Thermal decomposition method and thermal decomposition device for plastic

Abstract

This thermal decomposition method for a plastic comprises: a step for crushing a first plastic group including the plastic to obtain a crushed product; a step for causing a liquid substance to adhere to the crushed product; a step for mixing the crushed product to which the liquid substance is adhered and solid particles that promote thermal decomposition of the plastic, thereby obtaining a mixed product; and a step for thermally decomposing the plastic by charging the mixed product into a thermal decomposition container and heating the mixed product.

Description

Method and apparatus for thermal decomposition of plastics

[0001] The present disclosure relates to a method and apparatus for pyrolysis of plastics.

[0002] From the start of industrial production of plastics to the present day, various chemical structures have been proposed and marketed to satisfy the various properties required for product use. In recent years, in order to further improve durability during use, high-strength fibers and fillers, as well as various additives such as antioxidants, have been compounded, and the trend toward diversification of plastics continues to expand.

[0003] Due to this background, plastics that have outlived their usefulness as products are often not a single type of plastic but a mixture of many different types. Because a mixture of many different types of plastics prevents the original properties of plastics from being expressed, it is becoming increasingly important to develop technology that can thermally decompose used plastics and recycle them as useful resources.

[0004] Patent Document 1 discloses a method for thermally decomposing plastic by irradiating microwaves to plastic that has been mixed with a heat generating medium that absorbs microwaves to generate heat (hereinafter also referred to as a "microwave heat generating medium") and a catalyst compound that promotes the thermal decomposition of the plastic.

[0005] Patent Documents 2, 3 and 4 disclose methods for pyrolyzing plastics, in which a portion of the pyrolysis product of the plastics is refluxed to the pyrolysis vessel.

[0006] Japanese Patent Application Laid-Open No. 2005-220179 Japanese Patent Application Laid-Open No. 10-204443 Japanese Patent Application Laid-Open No. 2012-530810 International Publication No. 2021 / 230312

[0007] In Patent Document 1, the contact area between the plastic and the microwave heat generating medium and catalyst compound is increased by crushing the plastic, thereby improving the rate of thermal decomposition by microwave irradiation and the heating efficiency.

[0008] However, it is difficult to reduce the particle size of various used plastics to the same particle size as the microwave heating medium and catalyst compound. Therefore, when they are mixed, classification occurs, and the microwave heating medium and catalyst compound are localized at the bottom of the mixture, resulting in a loss of homogeneity of the mixture. If the homogeneity of the mixture is lost, the temperature within the mixture will be uneven when microwaves are irradiated, resulting in a problem of reduced efficiency in the thermal decomposition of the plastics.

[0009] In Patent Documents 2, 3, and 4, a portion of the pyrolysis products of the plastics is returned to the pyrolysis vessel. In this case, the temperature inside the pyrolysis vessel differs from the temperature of the returned pyrolysis products, causing fluctuations in the temperature inside the pyrolysis vessel, making it difficult to pyrolyze the used plastics at a constant temperature, resulting in a problem of reduced efficiency in the pyrolysis of the plastics.

[0010] An object of the present disclosure is to provide a method and apparatus for pyrolysis of plastics with good pyrolysis efficiency.

[0011] The method for thermally decomposing plastics disclosed herein comprises the steps of crushing a first group of plastics containing plastics to obtain crushed material, attaching a liquid substance to the crushed material, mixing the crushed material with the liquid substance attached thereto with solid particles that promote the thermal decomposition of the plastics to obtain a mixture, and introducing the mixture into a pyrolysis vessel and heating the mixture to thermally decompose the plastics.

[0012] The pyrolysis apparatus disclosed herein is a pyrolysis apparatus used in the above-described method for pyrolyzing plastics, and includes a mixing vessel in which the step of obtaining the mixture is carried out, and a pyrolysis vessel in which the step of pyrolyzing the plastic is carried out.

[0013] According to the present disclosure, it is possible to provide a method and apparatus for thermally decomposing plastics with good thermal decomposition efficiency.

