Treatment method and mixture

Abstract

To provide a treatment method which can efficiently decompose plastics in a short time and can effectively utilize the plastics, and to provide a mixture which can be suitably used for producing hydrogen gas and carbon nanotubes.SOLUTION: In the treatment method, a mixture containing a raw material containing plastics and a catalyst containing an iron-based catalyst is irradiated with microwaves to selectively heat and activate the iron-based catalyst, and the plastics are decomposed in the presence of the iron-based catalyst to produce hydrogen gas and carbon nanotubes. The iron-based catalyst preferably contains nanoparticles represented by FeAlOx. The raw material preferably contains waste plastic.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a processing method and a mixture. [Background technology]

[0002] Plastics are used in a variety of fields. Although the recycling rate of plastics has been increasing in recent years, there are still some plastics that are difficult to recycle, and such plastics are often disposed of in landfills, and therefore cannot be said to be being used effectively.

[0003] Therefore, technologies have been proposed for effectively utilizing plastic waste using various recycling facilities such as solvolysis facilities, thermal decomposition facilities, cracker facilities, partial oxidation gasification facilities, energy generation / energy production facilities, and solidification facilities (see, for example, Patent Document 1).

[0004] However, such technology has problems such as the need for very large facilities, difficulty in application to plastic waste that does not contain polyethylene terephthalate (PET), and a significant drop in processing efficiency when the plastic waste contains a high proportion of plastic components other than polyethylene terephthalate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2023-513571 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a processing method that can efficiently decompose plastics in a short time, enabling the effective use of plastics, and to provide a mixture that can be suitably used to produce hydrogen gas and carbon nanotubes. [Means for solving the problem]

[0007] Such an object can be achieved by the present invention described below. The processing method of the present invention is characterized in that microwaves are applied to a mixture containing a raw material including plastic and a catalyst including an iron-based catalyst, thereby selectively heating and activating the iron-based catalyst, and the plastic is decomposed in the presence of the iron-based catalyst to produce hydrogen gas and carbon nanotubes.

[0008] In the present invention, the iron-based catalyst is FeAlO x It is preferable that the nanoparticles include nanoparticles represented by the formula: In the present invention, the raw material preferably contains waste plastic.

[0009] In the present invention, the plastic preferably contains at least one selected from the group consisting of polyolefin resin, polyester resin, polycarbonate, and phenol resin.

[0010] In the present invention, it is preferable that the mixture further contains at least one selected from the group consisting of polyhydric alcohol compounds, water, hydrates, and hydroxides.

[0011] In the present invention, the polyhydric alcohol compound is preferably at least one selected from the group consisting of cellulose, sucrose, and polyvinyl alcohol.

[0012] In the present invention, the carbon nanotubes preferably include single-walled carbon nanotubes.

[0013] The mixture of the present invention is a mixture used to produce hydrogen gas and carbon nanotubes from raw materials including plastics, The method is characterized by including the raw material, a catalyst including an iron-based catalyst, and at least one selected from the group consisting of a polyhydric alcohol compound, water, a hydrate, and a hydroxide. [Effects of the Invention]

[0014] According to the present invention, a processing method can be provided that can efficiently decompose plastics in a short time, enabling the effective use of plastics, and a mixture that can be suitably used to produce hydrogen gas and carbon nanotubes can be provided. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a gas chromatogram of the product (gas) obtained in the first cycle in Examples 1, 3, 5 and 11. [Figure 2] FIG. 2 shows Raman spectra of the products (solids) obtained in each cycle in Examples 1 and 3. [Figure 3] FIG. 3 is an electron microscope photograph of the product (solid) obtained in the 10th cycle in Examples 1 and 2. [Figure 4] FIG. 4 is an electron microscope photograph of the product (solid) obtained in the fifth cycle in Examples 5, 7, 9 and 11. [Figure 5] FIG. 5 is a graph showing the hydrogen gas conversion rate in each cycle in Examples 1 to 4. [Figure 6] FIG. 6 is a graph showing the hydrogen gas conversion rate in each cycle in Examples 5 and 6. [Figure 7] FIG. 7 is a diagram showing the concentrations of gas components contained in the generated gas in each cycle in Example 5. [Figure 8] FIG. 8 is a diagram showing the concentrations of gas components contained in the generated gas in each cycle in Example 6. [Figure 9] FIG. 9 is a graph showing the hydrogen gas conversion rate in each cycle in Examples 7 and 8. [Figure 10]FIG. 10 is a diagram showing the concentrations of gas components contained in the generated gas in each cycle in Example 7. [Figure 11] FIG. 11 is a diagram showing the concentrations of gas components contained in the generated gas in each cycle in Example 8. [Figure 12] FIG. 12 is a graph showing the hydrogen gas conversion rate in each cycle in Example 15 together with the hydrogen gas conversion rate in each cycle in Examples 1 and 3. [Figure 13] FIG. 13 is a graph showing the hydrogen gas conversion rate in each cycle in Example 16. [Figure 14] FIG. 14 is a diagram showing the concentrations of gas components contained in the generated gas in each cycle in Example 16. [Figure 15] FIG. 15 shows XRD spectra of the products (solids) obtained in each cycle in Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described in detail below. It should be noted that the measurements and treatments described in this specification were carried out at room temperature (23°C) unless otherwise specified.

[0017] [1] Processing method The processing method of the present invention is characterized by irradiating a mixture containing a raw material including plastic and a catalyst including an iron-based catalyst with microwaves, thereby selectively heating and activating the iron-based catalyst, and decomposing the plastic in the presence of the iron-based catalyst to produce hydrogen gas and carbon nanotubes.

[0018] By irradiating a mixture containing a plastic and an iron-based catalyst with microwaves, it is possible to selectively heat a specific substance in the mixture, more specifically, the iron-based catalyst.

[0019] When heated by microwaves, the iron-based catalyst becomes more active as a catalyst, and heat conduction effectively heats the plastic in the mixture around the iron-based catalyst. When heated, the plastic undergoes thermal decomposition; in other words, the heat breaks the carbon-hydrogen bond, producing hydrogen and atomic carbon. This carbon precipitates and grows on the surface of the iron-based catalyst particles, producing carbon nanotubes.

[0020] In particular, by selectively heating an iron-based catalyst with microwaves, a temperature difference is created between the catalyst portion and the surrounding plastic portion. In other words, the catalyst portion is hotter and the plastic portion is cooler than the catalyst portion. This temperature difference between the catalyst portion and the plastic portion creates a temperature non-equilibrium state, accelerating the thermal decomposition reaction of the plastic. This allows the thermal decomposition reaction of plastic to be carried out efficiently in a short time.

