Method for producing plastic waste mixture and method for recycling plastic waste

Abstract

To provide a method for producing a plastic waste mixture, which allows thermal decomposition of various types of plastic waste with one recycling apparatus and also stable operation of the recycling apparatus.SOLUTION: A method for producing a plastic waste mixture has the following: a first sorting step for sorting n types of plastic waste into a plurality of groups in accordance with a first sorting reference set on the basis of at least one property correlating with a plastic waste recycling condition; and a mixing step ST-M for selecting at least two types of plastic waste in total from among the plurality of groups sorted in the first sorting step ST-1 in accordance with a mixing reference corresponding to the plastic waste recycling condition, and obtaining a plastic waste mixture for thermal decomposition by adjusting a mixing ratio of the at least two types of plastic waste. n is an integer equal to or greater than 2.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] The present invention relates to a method for producing a waste plastic mixture and a method for recycling waste plastics. [Background technology]

[0002] Because plastics are strong and non-corrosive, marine pollution caused by dumped used plastics (waste plastics) has become a global issue.Waste plastics are a variety of plastics, mainly consisting of the four major general-purpose resins: polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). As the problem of waste plastic disposal becomes more serious, chemical recycling, in which waste plastic is thermally decomposed to recover olefin gas, decomposition oil, etc., has attracted attention, and various studies have been conducted on chemical recycling methods and recycling devices.

[0003] For example, Patent Document 1 discloses a chemical recycling method for waste plastics, which includes a pretreatment step of separating polyolefin-based plastics from other plastics from waste plastics, a thermal decomposition step of vaporizing the separated polyolefin-based plastics by thermal decomposition, a catalytic decomposition step of thermally decomposing the pyrolysis gas obtained in the thermal decomposition step in the presence of a silicate catalyst to generate a gas phase component consisting of hydrogen and lower hydrocarbons having 2 to 4 carbon atoms and a liquid phase component mainly consisting of aromatic hydrocarbons, a step of separating hydrogen from the gas phase component discharged from the catalytic decomposition step to obtain lower hydrocarbons having 2 to 4 carbon atoms, and a step of separating the liquid phase component obtained in the catalytic decomposition step into aromatic hydrocarbons mainly consisting of benzene, toluene, and xylene. This chemical recycling method is characterized in that the catalytic decomposition step uses multiple catalytic decomposition tanks to sequentially repeat the steps of catalytic decomposition, catalyst regeneration, and standby as necessary. Patent Document 2 also discloses a method for producing a material recycled product from used plastics so as to material recycle the used plastics before processing them into chemically recycled products. This method for producing a material recycled product includes a step of determining the uses of the material recycled product and the chemically recycled product before carrying out the material recycling, and a step of removing harmful elements or substances from the used plastics to an extent that they can be used for the uses of both recycled products based on the determined uses of both recycled products.

[0004] Also, efforts are being made to improve the efficiency of plastic recycling. For example, Patent Document 3 discloses a plastic product collection container that is used to manufacture plastic products using waste plastic as a raw material and then collects the products after use, and is characterized in that identification information corresponding to the content (including the range of content) of a specified substance contained in the waste plastic is added to the plastic product, and the container accepts the used plastic products for recycle. Furthermore, Patent Document 4 discloses a recycling method in which a disposal method for a product that is to be discarded and reused after use is selected based on the structure of the product at the time of manufacture, and the selected disposal method is displayed on the product. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-154517 A [Patent Document 2] JP 2004-161014 A [Patent Document 3] JP 2004-075162 A [Patent Document 4] JP 1996-323337 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the recycling method described in Patent Document 1, waste plastics are separated into polyolefin-based plastics and other plastics (such as plastics containing halogen elements) in a pretreatment process, and then the polyolefin-based plastics are thermally decomposed to generate pyrolysis gas. In the material recycled product manufacturing method described in Patent Document 2, harmful elements or substances are removed in advance from used plastics to the extent that they can be used for material recycled products and chemical recycled products, and then material recycling is carried out. In recent years, there has been a demand in chemical recycling to be able to thermally decompose a variety of waste plastics in the same recycling equipment, and to operate the recycling equipment stably. Patent Document 3 describes adding identification information such as the amount of waste plastic contained in a plastic product, and Patent Document 4 describes indicating the disposal method after use on a plastic product in advance, but neither document pays any attention to the thermal decomposition of multiple types of waste plastics in the same recycling equipment.

[0007] The present invention aims to provide a method for producing a waste plastic mixture that can thermally decompose a variety of waste plastics in the same recycling equipment and can operate the recycling equipment stably, and a method for recycling waste plastics. [Means for solving the problem]

[0008] [1] A method for producing a waste plastic mixture, comprising: a first classification step of classifying n types of waste plastics into a plurality of groups in accordance with a first classification criterion set based on one or more properties correlated with the recycling conditions of the waste plastics; and a mixing step of selecting a total of two or more types of waste plastics from the plurality of groups classified in the first classification step in accordance with a mixing criterion corresponding to the recycling conditions of the waste plastics, and adjusting and mixing the two or more types of waste plastics to obtain a waste plastic mixture for pyrolysis, where n is an integer of 2 or more.

[0009] [2] The waste plastics classified into the plurality of groups in the first classification process are further classified into a plurality of groups according to a second classification criterion set based on the one or more properties correlated with the recycling conditions of the waste plastics, and the mixing process is a process of selecting a total of two or more types of waste plastics from the plurality of groups classified in the first classification process and the plurality of groups classified in the second classification process according to a mixing criterion corresponding to the recycling conditions of the waste plastics, adjusting the mixing ratio of the two or more types of waste plastics and mixing them to obtain a waste plastic mixture for pyrolysis, and the first classification criterion and the second classification criterion are different from each other. A method for producing the waste plastic mixture described in [1] above.

