JP7820757B2 - Method for separating inorganic substances from waste plastic materials, method for regenerating plastic materials from waste plastic materials, and method for producing plastic materials - Google Patents

Description

The present invention relates to a method for separating inorganic substances from waste plastic materials, a method for recycling plastic materials from waste plastic materials, and a method for manufacturing plastic materials. More specifically, the present invention relates to various methods and manufacturing methods for effectively removing inorganic substances such as pigments and fillers that can be an obstacle in the recycling of plastic materials from waste plastic materials or the manufacturing of plastic materials.

Plastic products generally contain a variety of inorganic substances to impart design and functionality. For example, plastic products used as food packaging have an aluminum film vapor-deposited on them, and also contain pigments for coloring the product packaging design, as well as inorganic substances as fillers. The types and amounts of these inorganic substances contained in plastic products vary widely from product to product, which can hinder material recycling, which involves directly recycling waste plastic materials.

Meanwhile, in the field of chemical recycling, attempts have been made to use waste plastic as incineration ash during cement production, as a reducing agent for blast furnaces, and as a chemical raw material for coke ovens. However, these technologies ultimately result in the waste plastic material turning into carbon dioxide, which poses a problem from the perspective of resource recycling. For this reason, in recent years, chemical recycling technologies such as oilification without combustion, which produce substances more similar to plastic materials, have become increasingly important as a way to make more effective use of waste plastic materials.

The majority of plastic materials that make up waste plastics are hydrocarbon-based plastic materials such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), which can be converted into oil by simply heating them. However, to separate the resulting oil from the inorganic residue, a typical method is to heat the decomposition product to a temperature higher than the temperature required for oil conversion (400°C), completely vaporizing the decomposition product of the plastic material, resulting in inorganic-free vapor, which is then separated from the inorganic matter (see, for example, Patent Documents 1 and 2). However, heating to a temperature higher than the temperature required for oil conversion is undesirable both economically and in terms of energy balance, and failing to vaporize the product makes it difficult to separate the inorganic matter from the resulting oil.

Furthermore, if waste plastic materials are melted and fluidized by heating, coarse inorganic matter can be removed by passing the material through a screen or the like (see, for example, Patent Document 3), but most inorganic matter is highly dispersed in the waste plastic materials as fine particles, and such fine particles cannot be removed by passing the material through a screen or the like.

The present invention therefore aims to provide a method for separating inorganic substances from waste plastic materials that consumes less energy than conventional methods and is capable of removing inorganic fine particles highly dispersed in waste plastic materials.

Special Publication No. 2013-523944 Japanese Patent Application Publication No. 5-245463 Japanese Patent Application Publication No. 9-268297

The inventors of the present invention conducted extensive research in light of the above-mentioned problems. As a result, they discovered that the above-mentioned problems can be solved by a method for separating inorganic matter from waste plastic material, which includes a phase separation step in which a highly polar solvent that is immiscible with hydrocarbon oil is added to waste plastic material that has been fluidized in a predetermined amount or less of hydrocarbon oil under predetermined temperature conditions, thereby causing phase separation of the inorganic matter, and thus completed the present invention. Specifically, the present invention encompasses the following aspects.

[1] A method for separating inorganic matter from waste plastic material containing plastic components and inorganic matter, comprising a phase separation step of adding a highly polar solvent that is immiscible with hydrocarbon oil to 100 parts by mass of waste plastic material fluidized in 1,000 parts by mass or less of hydrocarbon oil at a temperature within the range of 25°C to 250°C, thereby separating the inorganic matter into phases.

[2] The method for separating inorganic matter from waste plastic material described in [1], wherein the hydrocarbon oil contains 20% to 100% by volume of hydrocarbons having 8 or more carbon atoms and a melting point of 150°C or less, and the highly polar solvent is at least one selected from the group consisting of an organic solvent having a boiling point of 120°C or higher and having at least one polar group selected from hydroxyl groups, ether groups, ester groups, sulfoxyl groups, sulfonyl groups, amino groups, amide groups, and nitrile groups; and water.

[3] The method for separating inorganic substances from waste plastic material described in [1] or [2], further comprising a heating step of heating the waste plastic material to fluidize it in the hydrocarbon oil prior to the phase separation step.

[4] The method for separating inorganic matter from waste plastic material described in [3], which includes a filtration step, after the heating step and prior to the phase separation step, of filtering the fluidized waste plastic material to separate coarse solid particles from the fluidized waste plastic material.

[5] A method for separating inorganic substances from waste plastic materials according to [3] or [4], wherein the heating step is carried out in an inert gas atmosphere at a temperature of 330°C or higher and 420°C or lower for 1 hour or higher and 20 hours or lower.

