Method and apparatus for pyrolysis of plastics

Abstract

This method for thermally decomposing plastics comprises the steps of: crushing a first plastic group containing plastics to obtain crushed material; adhering a liquid substance to the crushed material; 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; and pouring the mixture into a pyrolysis vessel and heating the mixture to thermally decompose the plastics.

Description

[Technical field]

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

[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 characteristics required during 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 added, and the trend toward diversification of plastics continues to expand.

[0003] Due to this background, plastics that have completed their role as products and are collected are often not a single type of plastic, but a mixture of many different types of plastics. Since the inherent properties of plastics cannot be expressed in a mixture of many different types of plastics, 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 pyrolyzing plastic by irradiating microwaves to plastic that has been mixed with a heat generating medium that absorbs microwaves and generates heat (hereinafter also referred to as a "microwave heat generating medium") and a catalytic compound that promotes the pyrolysis of plastic.

[0005] Patent Documents 2, 3 and 4 disclose methods for pyrolyzing plastics, in which a portion of the products of pyrolysis of plastics is returned to a pyrolysis vessel. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-220179 A [Patent Document 2] Japanese Patent Application Publication No. 10-204443 [Patent Document 3] Special Publication No. 2012-530810 [Patent Document 4] International Publication No. 2021 / 230312 Summary of the Invention [Problem to be solved by the invention]

[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 pyrolysis and heating efficiency by microwave irradiation.

[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 these are mixed, classification occurs, and the microwave heating medium and catalyst compound are localized at the bottom of the mixture, which impairs the homogeneity of the mixture. If the homogeneity of the mixture is impaired, there is a problem that the temperature in the mixture becomes non-uniform when microwaves are irradiated, and the efficiency of thermal decomposition of the plastics decreases.

[0009] In Patent Documents 2, 3, and 4, a part of the pyrolysis product of the plastic is returned to the pyrolysis vessel. In this case, since the temperature inside the pyrolysis vessel differs from the temperature of the returned pyrolysis product, the temperature inside the pyrolysis vessel fluctuates, making it difficult to pyrolyze used plastics at a constant temperature, and there is a problem that the efficiency of pyrolysis of plastics decreases.

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

[0011] The method for pyrolyzing plastics disclosed herein comprises the steps of: A step of crushing a first plastic group containing plastic to obtain crushed material; A step of applying a liquid substance to the crushed material; A step of mixing the crushed material to which the liquid substance is attached with solid particles that promote the thermal decomposition of the plastic to obtain a mixture; and a step of pouring the mixture into a pyrolysis vessel and heating the mixture to pyrolyze the plastic.

[0012] The pyrolysis apparatus of the present disclosure is a pyrolysis apparatus used in the above-mentioned method for pyrolyzing plastics, a mixing vessel in which the step of obtaining the mixture is carried out; and a pyrolysis vessel in which the process of pyrolyzing the plastic is carried out. Effect of the Invention

[0013] According to the present disclosure, it is possible to provide a method and an apparatus for pyrolyzing plastics with good pyrolysis efficiency. [Brief description of the drawings]

[0014] [Figure 1] 1 is a flowchart showing a method for thermally decomposing plastics according to a first embodiment. [Diagram 2] FIG. 2 is a diagram for explaining the step of adhering a liquid substance to the crushed material in the first embodiment. [Diagram 3] FIG. 2 is a diagram for explaining a process for obtaining the mixture of the first embodiment. [Figure 4] FIG. 2 is a diagram for explaining the process of pyrolyzing the plastic of the first embodiment. [Diagram 5] FIG. 1 is a diagram for explaining a conventional process for obtaining a mixture. [Figure 6] FIG. 1 is a diagram for explaining a conventional process for pyrolyzing plastics. [Figure 7] FIG. 11 is a diagram showing an example of a pyrolysis system using a plastic pyrolysis device according to a second embodiment. [Figure 8] FIG. 11 is a diagram showing an example of a pyrolysis system using a plastic pyrolysis device according to a second embodiment. [Figure 9]FIG. 11 is a diagram showing an example of a pyrolysis system using a plastic pyrolysis device according to a second embodiment. [Figure 10] FIG. 11 is a diagram showing an example of a pyrolysis system using a plastic pyrolysis device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

[0017] The plastic decomposition method of the first embodiment has good thermal decomposition efficiency, the reason for which is presumed to be as follows.