[0021] Microwaves can be used to directly heat the iron-based catalyst with electromagnetic energy, providing the thermal energy required for the catalytic reaction, thereby accelerating the catalytic reaction. In particular, the temperature in the vicinity of the iron-based catalyst, where the thermal decomposition reaction of plastics is likely to proceed, can be efficiently increased, while the temperature in the area away from the iron-based catalyst, where the thermal decomposition reaction of plastics is less likely to proceed, can be prevented from being increased more than necessary, thereby improving the overall energy efficiency of the thermal decomposition reaction of plastics. In other words, the total energy required to promote the thermal decomposition reaction of plastics can be reduced. Furthermore, by directly and selectively heating the iron-based catalyst with microwaves, the temperature of the entire mixture can be kept lower than when the entire mixture is heated.

[0022] In addition, adjusting the microwave output and heating time makes it easier to control the temperature of the iron-based catalyst.

[0023] In addition, the application of microwave heating as a source of thermal energy will contribute significantly to reducing CO2 emissions during heating processes, i.e., decarbonization (carbon neutrality).

[0024] As described above, the processing method of the present invention can decompose raw materials including plastics efficiently in a short time, and instead of disposing of them or simply recycling them as in the past, it becomes possible to simultaneously produce hydrogen gas, which is attracting attention as a fuel, and carbon nanotubes, which are expected to be next-generation materials. In other words, highly effective use of plastics becomes possible.

[0025] The excellent effects of the present invention can be obtained by the processing method having the above-mentioned configuration, and cannot be obtained if the processing method does not have the above-mentioned configuration.

[0026] For example, if the catalyst does not contain an iron-based catalyst, irradiating the mixture with microwaves will not selectively heat and activate the catalyst, and the thermal decomposition reaction of the plastic will not proceed sufficiently.

[0027] Furthermore, for example, if the mixture is heated by a method other than microwave irradiation, the catalyst cannot be selectively heated and activated, and the thermal decomposition reaction of the plastic cannot proceed smoothly.

[0028] Furthermore, when a catalyst other than an iron-based catalyst is used instead of an iron-based catalyst, the above-mentioned microwave-assisted catalytic reaction cannot be favorably promoted. For example, when a nickel-based catalyst is used instead of an iron-based catalyst, the catalyst cannot be selectively heated by microwaves, and the above-mentioned temperature non-equilibrium state cannot be favorably promoted. For example, even when a nickel-based catalyst is used, it is possible to heat the catalyst by placing a member made of a material that favorably absorbs microwaves (e.g., silicon carbide) in contact with the catalyst. However, in such a case, the catalyst is indirectly heated by heat conduction from the member, and is not selectively or directly heated. Therefore, the above-mentioned temperature non-equilibrium state cannot be achieved, and therefore the above-mentioned temperature non-equilibrium state cannot be favorably promoted.

[0029] [1-1]Mixture The mixture includes a raw material including a plastic and a catalyst including an iron-based catalyst.

[0030] [1-1-1] Raw materials containing plastic Examples of plastics include polyethylenes such as low-density polyethylene, linear polyethylene, medium-density polyethylene, high-density polyethylene, and very low-density polyethylene; polypropylenes such as random copolymer polypropylene, block copolymer polypropylene, and homopolypropylene; polyolefin resins such as polybutene, polybutadiene, and polymethylpentene; ionomers such as ethylene-vinyl acetate copolymers, zinc ion crosslinkers, and sodium ion crosslinkers; olefin copolymers such as ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid ester (random, alternating) copolymers, ethylene-propylene copolymers, ethylene-butene copolymers, and ethylene-hexene copolymers; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polybutylene naphthalate; polyurethanes; polyimides; polyamides; polyether ketones such as polyether ether ketones; polyethersulfones; and polystyrenes. Examples of suitable materials include fluororesins such as poly(tetrafluoroethylene) homopolymer (PTFE), poly(hexafluoroethylene), poly(tetrafluoroethylene-hexafluoroethylene), and poly(tetrafluoroethylene-ethylene-propylene); chlorinated resins such as chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, polyvinyl chloride, and polyvinylidene chloride; thermoplastic resins such as acrylonitrile-butadiene-styrene copolymer (ABS resin), silicone resin, cellulose resin, (meth)acrylic resin, polyester-based thermoplastic elastomer, polyvinyl isoprene, polycarbonate, polyacetal, polyphenylene oxide, and polyphenylene sulfide; and thermosetting resins such as polyimide resin, polyamide resin, epoxy resin, phenolic resin, amino resin, unsaturated polyester resin, cation exchange resins mainly containing sulfonic acid groups, Nafion, anion exchange resins mainly containing quaternary ammonium groups, and thermosetting elastomers. Biomass-derived plastics are also acceptable.

[0031] The raw material containing plastic used in the present invention can suitably contain at least one of the above materials.

[0032] The raw material containing plastic used in the present invention preferably contains at least one selected from the group consisting of polyolefin resin, polyester resin, polycarbonate and phenol resin. This makes it possible to more suitably obtain hydrogen gas and carbon nanotubes.

[0033] In particular, when the raw material containing plastic used in the present invention contains a polyolefin resin, since the polyolefin resin does not contain oxygen O as a constituent element, when the reaction is carried out in an atmosphere that is substantially free of oxygen (for example, an atmosphere in which the partial pressure of oxygen is 0.1 kPa or less), it is possible to suitably prevent carbon C from being emitted as a greenhouse gas, and to produce a larger number of carbon nanotubes.

[0034] However, if the plastic does not contain oxygen (O) as a constituent element, the reduction action in the hydrogen generation reaction and the action of the carbon (C) produced will consume the oxygen derived from the catalyst under high temperature conditions exceeding 600°C, making it easier for the iron-based catalyst to carbonize and undergo reduction reactions. Therefore, it is preferable to use an iron-based catalyst reduction inhibitor, as described below, in combination.

[0035] When the plastic-containing raw material used in the present invention contains a polyester resin, oxygen O is included as a constituent element, and therefore the carbonization reaction and reduction reaction of the iron-based catalyst can be suitably prevented, and the catalytic activity can be suitably maintained for a longer period of time.

[0036] Furthermore, when the plastic-containing raw material used in the present invention contains polycarbonate, oxygen O is included as a constituent element, and therefore the carbonization reaction and reduction reaction of the iron-based catalyst can be suitably prevented, and the catalytic activity can be suitably maintained for a longer period of time.