[0014] FIG. 1 is a flowchart showing a method for thermally decomposing plastics according to embodiment 1. FIG. 2 is a diagram illustrating a process for adhering a liquid substance to crushed material according to embodiment 1. FIG. 3 is a diagram illustrating a process for obtaining a mixture according to embodiment 1. FIG. 4 is a diagram illustrating a process for thermally decomposing plastics according to embodiment 1. FIG. 5 is a diagram illustrating a process for obtaining a conventional mixture. FIG. 6 is a diagram illustrating a conventional process for thermally decomposing plastics. FIG. 7 is a diagram illustrating an example of a thermal decomposition system using the thermal decomposition device for plastics according to embodiment 2. FIG. 8 is a diagram illustrating an example of a thermal decomposition system using the thermal decomposition device for plastics according to embodiment 2. FIG. 9 is a diagram illustrating an example of a thermal decomposition system using the thermal decomposition device for plastics according to embodiment 2. FIG. 10 is a diagram illustrating an example of a thermal decomposition system using the thermal decomposition device for plastics according to embodiment 2.

[0015] Hereinafter, embodiments of the present disclosure will be described. In the drawings, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

[0016] Embodiment 1. As shown in Figure 1, a method for thermally decomposing plastics according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a method for thermally decomposing plastics, comprising the steps of: crushing a first group of plastics containing plastics to obtain crushed material (S1); adhering a liquid substance to the crushed material (S2); mixing the crushed material with the liquid substance adhered thereto with solid particles that promote the thermal decomposition of the plastics to obtain a mixture (S3); and charging the mixture into a pyrolysis vessel and heating the mixture to thermally decompose the plastics (S4).

[0017] The method for decomposing plastics according to the first embodiment has good thermal decomposition efficiency. The reason for this is presumed to be as follows.

[0018] In the plastic decomposition method of embodiment 1, a liquid substance is applied to crushed plastic material to wet the surface of the crushed material, and then the crushed material with the liquid substance applied is mixed with solid particles that promote the thermal decomposition of the plastic to obtain a mixture. When the surface of the crushed plastic material is wet, solid particles can be supported on the surface of the crushed material, and separation of the crushed material and solid particles can be suppressed even if the particle sizes of the crushed plastic material and the solid particles are not identical. Furthermore, separation of the crushed material and solid particles can be suppressed even after the mixture is introduced into the pyrolysis vessel. This allows the homogeneity of the mixture to be maintained in the pyrolysis vessel, and the plastic can be thermally decomposed stably at the desired temperature while the crushed plastic material and solid particles are in sufficient contact with each other.

[0019] In the past, when thermally decomposing plastics, the plastics were crushed to sizes of approximately 10 mm. However, because the solid particles that accelerate the thermal decomposition reaction of plastics are typically fine particles of 1 mm or less, simply mixing the crushed plastics with the solid particles results in classification within the mixture, resulting in the solid particles being localized at the bottom of the mixture and impairing the homogeneity of the mixture. In this state, the crushed plastics and the solid particles cannot be sufficiently contacted with each other to undergo the thermal decomposition reaction. Furthermore, temperature variations occur within the mixture during the thermal decomposition reaction. As a result, stable thermal decomposition of plastics has not been achieved.

[0020] <Step of Obtaining Crushed Material> In the step of obtaining crushed material, the first plastics group containing plastics is crushed to obtain crushed material.

[0021] There are no particular limitations on the plastics included in the first plastic group to be subjected to the thermal decomposition treatment in embodiment 1. For example, the plastics may be single plastics recovered by methods such as manual disassembly or in-plant sorting, or used plastics such as mixed plastics recovered as is without undergoing any particular purification treatment.

[0022] Materials contained in single plastics and mixed plastics include thermoplastic resins such as polypropylene, polyethylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, and polyamide; thermosetting resins such as epoxy resin, phenolic resin, unsaturated polyester, polyurethane, and melamine resin; and cross-linked rubbers such as natural rubber, isoprene rubber, butyl rubber, chloroprene rubber, silicone rubber, and fluororubber. These materials may contain fillers such as fibers and talc, carbon black and titanium dioxide, and additives such as antioxidants, UV absorbers, plasticizers, and paraffin wax. Two or more types of plastics may be mixed together, with no particular restrictions on the blend ratio.