[6] The method for separating inorganic matter from waste plastic material described in any one of [3] to [5], wherein the plastic component includes at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC).

[7] The method for separating inorganic substances from waste plastic material described in [6], wherein the waste plastic material contains polyvinyl chloride, and hydrogen chloride is removed by vaporization in the heating step.

[8] The method for separating inorganic substances from waste plastic material described in [6], wherein the waste plastic material contains polystyrene, and the styrene monomer is vaporized and recovered in the heating step.

[9] A method for separating inorganic substances from waste plastic material according to any one of [1] to [8], wherein the weight-average molecular weight Mw of the fluidized waste plastic material is 1,000 or more and 8,000 or less.

[10] A method for regenerating plastic materials from waste plastic materials containing plastic components and inorganic matter, comprising: a phase separation step of adding a highly polar solvent immiscible with the hydrocarbon oil to 100 parts by mass of waste plastic material fluidized in 1,000 parts by mass or less of hydrocarbon oil at a temperature in the range of 25°C to 250°C to phase separate the inorganic matter; a recovery step of recovering the plastic components from the hydrocarbon oil; and a regeneration step of recovering plastic materials from the recovered plastic components.

[11] A method for producing a plastic material using waste plastic material containing plastic components and inorganic matter, the method comprising: a phase separation step in which a highly polar solvent immiscible with the hydrocarbon oil is added to 100 parts by mass of waste plastic material fluidized in 1,000 parts by mass or less of hydrocarbon oil at a temperature within a range of 25°C to 250°C to cause phase separation of the inorganic matter; a recovery step in which the plastic components are recovered from the hydrocarbon oil; and a plastic material production step in which a plastic material is produced from the recovered plastic components.

The method for separating inorganic matter from waste plastic material of the present invention fluidizes the waste plastic material in hydrocarbon oil and does not perform thermal decomposition until the plastic components that make up the waste plastic material are vaporized, so it can be carried out with less energy consumption than conventional methods. Furthermore, because a highly polar solvent that is immiscible with hydrocarbon oil is added to cause phase separation of the inorganic matter, it is possible to effectively remove even inorganic fine particles that are highly dispersed in the waste plastic material.

1 is a diagram showing the results of analysis of heat-treated waste plastic material in Test Example 1 using a differential scanning calorimeter (DSC). 1 is a diagram showing the results of analysis of heat-treated HDPE in Test Example 2 using a differential scanning calorimeter (DSC). 1 is a diagram showing the results of evolved gas analysis-mass spectrometry (EGA-MS) measurement of HDPE-20% PS in Test Example 2.

<Method for separating inorganic substances from waste plastic materials>
The method for separating inorganic substances from waste plastic materials according to this embodiment will be described in detail below.

The method for separating inorganic matter from waste plastic material of this embodiment includes a phase separation step in which a highly polar solvent immiscible with hydrocarbon oil is added to waste plastic material fluidized at a temperature in the range of 25°C to 250°C, thereby causing phase separation of the inorganic matter. Furthermore, the method for separating inorganic matter from waste plastic material of this embodiment preferably includes, prior to the phase separation step, a heating step in which the waste plastic material is heated to fluidize it in the hydrocarbon oil, and/or a filtration step in which the fluidized waste plastic material is filtered to separate coarse solid particles from the fluidized waste plastic material. The method for separating inorganic matter from waste plastic material of this embodiment fluidizes the waste plastic material in hydrocarbon oil and does not perform thermal decomposition until the plastic components constituting the waste plastic material are vaporized, thereby consuming less energy than conventional methods. Furthermore, since the resulting plastic components have only been minimally reduced in molecular weight, they can be used as plastic raw materials directly, or they can be input into a heavy oil cracking process in a petrochemical process to produce chemical raw materials. Furthermore, a highly polar solvent that is immiscible with hydrocarbon oil is added to cause phase separation of inorganic substances, making it possible to effectively remove even inorganic fine particles that are highly dispersed in waste plastic materials.

[Heating process]
The heating step is a step of heating the waste plastic material to make it fluidized in the hydrocarbon oil at a temperature condition in the range of 25° C. to 250° C. Although the present invention is not bound by any theory, by heating the waste plastic material, the plastic components contained in the waste plastic material undergo thermal decomposition, resulting in scission of polymer chains and making the waste plastic material fluidized at a predetermined temperature.

The heating process is preferably carried out in an inert gas at a temperature of 330°C to 420°C for 1 hour to 20 hours. More specifically, the heating temperature in the heating process is 350°C, 375°C, 400°C, etc., and the heating time is 5 hours, 10 hours, or 15 hours. Examples of inert gases include nitrogen gas and rare gases such as argon gas. By carrying out the heating process under the above conditions, it is possible to suppress excessive thermal decomposition of the plastic components contained in the waste plastic material into volatile compounds, etc., and oxidation reactions of the plastic components, while reducing the molecular weight of the plastic components and fluidizing the waste plastic material in an easily handleable manner.