[0018] In the plastic decomposition method of the first embodiment, a liquid substance is applied to the crushed plastic to wet the surface of the crushed plastic, and then the crushed plastic to which the liquid substance is 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 is wet, solid particles can be supported on the surface of the crushed plastic, and even if the particle size of the crushed plastic and the solid particles are not the same, classification of the crushed plastic and the solid particles can be suppressed. In addition, classification of the crushed plastic and the solid particles can be suppressed even after the mixture is put into the pyrolysis vessel. This allows the homogeneity of the mixture to be maintained in the pyrolysis vessel, and the plastic can be stably pyrolyzed at a desired temperature with sufficient contact between the crushed plastic and the solid particles.

[0019] In the past, when plastics were pyrolyzed, they were crushed to about 10 mm in size. However, the solid particles that accelerate the pyrolysis reaction of plastics are usually fine particles of 1 mm or less. Therefore, simply mixing the crushed plastics with the solid particles causes classification in the mixture, and the solid particles are localized at the bottom of the mixture, compromising the homogeneity of the mixture. In this state, the crushed plastics and the solid particles cannot be pyrolyzed in sufficient contact with each other. In addition, temperature variations occur in the mixture during the pyrolysis reaction. As a result, it was not possible to stably pyrolyze the plastics.

[0020] <Process for obtaining crushed material> In the process of obtaining the crushed material, the first plastics group containing plastics is crushed to obtain the crushed material.

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

[0022] Substances 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 crosslinked rubbers such as natural rubber, isoprene rubber, butyl rubber, chloroprene rubber, silicone rubber, and fluororubber. These substances may contain fillers such as fibers and talc, fillers such as carbon black and titanium dioxide, and additives such as antioxidants, ultraviolet absorbers, plasticizers, and paraffin wax. Two or more types of plastics may be mixed together, and there are no particular restrictions on the mixing ratio.

[0023] When the plastic to be treated is used plastic, it is difficult to mix uniformly 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 they are. On the other hand, soft waste plastics such as polystyrene foam and agricultural films 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, 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 the solid particles can be easily dispersed and attached to the surface of the crushed plastic material when mixed with the solid particles.

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

[0026] <Step of attaching liquid substance to crushed material> In the step of applying a liquid substance to the crushed material, the liquid substance is applied to the crushed material. In the step of applying a liquid substance to the crushed material, as shown in FIG. 2, the crushed material 2 is put into a mixing vessel 11, and a liquid substance (not shown) is sprayed onto the crushed material 2 in the mixing vessel 11, so that the liquid substance can be applied to the crushed material 2. The liquid substance may also be applied to the crushed material before it is put into the mixing vessel. When the liquid substance is applied to the crushed material, the surface of the crushed material becomes wet, which makes it easier to support solid particles on the surface of the crushed material in the mixing step described later.

[0027] The method of spraying the liquid substance on 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 on 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 can wet the surface of the crushed material. For example, the mass ratio of the crushed material to the liquid substance can be 99:1 to 75:25.

[0029] The step of applying the liquid substance to the crushed material is preferably carried out under a temperature condition equal to or lower than 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] <Liquid substances> The liquid substance is preferably the same as at least a part of the pyrolysis products of the plastics included in the first plastic group, which eliminates the need for a process for 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 pyrolysis of plastics.

[0031] The liquid substance is preferably at least a part of the pyrolysis product obtained by pyrolyzing a second plastic group, which contains the same type of plastic as the plastic contained in the first plastic group, in a pyrolysis vessel, and refluxing the pyrolysis product of the plastic. The pyrolysis product of the plastic contains heavy components that are not fully pyrolyzed. By refluxing a part of the pyrolysis product of the second plastic group and using it as a liquid substance to be sprayed on the crushed material of the first plastic group, the heavy components can be pyrolyzed again to make them lighter, thereby increasing the value of the pyrolysis product.

[0032] <Step of Obtaining Mixture> In the step of obtaining a mixture, the crushed material to which the liquid substance is attached is mixed with solid particles that promote the thermal decomposition of plastic to obtain a mixture. In the step of obtaining a mixture, as shown in Fig. 3, solid particles 3 are introduced into a mixing vessel 11 containing crushed material 2 to which the liquid substance is attached, and mixed to obtain a mixture 4. In the first embodiment, since the liquid substance is attached to the surface of the crushed material and the surface of the crushed material is in a wet state, the solid particles are easily supported on the surface of the crushed material, and classification of the crushed material and the solid particles is suppressed.