[0023] When the plastic to be processed is used plastic, it is difficult to uniformly mix it with solid particles that accelerate the thermal decomposition reaction of the plastic in the discarded product form. For this reason, the plastic is crushed into a crushed state using a machine such as a crusher. Thick-walled molded products such as television housings and bathtubs can be crushed as is. On the other hand, soft waste plastics such as polystyrene foam and agricultural film cannot be crushed into small pieces as they are. For this reason, it is preferable to compress soft waste plastics into ingots or blocks before crushing them, and then crush them into small pieces using a crusher.

[0024] The maximum diameter of the crushed material of the first plastic group is preferably 1 mm or more and 20 mm or less, and more preferably 5 mm or more and 10 mm or less, so that when mixed with the solid particles, the solid particles are easily dispersed and adhered to the surface of the crushed plastic material.

[0025] The method for crushing the first plastic group is not particularly limited. For example, a crusher utilizing methods such as compression, impact, shear, and friction can be used. Specifically, devices such as a jaw crusher, cone crusher, impact crusher, screw crusher, and freeze crusher can be used.

[0026] <Step of Applying Liquid Substance to Crushed Material> In the step of applying a liquid substance to crushed material, the liquid substance is applied to the crushed material. In the step of applying a liquid substance to crushed material, as shown in FIG. 2 , crushed material 2 is placed in a mixing container 11, and a liquid substance (not shown) is sprayed onto the crushed material 2 in the mixing container 11, thereby applying the liquid substance to the crushed material 2. Alternatively, the liquid substance may be applied to the crushed material before being placed in the mixing container. Applying the liquid substance to the crushed material wets the surface of the crushed material, which makes it easier to support solid particles on the surface of the crushed material in the mixing step described below.

[0027] The method for spraying the liquid substance onto the crushed material is not particularly limited. For example, a spray, a power sprayer, a dripping device, etc. can be used. When spraying the liquid substance onto the crushed material, the crushed material may be stirred with a stirring rod or the like.

[0028] The amount of liquid substance to be sprayed on the crushed material is not particularly limited as long as it is capable of wetting the surface of the crushed material. For example, the mass ratio of crushed material to liquid substance can be from 99:1 to 75:25.

[0029] The step of applying the liquid substance to the crushed material is preferably carried out at a temperature below the volatilization temperature of the liquid substance, which suppresses the volatilization of the liquid substance and keeps the surface of the crushed material wet.

[0030] The liquid substance is preferably the same as at least a portion of the pyrolysis products of the plastics included in the first plastic group. This eliminates the need for a step of separating the liquid substance from the pyrolysis products of the plastics to be treated, thereby simplifying the device configuration and reducing the running costs for the thermal decomposition of plastics.

[0031] The liquid substance is preferably a reflux of at least a portion of the pyrolysis product obtained by pyrolyzing a second group of plastics containing the same type of plastic as the plastics contained in the first group of plastics in a pyrolysis vessel. The pyrolysis product of the plastics contains heavy components that have not been pyrolyzed sufficiently. By refluxing a portion of the pyrolysis product of the second group of plastics and using it as a liquid substance to be sprayed on the crushed material of the first group of plastics, the heavy components can be pyrolyzed again to lighten them, thereby increasing the value of the pyrolysis product.

[0032] <Process for Obtaining a Mixture> In the process for obtaining a mixture, crushed material having a liquid substance attached thereto is mixed with solid particles that promote the thermal decomposition of plastics to obtain a mixture. In the process for obtaining a mixture, as shown in Figure 3, solid particles 3 are introduced into a mixing vessel 11 containing crushed material 2 having a liquid substance attached thereto, and mixed to obtain a mixture 4. In the first embodiment, the liquid substance is attached to the surface of the crushed material, and the surface of the crushed material is wet, so that the solid particles are easily supported on the surface of the crushed material, and separation of the crushed material and the solid particles is suppressed.

[0033] In the prior art, no liquid substance adheres to the surface of the crushed material, and the surface of the crushed material is not wetted. As a result, as shown in Figure 5, the crushed material 2 and solid particles 3 are separated, and after mixing, the solid particles 3 are localized in the lower part of the mixing vessel 11.