[0010] [3] When the first classification process is the first classification process and the second classification process is the second classification process, the classification process includes up to m-th classification processes, and the third classification process or the third to m-th classification processes are each independently a process of further classifying the waste plastics classified into a plurality of groups in the classification process performed one step before into a plurality of groups according to the k-th classification criterion set based on the one or more properties correlated with the recycling conditions of the waste plastics, and the mixing process is a process of selecting a total of two or more types of waste plastics from the plurality of groups classified in the first to m-th classification processes according to a mixing criterion according to the recycling conditions of the waste plastics, and adjusting and mixing the two or more types of waste plastics to obtain a waste plastic mixture for pyrolysis, where m is an integer of 4 or more, k is an integer of 3 or more, and the k classification criterion is different from the first classification criterion and the second classification criterion, and when there are a plurality of the k classification criterions, the plurality of the k classification criterions are different from each other; A method for producing the waste plastic mixture described in [2] above.

[0011] [4] The recycling conditions are one or more selected from the group consisting of the type of the waste plastic and impurities contained in the waste plastic; A method for producing a waste plastic mixture described in any one of [1] to [3] above.

[0012] [5] A method for producing a waste plastic mixture described in any one of [1] to [4], wherein the property is one or more selected from the group consisting of the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the n types of waste plastics, the content of oxygen atoms contained in each of the n types of waste plastics, the content of chlorine atoms contained in each of the n types of waste plastics, the content of nitrogen atoms contained in each of the n types of waste plastics, and the content of inorganic matter contained in each of the n types of waste plastics.

[0013] [6] The first classification criterion is at least one of the following classification criteria: whether the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the n types of waste plastics is 50% by mass or more; whether the content of oxygen atoms contained in each of the n types of waste plastics is 5% by mass or less; whether the content of chlorine atoms contained in each of the n types of waste plastics is 5% by mass or less; whether the content of nitrogen atoms contained in each of the n types of waste plastics is 5% by mass or less; and whether the content of inorganic matter contained in each of the n types of waste plastics is 10% by mass or less. A method for producing a waste plastic mixture described in any one of [1] to [5] above.

[0014] [7] The mixing process is a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 50% by mass or more as the mixing standard. A method for producing a waste plastic mixture described in any one of [1] to [6].

[0015] [8] The mixing step is a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of oxygen atoms in the waste plastic mixture is 5% by mass or less as the mixing standard. A method for producing a waste plastic mixture described in any one of [1] to [7] above.

[0016] [9] The mixing step is a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of chlorine atoms in the waste plastic mixture is 5% by mass or less as the mixing standard. A method for producing a waste plastic mixture described in any one of [1] to [8] above.

[0017]

[10] The mixing step is a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of nitrogen atoms in the waste plastic mixture is 5% by mass or less as the mixing standard. A method for producing a waste plastic mixture described in any one of [1] to [9] above.

[0018]

[11] The mixing process is a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of inorganic matter in the waste plastic mixture is 10% by mass or less as the mixing standard. A method for producing a waste plastic mixture described in any one of claims [1] to

[10] .

[0019]

[12] A method for recycling waste plastics, comprising a step of obtaining at least one of a decomposition gas and a decomposition oil by thermally decomposing a waste plastic mixture produced by the method for producing a waste plastic mixture described in any one of [1] to

[11] above, wherein the decomposition gas is used as a recycled gas and the decomposition oil is used as a recycled oil. Effect of the Invention

[0020] According to one aspect of the present invention, it is possible to provide a method for producing a waste plastic mixture and a method for recycling waste plastics, which can pyrolyze a variety of waste plastics in the same recycling equipment and can operate the recycling equipment stably. [Brief description of the drawings]

[0021] [Figure 1A] FIG. 2 is a block diagram showing an example of a manufacturing method according to the first embodiment. [Figure 1B] FIG. 2 is a diagram for explaining an example of a manufacturing method according to the first embodiment. [Diagram 2] FIG. 11 is a block diagram showing an example of a manufacturing method according to a second embodiment. [Figure 3A] FIG. 11 is a block diagram showing another example of the manufacturing method according to the second embodiment. [Figure 3B] FIG. 11 is a view for explaining another example of the manufacturing method according to the second embodiment. [Figure 4] FIG. 11 is a diagram for explaining an example of a manufacturing method according to Modification 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In this specification, a numerical range expressed using "to" means a range that includes the numerical value before "to" as the lower limit and the numerical value after "to" as the upper limit.

[0023] [First embodiment] [Method for producing waste plastic mixture] The manufacturing method of the waste plastic mixture according to the first embodiment (hereinafter also referred to as the manufacturing method according to the present embodiment) includes a first classification step of classifying n types of waste plastics into a plurality of groups according to a first classification criterion set based on one or more properties correlated with the recycling conditions of the waste plastics, and a mixing step of selecting a total of two or more types of waste plastics from the plurality of groups classified in the first classification step according to a mixing criterion corresponding to the recycling conditions of the waste plastics, adjusting the mixing ratio of the two or more types of waste plastics, and mixing them to obtain a waste plastic mixture for pyrolysis. n is an integer of 2 or more. The waste plastic mixture produced by the manufacturing method according to this embodiment can be thermally decomposed in a recycling device (such as a pyrolysis furnace) to produce at least one of a recyclable decomposition gas and a decomposition oil. Hereinafter, the recyclable cracked gas may be referred to as recycled gas, and the recyclable cracked oil may be referred to as recycled oil. At least one of the recycled gas and the recycled oil is refined in various plants and then used (recycled) for various purposes. In addition, the waste plastic mixture produced by the production method according to the present embodiment can be pyrolyzed in a recycling device to generate pyrolysis gas, which can be burned and the combustion heat can be used for various purposes. Similarly, the pyrolysis of the waste plastic mixture can be pyrolyzed to generate pyrolysis oil together with pyrolysis residue (e.g., char, etc.), which can be burned and the combustion heat can be used for various purposes. Hereinafter, the cracked gas used as combustion heat may be referred to as "recycled gas for combustion heat", and the cracked oil used as combustion heat may be referred to as "recycled oil for combustion heat".

[0024] In order to stably operate waste plastic recycling equipment (such as a pyrolysis furnace), it is necessary to keep the properties of the waste plastic introduced into the equipment as uniform as possible. However, in reality, waste plastics come in a wide variety of types, and since various plastics are mixed together during the disposal process, their properties are not uniform. In addition, the properties of waste plastics differ depending on the source of discharge. For this reason, in the past, waste plastics introduced into recycling equipment were selected by limiting the source of discharge, and only waste plastics that met the raw material specifications were introduced into the equipment. Waste plastic that meets the raw material specifications means that the properties of the waste plastic meet the specifications of the recycling equipment. Therefore, the waste plastic that meets the raw material specifications differs depending on the type of recycling equipment.