When carrying out the heating process, a catalyst may be used to lower the molecular weight of the plastic components that make up the waste plastic material. Suitable catalysts include, for example, beta zeolite and natural zeolite. By using these catalysts, the plastic components that make up the waste plastic material can be uniformly lowered in molecular weight even at lower temperatures. The amount of catalyst used is preferably 5 to 200 parts by mass per 100 parts by mass of the waste plastic material.

In this embodiment, the plastic contained in the waste plastic material preferably includes at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). It is preferable to appropriately change the processing conditions for the heating process, etc., depending on the type of plastic component contained in the waste plastic material. In the case of municipal waste, waste plastic material is typically provided as a mixture of a wide variety of plastic materials containing the five components listed above. Therefore, in order to fully fluidize the waste plastic material, it is acceptable for some plastic materials to decompose and vaporize during the heating process. In the case of industrial waste, relatively homogeneous waste plastic material consisting of specific plastic components and with a molecular weight distribution within a certain range may be obtained. In such cases, it is preferable to set the processing conditions for the heating process according to the type and molecular weight of the plastic components that make up the waste plastic material. When separating inorganic substances from waste plastic material that is municipal waste, a laboratory-scale separation device may be used, but it can also be carried out on an industrial level in various plants, such as oil refineries.

In addition to the plastics listed above, the waste plastic material may contain polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycarbonate (PC), polyamide, polyurethane, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, etc., in a proportion not exceeding 20% by mass of the total amount of the waste plastic material, preferably 15% by mass or less, and more preferably 10% by mass or less. Even if these plastics are mixed in the above proportions, the method for separating inorganic matter from waste plastic material of this embodiment can be carried out effectively.

If volatile components are generated during the heating process, it is preferable to remove or recover these volatile components depending on their usefulness. For example, if the waste plastic material contains polyvinyl chloride, it is preferable to vaporize and remove the hydrogen chloride generated when heating the polyvinyl chloride during the heating process. This allows the chlorine content of the fluidized waste plastic material to be reduced after fluidizing the waste plastic material. Furthermore, if the waste plastic material contains polystyrene, it is preferable to vaporize and recover the styrene monomer generated during the heating process. The recovered styrene monomer can also be reused, for example, in the production of polystyrene.

The weight-average molecular weight Mw of the waste plastic material fluidized by the heating step is preferably 1,000 or more and 8,500 or less, more specifically, 2,600, 4,000, 8,000, etc. By having the weight-average molecular weight of the waste plastic material within this range, the waste plastic material will be sufficiently fluidized in a state mixed with hydrocarbons or will be fluidized on its own within the treatment temperature range of the method for separating inorganic matter from waste plastic material of this embodiment, making it easier to separate inorganic matter from the waste plastic material. Note that if the waste plastic material to which the method for separating inorganic matter from waste plastic material of this embodiment is applied has a weight-average molecular weight within the above range before undergoing the heating step, the phase separation step described below may be carried out without carrying out the heating step.

[Filtration process]
In the filtration, the fluidized waste plastic material is filtered to separate coarse solid particles from the fluidized waste plastic material. This filtration step is preferably carried out using a filter, screen, etc. that can be commonly used by those skilled in the art. The filter or screen preferably has a mesh size of 0.3 mm or more and 3 mm or less, and more specifically, it is more preferable to use a mesh filter or the like having a mesh size of 1.2 mm, 1.4 mm, 2.0 mm, etc. This mesh filter preferably has heat resistance to such an extent that it does not deform even at the temperature at which the method for separating inorganic substances from waste plastic material is performed. For example, a metal mesh filter such as a stainless steel mesh filter is more preferable.

[Phase separation process]
As described above, the method for separating inorganic matter from waste plastic material of this embodiment includes a phase separation step in which a highly polar solvent immiscible with hydrocarbon oil is added to waste plastic material fluidized in hydrocarbon oil at a temperature in the range of 25°C to 250°C to phase separate the inorganic matter. Here, when fluidizing the waste plastic material in hydrocarbon oil, the amount of hydrocarbon oil used is preferably 1,000 parts by mass or less, preferably 20 parts by mass to 250 parts by mass, for example, 25 parts by mass, 100 parts by mass, or 233 parts by mass, per 100 parts by mass of the waste plastic material. By using an amount of hydrocarbon oil within the above range, the waste plastic material can be fluidized to an extent that inorganic matter can be separated from the waste plastic material, while preventing an increase in energy consumption due to excessive use of hydrocarbon oil. Note that if the waste plastic material is sufficiently fluidized at the above-mentioned predetermined temperature without using hydrocarbon oil, hydrocarbon oil may not be used.