[0037] Furthermore, when the plastic-containing raw material used in the present invention contains a thermosetting resin, the following effects can be obtained. That is, thermosetting resins are more difficult to recycle than thermoplastic resins, and have traditionally been incinerated or disposed of in landfills. However, in the present invention, even when a thermosetting resin is used as the plastic, hydrogen gas and carbon nanotubes can be efficiently produced. In other words, since the present invention can effectively utilize even thermosetting resins, the effects of the present invention are more pronounced when the plastic-containing raw material used in the present invention contains a thermosetting resin.

[0038] In particular, when the plastic-containing raw material used in the present invention contains a phenolic resin, oxygen O is included in the constituent elements, so that the carbonization reaction and reduction reaction of the iron-based catalyst can be suitably prevented, and the catalytic activity can be suitably maintained for a longer period of time.

[0039] The plastic-containing raw material used in the present invention is not particularly limited, but preferably includes waste plastics such as plastic products discarded after use, plastic dregs generated during the manufacturing process, and waste containing plastic as the main component.

[0040] Although some waste plastics have been recycled, products containing recycled waste plastics generally have inferior properties compared to those made from virgin resin materials and are not suitable for producing high-value-added products. Furthermore, waste plastics can sometimes contain relatively high levels of impurities, making the above-mentioned problems more pronounced. In contrast, the present invention can utilize waste plastics as a raw material for high-value carbon nanotubes and hydrogen gas, which is highly useful as a carbon dioxide-free fuel or a raw material for chemical synthesis. Therefore, the effects of the present invention are more pronounced when the plastic-containing raw material used in the present invention contains waste plastics.

[0041] When using waste plastics as raw materials containing plastics, it is preferable to pretreat the raw materials, such as by washing, removing impurities, crushing, cutting, etc. This allows the thermal decomposition reaction of the plastic to proceed more efficiently.

[0042] The raw material containing plastic may be contained in any form in the mixture. More specifically, the raw material containing plastic may be contained in the mixture in the form of, for example, a sheet, a strip, a pellet, a powder, a fiber, a fabric, or the like.

[0043] The content of plastic in the raw material containing plastic is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0044] This makes it possible to suppress the amount of undesired products produced and to suppress the amount of unreacted components remaining after carrying out the treatment method of the present invention.

[0045] The plastic content in the mixture is preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 80% by mass or less, and even more preferably 30% by mass or more and 70% by mass or less. This allows the desired reaction to proceed more efficiently.

[0046] [1-1-2] Catalyst The catalyst preferably comprises, and is preferably composed primarily of, an iron-based catalyst. This makes it possible to more significantly exhibit the above-described effects of the present invention.

[0047] In this specification, the term "mainly" refers to the component that has the highest content among the target components.

[0048] Iron-based catalysts have two main roles in the thermal decomposition of plastics: they function as a catalyst to decompose the constituent molecules of plastics on their surfaces, and as a heating element that effectively absorbs microwaves and converts their energy into heat.

[0049] This allows the entire mixture to heat faster and more evenly, resulting in fewer by-products being produced from the thermal decomposition of the plastic.

[0050] The iron-based catalyst may be any catalyst containing Fe, but FeAlO x It is preferable that the nanoparticles include nanoparticles represented by the formula:

[0051] This allows the iron-based catalyst to be more selectively and efficiently heated and activated by microwave irradiation, allowing the thermal decomposition reaction of plastics to proceed more favorably.

[0052] Furthermore, because the catalyst is nanoparticles, carbon nanotubes grow from each nano-sized catalyst particle, so carbon nanotubes can be produced efficiently even with a small amount of catalyst particles used. Furthermore, because nano-sized catalyst particles are used, the surface area per unit amount of catalyst particles used is large. Therefore, carbon nanotubes can be produced efficiently.

[0053] Such FeAlO x The nanoparticles represented by the formula (I) can be synthesized by the sol-gel method using, for example, Fe(NO3)3·9H2O, Al(NO3)3·9H2O, and citric acid as raw materials.

[0054] In this specification, the term "nanoparticles" refers to particles having an average particle size of 1 nm to 100 nm, the average particle size being determined by dynamic light scattering.

[0055] The catalyst may be contained in the mixture in any form. More specifically, the catalyst may be contained in the mixture in the form of, for example, a sheet, a strip, a pellet, or a powder.

[0056] In the mixture, the ratio of the raw material containing plastic to the iron-based catalyst is, by mass, raw material containing plastic: catalyst (FeAlO x ) is preferably 1:2 or more and 6:2 or less.

[0057] This allows the entire mixture to be heated more quickly and more uniformly, allowing the thermal decomposition reaction of the plastic to proceed more efficiently.

[0058] [1-1-3] Iron-based catalyst reduction inhibitor The mixture used in the processing method of the present invention may contain a raw material containing plastic and a catalyst containing an iron-based catalyst, and may further contain an iron-based catalyst reduction inhibitor, which is at least one selected from the group consisting of polyhydric alcohol compounds, water, hydrates, and hydroxides. In other words, the mixture of the present invention (a mixture used to produce hydrogen gas and carbon nanotubes from a raw material containing plastic) may contain the raw material, a catalyst containing an iron-based catalyst, and at least one iron-based catalyst reduction inhibitor, which is selected from the group consisting of polyhydric alcohol compounds, water, hydrates, and hydroxides.

[0059] This provides the following effects: In other words, by heating the iron-based catalyst with microwaves, the temperature of the iron-based catalyst rises to several hundred degrees Celsius. x When iron-based oxides such as those mentioned above are contained in a catalyst, repeated microwave heating can reduce and even carbonize the iron-based oxides at high temperatures. If this phenomenon progresses, the catalytic activity will decrease significantly.

[0060] In contrast, by adding at least one selected from the group consisting of polyhydric alcohol compounds, water, hydrates, and hydroxides to the mixture, the oxidation state of the iron-based catalyst can be favorably maintained, catalyst degradation can be suppressed, and catalytic activity can be stably maintained at an excellent level over a long period of time. Furthermore, the catalyst life is extended, which is advantageous in terms of cost. The reason for this effect is believed to be as follows: By adding at least one selected from the group consisting of polyhydric alcohol compounds, water, hydrates, and hydroxides to the mixture, oxygen atoms (O) are present around the iron-based oxide, preventing the thermal reduction of the iron-based oxide and maintaining the oxidation state. In particular, adding at least one selected from the group consisting of polyhydric alcohol compounds, hydrates, and hydroxides can stably exhibit the function of preventing reduction.