[0034] The mixing method may be either manual or mechanical, as long as it can mix the charged materials.

[0035] The step of obtaining the mixture is preferably carried out at a temperature below the volatilization temperature of the liquid substance, which suppresses the volatilization of the liquid substance and keeps the surface of the crushed material wet.

[0036] <Solid Particles> Solid particles accelerate the thermal decomposition of plastics. Solid particles have the effect of rapidly raising the temperature of plastics they come into contact with above the thermal decomposition temperature when irradiated with microwaves, or the effect of chemically accelerating the decomposition reaction of plastics, or both of these effects. Hereinafter, these effects will also be referred to as the catalytic effect of solid particles.

[0037] <Microwave Heating Medium> The catalytic effect of solid particles will be described below, which is that they rapidly heat up when irradiated with microwaves, quickly raising the temperature of plastics that come into contact with them to above the thermal decomposition temperature.

[0038] Microwave heating is known as one method for heating objects. The degree of heating of an irradiated material by microwave irradiation is determined in proportion to the dielectric loss factor (εr × tanδ), which is the product of the relative permittivity (εr) and the dielectric loss angle (tanδ) specific to the irradiated material. Microwave heating can selectively and directly heat the heated material, and therefore has the advantage of being able to heat the irradiated material uniformly and quickly compared to heat transfer heating methods. By using a microwave heating medium as the solid particle, which rapidly heats when irradiated with microwaves, plastics can be heated uniformly and quickly.

[0039] As the microwave heating medium, a material with a high dielectric loss coefficient is used, which is effective in improving the heating efficiency during microwave irradiation. Examples of the microwave heating medium that can be used include carbon materials such as graphite, carbon black, activated carbon, carbon fiber, and boron carbide, silicon, silicon carbide, iron oxide, iron, aluminum, copper oxide, silver sulfide, copper bromide, copper chloride, cobalt, tricobalt tetroxide, nickel oxide, manganese dioxide, molybdenum, molybdenum sulfide, lead sulfide, titanium boride, vanadium, tungsten, tungsten trioxide, zinc, and zinc chloride.

[0040] It is preferable to select a microwave heating medium with a large dielectric loss coefficient for the solid particles. When the solid particles and crushed material are uniformly mixed and the solid particles are heated by microwave irradiation, temperature variations within the pyrolysis vessel are eliminated, making it easier to pyrolyze the plastic at a constant temperature.

[0041] On the other hand, if the crushed material and solid particles are separated in the pyrolysis vessel, when the solid particles are heated by microwave irradiation, the lower part of the pyrolysis vessel where the solid particles are concentrated is selectively heated, causing temperature unevenness within the pyrolysis vessel and making it impossible to pyrolyze the plastic at a constant temperature.

[0042] <<Cracking reaction promoting catalyst>> The decomposition reaction of plastics can be promoted by using a catalyst that chemically promotes the decomposition reaction of plastics (also referred to as a "cracking reaction promoting catalyst") as a solid particle. Examples of the cracking reaction promoting catalyst include zeolites used in the catalytic cracking of petroleum, solid acid catalysts such as carbon-based catalysts, and basic metal oxide-based solid catalysts.

[0043] Specific examples of the decomposition reaction-accelerating catalyst include solid acid catalysts such as crystalline silica-alumina compounds, amorphous silica-alumina compounds, aluminum oxide, silicon oxide, silica-magnesia compounds, zinc oxide, bauxite, natural earth (activated clay, acid clay, etc.), iron oxide, copper oxide, nickel oxide, molybdenum oxide, sulfated zirconia, sulfated nanographene, activated carbon, etc. Examples of basic metal oxide solid catalysts that can be used include barium oxide, potassium oxide, sodium oxide, rubidium oxide, magnesium oxide, calcium oxide, strontium oxide, chromium oxide, iron oxide, copper oxide, cobalt oxide, and zinc oxide.