(hydrocarbon oil)
The hydrocarbon oil that can be used in the phase separation step is not particularly limited as long as it is a hydrocarbon oil that exists as a liquid at a temperature in the range of 25°C to 250°C, but examples thereof include those containing 20% to 100% by volume, preferably 50% to 100% by volume, of hydrocarbons having 8 or more carbon atoms and a melting point of 150°C or less. The hydrocarbon oil may be composed of a single type of molecule or a mixture of multiple types. Using the boiling points distilled by the TBP (True Boiling Point) method of ASTM D2892 as a guide, hydrocarbon oils such as kerosene fractions of 150°C to 250°C and diesel fractions of 250°C to 380°C can be used. Specific examples of individual molecular species contained in these hydrocarbon oils include: chain saturated hydrocarbons such as octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane (n-cetane), isocetane, heptadecane, octadecane, nonadecane, icosane, eicosane, heneicosane, heneicosane, docosane, tricosane, tetracosane, and pentacosane; and chain unsaturated hydrocarbons such as octene, octyne, nonene, nonyne, decene, decene, undecene, undecyne, dodecene, dodecyne, tridecene, tridecyne, tetracosane, and tetracosane. Examples of the hydrocarbon oils include toradecene, tetradecene, pentadecene, pentadecene, hexadecene, hexadecene, heptadecene, heptadecene, octadecene, octadecene, nonadecene, nonadecene, icosene, icosine, eicosene, eicosine, henicosene, henicosene, heneicosine, heneicosene, heneicosine, docosene, docosine, tricosene, tricosine, tetracosene, tetracosine, pentacosene, and pentacosine; examples of the saturated cyclic hydrocarbons include cyclooctane and decahydronaphthalene; and examples of the unsaturated cyclic hydrocarbons include 1,5-cyclooctadiene. Hydrocarbon oils containing these hydrocarbons can maintain their liquid properties during the method for separating inorganic matter from waste plastic materials according to this embodiment, and tend not to require a large amount of energy when finally separated from the recycled plastic material, and are therefore suitable for use in this embodiment.

(Highly polar solvent)
The highly polar solvent that can be used in the phase separation step is not particularly limited, as long as it is immiscible with the hydrocarbon oil and has a certain degree of affinity for the inorganic substances contained in the waste plastic material. Examples of such highly polar solvents include at least one selected from the group consisting of organic solvents having a boiling point of 120°C or higher and containing at least one polar group selected from hydroxyl, ether, ester, sulfoxyl, sulfonyl, amino, amide, and nitrile groups; and water. Specific examples of these highly polar solvents containing at least one polar group selected from hydroxyl, ether, ester, sulfoxyl, sulfonyl, amino, amide, and nitrile groups include polyalkylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, and polybutylene glycol; dimethyl sulfoxide, N,N-dimethylformamide, sulfolane, and N-methylpyrrolidone. Among the above-mentioned highly polar solvents, polyalkylene glycol and water are preferred from the viewpoints of ease of handling and miscibility with hydrocarbon oil. In addition, to promote separation of inorganic substances, acids, bases, chelating agents, etc. capable of dissolving inorganic substances can be added to the solvent. Specifically, hydrofluoric acid, oxalic acid, and ammonium fluoride can be added to water or polyalkylene glycol.

The boiling point of the highly polar solvent used in the phase separation process is preferably 120°C or higher, more specifically, 197°C (e.g., in the case of ethylene glycol), 244°C (e.g., in the case of diethylene glycol), 189°C (e.g., in the case of dimethyl sulfoxide), etc. By ensuring that the boiling point of the highly polar solvent falls within the above range, the phase separation process can be more easily carried out within the temperature range in which the waste plastic material can be fluidized. Furthermore, the amount of highly polar solvent used is preferably 20 to 300 parts by mass per 100 parts by mass of the hydrocarbon oil, more specifically, 60, 133, and 220 parts by mass. By ensuring that the amount of highly polar solvent used falls within the above range, it is possible to separate a high proportion of inorganic matter contained in the waste plastic material efficiently.

<Method for regenerating plastic materials from waste plastic materials and method for producing plastic materials>
The method for separating inorganic substances from waste plastic material of this embodiment can be configured as a method for regenerating plastic materials from waste plastic material or a method for manufacturing plastic materials by adding a recovery step of recovering the plastic components in the hydrocarbon oil and a regeneration step of regenerating plastic materials from the recovered plastic components, or a plastic material manufacturing step of manufacturing plastic materials. The method for regenerating plastic materials from waste plastic material and the method for manufacturing plastic materials according to this embodiment will be described in detail below.