[0025] The inventors have discovered that by classifying n types of waste plastics into waste plastic groups by grade in accordance with a first classification criterion based on their properties (first classification process), and then in the subsequent mixing process, selecting two or more types of waste plastics from the multiple waste plastic groups classified by grade and mixing them in a specific ratio, it is possible to obtain a waste plastic mixture that complies with the raw material specifications of the recycling equipment and has uniform properties. Since the waste plastic mixture introduced into the recycling equipment has these properties maintained uniformly, the recycling equipment can operate stably. In addition, in the mixing process according to the present embodiment, for example, waste plastics that meet the raw material specifications (hereinafter referred to as waste plastics with properties G1) and waste plastics that do not meet the raw material specifications (hereinafter referred to as waste plastics with properties G2) can be selected from a plurality of waste plastic groups classified by grade, and the ratio of each waste plastic can be adjusted and mixed. Therefore, for example, by setting a difference in the ratio of waste plastics with properties G1 and G2 (ratio of waste plastics with properties G1>ratio of waste plastics with properties G2), and mixing waste plastics with properties G1 and waste plastics with properties G2, a waste plastic mixture that meets the raw material specifications can be obtained. In this way, in the manufacturing method according to this embodiment, waste plastics of different grades are selected from multiple groups of waste plastics classified by grade, and their mixing ratio is adjusted, so that waste plastics that could not be processed individually because they do not meet the raw material specifications (in the above case, waste plastics with properties G2) can be processed in the recycling equipment as a waste plastic mixture that meets the raw material specifications. Therefore, according to this embodiment, a method for producing a waste plastic mixture is realized that can thermally decompose various types of waste plastics in the same recycling apparatus and can operate the recycling apparatus stably.

[0026] In the recycling device, the decomposition gas or decomposition oil and decomposition residue produced by thermally decomposing the "waste plastic mixture" produced by the manufacturing method according to this embodiment are combusted in a combustion device, and the combustion heat is used in the recycling device. In other words, the decomposition gas is used as a "recycle gas for combustion heat", and the decomposition oil and the decomposition residue are used as a "recycle oil for combustion heat". When the cracked gas is used as a "recycled gas for combustion heat", the cracked oil is preferably used as a recycled oil. When the cracked oil is used together with the cracked residue as "recycled oil for combustion heat", the cracked gas is preferably used as a recycled gas. When such a recycling device is used, the mixing step according to this embodiment is preferably carried out by the method of aspect 1 or aspect 2.

[0027] (Aspect 1) The mixing process according to the first embodiment, for example, involves selecting two or more types of waste plastics from a group of multiple waste plastics and adjusting the mixing ratio of each waste plastic according to the mixing criteria (1) to (2) above, in which (1) when the waste plastic mixture is thermally decomposed, a specific amount of decomposition gas containing a target component (e.g., light olefins) as a main component is generated, and (2) the amount of impurities in the decomposition gas is not more than a specific amount (e.g., not more than 5 mass%).

[0028] (Aspect 2) In the mixing step according to the second aspect, for example, when the waste plastic mixture (1S) is thermally decomposed, a specific amount of the target decomposition oil is generated together with the decomposition residue, and the impurities in the decomposition oil (2S) are a specific amount or less (for example, 5 mass% or less), according to the mixing criteria (1S) to (2S), two or more types of waste plastics are selected from a plurality of waste plastic groups, and the mixing ratio of each waste plastic is adjusted. Examples of impurities in the decomposition oil include organic chlorine compounds (such as chlorobenzene) and organic nitrogen compounds (such as benzonitrile). When the waste plastic mixture obtained in the mixing step according to the first or second embodiment is thermally decomposed, a specific amount of "recycled gas for combustion heat" or "recycled oil for combustion heat" is generated, so that the combustion state in the combustion device that burns the recycled gas or recycled oil for combustion heat can be stabilized. In addition, the combustion heat generated in the combustion device can be used as the heat when the waste plastic mixture is thermally decomposed. Since the combustion heat is supplied to the recycling device, the recycling device can be operated efficiently.

[0029] Each step of the manufacturing method according to this embodiment will be described.

[0030] <1st classification process> The first classification step is a step of classifying the n types of waste plastics into a plurality of groups according to a first classification criterion set based on one or more properties that correlate with the recycling conditions of the waste plastics. The production method according to this embodiment can be carried out so long as n is an integer of 2 or more. n may be 3 or more, 5 or more, 10 or more, 20 or more, or 50 or more. On the other hand, from the viewpoint of managing the waste plastic raw material to a certain quality, it is preferable that n is smaller (i.e., the number of types of waste plastics handled is smaller). Therefore, the upper limit of n is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, even more preferably 200 or less, and even more preferably 100 or less. From the viewpoint of treating various types of waste plastics while controlling the quality of the waste plastic raw materials at a certain level, n is usually 50 or more and 300 or less, preferably 50 or more and 200 or less, and more preferably 50 or more and 100 or less. In the first classification process, the recycling conditions correspond to the specifications of the recycling device. Correlation with the recycling conditions means correlation with the specifications of the recycling device. In the manufacturing method according to the present embodiment, the recycling conditions are preferably one or more selected from the group consisting of the type of waste plastic and impurities contained in the waste plastic. Examples of the impurities contained in the waste plastic include oxygen atoms, chlorine atoms, nitrogen atoms, and inorganic substances.

[0031] (R1) When the recycling apparatus is a pyrolysis furnace that generates a light olefin-containing gas as a recycled gas, the type of waste plastic correlated with the recycling conditions is at least one of polypropylene-based plastics and polyethylene-based plastics.

[0032] (R2) In the case where the recycling device is a pyrolysis furnace that generates a terephthalic acid-containing gas as a recycled gas, the type of waste plastic correlated with the recycling conditions is a polyethylene terephthalate-based plastic.

[0033] (R3) In the case where the recycling apparatus is a pyrolysis furnace that produces a styrene-containing gas as a recycled gas, the type of waste plastic correlated with the recycling conditions is polystyrene-based plastic.