[0061] In particular, since polyhydric alcohols contain hydrogen atoms (H) and carbon atoms (C) in addition to oxygen atoms (O), polyhydric alcohols themselves can function as raw materials for hydrogen gas and carbon nanotubes, as well as plastics.

[0062] In this specification, the term "polyhydric alcohol compound" refers to a compound having multiple alcoholic hydroxyl groups in the molecule, but does not include the plastics mentioned above.

[0063] Typical examples of polyhydric alcohol compounds include sugars, polyphenols, and polyvinyl alcohol polymers. Examples of sugars include the monosaccharide glucose, the disaccharide sucrose, fructose, and maltose, the oligosaccharide raffinose and dextrin, and the polysaccharide cellulose, hemicellulose, starch, and pectin. Examples of polyphenols include catechin, persimmon tannin, phenolic resin, and bituminous coal. Examples of polyvinyl alcohol polymers include polyvinyl alcohol and vinylon. One or a combination of two or more selected from these can be used, but at least one selected from the group consisting of cellulose, sucrose, and polyvinyl alcohol is preferred. This makes it possible to more significantly exhibit the above-mentioned effects.

[0064] Among polyhydric alcohols, cellulose is the main component of plant cell walls and plant fibers and is widely found in plant-derived materials, particularly in cotton, hemp, and wood, making it the most abundant biomass on Earth. Cellulose is also found in waste products made from plant-derived materials (e.g., paper products, building materials, etc.), inedible parts of plants such as grains and vegetables, food waste, and weeds. Effective utilization of this abundant cellulose is extremely important from the perspective of the SDGs and other goals.

[0065] As the raw material containing cellulose, it is preferable to use, for example, plants, products produced from plants, waste paper, livestock excrement, food waste, wood generated from construction, or waste containing sewage sludge.

[0066] This will reduce waste and CO2 emissions during waste incineration, thereby easing the burden on the environment.

[0067] When using the above waste materials as a raw material containing cellulose, it is preferable to subject the raw material to pretreatment, such as washing, removal of impurities, and cutting. This allows the thermal decomposition reaction of cellulose to proceed more efficiently.

[0068] The cellulose-containing raw material may contain components other than cellulose as a chemical substance (compound), such as hemicellulose and lignin.

[0069] For example, when wood is used as a raw material containing cellulose, the wood contains hemicellulose and lignin in addition to cellulose, which is the main component.

[0070] Hemicellulose is not a single compound, but a general term for polysaccharides extracted from plants with alkali, and has a more complex structure than cellulose. Hemicellulose binds cellulose fibers and mediates the bond with lignin.

[0071] Although the details of lignin are not fully understood, it has a very complex chemical structure. Lignin is the main component of wood and acts as an adhesive between cells.

[0072] In a raw material containing cellulose and lignin, if the proportion of cellulose is high, the amount of hydrogen gas produced increases but the amount of carbon nanotubes produced decreases, whereas if the proportion of lignin is high, the amount of carbon nanotubes produced increases but the amount of hydrogen gas produced decreases.

[0073] In this way, by adjusting the ratio of cellulose to lignin, it is possible to adjust the production ratio of hydrogen gas and carbon nanotubes.

[0074] More specifically, for example, by using chemical pulp (including waste paper, etc.) from which lignin has been removed by refining as a raw material containing cellulose, and applying the processing method of the present invention, hydrogen gas can be obtained more efficiently.

[0075] Furthermore, carbon nanotubes can be obtained more efficiently by mixing lignin removed during the chemical pulp production process with raw materials with a high cellulose content, such as wood, waste paper, and scraps of paper products, to produce a mixture with an increased lignin content. In particular, although some of the lignin removed during the chemical pulp production process is used as fuel (lignin-containing waste liquid), as a raw material for vanillin flavoring, or as a component of adhesives, it cannot be said that it is being fully utilized. Being able to suitably utilize such lignin for the production of higher-value-added carbon nanotubes is a major advantage.

[0076] When the cellulose-containing raw material also contains lignin, the mass ratio of cellulose:lignin is preferably 75:25 or more and 25:75 or less.

[0077] This makes it possible to make both the amount of hydrogen gas produced and the amount of carbon nanotubes produced suitable.

[0078] The cellulose-containing raw material may be contained in any form in the mixture. More specifically, the cellulose-containing raw material may be contained in the mixture in the form of, for example, a sheet, a strip, a pellet, a powder, or the like. The cellulose-containing raw material may also be contained in a defibrated state.

[0079] When the mixture used in the treatment method of the present invention contains cellulose, the ratio of cellulose to plastic, by mass, is preferably cellulose:plastic = 30:70 or more and 95:5 or less, more preferably cellulose:plastic = 40:60 or more and 90:10 or less, and even more preferably cellulose:plastic = 50:50 or more and 85:15 or less.

[0080] This makes it possible to make the above-mentioned effects more pronounced, and in particular to improve the amount of carbon nanotubes produced.

[0081] By including water in the mixture, for example, carbon adhering to the catalyst surface can be removed, keeping the catalyst surface clean and extending its life.

[0082] In particular, by including water in the mixture together with the polyhydric alcohol compound as described above, the evaporation of water during microwave heating can be effectively suppressed, and the above-mentioned effects can be more significantly exhibited.

[0083] Examples of the hydrates include iron(III) oxide monohydrate. Examples of the hydroxide include iron (II) hydroxide, iron (III) hydroxide, and aluminum hydroxide, and one or more selected from these can be used in combination.

[0084] The polyhydric alcohol compound, hydrate, and hydroxide may be contained in the mixture in any form, more specifically, the polyhydric alcohol compound, hydrate, and hydroxide may be contained in the mixture in the form of, for example, a sheet, a strip, a pellet, a powder, or a fiber.

[0085] Many plastics contain less oxygen atoms (O) than iron-based catalyst reduction-inhibitors. Therefore, when the mixture used in the treatment method of the present invention contains a large amount of plastic, the reduction of the iron-based catalyst, in other words, deterioration of the iron-based catalyst, is more likely to progress, and the effect of using an iron-based catalyst reduction-inhibitor is more pronounced.

[0086] More specifically, when the plastic content in the mixture used in the treatment method of the present invention is 75 mass % or more, the effect of using an iron-based catalyst reduction inhibitor is more pronounced.

[0087] In the mixture, the mass ratio of the plastic-containing raw material to the iron-based catalyst reduction inhibitor is preferably 25:75 or more and 75:25 or less. This makes the above-mentioned effects more pronounced.

[0088] [1-1-4] Other ingredients The mixture may also contain components other than those mentioned above. However, the content of components other than those mentioned above in the mixture used in the treatment method of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0089] [1-2] Microwave When microwaves are irradiated onto the mixture, the iron-based catalyst contained in the mixture is directly and selectively heated and activated.

[0090] By using microwaves, it is not necessary to heat the entire reaction vessel in which the reaction is carried out to a high temperature, which makes it possible to simplify the process and the equipment and make them less expensive, and also allows for more efficient use of energy, which is preferable from the viewpoints of energy conservation and reducing the environmental load.

[0091] The frequency of microwaves is generally between 300 MHz and 300 GHz, but it is preferable to use a frequency band permitted for industrial use as the ISM band (Industrial Scientific and Medical Band), and the peak frequency is preferably between 900 MHz and 30 GHz, more preferably between 2.40 GHz and 2.50 GHz, and even more preferably 2.45 GHz.

[0092] This makes it possible to suppress deterioration of the iron-based catalyst due to heat, while also allowing the catalyst to be sufficiently heated and activated, allowing the thermal decomposition reaction of plastics and the like to proceed more efficiently.

[0093] The microwave output per unit mass of the mixture is preferably 10 W / g or more and 1500 W / g or less, more preferably 100 W / g or more and 850 W / g or less, and even more preferably 300 W / g or more and 750 W / g or less.

[0094] This makes it possible to suppress deterioration of the iron-based catalyst due to heat, while also allowing the catalyst to be sufficiently heated and activated, allowing the thermal decomposition reaction of plastics and the like to proceed more efficiently.

[0095] The heating time using microwaves is preferably from 30 seconds to 30 minutes, more preferably from 1 minute to 20 minutes, and even more preferably from 3 minutes to 10 minutes.

[0096] The temperature of the mixture during microwave irradiation is preferably 100°C or higher and 1200°C or lower, more preferably 300°C or higher and 900°C or lower, and even more preferably 400°C or higher and 700°C or lower.

[0097] This allows the catalyst to be sufficiently heated and activated while suppressing thermal degradation of the iron-based catalyst, allowing the thermal decomposition reaction of plastics, etc. to proceed more efficiently, improving the yield of hydrogen and carbon nanotubes, and more effectively preventing the processing time from becoming longer than necessary and reducing the productivity of hydrogen and carbon nanotubes.

[0098] The mixture may be irradiated with microwaves in either single mode or multimode, but multimode irradiation is preferred.

[0099] Compared with single-mode microwave irradiation, multi-mode microwave irradiation allows for easier catalyst temperature management and microwave output control, making it easier to maintain stable pyrolysis reactions of plastics, etc. Furthermore, multi-mode microwave irradiation allows for the processing of many mixtures at once, and also makes the mixtures and products easier to handle.

[0100] Furthermore, when irradiating the mixture with microwaves, if the atmosphere contains flammable gases such as hydrogen and oxidizing gases such as air and oxygen when carbon nanotubes are produced, the quality and yield of the product will decrease until the oxygen is consumed by the combustion reaction. Therefore, it is preferable to irradiate the mixture with microwaves in an inert gas atmosphere, replacing the atmosphere with an inert gas such as nitrogen, helium, neon, argon, or carbon dioxide.

[0101] This allows the carbon nanotubes to grow smoothly, and also makes it possible to easily recover the hydrogen gas and carbon nanotubes as products from the residue after the reaction.

[0102] Microwave irradiation may be carried out in multiple steps. In such a case, it is preferable that the sum of the times of the multiple microwave treatments satisfies the above-mentioned condition for the microwave heating time.

[0103] Furthermore, the microwave irradiation conditions (for example, microwave frequency, output, mode, and atmosphere during microwave irradiation) may be changed midway.

[0104] For example, when irradiating the mixture with microwaves, the microwave irradiation conditions may be constant, or the microwave irradiation conditions may be controlled so that the temperature rise rate and heating temperature of the mixture are constant.

[0105] Furthermore, the mixture may be subjected to a treatment such as stirring during microwave irradiation or between multiple microwave irradiation treatments.

[0106] [1-3] Treatment of residues after microwave irradiation After the mixture is heated, the residue in the reaction vessel may be washed with an acid or the like.

[0107] This allows the carbon nanotubes to be recovered in a suitable manner. In particular, by performing acid washing, catalyst particles adhering to the outside of the carbon nanotubes can be easily and reliably dissolved and removed, thereby increasing the purity of the carbon nanotubes.

[0108] Furthermore, when the carbon nanotubes produced by the processing method of the present invention include single-walled carbon nanotubes as described below, the purity of the single-walled carbon nanotubes can be suitably increased by using an organic solvent such as N-methyl-2-pyrrolidone (NMP) or benzene.

[0109] [2] Product Next, the product obtained by the treatment method of the present invention will be described.

[0110] The products obtained by the treatment method of the present invention include a product gas containing hydrogen gas and carbon nanotubes. Because the produced hydrogen is gaseous and the carbon nanotubes are solid, they can be suitably separated and recovered without complex treatment.

[0111] [2-1] Carbon nanotubes Carbon nanotubes are seamless cylindrical materials made from graphene. Generally, single-walled carbon nanotubes are those with a single layer of cylinder, while multi-walled carbon nanotubes are those with multiple cylinders of different diameters stacked in layers.

[0112] In particular, the carbon nanotubes obtained by the treatment method of the present invention preferably include single-walled carbon nanotubes.

[0113] Single-walled carbon nanotubes have been attracting attention as an extremely superior material, exhibiting significantly higher performance than multi-walled carbon nanotubes, for example, being lightweight with a density half that of aluminum, yet 20 times stronger than steel, 10 times more thermally conductive than copper, and 1,000 times more electrically conductive than copper. For example, single-walled carbon nanotubes are highly transparent and have excellent electrical conductivity, making them suitable for use in transparent conductive films, etc.

[0114] Furthermore, such single-walled carbon nanotubes are soluble in organic solvents such as N-methyl-2-pyrrolidone (NMP) and benzene, and can therefore be easily extracted and purified from a product obtained as a mixture of multiple compounds.

[0115] This makes it possible to obtain single-walled carbon nanotubes of higher purity and better quality, and thus makes them even more valuable.

[0116] According to the present invention, as described above, by optimizing the various conditions in the treatment method, it is possible to obtain such high-quality single-walled carbon nanotubes in high yield.

[0117] [2-2] Produced gas The product gas obtained by the treatment method of the present invention contains hydrogen gas (H2).

[0118] The product gas obtained by the treatment method of the present invention may contain other gas components in addition to hydrogen gas. Such gas components include, for example, carbon monoxide gas (CO).

[0119] Hydrogen gas can be suitably used, for example, as a clean fuel that does not emit carbon dioxide. Hydrogen can also be suitably used, for example, as a reducing agent or a raw material for various chemical syntheses.

[0120] Carbon monoxide gas can also be suitably used as a raw material for synthesizing chemical products such as alcohols and carboxylic acids, and plastics such as polycarbonate.

[0121] Hydrogen and carbon monoxide may also be used in applications such as SynGas, methanation, etc.

[0122] SynGas is a mixture of hydrogen and carbon monoxide, and is a basic feedstock in C1 chemistry, as well as being used as jet fuel and fuel for power generation.

[0123] Methanation is a technology that synthesizes methane (CH4) by reacting carbon monoxide with hydrogen, and can be carried out using conventional natural gas facilities as is.

[0124] The gas components contained in the produced gas may be separated as needed. Examples of methods for separating the gas components contained in the produced gas include cryogenic separation, adsorption separation, and membrane separation.

[0125] Cryogenic separation is a method of fractionating a mixed gas by cooling it to a low temperature of around -200°C. With cryogenic separation, since the boiling points of each gas component in the mixed gas are different (H2: -252.9°C, CO: -191.5°C), multiple gas components can be separated and recovered.

[0126] Adsorption separation is a method of removing specific gas components (for example, carbon monoxide gas) using a porous adsorbent, and can be carried out by a relatively simple process. Examples of porous adsorbents include activated carbon, zeolite, and metal catalysts.

[0127] Furthermore, the pressure swing adsorption (PSA) method makes it possible to concentrate and extract specific gas components (such as carbon monoxide gas) through a pressurization and decompression process.

[0128] Membrane separation is a method of separating a specific gas component (e.g., hydrogen gas) from a mixed gas using a metal membrane or a polymer membrane, thereby separating that gas component from other gas components (e.g., other carbon monoxide gases).

[0129] As explained above, according to the processing method of the present invention, carbon nanotubes can be obtained without the need for expensive equipment such as a CVD apparatus, etc. Furthermore, by simply heating a mixture of raw materials containing plastic and a catalyst containing an iron-based catalyst with microwaves, solid plastic can be thermally decomposed to produce hydrogen gas and carbon nanotubes.

[0130] In other words, the processing method of the present invention can also be applied as a method for producing hydrogen gas and carbon nanotubes.

[0131] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these.

[0132] For example, the processing method of the present invention may include processing other than that described above (for example, pre-processing, intermediate processing, post-processing, etc.). [Example]

[0133] The present invention will be described in detail below based on specific examples, but the present invention is not limited thereto. Treatments and measurements in the following examples, for which no temperature conditions are specified, were carried out at room temperature (23°C).

[0134] [3] Processing of raw materials containing plastics The plastic-containing raw material was treated as follows.

[0135] Example 1 High-density polyethylene (HDPE) as plastic: 2.0 g, and FeAlO as iron-based catalyst x Nanoparticles represented by the formula: 2.0 g were weighed and mixed to obtain a mixture.

[0136] The resulting mixture was sealed in a quartz test tube. The mixture was fixed by sandwiching it between quartz wool from above and below. After creating a nitrogen gas atmosphere inside the test tube, the tube was capped with a silicone rubber stopper.

[0137] The sample prepared above was heated by microwave irradiation. Microwave irradiation was performed using a Shikoku Instruments Co., Ltd. "μReactor Ex" microwave heating device in multimode. The microwave frequency was 2.45 GHz. First, the microwave output was controlled to maintain a constant heating rate (approximately 60°C / min) until the mixture temperature rose from 100°C to 700°C. After that, the microwave output was controlled to maintain the mixture at 700°C for 20 minutes. The mixture was then allowed to cool to 100°C.

[0138] The above thermal cycle was counted as one cycle and this cycle was repeated 10 times. From the second cycle onwards, 2.0 g of HDPE (raw material for hydrogen and carbon nanotubes) was further added to the product obtained in the previous cycle, and the heat treatment was repeated under the same conditions.

[0139] Example 2 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.5 g of high-density polyethylene (HDPE) as plastic, 0.5 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 1, except that a mixture of 1.5 g of HDPE and 0.5 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0140] Example 3 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of high-density polyethylene (HDPE) as plastic, 1.0 g of cellulose, and FeAlO as an iron-based catalyst. xThe treatment was carried out in the same manner as in Example 1, except that a mixture of 1.0 g of HDPE and 1.0 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0141] Example 4 The mixture to be subjected to microwave irradiation in the first cycle consisted of 0.5 g of high-density polyethylene (HDPE) as plastic, 1.5 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 1, except that a mixture of 0.5 g of HDPE and 1.5 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0142] Example 5 The mixture subjected to microwave irradiation in the first cycle consisted of 2.0 g of polycarbonate (PC) as plastic and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 1, except that a mixture of 2.0 g of nanoparticles represented by the formula (I) and 2.0 g of PC was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0143] Example 6 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of polycarbonate (PC) as plastic, 1.0 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 1, except that a mixture of 1.0 g of PC and 1.0 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0144] Example 7 The mixture subjected to microwave irradiation in the first cycle consisted of 2.0 g of polypropylene (PP) as plastic and FeAlO as an iron-based catalyst.x The treatment was carried out in the same manner as in Example 1, except that a mixture of 2.0 g of nanoparticles represented by the formula (I) and 2.0 g of PP was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards, and the number of thermal cycle repetitions was changed from 10 to 5.

[0145] Example 8 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of polypropylene (PP) as plastic, 1.0 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 1.0 g of PP and 1.0 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0146] Example 9 The mixture to be subjected to microwave irradiation in the first cycle consisted of 2.0 g of polyethylene terephthalate (PET) as plastic and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 2.0 g of nanoparticles represented by the formula (I) and 2.0 g of PET was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0147] Example 10 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of polyethylene terephthalate (PET) as plastic, 1.0 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 1.0 g of PET and 1.0 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0148] Example 11 The mixture subjected to microwave irradiation in the first cycle consisted of 2.0 g of phenolic resin (PF) as plastic and FeAlO as iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 2.0 g of nanoparticles represented by the formula (I) and 2.0 g of PF was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0149] Example 12 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of phenolic resin (PF) as plastic, 1.0 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 1.0 g of PF and 1.0 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0150] Example 13 The mixture to be subjected to microwave irradiation in the first cycle consisted of 2.0 g of polyvinyl chloride (PVC) as plastic and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 2.0 g of nanoparticles represented by the formula (I) and 2.0 g of PVC was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0151] Example 14 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of polyvinyl chloride (PVC) as plastic, 1.0 g of cellulose, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 7, except that a mixture of 1.0 g of PVC and 1.0 g of cellulose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0152] Example 15 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of high-density polyethylene (HDPE) as plastic, 1.0 g of sucrose as an iron-based catalyst reduction inhibitor, and FeAlO as an iron-based catalyst. x The treatment was carried out in the same manner as in Example 1, except that a mixture of 1.0 g of HDPE and 1.0 g of sucrose was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards, and the number of thermal cycle repetitions was changed from 10 to 3.

[0153] Example 16 The mixture to be subjected to microwave irradiation in the first cycle consisted of 1.0 g of high density polyethylene (HDPE) as plastic, 1.0 g of polycarbonate (PC) as plastic, and FeAlO as iron-based catalyst. x The treatment was carried out in the same manner as in Example 15, except that a mixture of 1.0 g of HDPE and 1.0 g of PC was used as the "raw material for hydrogen and carbon nanotubes" added from the second cycle onwards.

[0154] Example 17 Waste plastic: 2.0 g and FeAlO as an iron-based catalyst x The nanoparticles represented by the formula: 2.0 g were weighed and mixed to obtain a mixture. The waste plastic used in this example contained 46 mass % polyethylene (PE) and 48 mass % polypropylene (PP).

[0155] The resulting mixture was sealed in a quartz test tube. The mixture was fixed by sandwiching it between quartz wool from above and below. After creating a nitrogen gas atmosphere inside the test tube, the tube was capped with a silicone rubber stopper.

[0156] The sample prepared above was heated by microwave irradiation. Microwave irradiation was performed using a Shikoku Instruments Industry Co., Ltd. "μReactor Ex" microwave heating device in multimode. The microwave frequency was 2.45 GHz. First, the microwave output was controlled to maintain a nearly constant heating rate (approximately 60°C / min) until the mixture temperature rose from 100°C to 700°C. After that, the microwave output was controlled so that the mixture maintained 700°C for 20 minutes. The material was then allowed to cool to room temperature.

[0157] [4] Analysis The products obtained by the treatment methods of the above examples were subjected to the following analyses.

[0158] [4-1] Analysis by gas chromatography The products obtained by the treatment methods of the above examples were analyzed by gas chromatography.

[0159] Gas chromatography was performed using a Shimadzu GC-2014. Argon gas was used as the carrier gas, the flow rate was 50 mL / min, the column temperature was increased from 40°C to 200°C at a rate of 10°C / min, and the detector temperature was 200°C, and a gas chromatogram was obtained.

[0160] As a result, it was confirmed that hydrogen gas was produced in each of the above examples. In particular, in each of the above examples, most of the gas obtained was hydrogen gas, and the production of by-products such as carbon monoxide gas, carbon dioxide gas, methane, and ethane was significantly suppressed to a low level.

[0161] [4-2] Raman Spectroscopic Analysis The products obtained by the treatment methods of the above examples were analyzed by Raman spectroscopy.

[0162] A Raman spectrum was obtained by measurement using a Raman spectrometer ("LabRAM HR-800" manufactured by HORIBA Jobin Yvon) at a laser wavelength of 633 nm.

[0163] The Raman spectrum of carbon nanotubes is usually attributed to four modes: the radial breathing mode (RBM), the D-band, the G-band, and the G'-band.

[0164] From the measurement results, peaks specific to carbon nanotubes were observed in each of the above examples, which confirmed that carbon nanotubes were produced.

[0165] Furthermore, among the four modes mentioned above, the RBM is not observed in multi-walled nanotubes, ordinary graphite, or diamond, suggesting the presence of single-walled carbon nanotubes. The RBM peak usually appears at a wavenumber of 100 cm -1 More than 600cm -1 It is observed in the low wavenumber region below.

[0166] From the measurement results, in Examples 1 to 15, an RBM peak was observed in the low wavenumber region, which confirmed that single-walled carbon nanotubes were produced in addition to multi-walled carbon nanotubes.

[0167] [4-3] Analysis by XRD The products obtained by the treatment methods of the above examples were analyzed by XRD.

[0168] From the measurement results, peaks specific to carbon nanotubes were observed in each of the above examples, which confirmed that carbon nanotubes were produced.

[0169] [4-4] Observation using a scanning electron microscope (SEM) The products obtained by the treatment methods of the above examples were observed using an electron microscope (SEM).

[0170] As a result, it was confirmed that fibrous carbon (carbon nanotubes) was produced in each of the above examples.

[0171] From the above results, in each of the above examples, hydrogen gas and carbon nanotubes could be produced simultaneously by activating the iron-based catalyst through microwave irradiation and pyrolyzing the plastic.

[0172] Figure 1 is a gas chromatogram of the product (gas) obtained in the first cycle in Examples 1, 3, 5, and 11. Figure 2 is a Raman spectrum of the product (solid) obtained in each cycle in Examples 1 and 3. Figure 3 is an electron microscope photograph of the product (solid) obtained in the 10th cycle in Examples 1 and 2. Figure 4 is an electron microscope photograph of the product (solid) obtained in the fifth cycle in Examples 5, 7, 9, and 11.

[0173] In particular, it can be seen from FIG. 1 that in each of the Examples, most of the gas obtained was hydrogen gas, and the production of by-products such as carbon monoxide gas, carbon dioxide gas, methane, and ethane was significantly suppressed.

[0174] 2, it was confirmed that carbon nanotubes were produced in all Examples. In particular, in Example 1, in which the mixture subjected to the treatment method contained a higher content of plastics than in Example 3, all of the above peaks appeared sharper, confirming that carbon nanotubes of higher purity were produced. In Example 3 as well, as the number of cycles increased, the above peaks became sharper, indicating that the purity of the carbon nanotubes improved.

[0175] [5] Study on the deterioration of iron-based catalysts Next, we investigated the deterioration of iron-based catalysts when repeatedly heated by microwaves.

[0176] Specifically, the gaseous products obtained in each cycle of each of the above examples were analyzed by gas chromatography and XRD.

[0177] FIG. 5 is a graph showing the hydrogen gas conversion rate in each cycle in Examples 1 to 4. FIG. 6 is a graph showing the hydrogen gas conversion rate in each cycle in Examples 5 and 6. FIG. 7 is a graph showing the concentrations of gas components contained in the product gas in each cycle in Example 5. FIG. 8 is a graph showing the concentrations of gas components contained in the product gas in each cycle in Example 6. FIG. 9 is a graph showing the hydrogen gas conversion rate in each cycle in Examples 7 and 8. FIG. 10 is a graph showing the concentrations of gas components contained in the product gas in each cycle in Example 7. FIG. 11 is a graph showing the concentrations of gas components contained in the product gas in each cycle in Example 8. FIG. 12 is a graph showing the hydrogen gas conversion rate in each cycle in Example 15, together with the hydrogen gas conversion rate in each cycle in Examples 1 and 3. FIG. 13 is a graph showing the hydrogen gas conversion rate in each cycle in Example 16. FIG. 14 is a graph showing the concentrations of gas components contained in the product gas in each cycle in Example 16. FIG. 15 shows XRD spectra of the products (solids) obtained in each cycle in Examples 1 to 3.

[0178] The hydrogen gas conversion rate [%] is calculated from the ratio of the ideal amount of H2 calculated from the theoretical amount to the amount of H2 actually produced (amount of H2 produced / ideal amount of H2) x 100.

[0179] 5 to 14, it can be seen that the hydrogen gas conversion rate tends to decrease as the number of cycles increases, but the decrease in the hydrogen gas conversion rate tends to be suppressed by the use of an iron-based catalyst reduction inhibitor. This is thought to be because the use of an iron-based catalyst reduction inhibitor suppresses the deterioration of the iron-based catalyst due to the thermal cycle.

[0180] 15, it can be seen that the Fe3C peak tends to become larger as the number of cycles increases, but it can be confirmed that the timing of the appearance of the Fe3C peak can be delayed by using an iron-based catalyst reduction inhibitor. This is thought to be because the use of an iron-based catalyst reduction inhibitor suppresses the deterioration of the iron-based catalyst due to thermal cycling.

[0181] [6] Heating conditions for the mixture The heating conditions for the mixture were investigated.

[0182] [6-1] Examination of microwave irradiation conditions First, the microwave irradiation conditions were examined.

[0183] In each of the above examples, the microwave output was controlled so that the temperature of the mixture rose from 100°C to 700°C at a substantially constant heating rate (approximately 60°C / min), and then the microwave output was controlled so that the mixture, once it had reached 700°C, was maintained at 700°C for 20 minutes, thereby heating the mixture. In contrast, here, the microwave output was set to a constant value of 700 W, and the microwave irradiation time was set to 50 minutes, thereby heating the mixture.

[0184] For each case, graphs were created showing the change in microwave output and mixture temperature over time. In both cases, hydrogen gas and carbon nanotubes were efficiently produced. However, it was found that controlling the microwave output so that the heating temperature was constant was easier to control the temperature of the mixture and improve reproducibility than heating at a constant microwave output.

[0185] [6-2] Examination of the heating temperature of the mixture The heating temperature of the mixture was examined below.

[0186] In each of the above examples, the maximum temperature of the mixture was set to 700°C and maintained at this maximum temperature for 20 minutes, whereas in this example, the maximum temperature of the mixture was changed in various ways within the range of 300°C to 900°C.

[0187] The products obtained in each case were analyzed by gas chromatography, and it was found that hydrogen gas could be produced efficiently in all cases, but that the hydrogen gas concentration in the produced gas and the hydrogen gas conversion rate were both greatest when the heating temperature (maximum temperature) was 700°C.

[0188] Furthermore, when the treatment was carried out in the same manner as in the above example, except that polyvinyl alcohol was used as the iron-based catalyst reduction inhibitor instead of cellulose or sucrose, excellent results were obtained similarly to those described above.

[0189] In addition, treatment was carried out in the same manner as in the above examples, except that cellulose, sucrose, and water, hydrate (iron (III) oxide monohydrate), or hydroxide (iron (II) hydroxide, iron (III) hydroxide, aluminum hydroxide) were used in combination as iron-based catalyst reduction inhibitors, and similar excellent results were obtained. [Industrial Applicability]

[0190] The processing method of the present invention is characterized by irradiating a mixture containing a raw material containing plastic and a catalyst containing an iron-based catalyst with microwaves to selectively heat and activate the iron-based catalyst, and decomposing the plastic in the presence of the iron-based catalyst to produce hydrogen gas and carbon nanotubes. This makes it possible to provide a processing method that can efficiently decompose plastics in a short period of time and enable the effective use of plastics.

[0191] The mixture of the present invention is a mixture used to produce hydrogen gas and carbon nanotubes from raw materials including plastics, and is characterized by containing the raw materials, a catalyst including an iron-based catalyst, and at least one selected from the group consisting of polyhydric alcohol compounds, water, hydrates, and hydroxides. This makes it possible to provide a mixture that can be suitably used to produce hydrogen gas and carbon nanotubes. Therefore, the processing method and mixture of the present invention have industrial applicability.

Claims

1. A processing method characterized by irradiating a mixture containing a raw material including plastic and a catalyst including an iron-based catalyst with microwaves to selectively heat and activate the iron-based catalyst, and decomposing the plastic in the presence of the iron-based catalyst to produce hydrogen gas and carbon nanotubes.

2. The iron-based catalyst is FeAlO ｘ The method of claim 1 , wherein the nanoparticles are represented by the formula:

3. 3. The method according to claim 1, wherein the raw material contains waste plastic.

4. 3. The method according to claim 1, wherein the plastic comprises at least one selected from the group consisting of polyolefin resin, polyester resin, polycarbonate, and phenolic resin.

5. 3. The treatment method according to claim 1, wherein the mixture further contains at least one selected from the group consisting of a polyhydric alcohol compound, water, a hydrate, and a hydroxide.

6. 6. The method according to claim 5, wherein the polyhydric alcohol compound is at least one selected from the group consisting of cellulose, sucrose, and polyvinyl alcohol.

7. The method according to claim 1 or 2, wherein the carbon nanotubes include single-walled carbon nanotubes.

8. A mixture used to produce hydrogen gas and carbon nanotubes from raw materials, including plastics; A mixture comprising the raw material, a catalyst including an iron-based catalyst, and at least one selected from the group consisting of a polyhydric alcohol compound, water, a hydrate, and a hydroxide.

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