[Recovery process]
In the recovery step, the plastic components are recovered from the hydrocarbon oil. Depending on the mass-average molecular weight of the resulting plastic components, the solubility of the plastic components in the hydrocarbon oil, and the melting point and boiling point of the hydrocarbon oil, methods such as cooling the hydrocarbon oil containing the dissolved plastic components to separate the dissolved plastic components, or heating/reducing the pressure of the hydrocarbon oil containing the dissolved plastic components to evaporate at least a portion of the hydrocarbon oil can be used, or these methods can be used in combination. Typically, when the dissolved plastic components are separated by cooling the hydrocarbon oil containing the dissolved plastic components, it may be possible to separate only the plastic components by cooling the hydrocarbon oil to a temperature above the melting point of the hydrocarbon oil but below the melting point of the plastic components.

[Recycling process, plastic material manufacturing process]
The method for regenerating plastic materials from waste plastic materials of this embodiment includes a regeneration step of regenerating plastic materials from recovered plastic components. Furthermore, the method for producing plastic materials of this embodiment includes a plastic material production step of producing plastic materials. This regeneration step is a step carried out when regenerating plastic materials from waste plastic materials, and is characterized in that the raw materials for the plastic materials are limited to waste plastic materials. However, there is no substantial difference between this method and a plastic material production step for producing plastic materials in that a plastic material is ultimately produced. Furthermore, since the raw materials used in producing the plastic material in this embodiment are also waste plastic materials, the method for producing plastic materials of this embodiment can also be described as a method for regenerating plastic materials from waste plastic materials.

In the recycling process and plastic material manufacturing process, the plastic components recovered in the recovery process are refined, if necessary, by methods known to those skilled in the art, and then various reactants, catalysts, etc. are added to the mixture to polymerize it, yielding a plastic material. The resulting plastic material can be molded appropriately by methods known to those skilled in the art and used for applications substantially similar to those of plastic materials obtained from petroleum feedstocks. General methods for manufacturing plastic materials are explained in detail in the Practical Plastic Molding Processing Handbook (edited by the Japan Plastics Molding Industry Association, 1963) and the Plastic Molding Material Business Handbook (Chemical Daily Co., Ltd., 2022 edition), the contents of which are incorporated herein by reference.

The present invention will now be described in detail with reference to examples. However, the present invention is not limited to the examples described below.

<Test Example 1: Heat treatment of waste plastic material>
The heat treatment of waste plastic materials (crushed plastic containers and packaging) was carried out by heating 15 g of waste plastic materials placed in a glass inner tube in a stainless steel container under an argon atmosphere at the temperature and time listed in Table 1. When a catalyst was used, 1.5 g of granular catalyst was added to the glass inner tube along with the waste plastic materials. Gas products generated during the reaction were collected in a gas bag as needed. The pressure during the reaction was atmospheric. The weights of the solids (hereinafter sometimes referred to as "pretreated material"), oil, and gas generated after the reaction were each weighed. The "recovery loss" refers to the difference between the weight of the waste plastic material before treatment and the total weight of the resulting pretreated material, oil, and gas. The ratio of the total weight of the resulting pretreated material, oil, and gas to the weight of the waste plastic material before treatment was defined as the "recovery rate." The melting point and molecular weight of the resulting pretreated material were measured using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The average molecular weight was calculated by recalculating the polystyrene-equivalent molecular weight obtained by GPC into polyethylene-equivalent and polypropylene-equivalent molecular weights, respectively, based on the ratio of the Q factors, assuming the Q factor of polyethylene to be 17.7 and the Q factor of polystyrene to be 41.3. The results are shown in Figure 1 and Table 1.

As is clear from Table 1, by subjecting waste plastic material to heat treatment, the plastic components are reduced in molecular weight, further reducing the weight-average molecular weight. Furthermore, as is clear from the results in Figure 1, the endothermic peak in differential scanning calorimetry analysis of heat-treated waste plastic material shifts to a lower temperature range, indicating a lower melting point.

<Test Example 2: Examination of the residual rate of chlorine and styrene after heat treatment>
A mixture of 15 g of high-density polyethylene (HDPE) and 2% polyvinyl chloride (HDPE-2% PVC) and a mixture of 15 g of high-density polyethylene (HDPE) and 20% polystyrene (PS) (HDPE-20% PS) were subjected to heat treatment in accordance with Test Example 1. The weights of the solids, oil, and gas produced after the reaction were weighed, and the residual chlorine rate in the pretreated HDPE-2% PVC was measured. The residual chlorine rate was determined using a chloride ion-selective electrode after mineralization using the sodium biphenyl method. Details of the sodium biphenyl method are described in Journal of the Chemical Society of Japan, 1988, (12), pp. 2021-2025, the contents of which are incorporated herein by reference. The results are summarized in Table 2 and Figure 2.