[0034] (R4) When the recycling device is a pyrolysis furnace that generates a methyl methacrylate-containing gas as a recycled gas, the type of waste plastic correlated with the recycling conditions is a (meth)acrylic plastic. (Meth)acrylic means acrylic or methacrylic.

[0035] (R5) In the case where the recycling device is a pyrolysis furnace that produces recycled oil, the type of waste plastic correlated with the recycling conditions is at least one of polypropylene-based plastics, polyethylene-based plastics, and polystyrene-based plastics.

[0036] In the first classification process, the properties will vary depending on the type of recycled gas or recycled oil produced by thermal decomposition of the waste plastic mixture, but are preferably one or more selected from the group consisting of the content of plastics derived from the type of recycled gas or recycled oil contained in each of the n types of waste plastics, the content of oxygen atoms contained in each of the n types of waste plastics, the content of chlorine atoms contained in each of the n types of waste plastics, the content of nitrogen atoms contained in each of the n types of waste plastics, and the content of inorganic matter contained in each of the n types of waste plastics.

[0037] In the following, a preferred embodiment will be described in which the recycle apparatus is a pyrolysis furnace that produces a light olefin-containing gas as the recycle gas. The preferred embodiments of the recycling apparatus in the cases of (R2) to (R4) are similar to the preferred embodiment of (R1), and therefore in the following description, "polypropylene-based plastics and polyethylene-based plastics" can be replaced with "polyethylene terephthalate-based plastics" in the case of (R2), with "polystyrene-based plastics" in the case of (R3), and with "(meth)acrylic-based plastics" in the case of (R4). A preferred embodiment in which the recycle apparatus is the above-mentioned (R5) can also be the same as a preferred embodiment in which the recycle apparatus is a pyrolysis furnace that produces a light olefin-containing gas as a recycle gas.

[0038] In the manufacturing method according to this embodiment, the property is preferably one or more selected from the group consisting of the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the n types of waste plastics, the content of oxygen atoms contained in each of the n types of waste plastics, the content of chlorine atoms contained in each of the n types of waste plastics, the content of nitrogen atoms contained in each of the n types of waste plastics, and the content of inorganic matter contained in each of the n types of waste plastics.

[0039] The content of oxygen atoms is measured using an oxygen analyzer (vario EL cube, manufactured by elementar). The content of chlorine atoms is measured by combustion ion chromatography using the following analytical instrument. (analytical equipment) Combustion unit: Nitto Seiko Analytech Co., Ltd., part number AQF-2100H Ion chromatography unit: Thermo Fisher Scientific, product number Dionex Integrion RFIC The nitrogen atom content is measured using a CHN meter (elementar, product number: vario EL cube). The content of inorganic matter is measured according to the ash content test method described in JIS K2272 (1998).

[0040] In the manufacturing method according to the present embodiment, the first classification criterion is: (C1) Whether the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the n types of waste plastics is 50% by mass or more; (C2) Whether the content of oxygen atoms contained in each of the n types of waste plastics is 5 mass% or less; (C3) Whether the content of chlorine atoms contained in each of n types of waste plastics is 5 mass% or less, (C4) Whether the content of nitrogen atoms contained in each of the n types of waste plastics is 5% by mass or less, and (C5) It is preferable that the classification criterion is at least one of whether the content of inorganic matter contained in each of the n types of waste plastics is 10 mass % or less.

[0041] The first classification criterion of (C1) is: It is more preferable that the classification criterion be whether the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the n types of waste plastics is 75 mass% or more. If the total content of polypropylene-based plastics and polyethylene-based plastics is 75 mass % or more, the amount of light olefin gas produced increases, and small amounts of cracked oil and cracked residue are produced. On the other hand, if the total content of polypropylene-based plastics and polyethylene-based plastics is less than 75 mass %, the amount of light olefin gas produced will be small, and large amounts of cracked oil and cracked residue will be produced. As mentioned above, the generated decomposition oil and decomposition residue can be used as "recycled oil for combustion heat", and the combustion heat generated by burning this recycled oil for combustion heat in a combustion device can be used as heat when thermally decomposing waste plastics. Therefore, when the combustion heat generated by burning the cracked oil and the cracked residue (recycled oil for combustion heat) is used as heat for thermally decomposing the waste plastic mixture, it is necessary to appropriately generate the cracked oil and the cracked residue while ensuring the production amount of light olefin gas. In such a case, it is preferable that the mixing process according to this embodiment adjusts the mixing ratio of the two (waste plastics of different grades) in consideration of the balance between "waste plastics with a total content of polypropylene-based plastics and polyethylene-based plastics of 75% by mass or more" and "waste plastics with a total content of less than 75% by mass" classified according to the first classification standard. By adjusting the mixing ratio of different grades of waste plastics, the combustion conditions in the combustion device that burns the cracked oil and decomposition residues can be kept stable, and the combustion heat generated by the combustion of the cracked oil and decomposition residues can be steadily supplied to the recycling device.

[0042] When the oxygen atom content is set as the standard of the raw material specifications to be more than 5 mass% and not more than 10 mass%, the first classification criterion of (C2) is as follows: The classification criteria may be whether the content of oxygen atoms contained in each of the n types of waste plastics is 5% by mass or less, whether the content of the oxygen atoms is more than 5% by mass and less than 10% by mass, or whether the content of the oxygen atoms is more than 10% by mass and less than 15% by mass. Waste plastic with an oxygen atom content of 5% by mass or less has a low concentration of oxygen atoms as an impurity, and therefore is usually within the range of raw material specifications and can be considered to be of good quality. Waste plastics with an oxygen atom content of more than 5% by mass and no more than 10% by mass are within the raw material specifications and can be considered to have guaranteed quality. Waste plastics with an oxygen atom content of more than 10% by mass and not more than 15% by mass are outside the range of the raw material specifications, and traditionally have not been treated by recycling equipment. Therefore, in the mixing process, for example, by adjusting the mixing ratio of waste plastics taking into consideration the balance between "waste plastics with an oxygen atom content of 5% by mass or less," "waste plastics with an oxygen atom content of more than 5% by mass and less than 10% by mass," and "waste plastics with an oxygen atom content of more than 10% by mass and less than 15% by mass," which are classified according to the first classification standard, it becomes possible to process waste plastics that previously could not be processed individually because they did not meet the raw material specifications (in the above case, waste plastics with an oxygen atom content of more than 10% by mass and less than 15% by mass).