[0044] The solid particles preferably contain one or both of a microwave heat generating medium and a catalyst that chemically accelerates the decomposition reaction of the plastic. The solid particles may consist of a microwave heat generating medium, a decomposition reaction accelerating catalyst, or both a microwave heat generating medium and a decomposition reaction accelerating catalyst.

[0045] The size of the solid particles is preferably 0.01 μm or more and 500 μm or less, more preferably 0.1 μm or more and 250 μm or less, so that they can be easily dispersed and attached to the surface of the crushed plastics.

[0046] The mixing ratio of the crushed material to the solid particles is not particularly limited as long as it can promote the thermal decomposition of the crushed material. For example, the mixing ratio (mass ratio) of crushed material to solid particles can be 99:1 to 50:50.

[0047] <Process for Pyrolyzing Plastics> In the process for pyrolyzing plastics, a mixture is placed in a pyrolysis vessel and heated to pyrolyze the plastics. In the process for pyrolyzing plastics, as shown in FIG. 4 , a mixture 4 of crushed material 2 and solid particles 3 is placed in a pyrolysis vessel 12, and the mixture 4 is heated. In the first embodiment, solid particles are easily supported on the surface of the crushed material, so that separation of the crushed material and solid particles is suppressed even after the mixture is placed in the pyrolysis vessel. This allows the crushed plastics to be thermally decomposed stably at a desired temperature while maintaining a constant temperature in the pyrolysis vessel with sufficient contact between the crushed plastics and the solid particles, enabling efficient pyrolysis of used plastics.

[0048] In the prior art, no liquid substance adheres to the surface of the crushed material, and the surface of the crushed material is not wet, so the crushed material 2 and solid particles 3 are separated in the pyrolysis vessel 12, as shown in Figure 6. Even if pyrolysis is carried out in this state, the crushed material and the solid particles are not in sufficient contact with each other, so the catalytic effect of the solid particles cannot be obtained, and the pyrolysis efficiency decreases.

[0049] The heating method is not particularly limited. For example, heating by microwave irradiation, heating using a heater or boiler, or heating by blowing in heated steam can be used. Microwave heating can selectively and directly heat the heated substance, so the irradiated substance can be heated uniformly and quickly. For this reason, the process of pyrolyzing plastics preferably includes a process of heating the mixture by irradiating the mixture with microwaves.

[0050] The method for generating microwaves is not particularly limited. For example, a magnetron, which is inexpensive and mass-produced, or a semiconductor oscillator, which is easier to control the oscillation frequency and phase than a magnetron, can be used.

[0051] When heating by microwave irradiation, localized heating may occur depending on the shape of the sample. Measures to reduce this localized heating include irradiating microwaves from multiple ports and using a stirrer fan to diffuse the microwaves.

[0052] Embodiment 2. A thermal decomposition device for plastics according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") is a thermal decomposition device used in the thermal decomposition method of Embodiment 1, and is a thermal decomposition device including a mixing vessel in which a step of obtaining a mixture is carried out, and a thermal decomposition vessel in which a step of thermally decomposing plastics is carried out.

[0053] 7 to 10 are diagrams showing an example of a pyrolysis system using the pyrolysis device for plastics according to embodiment 2. In FIGS. 7 to 10, the configuration depicted within the square frames is the configuration of the pyrolysis device for plastics according to embodiment 2. The pyrolysis device for plastics according to embodiment 2 includes a mixing vessel that mixes crushed plastic material with a liquid substance attached thereto with solid particles to produce a mixture, and a pyrolysis vessel that heats the mixture of crushed material and solid particles to pyrolyze it.

[0054] In the mixing vessel, crushed material with a liquid substance attached is mixed with solid particles that promote the thermal decomposition of plastics to produce a mixture. The mixing vessel serves to effectively mix different types and shapes of plastics with solid particles to produce a uniform mixture. As long as the materials fed into the mixing vessel can be mixed, either manually or by power, the mixing vessel may be either manual or powered. Powered mixing vessels may be configured to have rotating blades installed inside the mixing vessel, a vertically rotating mixing vessel body, or an inclined mixing vessel that rotates around an inclined axis. The mixing vessel may have an inlet for recycling a portion of the plastic thermal decomposition products.