[0033] In the conventional technology, no liquid substance adheres to the surface of the crushed material, and the surface of the crushed material is not wet. Therefore, as shown in Fig. 5, the crushed material 2 and the solid particles 3 are separated, and the solid particles 3 are localized in the lower part of the mixing vessel 11 after mixing.

[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 under a temperature condition equal to or lower than the volatilization temperature of the liquid substance, which suppresses the volatilization of the liquid substance and allows the surface of the crushed material to be kept wet.

[0036] ≪Solid particles≫ Solid particles accelerate the thermal decomposition of plastics. The solid particles have the effect of rapidly raising the temperature of the 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 are also referred to as the catalytic effect of solid particles.

[0037] <Microwave heating medium> Among the catalytic effects of solid particles, we will explain their effect of rapidly raising the temperature of plastics that come into contact with them above their thermal decomposition temperature when irradiated with microwaves.

[0038] Heating by microwave irradiation is known as one method of heating objects. The degree of heating of an irradiated material by microwave irradiation is determined in proportion to the dielectric loss coefficient (εr × tan δ), which is the product of the specific dielectric constant (εr) and the dielectric loss angle (tan δ) of the irradiated material. Since microwave heating can directly heat the heated material selectively, it has the advantage of being able to heat the irradiated material uniformly and quickly compared to heat transfer methods. By using a microwave heating medium as a solid particle that rapidly rises in temperature 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 to effectively improve the heating efficiency during microwave irradiation. As the microwave heating medium, 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, zinc chloride, and the like can be used.

[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 the crushed material are mixed uniformly and the solid particles are heated by microwave irradiation, the temperature unevenness in the pyrolysis vessel is eliminated, making it easy 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, resulting in temperature unevenness in the pyrolysis vessel and making it impossible to pyrolyze the plastic at a constant temperature.

[0042] <Decomposition reaction promotion catalyst> The decomposition reaction of plastics can be accelerated by using a catalyst that chemically accelerates the decomposition reaction of plastics as the solid particle (also referred to as a "catalyst for promoting the decomposition reaction"). As the catalyst for promoting the decomposition reaction, zeolite used in catalytic cracking of petroleum, solid acid catalysts including carbon-based catalysts, and basic metal oxide-based solid catalysts can be used.

[0043] Specific examples of the decomposition reaction-promoting 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, zinc oxide, etc.

[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 be made of a microwave heat generating medium, may be made of a decomposition reaction accelerating catalyst, or may be made of 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, and 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 the crushed material to the solid particles can be crushed material:solid particles=99:1 to 50:50.

[0047] <Plastic pyrolysis process> In the process of pyrolyzing plastics, the mixture is put into a pyrolysis vessel and heated to pyrolyze the plastics. In the process of pyrolyzing plastics, as shown in FIG. 4, a mixture 4 of crushed material 2 and solid particles 3 is put into a pyrolysis vessel 12 and the mixture 4 is heated. In the first embodiment, since the solid particles are easily supported on the surface of the crushed material, the classification of the crushed material and the solid particles is suppressed even in the mixture after being put into the pyrolysis vessel. As a result, the crushed plastics can be stably pyrolyzed at a desired temperature while keeping the temperature in the pyrolysis vessel constant with the crushed plastics and the solid particles in sufficient contact with each other, and the pyrolysis of used plastics with good pyrolysis efficiency is possible.

[0048] In the conventional technology, since no liquid substance adheres to the surface of the crushed material and the surface of the crushed material is not wet, the crushed material 2 and solid particles 3 are separated in the pyrolysis vessel 12 as shown in Fig. 6. Even if pyrolysis is performed 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, and heating by blowing in heated steam can be used. Microwave heating can directly heat the heated material selectively, so that the irradiated material can be heated uniformly and quickly. For this reason, the step of pyrolyzing plastics preferably includes a step of heating the mixture by irradiating the mixture with microwaves.

[0050] There are no particular limitations on the method for generating microwaves. 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 diffusely reflect microwaves.

[0052] Embodiment 2 A plastic pyrolysis apparatus according to one embodiment of the present disclosure (hereinafter also referred to as "embodiment 2") is a pyrolysis apparatus used in the pyrolysis method of embodiment 1, and is provided with a mixing container in which a process for obtaining a mixture is carried out, and a pyrolysis container in which a process for pyrolyzing plastic 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 configurations shown in the square frames are the configurations 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 having a liquid substance attached thereto with solid particles to produce a mixture, and a pyrolysis vessel that heats the mixture of the crushed material and the solid particles to pyrolyze it.