[0043] When the content of chlorine atoms is set to be more than 5% by mass and not more than 10% by mass as the standard of the raw material specifications, the first classification criterion of (C3) is as follows: The classification criteria may be whether the content of chlorine atoms contained in each of the n types of waste plastics is 5% by mass or less, whether the content of chlorine atoms is more than 5% by mass and less than 10% by mass, or whether the content of chlorine atoms is more than 10% by mass and less than 15% by mass.

[0044] When the nitrogen atom content is set as the standard of the raw material specifications to be more than 5 mass% and not more than 10 mass%, the first classification criterion of (C4) is as follows: The classification criteria may be whether the content of nitrogen atoms contained in each of the n types of waste plastics is 5% by mass or less, whether the content of the nitrogen atoms is more than 5% by mass and less than 10% by mass, or whether the content of the nitrogen atoms is more than 10% by mass and less than 15% by mass.

[0045] If the content of inorganic matter is more than 10% by mass and not more than 20% by mass as the standard of the raw material specifications, the first classification criterion of (C5) is as follows: The classification criteria may be whether the content of inorganic matter contained in each of the n types of waste plastics is 10% by mass or less, whether the content of the inorganic matter is more than 10% by mass and less than 20% by mass, or whether the content of the inorganic matter is more than 20% by mass and less than 30% by mass.

[0046] <Second classification process> In the manufacturing method according to this embodiment, it is preferable to further include a second classification process for further classifying the waste plastic classified into multiple groups in the first classification process into multiple groups according to a second classification criterion set based on the one or more properties that correlate with the recycling conditions of the waste plastic. In this case, the mixing step is a step of selecting two or more kinds of waste plastics in total from the multiple groups classified in the first classification step and the multiple groups classified in the second classification step according to a mixing standard corresponding to the recycling conditions of the waste plastics, adjusting the mixing ratio of the two or more kinds of waste plastics, and mixing them to obtain a waste plastic mixture for pyrolysis. The first classification standard and the second classification standard are different from each other. The recycling conditions in the second classification step are preferably one or more selected from the group consisting of the type of waste plastics and impurities contained in the waste plastics. The second classification criterion in the second classification step can be selected from, for example, the above-mentioned first classification criterion, provided that the first classification criterion and the second classification criterion are different from each other. The manufacturing method according to the present embodiment includes the second classification process, which allows two or more types of waste plastics to be selected from a larger number of groups of waste plastics classified into grades, compared to a method including only the first classification process. This allows for the production of a waste plastic mixture that is more in line with the raw material specifications and has more uniform properties.

[0047] <Mixing process> The mixing process is a process in which a total of two or more types of waste plastics are selected from the multiple groups classified in the first classification process according to mixing standards that correspond to the recycling conditions of the waste plastics, and the mixing ratio of the two or more types of waste plastics is adjusted and mixed to obtain a waste plastic mixture for pyrolysis. In the mixing step, the mixing standard according to the recycling conditions means the mixing conditions that satisfy the specifications of the recycling device. As the mixer used in the mixing step, a known mixer and a known pretreatment facility can be used.

[0048] In the manufacturing method according to this embodiment, the mixing process is preferably a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 50 mass% or more as the mixing standard. The mixing process is preferably a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is more preferably 60 mass% or more, even more preferably 70 mass% or more, and even more preferably 80 mass% or more, as the mixing standard.

[0049] In the manufacturing method according to this embodiment, the mixing step is preferably a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of oxygen atoms in the waste plastic mixture is 5% by mass or less as the mixing standard. The mixing process is preferably a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of oxygen atoms in the waste plastic mixture is more preferably 4 mass% or less, and even more preferably 3 mass% or less, as the mixing standard.

[0050] In the manufacturing method according to this embodiment, the mixing step is preferably a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of chlorine atoms in the waste plastic mixture is 5 mass% or less as the mixing standard. The mixing process is preferably a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of chlorine atoms in the waste plastic mixture is more preferably 4 mass% or less, and even more preferably 3 mass% or less, as the mixing standard.

[0051] In the manufacturing method according to this embodiment, the mixing step is preferably a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of nitrogen atoms in the waste plastic mixture is 5 mass% or less as the mixing standard. The mixing process is preferably a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of nitrogen atoms in the waste plastic mixture is more preferably 4 mass% or less, and even more preferably 3 mass% or less, as the mixing standard.

[0052] In the manufacturing method according to this embodiment, the mixing step is preferably a step of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of inorganic matter in the waste plastic mixture is 10 mass% or less as the mixing standard. The mixing process is preferably a process of adjusting and mixing the mixing ratios of the two or more types of waste plastics so that the content of inorganic matter in the waste plastic mixture is more preferably 8 mass% or less, and even more preferably 6 mass% or less, as the mixing standard.

[0053] An example of a manufacturing method according to this embodiment will be described with reference to FIGS. 1A and 1B. Fig. 1A is a block diagram showing an example of a manufacturing method according to the present embodiment, and Fig. 1B is a diagram for explaining an example of the manufacturing method according to the present embodiment.

[0054] The method for producing a waste plastic mixture shown in FIGS. 1A and 1B includes a first classification step ST-1, a second classification step ST-2, and a mixing step ST-M. FIG. 1B shows nine types of waste plastics as an example of n types of waste plastics. The first classification process ST-1 classifies the nine types of waste plastics into a waste plastic group with property A (the total content of polypropylene-based plastics and polyethylene-based plastics is 75% by mass or more) and a waste plastic group with property B (the total content of polypropylene-based plastics is less than 75% by mass) according to the first classification criterion of whether the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the nine types of waste plastics is 75% by mass or more. The second classification process ST-2 is carried out according to the second classification criteria of whether the content of oxygen atoms contained in each of the nine types of waste plastics is 5 mass% or less, whether the content of oxygen atoms is more than 5 mass% and less than 10 mass%, and whether the content of oxygen atoms is more than 10 mass% and less than 15 mass%, The waste plastics with property A (four types) are classified into a waste plastics with property A1 (the oxygen atom content is 5% or less by mass), a waste plastics with property B1 (the oxygen atom content is more than 5% and less than 10% by mass), and a waste plastics with property C1 (the oxygen atom content is more than 10% and less than 15% by mass), and the waste plastics with property B (five types) are classified into a waste plastics with property A1, a waste plastics with property B1, and a waste plastics with property C1, in the same way as the waste plastics with property A.