[0055] In the heating vessel, the mixture is heated and the plastic is pyrolyzed. There are no particular limitations on the heating means provided in the heating vessel as long as it can heat the mixture that has been introduced. Examples of the heating means that can be used include a microwave irradiator, a heater, a boiler, and a heated steam generator.

[0056] The pyrolysis device may further include a sprayer for spraying a liquid substance onto the crushed material to cause the liquid substance to adhere to the crushed material. The location of the sprayer is not particularly limited as long as the liquid substance can be sprayed onto the crushed material before the crushed material is mixed with the solid particles in the mixing container. For example, the sprayer may be attached to the mixing container so as to spray the liquid substance onto the crushed material contained in the mixing container, or may be attached to the storage container so as to spray the liquid substance onto the crushed material contained in the storage container, or may be attached to the conveying path so as to spray the liquid substance onto the crushed material on the conveying path between the storage container and the mixing container.

[0057] The pyrolysis device can include a storage container for storing crushed plastic material, a cooler for cooling and liquefying gas components generated from the pyrolysis container, and a solid-liquid separator for separating liquid components and pyrolysis residue from the slurry components generated from the pyrolysis container. The pyrolysis device can also be equipped with devices that are generally combined as a plastic pyrolysis device, such as a chlorine immobilization tank, a condenser, and a burner.

[0058] In the pyrolysis system shown in Figure 7, a liquid substance is applied to the crushed material of the first plastic group stored in a storage container. The liquid substance is obtained by returning a portion of liquid component B recovered from the slurry component of the pyrolysis product obtained by pyrolyzing the second plastic group in the pyrolysis container prior to the pyrolysis of the first plastic group to the storage container. Specifically, the slurry component is separated into liquid component B and pyrolysis residue in a solid-liquid separator, and liquid component B is sprayed on the crushed material in the storage container. Next, the crushed material with the liquid substance applied and solid particles are placed in a mixing container and mixed to produce a mixture. The mixture is placed in the pyrolysis container and heated, whereby the plastics are thermally decomposed to obtain a pyrolyzed product.

[0059] Next, the slurry component of the pyrolyzed product in the pyrolysis vessel is separated into liquid component B and pyrolysis residue in a solid-liquid separator. A portion of the new liquid component B is used as a liquid substance in the next cycle of the pyrolysis system, and another portion is recovered as a recovered liquid. The gas component of the pyrolyzed product is cooled in a cooler to become liquid component A, which is recovered as a recovered liquid. The recovered liquid can be purified to a high degree and used as a chemical raw material or fuel, and can be used for a wide range of purposes other than these.

[0060] The pyrolysis system shown in Figure 8 has the same configuration as the pyrolysis system shown in Figure 7, except that liquid component B is returned to a mixing vessel rather than a storage vessel, and the liquid substance is attached to the crushed material of the first plastic group in the mixing vessel rather than in a storage vessel.

[0061] 7 and 8, liquid component B recovered from the slurry component of the pyrolysis product contains more heavy components than liquid component A recovered by cooling the gas component of the pyrolysis product. Therefore, by using liquid component B as the liquid substance to be sprayed on the crushed plastic material, the heavy components contained in liquid component B can be pyrolyzed again to lighten them, thereby increasing the value of the pyrolysis product.

[0062] The location where liquid component B is refluxed and sprayed as a liquid substance onto the crushed plastic material is not limited to the storage container or the mixing container, but may be during transport between the storage container and the mixing container.

[0063] The pyrolysis system shown in Figure 9 has the same configuration as the pyrolysis system shown in Figure 7, except that the liquid substance is part of the recovered liquid obtained by adding together liquid component B recovered from the slurry component of the pyrolysis product and liquid component A recovered by cooling the gas component.

[0064] 9, a portion of liquid component B is used as the returned liquid material, so that the heavy components in liquid component B can be pyrolyzed again to lighter components. Furthermore, a portion of liquid component A, which contains a large amount of light components, is used as the returned liquid material, so that the viscosity of the returned liquid material can be reduced, which offers the advantages of preventing clogging of the return pipe and reducing the transfer pressure.

[0065] The pyrolysis system shown in Figure 10 has the same configuration as the pyrolysis system shown in Figure 7, except that the liquid substance is part of liquid component A that is recovered by cooling the gas component of the pyrolysis product.

[0066] In the thermal decomposition system shown in Figure 10, liquid component A, which contains a large amount of light components, is used as the refluxed liquid material, which further reduces the viscosity of the refluxed liquid material, thereby providing advantages such as preventing clogging of the reflux piping and reducing the transfer pressure.

[0067] In the pyrolysis systems shown in Figures 9 and 10, the location where the recovered liquid is returned and sprayed as a liquid substance onto the crushed plastic material is not limited to the storage container, but can also be a mixing container, or during transportation from the storage container to the mixing container.

[0068] In Example 1, plastic was pyrolyzed using the pyrolysis system shown in Figure 8. Crushed polystyrene recovered from mixed plastics derived from used home appliances was used as the plastic to be pyrolyzed. The crushed polystyrene consisted of 95% by weight or more of polystyrene resin, and other components included polypropylene resin, ABS resin, PS / PPE resin, etc.

[0069] The crushed polystyrene material was flake-like crushed material with a maximum diameter of 5 mm to 10 mm and a wall thickness of 1 to 2 mm. 20.0 g of crushed polystyrene material was placed in a mixing container, and 4.0 ml of a liquid material recovered from the pyrolysis products of the crushed polystyrene material, which had been separately prepared, was sprayed onto the crushed polystyrene material to adhere the liquid material to the crushed polystyrene material. 4.0 g of iron oxide (II, III; magnetite, Kojundo Chemical Laboratory) particles (particle diameter 180 μm or less) were added as a microwave heating medium to the crushed polystyrene material with stirring to obtain a mixture. The mixture was transferred to a quartz glass vial, which served as a pyrolysis container, and placed in a microwave heating device. At this point, no separation of the mixture was observed within the vial.

[0070] A 2.45 GHz magnetron oscillator was used as the heating source, and the reflected power that was not used for microwave heating was measured and the E / H tuner was adjusted successively to minimize the reflected power, thereby controlling microwave heating by ensuring that most of the input microwaves were used for the pyrolysis reaction.

[0071] The microwave heating device was a waveguide type single mode irradiation system. A through hole for temperature measurement was provided on the side of the waveguide, and the sample (mixture) temperature was measured through the through hole with a radiation thermometer. The radiation thermometer used had a minimum measurable temperature of 280°C. The temperature measurement point with the radiation thermometer was the center of the vial filled with the sample (mixture).

[0072] An outlet was provided in part of the waveguide to discharge the liquid and gas produced by pyrolysis, and the outlet was connected to a reflux facility. The reflux facility was designed to constantly cool the gas flow path with circulating water at 5°C, so that the liquid components produced by the pyrolysis reaction of the crushed polystyrene and the gas components liquefied in the reflux facility were retained in the lower part of the reflux facility.

[0073] The atmospheric air during pyrolysis was nitrogen, and nitrogen was constantly flowing into the waveguide of the microwave irradiation device at a rate of 0.4 L / min. The microwave irradiation power was profiled to increase the input power by 10 W per minute. As a result, it took 10 minutes from the start of microwave irradiation for the sample temperature to reach 400 °C. When the sample temperature reached 400 °C, the input power was adjusted and the temperature was maintained at 400 °C for 10 minutes to allow the pyrolysis reaction to proceed.

[0074] Pyrolysis was carried out at 400°C for 10 minutes, and after microwave irradiation was stopped, the vial was removed from the microwave heating device when it had cooled to room temperature, and the amount of residue of the crushed polystyrene was measured. The residue was 4.1g. Since the residue contained 4.0g of iron oxide, the amount of crushed polystyrene in the residue was 0.1g. 0.5% by weight of the 20.0g of crushed polystyrene introduced remained as residue. This indicated that almost all of the crushed polystyrene introduced into the reaction vessel was thermally decomposed. A brown liquefied product remained at the bottom of the reflux equipment.

[0075] Comparative Example 1 The configuration of the pyrolysis system in Comparative Example 1, the plastic to be pyrolyzed (20.0 g of crushed polystyrene), the mixing vessel, the microwave heating device, the microwave heating medium, the pyrolysis vessel (quartz glass vial), and the microwave irradiation device were the same as those in Example 1. When mixing the crushed polystyrene and the iron (II, III) oxide particles, the liquid substance used in Example 1 was not sprayed, and 20.0 g of crushed polystyrene and 4.0 g of iron (II, III) particles were stirred and mixed, then transferred to a quartz glass vial and placed in the microwave heating device. At this point, it was confirmed that the iron (II, III) oxide particles had been separated into the bottom of the vial.

[0076] The microwave heating was carried out in the same manner as in Example 1, and pyrolysis was carried out. It took 15 minutes from the start of microwave irradiation for the sample temperature to reach 400° C. Therefore, it was found that Comparative Example 1 required a longer time to reach the desired temperature than Example 1.

[0077] Pyrolysis was carried out at 400°C for 10 minutes, and after microwave irradiation was stopped, the vial was removed from the microwave heating device when it cooled to room temperature, and the amount of residue of the crushed polystyrene was measured. The residue was 10.5g. Since the residue contained 4.0g of iron oxide, the amount of crushed polystyrene in the residue was 6.5g. 32.5% by weight of the 20.0g of crushed polystyrene introduced remained as residue. Therefore, it was found that Comparative Example 1 had inferior pyrolysis efficiency to Example 1.

[0078] The heating time and sample temperature during microwave irradiation are shown in Table 1. Comparing Example 1 and Comparative Example 1, it can be seen that the temperature of the sample in Example 1 rose more quickly. In Example 1, the microwave heating medium was supported on the surface of the crushed polystyrene material in the vial and was uniformly dispersed within the vial, so the sample was heated uniformly without unevenness, promoting thermal decomposition of the sample and demonstrating excellent thermal decomposition efficiency.

[0079] On the other hand, in Comparative Example 1, it is presumed that iron (II, III) oxide particles of the microwave heating medium were separated into the lower part of the vial, causing local heating of the lower part of the vial. Therefore, while the temperature of the lower part of the vial was raised to the desired temperature of around 400°C, the temperature of the crushed polystyrene in the upper part of the vial was not raised to the thermal decomposition temperature, and thermal decomposition was carried out in a state where temperature unevenness occurred within the vial, resulting in a large amount of crushed polystyrene remaining as residue.

[0080]

[0081] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0082] 2 crushed material, 3 solid particles, 4 mixture, 11 mixing vessel, 12 pyrolysis vessel.

Claims

1. A method for thermally decomposing plastics, comprising the steps of: crushing a first group of plastics containing plastics to obtain crushed material; attaching a liquid substance to the crushed material; mixing the crushed material with the liquid substance attached thereto with solid particles that promote the thermal decomposition of the plastics to obtain a mixture; and pouring the mixture into a pyrolysis vessel and heating the mixture to thermally decompose the plastics.

2. The method for thermally decomposing plastics according to claim 1, wherein the step of obtaining the mixture is carried out at a temperature below the volatilization temperature of the liquid substance.

3. A method for thermally decomposing plastics according to claim 1 or claim 2, wherein the liquid substance is the same as at least a portion of the thermal decomposition products of the plastics.

4. A method for thermally decomposing plastics as described in claim 1 or claim 2, wherein the liquid substance is obtained by refluxing at least a portion of the pyrolysis product obtained by thermally decomposing a second group of plastics containing the same type of plastic as the plastic in the pyrolysis vessel.

5. A method for thermally decomposing plastics according to any one of claims 1 to 4, wherein the solid particles contain one or both of a microwave heating medium and a catalyst that chemically accelerates the decomposition reaction of the plastics.

6. A method for thermally decomposing plastics according to any one of claims 1 to 5, wherein the step of thermally decomposing the plastics includes a step of heating the mixture by irradiating the mixture with microwaves.

7. A pyrolysis apparatus used in the method for thermally decomposing plastics according to any one of claims 1 to 6, comprising: a mixing vessel in which the step of obtaining the mixture is carried out; and a pyrolysis vessel in which the step of thermally decomposing the plastics is carried out.

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