[0054] In the mixing vessel, the crushed material with the liquid substance attached thereto is mixed with solid particles that promote the thermal decomposition of the plastic to produce a mixture. The mixing vessel serves to effectively mix different types and shapes of plastics with the solid particles to produce a uniform mixture. As long as the charged materials can be mixed, the mixing vessel may be either manual or powered. In the case of a powered mixing vessel, a type in which a rotating blade installed inside the mixing vessel rotates, a type in which the mixing vessel body rotates up and down, or a type in which an inclined mixing vessel rotates around an inclined axis may be used. The mixing vessel may have an inlet for refluxing a portion of the thermal decomposition products of the plastic.

[0055] In the heating vessel, the mixture is heated and the plastic is pyrolyzed. The heating means provided in the heating vessel is not particularly limited as long as it can heat the mixture introduced therein. For example, a microwave irradiator, a heater, a boiler, a heated steam generator, etc. can be used as the heating means.

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

[0057] The pyrolysis device may include a storage vessel for storing the crushed plastic material therein, a cooler for cooling and liquefying the gas component generated from the pyrolysis vessel, and a solid-liquid separation device for separating the liquid component and pyrolysis residue from the slurry component generated from the pyrolysis vessel. The pyrolysis device may further include devices that are generally combined as a pyrolysis device for plastics, such as a chlorine fixation tank, a condenser, and a burner.

[0058] In the pyrolysis system shown in FIG. 7, a liquid substance is attached to the crushed material of the first plastic group stored in a storage vessel. The liquid substance is a part of the liquid component B recovered from the slurry component of the pyrolysis product obtained by pyrolyzing the second plastic group in the pyrolysis vessel before the pyrolysis of the first plastic group, which is returned to the storage vessel. 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 vessel. Next, the crushed material with the liquid substance attached and solid particles are put into a mixing vessel and mixed to produce a mixture. The mixture is put into the pyrolysis vessel and heated, whereby the plastics are pyrolyzed to obtain a pyrolyzed product.

[0059] Next, the slurry component of the pyrolysate in the pyrolysis vessel is separated into liquid component B and pyrolysis residue in a solid-liquid separator. Part of the new liquid component B is used as a liquid substance in the next cycle of the pyrolysis system, and the other part is recovered as a recovered liquid. The gas component of the pyrolysate 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 adhesion of the liquid substance to the crushed material of the first plastic group is performed in the mixing vessel rather than in a storage vessel.

[0061] In the pyrolysis systems shown in Figures 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 make them lighter, 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 which is the sum of liquid component B recovered from the slurry component of the pyrolysis product and liquid component A recovered by cooling the gas component.

[0064] In the thermal cracking system shown in Figure 9, part of liquid component B is used as the returned liquid material, so the heavy components in liquid component B can be thermally decomposed again to lighter components. Furthermore, part of liquid component A, which contains a large amount of light components, is used as the returned liquid material, so the viscosity of the returned liquid material can be reduced, providing 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 pyrolysis system shown in Figure 10, liquid component A containing a large amount of light components is used as the returned liquid material, which further reduces the viscosity of the returned liquid material, resulting in advantages such as reduced clogging of the return pipe and reduced 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 materials is not limited to the storage container, but may be a mixing container, or may be during transportation from the storage container to the mixing container. EXAMPLES

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

[0069] The crushed polystyrene was flake-like 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 was placed in a mixing container, and 4.0 ml of a liquid substance recovered from the pyrolysis product of the crushed polystyrene, which had been prepared separately, was sprayed on the crushed polystyrene to cause the liquid substance to adhere to the crushed polystyrene. 4.0 g of iron oxide (II, III; magnetite, Kojundo Kagaku Kenkyusho) particles (particle diameter 180 μm or less) was added as a microwave heating medium to the crushed polystyrene to which the liquid substance had adhered, and the mixture was obtained by stirring and mixing. The mixture was transferred to a quartz glass vial, which was a pyrolysis container, and placed in a microwave heating device. At this point, no classification of the mixture was observed in 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. The E / H tuner was successively adjusted to minimize the reflected power, thereby controlling microwave heating by ensuring that most of the input microwaves was used for the pyrolysis reaction.

[0071] The microwave heating device was a waveguide type single mode irradiation method. 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 the reflux equipment. The reflux equipment 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 equipment were retained at the bottom of the reflux equipment.