Furthermore, HDPE-20% PS was analyzed by evolved gas analysis-mass spectrometry (EGA-MS) to analyze the gas evolved at 20°C/min. The results are shown in Figure 3.

As shown in Figure 2, the endothermic peak in differential scanning calorimetry analysis of heat-treated waste plastic material shifted to a lower temperature range, indicating a lower melting point. Furthermore, as shown in Table 2, the residual chlorine rate in HDPE-2% PVC was lower than the calculated value, suggesting that hydrogen chloride was released as gas during heat treatment. Furthermore, as shown in Figure 3, for the pre-treated material obtained from HDPE-20% PS, the detected amount of the styrene monomer (m/z = 104) peak decreased in the treated material heat-treated at 400°C for 5 hours, suggesting that styrene monomer may be recovered by collecting the gas generated by heat treatment.

<Test Example 3: Elemental analysis of inorganic substances in waste plastic material from which inorganic substances have been removed>
11.6 g of the pre-treated waste plastic material, which had been heat-treated at 375°C for 5 hours, was melted at 120°C and poured onto a 1.4 mm mesh sieve. 0.6 g of the solids remaining on the sieve were recovered ("on the sieve"). Next, 1.0 g of the 10.0 g that permeated the sieve was dissolved in 3 mL of cetane as a hydrocarbon oil, followed by the addition of 4 mL of diethylene glycol as a highly polar solvent and stirring at 120°C for 3 hours, resulting in separation into a 0.9 g cetane layer ("cetane layer") and a 0.3 g diethylene glycol upper layer ("polar solvent layer"). Each fraction was calcined at 900°C for 2 hours and subjected to elemental analysis by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the distribution of inorganic matter in each fraction, calculated on a total basis. The results are shown in Table 3.

As can be seen from Table 3, all of the elements Na, Mg, Al, Si, Ca, Ti, Fe, and Ba were recovered as solids remaining on the sieve. Of these, the recovery rate of Al was particularly high, indicating that Al was effectively separated by filtration. Table 3 also shows that all of the elements Na, Mg, Al, Si, Ca, Ti, Fe, and Ba were recovered in the polar solvent. Of these, Na, Mg, Si, Ca, Fe, and Ba were most significantly distributed in the polar solvent.

<Test Example 4: Test 1 for removing inorganic substances from waste plastic material>
25.3 g of pre-treated waste plastic material, which had been heat-treated at 375°C for 5 hours, was mixed with 59.0 g of cetane (a hydrocarbon oil) and dissolved at 120°C. The mixture was then poured onto a sieve with 850 μm mesh openings. 1.9 g of solids remaining on the sieve ("on the sieve") and 80.7 g of the fraction that passed through the sieve ("cetane layer") were collected, and 1.9 g of fraction 1 and 1.6 g of fraction 2 were each calcined at 900°C for 2 hours. The resulting ash was subjected to elemental analysis by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the distribution of inorganic matter in each fraction, calculated on a total basis. The results are shown in Table 4.

<Test Example 5: Test 2 for removing inorganic substances from waste plastic materials>
[Test Example 5-1]
3.4 g of the cetane layer obtained in Test Example 4 (of which 2.5 g was cetane) was melted at 120°C, and this was added to 3 mL of ethylene glycol as a highly polar solvent, followed by stirring at 120°C. The resulting cetane layer ("cetane layer") and ethylene glycol layer ("polar solvent layer") were separated and calcined at 900°C for 2 hours, and elemental analysis was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount, and the distribution of each element. The above operation was performed twice.

[Test Example 5-2]
The procedure of Test Example 5-1 was repeated, except that 3 mL of diethylene glycol was used instead of 3 mL of ethylene glycol as the highly polar solvent. The solids remaining on the sieve, the cetane layer ("cetane layer"), and the diethylene glycol layer ("polar solvent layer") were separated and calcined at 900°C for 2 hours, and the amount of ash recovered in each fraction, calculated as the total amount, was determined by elemental analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES). The above procedure was repeated twice.

[Test Example 5-3]
The procedure of Test Example 5-1 was repeated, except that 3 mL of dimethyl sulfoxide (DMSO) was used instead of 3 mL of ethylene glycol as the highly polar solvent. The solids remaining on the sieve, the cetane layer ("cetane layer"), and the DMSO layer ("polar solvent layer") were separated and calcined at 900°C for 2 hours, and elemental analysis was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount. The above operation was performed once.

