a conjugated structure in which they are conjugated with the aromatic ring. As a result, the content of nitrogen-containing compound (A) in the waste plastic raw material (equivalent to the amount of nitrogen atoms bonded to the aromatic ring) exceeds 0.18% by mass, leading to a large generation rate of organic nitrogen-containing components in the decomposed oil and aqueous phase.

[0105] The reason for this is presumed to be that nitrogen-containing compounds (A), which have a conjugated structure in which the nitrogen atom bonded to the aromatic ring is conjugated with that aromatic ring, have a strong carbon-nitrogen double bond and are therefore less susceptible to thermal decomposition under thermal decomposition conditions, thus making decomposition into ammonia less likely.

[0106] Therefore, by using waste plastic raw materials in which the content ratio (equivalent to the amount of nitrogen atoms bonded to the aromatic ring) of nitrogen-containing compound (A) having a conjugated structure in which nitrogen atoms bonded to the aromatic ring are conjugated with the aromatic ring is below a predetermined value, it is expected that high-quality waste plastic decomposition oil with low residual organic nitrogen components can be obtained, and the burden on wastewater treatment can be further reduced.

[0107] The results above clearly show that the nitrogen-containing compound (A) contained in the waste plastic raw material affects the quality of the resulting plastic decomposition oil. Until now, when plastic decomposition oil was produced by decomposing waste plastic raw material, it was unclear how organic nitrogen-containing components other than ammonia, which cause a decrease in the quality of the plastic decomposition oil itself or the products obtained from the plastic decomposition oil, are generated, making it difficult to set the conditions necessary to improve the quality of the plastic decomposition oil. The present invention clarifies the cause of the generation of organic nitrogen-containing components other than ammonia contained in plastic decomposition oil, thereby making it possible to set the conditions necessary for the waste plastic raw material used in the production of plastic decomposition oil with desired quality.

Claims

1. A method for producing plastic decomposition oil, which includes decomposing waste plastic raw materials to obtain plastic decomposition oil, It is determined whether the content of nitrogen-containing compound (A) having a conjugated structure in which nitrogen atoms bonded to an aromatic ring are conjugated with the aromatic ring, contained in the waste plastic raw material (P1), exceeds a predetermined value relative to the total mass of the waste plastic raw material (P1). In the above determination, if the result exceeds the predetermined value, (i) Further mixing another plastic (P3) with the waste plastic raw material (P1), and after the content ratio of the nitrogen-containing compound (A) in the obtained waste plastic raw material (P4) is set to be less than or equal to the predetermined value relative to the total mass of the waste plastic raw material (P4), the waste plastic raw material (P4) is subjected to a decomposition treatment, or (ii) After removing a portion of the waste plastic raw material (P1) and making the content ratio of the nitrogen-containing compound (A) in the obtained waste plastic raw material (P2) less than or equal to the predetermined value relative to the total mass of the waste plastic raw material (P2), the waste plastic raw material (P2) is subjected to decomposition treatment. Includes, or, If, in the above determination, the result does not exceed the predetermined value, (iii) Including the decomposition treatment of the waste plastic raw material (P1), A method for producing plastic-degrading oil.

2. The method for producing plastic decomposition oil according to claim 1, wherein the predetermined value is 0.18% by mass in terms of nitrogen atoms.

3. The method for producing plastic decomposition oil according to claim 1, wherein the nitrogen-containing compound (A) includes a polyurethane polymer having a structural unit represented by the following general formula (1). -Ar-NH-C(=O)- (1) (In formula (1), Ar represents an aryl group which may have substituents.)

4. A method for producing plastic decomposition oil according to claim 1, wherein the nitrogen-containing compound (A) comprises a polyurethane polymer containing a structural unit selected from at least one selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate.

5. The method for producing plastic decomposition oil according to claim 1, wherein the nitrogen-containing compound (A) has at least one chemical structure selected from the group consisting of an aromatic hetero five-membered ring structure in which the heteroatom is nitrogen, an aromatic hetero six-membered ring structure in which the heteroatom is nitrogen, and an aniline structure and an aniline derivative structure.

6. The method for producing plastic decomposition oil according to claim 1, wherein the waste plastic raw material (P1) contains a nitrogen component.

7. A method for producing plastic decomposition oil according to any one of claims 1 to 6, wherein the waste plastic raw material (P1) contains 60% by mass or more of a polyolefin polymer based on the total mass of the waste plastic raw material (P1).

8. A method for producing plastic decomposition oil according to any one of claims 1 to 6, wherein the waste plastic raw material (P4) contains 60% by mass or more of a polyolefin polymer based on the total mass of the waste plastic raw material (P4).

9. A method for producing plastic decomposition oil according to any one of claims 1 to 6, wherein the waste plastic raw material (P2) contains 60% by mass or more of a polyolefin polymer based on the total mass of the waste plastic raw material (P2).

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