[0073] The atmospheric air during pyrolysis was nitrogen, and 0.4 L / min of nitrogen was constantly flowing into the waveguide of the microwave irradiation device. 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 sample was held 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 the 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 charged remained as residue. This showed that almost the entire amount of crushed polystyrene charged in the reaction vessel had been pyrolyzed. A brown liquefied product was retained 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 heat generating 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 oxide (II, III) particles, the liquid substance used in Example 1 was not sprayed, and 20.0 g of the crushed polystyrene and 4.0 g of the iron oxide (II, III) particles were stirred and mixed, then transferred to a quartz glass vial and placed in a microwave heating device. At this point, it was confirmed that the iron oxide (II, III) particles were classified at the bottom of the vial.

[0076] The microwave heating was performed in the same manner as in Example 1, and pyrolysis was performed. It took 15 minutes from the start of microwave irradiation until the sample temperature reached 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 the microwave irradiation was stopped, the vial was removed from the microwave heating device when the temperature of the vial had dropped 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 the pyrolysis efficiency of Comparative Example 1 was inferior to that of 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 quickly. In Example 1, the microwave heating medium was supported on the surface of the crushed polystyrene in the vial and was uniformly dispersed in the vial, so the sample was heated uniformly without unevenness, promoting the thermal decomposition of the sample and showing excellent thermal decomposition efficiency.

[0079] On the other hand, in Comparative Example 1, it is estimated that the iron (II, III) oxide particles of the microwave heating medium were classified at the bottom of the vial, and the bottom of the vial was locally heated. Therefore, the temperature of the bottom of the vial was raised to the desired temperature of about 400°C, but the crushed polystyrene at the top of the vial was not raised to the thermal decomposition temperature, and thermal decomposition was performed in a state where temperature unevenness occurred inside the vial, resulting in a large amount of crushed polystyrene remaining as residue.

[0080] [Table 1]

[0081] Although the embodiments and examples of the present disclosure have been described above, it is intended from the outset 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 as limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

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

Claims

1. A step of crushing a first plastic group containing plastic to obtain crushed material; A step of attaching a liquid substance to the crushed material; a step of mixing the crushed material to which the liquid substance is attached with solid particles that promote the thermal decomposition of the plastic to obtain a mixture; and charging the mixture into a pyrolysis vessel and heating the mixture to pyrolyze the plastic. A method for pyrolyzing plastics, wherein the liquid substance is identical to at least a portion of the pyrolysis products of the plastics.

2. A step of crushing a first plastics group containing plastics to obtain crushed material; A step of attaching a liquid substance to the crushed material; a step of mixing the crushed material to which the liquid substance is attached with solid particles that promote the thermal decomposition of the plastic to obtain a mixture; and charging the mixture into a pyrolysis vessel and heating the mixture to pyrolyze the plastic. A method for thermally decomposing plastics, wherein the liquid substance is obtained by refluxing at least a portion of the pyrolysis products obtained by thermally decomposing a second group of plastics containing the same type of plastic as the plastic in the pyrolysis vessel.

3. 3. The method for thermally decomposing plastics according to claim 1, wherein the step of obtaining the mixture is carried out at a temperature not exceeding the volatilization temperature of the liquid substance.

4. 3. The method for thermally decomposing plastics according to claim 1, 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.

5. 3. The method for thermally decomposing plastics according to claim 1, wherein the step of thermally decomposing the plastics includes a step of heating the mixture by irradiating the mixture with microwaves.

6. A pyrolysis apparatus used in the method for pyrolyzing plastics according to claim 1 or 2, a mixing vessel in which the step of obtaining the mixture is carried out; a pyrolysis vessel in which the step of pyrolyzing the plastic is carried out; a solid-liquid separator that separates a liquid component and a pyrolysis residue from the slurry component of the pyrolysis product in the pyrolysis vessel; A pyrolysis device, wherein a portion of the liquid component is used as the liquid substance.

7. A pyrolysis apparatus used in the method for pyrolyzing plastics according to claim 1 or claim 2, a mixing vessel in which the step of obtaining the mixture is carried out; a pyrolysis vessel in which the step of pyrolyzing the plastic is carried out; a cooler that cools and liquefies the gas component of the pyrolysis product in the pyrolysis vessel and recovers the liquid component; A pyrolysis device, wherein a portion of the liquid component is used as the liquid substance.

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