[Test Example 5-4]
The procedure of Test Example 5-1 was repeated, except that 4 mL of a 2 M hydrofluoric acid solution in ethylene glycol (2 M-HF-EG) was used instead of 3 mL of ethylene glycol as the highly polar solvent, and the temperature during stirring was 90°C. The solids remaining on the sieve, the cetane layer ("cetane layer"), and the 2 M HF layer ("polar solvent layer") were each separated and calcined at 900°C for 2 hours, and elemental analysis was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount. The above operation was performed once. Note that the ash reacted with the crucible during calcination, making it impossible to accurately measure the ash content in the polar solvent layer.

[Test Example 5-5]
Except for using 2 mL of water and 2 mL of 4M NaOH instead of 3 mL of ethylene glycol as the highly polar solvent and changing the temperature during stirring to 100°C, the procedure of Test Example 5-1 was followed. The solids remaining on the sieve, the cetane layer ("cetane layer"), and the water layer ("polar solvent layer") were each separated and calcined at 900°C for 2 hours, and elemental analysis was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount. The above operation was performed once. Note that during calcination, the crucible reacted with the ash, and although calcined ash was obtained, an accurate recovery rate could not be measured.

[Test Example 5-6]
3.4 g of the cetane layer obtained in Test Example 4 (of which 2.5 g was cetane) was melted at 120°C and added to 4 mL of a 3 M aqueous oxalic acid solution as a highly polar solvent, followed by stirring at 100°C. The resulting mixture was separated into layers, and 3 mL of diethylene glycol (DEG) was added to the cetane layer twice more to separate the cetane and diethylene glycol layers. The resulting cetane layer ("cetane layer"), diethylene glycol layer, and water layer ("polar solvent layer") were calcined at 900°C for 2 hours, and elemental analysis was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount. This procedure was performed once. When the diethylene glycol layer was calcined, the amount of ash obtained was approximately 0.1 mg.

[Test Examples 5-7]
Except for using 4 mL of a 2M NH ₄ F aqueous solution instead of 3 mL of ethylene glycol as the highly polar solvent and changing the temperature during stirring to 100°C, the procedure of Test Example 5-1 was followed. The solids remaining on the sieve, the cetane layer ("cetane layer"), and the water layer ("polar solvent layer") were each separated and calcined at 900°C for 2 hours, and elemental analysis was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount. The above operation was performed once. Note that the ash reacted with the crucible during calcination, making it impossible to accurately measure the ash in the polar solvent layer.

[Test Examples 5-8]
3.4 g of the cetane layer obtained in Test Example 4 (of which 2.5 g was cetane) was melted at 120°C, and this was added to 4 mL of a 2 M aqueous solution of hydrofluoric acid as a highly polar solvent, followed by stirring at 90°C. 3 mL of cetane and 4 mL of a 2 M aqueous solution of hydrofluoric acid were further added to this, and the cetane layer ("cetane layer"), after washing with pure water, was fired at 900°C for 2 hours, and elemental analysis was carried out by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the amount of ash recovered in each fraction, calculated as the total amount. Note that the ash reacted with the crucible during firing, making it impossible to accurately measure the ash content in the polar solvent layer.

[Test Example 5-9]
1.0 g of waste plastic material and 3 mL of ethylene glycol (EG) were added to a test tube and heated and stirred at 170°C. The solid content ("molten plastic layer") and the ethylene glycol layer were separated and calcined at 900°C for 2 hours, and the amount of ash recovered in each fraction was determined on a total basis.

The results are shown in Tables 5 and 6.

As is clear from Table 5, by adopting the method of the present invention, inorganic substances were distributed in the polar solvent layer, effectively separating the inorganic substances contained in the waste plastic material from the plastic components. Furthermore, as can be seen from Table 6, all of the elements Na, Mg, Al, Si, P, Ca, Ti, Fe, Zn, and Ba were recovered as solids remaining on the sieve. Of these, the recovery rate of Al was particularly high regardless of the solvent, indicating that Al was effectively separated by filtration. Furthermore, Table 6 shows that all of the elements Na, Mg, Al, Si, P, Ca, Ti, Fe, Zn, and Ba were recovered in the polar solvent. Of these, Mg, Si, P, Ca, Ti, Fe, and Zn were most significantly distributed in the polar solvent when using many solvents.