[0055] In the case of Fig. 1A and Fig. 1B, the mixing standard according to the recycling conditions of the waste plastics in the mixing step ST-M is, for example, "the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 60 mass% or more and the content of oxygen atoms is 5 mass% or less". In this case, the mixing step ST-M mixes, for example, waste plastic B-1 at a ratio of 1 (30 mass%), waste plastic A-1 or waste plastic C-1 at a ratio of 2 (30 mass%), waste plastic C-2 at a ratio of 3 (20 mass%), waste plastic A-2 at a ratio of 4 (0 mass%), waste plastic C-3 or waste plastic Z-1 at a ratio of 5 (10 mass%), and waste plastic B-2 or waste plastic D-3 at a ratio of 6 (10 mass%) from among the waste plastics group of properties A1 to C1 classified in the second classification step ST-2 according to the mixing standard. It is also possible to select both waste plastic A-1 and waste plastic C-1 in the mixing step ST-M and set the total ratio to ratio 2. The same applies to ratios 5 and 6. The obtained waste plastic mixture is adjusted so that the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 60% by mass or more and the oxygen atom content is 5% by mass or less to comply with the specifications of the recycling equipment. The mixing ratio of each waste plastic in the mixing step ST-M is not limited to that shown in FIG. 1B.

[0056] Second Embodiment The manufacturing method for a waste plastic mixture according to the second embodiment (hereinafter also referred to as the manufacturing method according to the second embodiment) is similar to the first embodiment, except that, compared to the manufacturing method according to the first embodiment, it has a third classification step or more classification steps than the third classification step. In the second embodiment, the differences from the first embodiment will be mainly described, and the description of similar items will be omitted or simplified by using the same reference numerals, for example.

[0057] FIG. 2 is a block diagram showing an example of a manufacturing method according to the second embodiment. In the manufacturing method according to the second embodiment, when the first classification step is the first classification step ST-11 and the second classification step is the second classification step ST-21, the manufacturing method further includes classification steps ST-m1 up to m-th classification step. In FIG. 2, the third classification step is denoted as ST-31. In this case, the multiple classification processes carried out for the third time or from the third time to the mth time are each independently processes for further classifying the waste plastic, which has been classified into multiple groups in the classification process carried out one step earlier, into multiple groups according to a kth classification criterion set based on the one or more properties that correlate with the recycling conditions of the waste plastic. The mixing process ST-M2 is a process for obtaining a waste plastic mixture for pyrolysis by selecting a total of two or more types of waste plastics from the multiple groups classified in the first to mth classification processes according to mixing standards corresponding to the recycling conditions of the waste plastics, and adjusting and mixing the mixing ratio of the two or more types of waste plastics. m is an integer of 4 or greater. k is an integer of 3 or greater. The kth classification criterion is different from the first classification criterion and the second classification criterion. When there are a plurality of the k classification criteria, the k classification criteria are different from each other.

[0058] It is preferable that the recycling conditions in the multiple classification processes carried out for the third time or from the third time to the mth time are one or more selected from the group consisting of the type of waste plastic and impurities contained in the waste plastic. The k-th classification criterion in the third classification step or the third to m classification steps can be selected from the first classification criterion described above, with the proviso that the first classification criterion to the (k-1)th classification criterion are different from each other.

[0059] The manufacturing method according to the second embodiment further includes the third classification step or more classification steps than the third classification step, so that the n types of waste plastics are classified into more grade-specific waste plastic groups, and two or more types of waste plastics can be selected from the classified multiple waste plastic groups. This makes it possible to obtain a waste plastic mixture that is more compliant with the raw material specifications and has more uniform properties.

[0060] FIG. 3A is a block diagram showing another example of the manufacturing method according to the second embodiment. FIG. 3B is a view for explaining another example of the manufacturing method according to the second embodiment.

[0061] The method for producing a waste plastic mixture shown in Figures 3A and 3B includes a first classification step ST-10, a second classification step ST-20, a third classification step ST-30, and a mixing step ST-M1. FIG. 3B shows 15 types of waste plastics as an example of n types of waste plastics. The first classification process ST-10 classifies the 15 types of waste plastics into a waste plastic group with property A (the total content of polypropylene-based plastics and polyethylene-based plastics is 75% by mass or more) and a waste plastic group with property B (the total content of polypropylene-based plastics is less than 75% by mass) according to the first classification criterion of whether the total content of polypropylene-based plastics and polyethylene-based plastics contained in each of the 15 types of waste plastics is 75% by mass or more. In the second classification process ST-20, the waste plastic group (8 types) with property A is classified into a waste plastic group with property A1 (the oxygen atom content is 5% or less by mass), a waste plastic group with property B1 (the oxygen atom content is 5% or more by mass and 10% or less by mass), and a waste plastic group with property C1 (the oxygen atom content is 10% or more by mass and 15% or less by mass), according to the second classification criteria of whether the oxygen atom content contained in each of the 15 types of waste plastic is 5% or less by mass, whether the oxygen atom content is more than 5% by mass and 10% or less by mass, and whether the oxygen atom content is more than 10% by mass and 15% or less by mass. Also, the waste plastic group (7 types) with property B is classified into a waste plastic group with property A1, a waste plastic group with property B1, and a waste plastic group with property C1, in the same manner as the waste plastic group with property A. The third classification process ST-30 classifies the waste plastic group with properties A1 to C1 classified from property A according to the third classification criteria of whether the content of chlorine atoms contained in each of the 15 types of waste plastics is 5% by mass or less, whether the content of chlorine atoms is more than 5% by mass and less than 10% by mass, and whether the content of chlorine atoms is more than 10% by mass and less than 15% by mass, into a waste plastic group with property A2 (the content of chlorine atoms is 5% by mass or less), a waste plastic group with property B2 (the content of chlorine atoms is more than 5% by mass and less than 10% by mass), and a waste plastic group with property C2 (the content of chlorine atoms is more than 10% by mass and less than 15% by mass). The waste plastics group of properties A1 to C1 classified based on property B are similarly classified into a waste plastics group of properties A2, a waste plastics group of properties B2, and a waste plastics group of properties C2.

[0062] In the case of Figures 3A and 3B, the mixing standard in the mixing process ST-M1 according to the waste plastic recycling conditions is "the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 60 mass% or more, and the content of oxygen atoms and chlorine atoms is both 5 mass% or less." In this case, the mixing process ST-M1 mixes, according to the mixing criteria, the waste plastic group of multiple properties A2 to C2 classified in the third classification process ST-30, for example, waste plastic B-1 in a ratio of 11, waste plastic A-3 in a ratio of 13, waste plastic B-3 in a ratio of 14, waste plastic A-1 in a ratio of 15, waste plastic C-1 in a ratio of 16, waste plastic B-4 or waste plastic D-1 in a ratio of 17, waste plastic C-2 in a ratio of 19, waste plastic B-2 in a ratio of 20, waste plastic A-2 in a ratio of 22, waste plastic D-2 in a ratio of 23, waste plastic Z-1 in a ratio of 24, waste plastic C-3 in a ratio of 25, waste plastic A-4 in a ratio of 26, and waste plastic D-3 in a ratio of 28. Ratio 11, ratio 13 to ratio 17, ratio 19 to ratio 20, ratio 22 to ratio 26, and ratio 28 are set arbitrarily (0 mass% or more) according to the mixing standard, but the total of all ratios is 100 mass%. In the mixing process ST-M1, both waste plastic B-4 and waste plastic D-1 may be selected, and the total ratio may be set to ratio 17. The resulting waste plastic mixture is adjusted so that the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 60% by mass or more, and the content of oxygen atoms and chlorine atoms are both 5% by mass or less, in order to comply with the specifications of the recycling equipment.

[0063] Third Embodiment [How to recycle waste plastic] A waste plastic recycling method according to a third embodiment (hereinafter also referred to as the recycling method according to the third embodiment) includes a step of obtaining at least one of a decomposition gas and a decomposition oil by thermally decomposing a waste plastic mixture produced by any one of the manufacturing methods according to the above-mentioned embodiments, and the decomposition gas is used as a recycled gas, and the decomposition oil is used as a recycled oil. Of the cracked gas and cracked oil produced in the above-mentioned obtaining process, only the cracked gas may be used as a recycled gas, only the cracked oil may be used as a recycled oil, or the cracked gas may be used as a recycled gas and the cracked oil may be used as a recycled oil. The cracked gas generated in the obtaining step is refined in various plants and then utilized for various purposes. The cracked gas generated in the obtaining step may be utilized as the aforementioned "recycle gas for combustion heat." The cracked oil produced in the obtaining step is refined in various plants and then used for various purposes. The cracked oil produced in the obtaining step may be used together with the cracked residue as the above-mentioned "recycled oil for combustion heat". When the cracked gas produced in the obtaining step is used as a "recycled gas for combustion heat", the cracked oil is preferably used as a recycled oil. When the cracked oil produced in the above-mentioned obtaining step is used together with the cracked residue as "recycled oil for combustion heat", the above-mentioned cracked gas is preferably used as a recycled gas.

[0064] In the recycling method according to the third embodiment, a waste plastic mixture having properties conforming to the specifications of the recycling device is thermally decomposed, so that a cracked gas, a cracked oil, or both a cracked gas and a cracked oil having uniform properties can be obtained. Therefore, the cracked gas having uniform properties can be used as a "recycled gas" or a "recycled gas for combustion heat", and the cracked oil having uniform properties can be used as a "recycled oil" or a "recycled oil for combustion heat". In the recycling method according to the third embodiment, the cracked gas produced in the obtaining step is preferably a light olefin-containing gas.

[0065] The present invention is not limited to the above-described embodiment, and may include modifications and improvements within the scope of the present invention.

[0066] [Modifications of the embodiment] [Variation 1] In the mixing process ST-M described as an example of the first embodiment, and the mixing process ST-M1 described as an example of the second embodiment, a total of two or more types of waste plastics were selected from the multiple waste plastic groups classified in the final (mth) classification process, but the method of selecting waste plastics is not limited to this. In the mixing process, a total of two or more types of waste plastics can be selected from the multiple waste plastic groups classified in the multiple classification processes performed from the first to mth times. The mth time corresponds to the second time in the case of Figures 1A and 1B, and corresponds to the third time in the case of Figures 3A and 3B. An example of a manufacturing method according to the first modification will be described with reference to FIG. In the manufacturing method according to the modified example 1, the first classification step ST-1 is synonymous with the first classification step ST-1 according to the first embodiment. The second classification step ST-2X according to the modified example 1 classifies the waste plastic group (4 types) of property A classified in the first classification step ST-1 into a waste plastic group of property A1, a waste plastic group of property B1, and a waste plastic group of property C1 according to the second classification standard described in the first embodiment, but does not classify the waste plastic group (5 types) of property B classified in the first classification step ST-1. Other than this point, it is the same as the second classification step ST-2 according to the first embodiment. In the mixing process ST-MX according to the first modification, from among the waste plastic groups with a plurality of properties A1 to C1 classified in the second classification process ST-2X and the waste plastic group with a property B classified in the first classification process ST-1, for example, the waste plastic B-1 is mixed at a ratio of 1X, the waste plastic A-1 or the waste plastic C-1 at a ratio of 2X, the waste plastic C-2 at a ratio of 3X, and any of the waste plastics with a property B at a ratio of 4X, according to the mixing criteria described in the first embodiment. The ratios 1X to 4X are set arbitrarily (0% by mass or more) according to the mixing criteria, but the total of all ratios is 100% by mass. In the mixing process ST-MX, both the waste plastic A-1 and the waste plastic C-1 may be selected and their total ratio may be set to the ratio 2X, or any two or more types of waste plastic may be selected from the waste plastic group with property B and their total ratio may be set to the ratio 4X. The resulting waste plastic mixture is adjusted so that at least the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture conforms to the specifications of the recycling device.

[0067] The polypropylene-based plastic and polyethylene-based plastic used in the above-mentioned embodiment will be described. A polypropylene-based plastic is a plastic whose main component is a polypropylene-based polymer, and a polyethylene-based plastic is a plastic whose main component is a polyethylene-based polymer. The main component means the component that accounts for the largest proportion of the components that constitute each plastic. For example, in the case of a plastic whose main component is a polypropylene-based polymer, the main component means that the polypropylene-based polymer accounts for 50% by mass or more of the total amount of the plastic, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Examples of polypropylene-based polymers include propylene homopolymers and copolymers of propylene with other monomers (such as propylene-olefin copolymers). Examples of polyethylene polymers include ethylene homopolymers (such as low density polyethylene and high density polyethylene) and copolymers of ethylene with other monomers (such as ABS resin and ethylene-olefin copolymer). [Industrial Applicability]

[0068] The method for producing a waste plastic mixture according to the present invention has industrial applicability since it can thermally decompose various types of waste plastics in the same recycling apparatus. [Explanation of symbols]

[0069] ST-1, ST-10, ST-11… the first classification process, ST-2, ST-20, ST-21, ST-2X… the second classification process, ST-30, ST-31… the third classification process, ST-M, ST-M1, ST-M2, ST-MX… the mixing process.

Claims

1. A first classification step involves classifying n types of waste plastics into multiple groups according to a first classification criterion set based on one or more properties that correlate with the recycling conditions of waste plastics, The system includes a mixing step in which, in accordance with mixing criteria corresponding to the recycling conditions of the waste plastics, a total of two or more types of waste plastics are selected from a plurality of groups classified in the first classification step, and the mixing ratio of the two or more types of waste plastics is adjusted and mixed to obtain a waste plastic mixture for thermal decomposition. n is an integer greater than or equal to 2. A method for producing waste plastic mixtures.

2. The process further includes a second classification step in which the waste plastics, which have been classified into multiple groups in the first classification step, are further classified into multiple groups according to a second classification criterion set based on one or more properties that correlate with the recycling conditions of the waste plastics, The mixing step is a process of obtaining a waste plastic mixture for thermal decomposition by selecting a total of two or more waste plastics from a plurality of groups classified in the first classification step and a plurality of groups classified in the second classification step, according to mixing criteria corresponding to the recycling conditions of the waste plastics, and adjusting the mixing ratio of the two or more waste plastics. The first classification criterion and the second classification criterion are different from each other. A method for producing a waste plastic mixture according to claim 1.

3. If the first classification step is considered the first classification step and the second classification step is considered the second classification step, then the system has up to m classification steps. The third or third through m classification steps are each independent steps of further classifying the waste plastics, which were classified into multiple groups in the previous classification step, according to a k-th classification criterion set based on one or more properties that correlate with the recycling conditions of the waste plastics. The mixing step involves selecting a total of two or more types of waste plastics from among multiple groups classified in the first to mth classification steps, according to mixing criteria corresponding to the recycling conditions of the waste plastics, and then mixing the two or more types of waste plastics while adjusting their mixing ratio to obtain a waste plastic mixture for thermal decomposition. m is an integer greater than or equal to 4, k is an integer greater than or equal to 3, The k classification criterion described above is different from the first classification criterion and the second classification criterion. If there are multiple k classification criteria, the multiple k classification criteria are different from each other. A method for producing a waste plastic mixture according to claim 2.

4. The recycling conditions are one or more selected from the group consisting of the type of waste plastic and the impurities contained in the waste plastic. A method for producing a waste plastic mixture according to claim 1 or claim 2.

5. The aforementioned properties are, The total amount of polypropylene-based plastics and polyethylene-based plastics contained in each of the n types of waste plastics, The oxygen atom content in each of n types of waste plastics, The amount of chlorine atoms contained in each of n types of waste plastics, The nitrogen atom content in each of the n types of waste plastics, and One or more selected from the group consisting of the inorganic content contained in each of the n types of waste plastics. A method for producing a waste plastic mixture according to claim 1 or claim 2.

6. The first classification criterion mentioned above is, Whether the total content of polypropylene-based plastics and polyethylene-based plastics in each of the n types of waste plastics is 50% by mass or more. Whether the oxygen atom content in each of the n types of waste plastics is 5% by mass or less, Whether the chlorine atom content in each of the n types of waste plastics is 5% by mass or less, Whether the nitrogen atom content in each of the n types of waste plastics is 5% by mass or less, and Whether or not the inorganic content in each of the n types of waste plastics is 10% by mass or less is at least one of the following classification criteria: A method for producing a waste plastic mixture according to claim 1 or claim 2.

7. The mixing step is a step of adjusting the mixing ratio of the two or more waste plastics so that the total content of polypropylene-based plastics and polyethylene-based plastics in the waste plastic mixture is 50% by mass or more, as the mixing standard. A method for producing a waste plastic mixture according to claim 1 or claim 2.

8. The mixing step is a step of adjusting the mixing ratio of the two or more waste plastics so that the oxygen atom content in the waste plastic mixture is 5% by mass or less, as the mixing standard. A method for producing a waste plastic mixture according to claim 1 or claim 2.

9. The mixing step is a process of adjusting the mixing ratio of the two or more waste plastics so that the chlorine atom content in the waste plastic mixture is 5% by mass or less, as the mixing standard. A method for producing a waste plastic mixture according to claim 1 or claim 2.

10. The mixing step is a process of adjusting the mixing ratio of the two or more waste plastics so that the nitrogen atom content in the waste plastic mixture is 5% by mass or less, as the mixing standard. A method for producing a waste plastic mixture according to claim 1 or claim 2.

11. The mixing step is a step of adjusting the mixing ratio of the two or more waste plastics so that the inorganic content in the waste plastic mixture is 10% by mass or less, as the mixing standard. A method for producing a waste plastic mixture according to claim 1 or claim 2.

12. The method comprises a step of obtaining at least one of a decomposition gas and a decomposition oil produced by thermally decomposing a waste plastic mixture manufactured by the method for producing a waste plastic mixture according to claim 1 or claim 2, The aforementioned decomposition gas is used as recycled gas. The aforementioned decomposed oil is used as recycled oil. Methods for recycling waste plastic.

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