Test Example 6: Synthesis of heat-treated HDPE or the like without a catalyst
15.0 g of each of high-density polyethylene (HDPE; Mw = 150,000), low-density polyethylene (PE(L); Mw = 4,000), ultra-high molecular weight polyethylene (PE(UH); Mw = 3,000,000), linear polyethylene (LLDPE; Mw = 50,000), and polypropylene (PP; Mw = 200,000) was heated at 375°C to 425°C for 2.5 to 10 hours without using a catalyst, and the yields of pretreated material, oil, and gas were determined. The results are shown in Table 6. These pretreated materials were tested for solubility in cetane. The results are shown in Table 7, where the "mixing ratio" refers to the weight ratio of added cetane to the weight of the pretreated material. The pretreated materials were also subjected to molecular weight analysis by gel permeation chromatography (GPC). The Q factor of polyethylene was 17.7, the Q factor of polypropylene was 26.4, and the Q factor of polystyrene was 41.3. The molecular weights calculated in terms of polystyrene by GPC were recalculated based on the ratio of the Q factors into polyethylene and polypropylene equivalents, respectively. The results are shown in Tables 7 and 8.

As can be seen from Table 7, both HDPE and LLDPE were reduced in molecular weight at 400°C, while PP was sufficiently reduced in molecular weight even at 375°C. Furthermore, Table 8 shows that the solubility of each plastic material in cetane was improved by heat treatment.

Claims (9)

A method for separating inorganic matter from waste plastic material containing plastic components and inorganic matter, comprising:
a heating step in which 100 parts by mass of waste plastic material is heated in an inert gas at a temperature of 330°C or higher and 420°C or lower for 1 hour or longer and 20 hours or shorter to fluidize the waste plastic material in 1,000 parts by mass or lower of hydrocarbon oil, thereby reducing the molecular weight of the plastic component;
a phase separation step of adding a highly polar solvent that is immiscible with the hydrocarbon oil to the waste plastic material fluidized in the hydrocarbon oil at a temperature in the range of 25°C to 250°C, thereby separating inorganic substances into phases ;
and
A method for separating inorganic substances from waste plastic materials, wherein the highly polar solvent is at least one selected from the group consisting of an organic solvent having at least one polar group selected from a hydroxyl group, an ether group, an ester group, a sulfoxyl group, a sulfonyl group, an amino group, an amide group, and a nitrile group, and having a boiling point of 120°C or higher; and water . 2. The method for separating inorganic substances from waste plastic materials according to claim 1, wherein the hydrocarbon oil contains 20% by volume to 100% by volume of hydrocarbons having 8 or more carbon atoms and a melting point of 150°C or less. After the heating step and prior to the phase separation step,
3. The method for separating inorganic substances from waste plastic material according to claim 1 or 2 , further comprising a filtration step of filtering the fluidized waste plastic material to separate coarse solid particles from the fluidized waste plastic material. 4. The method for separating inorganic substances from waste plastic materials according to claim 1 , wherein the plastic component comprises at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate ( PET ), and polyvinyl chloride (PVC). the waste plastic material comprises polyvinyl chloride;
5. The method for separating inorganic substances from waste plastic materials according to claim 4 , wherein hydrogen chloride is removed by vaporization in the heating step. the waste plastic material comprises polystyrene;
5. The method for separating inorganic substances from waste plastic materials according to claim 4 , wherein styrene monomer is vaporized and recovered in the heating step. 7. The method for separating inorganic substances from waste plastic material according to claim 1 , wherein the fluidized waste plastic material has a weight average molecular weight Mw of 1,000 or more and 8,000 or less. A method for regenerating plastic materials from waste plastic materials containing plastic components and inorganic substances, comprising:
a heating step in which 100 parts by mass of waste plastic material is heated in an inert gas at a temperature of 330°C or higher and 420°C or lower for 1 hour or longer and 20 hours or shorter to fluidize the waste plastic material in 1,000 parts by mass or lower of hydrocarbon oil, thereby reducing the molecular weight of the plastic component;
a phase separation step of adding a highly polar solvent that is immiscible with the hydrocarbon oil to the waste plastic material fluidized in the hydrocarbon oil at a temperature in the range of 25°C to 250°C, thereby separating inorganic substances into phases;
a recovery step of recovering the plastic component in the hydrocarbon oil;
a recycling step of recycling plastic materials from the recovered plastic components;
The method for regenerating plastic materials from waste plastic materials comprises: A method for producing a plastic material using waste plastic material containing plastic components and inorganic substances,
a heating step in which 100 parts by mass of waste plastic material is heated in an inert gas at a temperature of 330°C or higher and 420°C or lower for 1 hour or longer and 20 hours or shorter to fluidize the waste plastic material in 1,000 parts by mass or lower of hydrocarbon oil, thereby reducing the molecular weight of the plastic component;
a phase separation step of adding a highly polar solvent that is immiscible with the hydrocarbon oil to the waste plastic material fluidized in the hydrocarbon oil at a temperature in the range of 25°C to 250°C, thereby separating inorganic substances into phases;
a recovery step of recovering the plastic component in the hydrocarbon oil;
a plastic material production process for producing a plastic material from the recovered plastic components;
A method for producing a plastic material, comprising: