Thermal decomposition method for persistent composite plastic waste containing thermosetting plastic

Abstract

In order to thermally decompose a thermosetting plastic-containing persistent composite plastic waste represented by carbon fiber pipes, GFRP, solar panels, printed circuit boards, and waste tires, the present invention comprises: A) a thermal decomposition step for adding, to a thermal decomposition tank, a thermosetting plastic-containing persistent composite plastic waste which is a raw material to be subjected to a thermal process, and at least 20 wt%, preferably at least an equal amount, of a hydrogen-rich hydrocarbon-based plastic which is represented by PP and PE and which serves as a reaction accelerator, with respect to 100 wt% of the raw material to be subjected to a thermal process, causing a liquid phase-solid phase reaction to occur by holding the same at the melting point of the reaction accelerator for one to two hours, and then thermally decomposing the same through a gas phase-solid phase decomposition reaction by increasing the temperature to a thermal decomposition temperature to generate a hydrogen radical or a hydrocarbon radical from the reaction accelerator; and B) a recovery step for cooling and recovering a thermal decomposition oil obtained through thermal decomposition in the thermal decomposition tank; and, if needed, C) a separation step for washing, separating, and recovering metals, inorganic substances, or reinforcing fibers remaining in the thermal decomposition tank by using a glycol-based solvent. Here, examples of the hydrogen-rich hydrocarbon-based plastic include random cleavage or decomposition-type plastics represented by PE (LDPE or HDPE) and PP, which each have a high Arrhenius factor.

Description

Pyrolysis of difficult-to-decompose composite plastic waste containing thermosetting plastics

[0001] The present invention relates to a method for accelerating the thermal decomposition of difficult-to-decompose composite plastic waste containing thermosetting plastics, such as waste tires, solar panels, printed circuit boards (PCB), and fiber-reinforced plastics (FRP), by converting the solid-phase reaction of the thermosetting plastics into a liquid-solid phase reaction and a gas-solid phase reaction using a high-hydrogen-containing hydrocarbon-based plastic with a high Aurhenius factor as a decomposition accelerator.

[0002] Polymers that do not melt when heated, such as epoxy resins, urethanes, and rubber used in tires, are classified as "thermosetting plastics" and are distinct from thermoplastics. These thermosetting plastics are widely used in products requiring durability and heat resistance, such as automobiles and electrical appliances. Because their chemical bonds are significantly stronger than those of "thermoplastics," recycling is difficult when thermosetting plastics are used as the matrix in waste tires, wiring boards, fiber-reinforced plastics (FRP), and other products, unlike thermoplastics. Due to the strong bonds known as cross-linking, thermosetting plastics do not soften or melt even when reheated. Furthermore, because additives are contained in the resin, classification and sorting are difficult. Therefore, thermosetting resins are often recycled as fuel, using thermal energy. However, fiber-reinforced plastics (FRP) contain carbon and glass fibers, and wiring boards contain metals, making them unusable as fuel. Therefore, pyrolysis requires long, high-temperature processing times, which increases processing costs, while also severely degrading composite materials such as carbon fiber, making recycling and reuse difficult. For example, waste tires cannot be left unattended because they can breed mosquitoes, cause malaria epidemics, and cause fires, adversely affecting human health and the environment. Therefore, as a method for recycling waste tires, a dry distillation method has been proposed, in which waste tires are pyrolyzed in an oxygen-free environment to decompose and recover dry distillation gas, carbon black (carbide), scrap iron, etc. (Patent Documents 1 and 2). However, due to the high processing costs, most waste is crushed and landfilled or used as fuel. On the other hand, solar panels have a lifespan of 25 to 30 years. Those rapidly popularized in the 2000s will reach the end of their lifespan in the 2030s. It is estimated that approximately 170,000 to 250,000 tons of used solar panels will be discarded during this period. However, due to the lack of effective recovery methods and the lack of established methods for treating hazardous substances, methods such as crushing and physical separation (Patent Documents 3 and 4) are the predominant method.Furthermore, many printed circuit boards are used in electronic devices that require control, but there is no effective recycling method, and much of this ends up as industrial waste, resulting in approximately 200,000 to 500,000 tons of electronic waste being generated each year. However, only precious metals have been recovered through electrolytic recovery (Patent Document 5), and other heavy metals, despite being contaminants, are difficult to decompose or separate, so most are currently disposed of by incineration or burial. For persistent fiber-reinforced plastics (FRP), alcohol atmospheric pressure dissolution and subcritical water decomposition have been proposed, while laser beam irradiation (Patent Document 6) and hypochlorous acid contact methods (Patent Document 7) have also been proposed. However, these methods have poor processing efficiency, and 50 to 70% of the material is inorganic and difficult to burn, so the material is currently crushed and most of it is landfilled.

[0003] Japanese Patent Application Laid-Open No. 2003-286490 Japanese Patent Application Laid-Open No. 2024-55873 Utility Model Registration No. 23245211 Japanese Patent No. 5509834 WO2009 / 087908 Japanese Patent No. 7378123 Japanese Patent Application Laid-Open No. 2023-122265

[0004] However, even though persistent composite plastic waste containing thermosetting plastics is difficult to recycle, if not recycled, it will not only harm the environment as industrial waste but also result in a waste of resources. Therefore, efforts should be made to recover resources by applying appropriate recycling methods to waste tires, solar panels, printed circuit boards (PCBs), and fiber-reinforced plastics (FRPs). In particular, composite plastic waste containing difficult-to-recycle thermosetting plastics often contains metals, inorganic materials, and reinforcing fibers, which require different recovery methods. Therefore, so-called chemical recycling is difficult, and incineration or landfilling is the norm. However, from the perspective of resource conservation, there is an urgent need to develop a method for separating and recovering the components from persistent composite plastic waste containing thermosetting plastics for effective utilization. Therefore, in order to separate and effectively utilize the components from the composite plastic waste containing thermosetting plastics, as shown in Figure 3, considering that most plastic components thermally decompose at temperatures around 400°C and below 500°C, dry distillation pyrolysis seems to be the most suitable method for mass processing. However, because the pyrolysis process not only requires significant processing costs but also degrades the recovered components, such as reinforcing fibers, no large-scale projects are currently underway. The main reasons for this are the high temperature, high pressure, and long processing times required for the current pyrolysis process. The inventors conducted extensive research to reduce the processing costs of pyrolysis and discovered that, while the pyrolysis reaction of plastics is primarily a solid-phase reaction, when a high-hydrogen-containing hydrocarbon plastic with a high Aurhenius factor is used as the reaction solvent for the thermosetting plastic to be pyrolyzed, a liquid-solid reaction is initiated during pyrolysis. The high-hydrogen-containing hydrocarbon penetrates the thermosetting plastic matrix, and the solvent generates hydrogen radicals or hydrocarbon radicals in the atmosphere. These radicals then initiate a gas-solid reaction with the thermosetting plastic components in the waste, thereby accelerating the decomposition of the thermosetting plastic matrix, which is essentially a solid-phase reaction. The high hydrogen content plastics PE and PP used as decomposition accelerators have a high Arrhenius factor A (frequency factor) that governs the reaction rate K, which is thought to accelerate the reaction rate.

[0005] Based on this finding, the present invention aims to provide a method for pyrolyzing persistent composite plastic waste containing thermosetting plastics under atmospheric pressure in a short period of time.

[0006] Based on the findings of the high-hydrogen hydrocarbon plastics described above, the present invention provides a method for thermally decomposing refractory composite plastic waste containing thermosetting plastics, comprising: A) a pyrolysis step in which a high-hydrogen hydrocarbon plastic with a high Arrhenius factor is added to a pyrolysis vessel along with the refractory composite plastic waste containing thermosetting plastics, and the mixture is maintained at a temperature between the melting and decomposition initiation temperatures of the reaction accelerator for 1 to 2 hours to allow a liquid-solid phase reaction to occur. The temperature is then raised to the pyrolysis temperature to generate hydrogen or hydrocarbon radicals from the decomposition accelerator, resulting in thermal decomposition via a gas-solid phase decomposition reaction; B) a recovery step in which the pyrolysis oil obtained by pyrolysis in the pyrolysis vessel is cooled and recovered; and, optionally, C) a separation step in which metals, inorganic materials, or reinforcing fibers remaining in the pyrolysis vessel are washed and separated from the vessel with a glycol-based solvent. The high-hydrogen hydrocarbon plastics include random-cleavage or decomposition-type plastics, such as polyethylene (LDPE and HDPE) and polypropylene, which have high Arrhenius factors. These have high Arrhenius factors in the thermal decomposition reaction and promote the thermal decomposition reaction. Non-degradable composite plastic waste includes waste tires, solar panels, printed circuit boards (PCBs), and fiber-reinforced plastics (FRPs), which contain thermosetting plastics as the matrix plastic. Typical examples of thermosetting plastics include epoxy resins, phenolic resins, polyimide resins, unsaturated polyester resins, silicone resins, melamine resins, urea resins, vinyl ester resins, and diallyl phthalate resins. On the other hand, glycol-based solvents are preferably solvents consisting of one or a mixture of two or more of EG, DEG, or TEG, or solvents containing these as the main component. Here, "main component" means that other solvent components may be included as long as they do not impair the properties of EG, DEG, or TEG.

[0007] According to the present invention, when a high-hydrogen-content hydrocarbon-based plastic is added to a pyrolysis reactor as a decomposition accelerator, the high-hydrogen-content hydrocarbon-based plastic melts and surrounds the thermosetting plastic, which is normally a solid-phase reaction, initiating a liquid-solid reaction. It has been discovered that subsequent heating results in the generation of hydrogen radicals and hydrocarbon radicals in the atmosphere through thermal decomposition, thereby improving the rate of the pyrolysis reaction through gas-solid reaction. Considering this phenomenon, the reaction rate acceleration in pyrolysis reactions is thought to be as follows: While the pyrolysis of thermosetting plastics is typically dominated by solid-phase decomposition, the decomposition accelerator has a high hydrogen content, leading to a random decomposition pattern in which the main chain cleavage proceeds in a disordered manner, exhibiting a high Aurhenius factor, thereby accelerating the pyrolysis reaction. Therefore, it is believed that the liquid-solid reaction accompanies the pyrolysis reaction, which is primarily a solid-phase reaction. The subsequent generation of hydrogen radicals or hydrocarbon radicals in the furnace atmosphere induces a secondary gas-solid reaction, accelerating the decomposition reaction. This method of adding a decomposition accelerator to the solid-phase reaction of thermosetting plastics to accelerate the thermal decomposition of the thermosetting plastics through a liquid-solid phase reaction and then a gas-solid phase reaction is novel. ｒ０) (Study on the Pyrolysis Characteristics of Waste Plastics: Nippon Steel Technical Report No. 360) revealed that the thermal decomposition rate was more than two orders of magnitude higher than that of other plastics. Furthermore, the thermal decomposition pattern of this randomly decomposed hydrocarbon-based plastic is a chain scission process that easily generates gas. Furthermore, because this is a high-hydrogen-content, randomly decomposed hydrocarbon-based plastic, it is presumed that the generation of hydrogen and hydrocarbon radicals enhances the decomposition reaction rate. As a result, according to the present invention, the reaction time for the dry distillation pyrolysis reaction can be reduced to one-quarter or less under the same conditions. In this invention, high-hydrogen-content hydrocarbon-based plastics, such as PP and PE, are selected as decomposition accelerators for the thermal decomposition reaction of plastics. This is because: 1) they have a high Arrhenius factor, which accelerates the reaction; and 2) they are randomly decomposed hydrocarbon-based plastics with a high hydrogen content that easily generate hydrogen and hydrocarbon radicals. This is thought to be because, after the reaction accelerator melts and initiates a liquid-solid phase reaction, the hydrocarbon and hydrogen radicals formed by thermal decomposition initiate a gas-solid phase reaction, promoting the cleavage of carbon bonds in the raw material being heat-treated. Figure 3 shows the decomposition curves of various resins. PE is a compound of the formula [-CH ２ -CH ２ -], the monomer molecular weight is 28, and PP has the formula [-CH ２ -CH(CH ２ )-] and the monomer molecular weight is 44.

[0008] FIG. 1 is an explanatory diagram showing a schematic configuration of a first embodiment for carrying out the method of the present invention. FIG. 2 is an explanatory diagram showing a schematic configuration of a pyrolysis tank according to the first embodiment of the method of the present invention. FIG. 3 is a graph showing example pyrolysis curves of various resins. FIG. 4 is an explanatory diagram showing a schematic configuration of a second embodiment for carrying out the method of the present invention. FIG. 5 is a photograph showing the crude rCF recovered from a thick-walled carbon fiber pipe (a) by the method of the present invention, the rCF after cleaning (b), the epoxy decomposition product (c), the epoxy decomposition oil, and the separated epoxy decomposition product (d). FIG. 6 is a photograph showing the polyester powder (b), the GFRP pyrolysis oil (c), and the glass fiber (d) recovered from a thick-walled GFRP carbon piece (a) by the method of the present invention. FIG. 7 is a photograph showing the coke (b), the waste tire pyrolysis oil (c), and the metal (d) recovered from the pyrolysis of a waste tire (a) by the method of the present invention. FIG. 8 is a photograph showing the pyrolysis oil (b), the glass, the aluminum, and the silicon (c) recovered from the pyrolysis of a solar panel (a) by the method of the present invention. 1 is a photograph showing the copper foil (b), glass fiber (c), pyrolysis oil (d), and IC chip (e) recovered from a printed circuit board (a) after pyrolysis using the method of the present invention.

[0009] The present invention involves the thermal decomposition of persistent composite plastics containing thermosetting plastics. The process involves adding a high-hydrogen hydrocarbon plastic (e.g., PP or PE) as a reaction accelerator to a thermal decomposition vessel, along with the persistent composite plastic waste containing thermosetting plastics. The accelerator is added to the vessel at a temperature of at least 20 parts by weight per 100 parts by weight of the raw material, preferably at least one part by weight per 100 parts by weight of the raw material. The catalyst is then heated to a pyrolysis temperature to generate hydrogen or hydrocarbon radicals from the accelerator, resulting in thermal decomposition via a gas-solid decomposition reaction. The process also involves the cooling and recovery of the pyrolysis oil obtained from the pyrolysis vessel. Optionally, the process involves the separation and recovery of metals, inorganic materials, or reinforcing fibers remaining in the pyrolysis vessel. The present invention was then applied to the pyrolysis of carbon fiber pipes, GFRP, solar panels, printed circuit boards, and scrap tires, and its effectiveness was confirmed.

[0010] Example 1: Pyrolysis of Carbon Fiber Pipe with Epoxy Resin Matrix. 1) Step 1: To 61.9 g of carbon fiber pipe (20 mm thick) as shown in Figure 5(a), 74.3 g of HDPE resin and 1.9 g of caustic soda were added. The mixture was gradually heated from 350 to 420 °C under atmospheric pressure in a pyrolysis vessel and held for 1.5 hours to melt the HDPE resin. After a liquid-solid reaction, the temperature was increased from 420 to 500 °C over half an hour to pyrolyze the HDPE resin. After a gas-solid reaction, the resulting oil was collected, cooled, and recovered as pyrolysis oil. The pyrolysis oil yielded 60 g. Meanwhile, 53.8 g of crude rCF (Figure 5(b)) and 8.8 g of epoxy decomposition products (Figure 5(c)) remained in the pyrolysis vessel. 2) Step 2: The crude rCF shown in Figure 5(b) above was washed with TEG as a separating agent at 280°C, below the boiling point, for 0.5 hours under stirring, followed by rinsing with water, to obtain the rCF shown in Figure 5(b). While the conventional atmospheric pressure dissolution method (Hitachi Chemical) did not use a decomposition accelerator, it took 10 hours to treat a 10 mm thick carbon fiber pipe, the method of the present invention was able to treat a 20 mm thick pipe in 2.5 hours. Under the same conditions, a 40 mm thick pipe could be treated.

[0011] (Example 2) Thermal decomposition of GFRP 1) Step 1: 63.8 g of a GFRP piece (thickness 10 mm) with an unsaturated polyester resin matrix shown in FIG. 6(a) was mixed with 95.8 g of HDPE resin and slaked lime (Ca(OH) ２ 2.9 g of the HDPE resin was placed in a pyrolysis vessel and gradually heated from 372°C to 420°C under atmospheric pressure. The HDPE resin was melted and maintained for 1.5 hours. After the liquid-solid reaction, the temperature was increased from 420°C to 500°C over half an hour to pyrolyze the HDPE resin. After the gas-solid reaction, the oil was collected, cooled, and recovered as pyrolysis oil (see Figure 6(c)). The pyrolysis oil yield was 110 g. Meanwhile, polyester powder and crude glass fibers (Figure 6(b)) remained in the pyrolysis vessel. 2) Step 2: The crude rCF (Figure 6(a)) was washed with TEG as a separating agent at 200°C (below the boiling point) for 0.5 hours under stirring, followed by water rinsing, to obtain the glass fibers (Figure 6(d)). While the conventional method (without a decomposition accelerator) required 10 hours to process a 10 mm-thick GFRP, the method of the present invention was able to process the same GFRP in 2.5 hours.

[0012] Example 3: Pyrolysis of Solar Panels 1) Step 1: To 64.4 g of solar panels (see Figure 7(a)), 83.7 g of HDPE resin and 2.5 g of hydrated lime were added. The panels were gradually heated in a pyrolysis tank from 359°C to 420°C under atmospheric pressure over 2 hours. The HDPE resin melted and underwent a liquid-solid reaction. The temperature was then increased from 420°C to 500°C over 0.5 hours for pyrolysis. After the gas-solid reaction, the oil was collected, cooled, and recovered as pyrolysis oil (see Figure 7(b)). The pyrolysis oil yielded 73 g. Meanwhile, glass, aluminum, and silicone resin remained in the pyrolysis tank. 2) Step 2: The residue was washed with TEG at 100°C, yielding 57 g of glass, aluminum, and silicone resin (see Figure 7(c)). Thermosetting plastics are used as adhesives and sealants for solar panels.

[0013] (Example 4) Pyrolysis of Waste Tires 1) Step 1: To 53.4 g of waste tires shown in Figure 8(a), 69.4 g of HDPE resin and 2.1 g of hydrated lime were added, and the mixture was gradually heated in a pyrolysis tank from 360°C to 420°C under atmospheric pressure over two hours to melt the HDPE resin and cause a liquid-solid phase reaction. The temperature was then increased from 420°C to 500°C over half an hour to pyrolyze the resin and cause a gas-solid phase reaction, which was then collected, cooled, and recovered as pyrolysis oil (see Figure 7(b)). The amount of pyrolysis oil was 85 g. 2) Step 2: Meanwhile, the residue remaining in the pyrolysis tank was washed at 200°C using TEG, yielding the coke shown in Figure 8(c) and the metal shown in Figure 8(d).

[0014] Example 5: Pyrolysis of Printed Circuit Boards 1) Step 1: 62 parts by weight of printed circuit board (as shown in Figure 9(a)) was added with 35 parts by weight of LDPE resin and 3 parts by weight of slaked lime. The mixture was heated in a pyrolysis tank at atmospheric pressure from 370 to 430°C over one hour. The LDPE resin melted and held for one hour. After the liquid-solid reaction, the temperature was increased to 420 to 480°C and pyrolysis was continued for 0.5 hours. The gas-solid reaction occurred, which was then collected, cooled, and recovered as pyrolysis oil (see Figure 9(d)). The pyrolysis gas yielded 10 parts by weight and pyrolysis oil 25 parts by weight. Meanwhile, the remaining substrate (IC chip) remained in the pyrolysis tank. 2) Step 2: The residue was washed with TEG at 270°C, yielding 20 parts by weight of copper foil (as shown in Figure 9(b)), 15 parts by weight of glass fiber (as shown in Figure 9(c)), and 20 parts by weight of IC chips. Thermosetting plastics were used as adhesives and sealants in the printed circuit boards.

[0015] As evident from the experiments in Examples 1 to 4, HDPE was used as the decomposition accelerator, while LDPE was used in Example 5. The decomposition accelerator converts thermosetting plastics from a solid-phase reaction to a liquid-solid reaction, followed by a secondary gas-solid reaction, resulting in a thermal decomposition reaction in approximately two hours. This demonstrates that the pyrolysis of persistent composite plastic waste using thermosetting plastics can be completed in a short time, and the waste can be recovered as pyrolysis oil. Using PP instead of HDPE or LDPE provides the same Aurhenius factor (see Research on the Pyrolysis Characteristics of Waste Plastics: Nippon Steel Technical Report No. 360) and is a random-cleavage type plastic, resulting in similar results. While the above examples focused on the thermal decomposition of thermosetting plastics, the presence of thermoplastics is not a problem. The amount of decomposition accelerator used relative to the raw material to be heat-treated is approximately 20% of the thermosetting plastic in the raw material to be heat-treated, and a secondary gas-solid reaction will occur after the liquid-solid reaction. It is preferable to use an amount equal to or more than double the amount. If the raw material to be heat treated contains PE or PP, the content of these can be taken into consideration.

[0016] The configuration of an apparatus for carrying out the method of the present invention will now be described with reference to the drawings. Fig. 1 shows a pyrolysis apparatus 10 according to a first embodiment. The pyrolysis apparatus 10 according to the first embodiment includes a pyrolysis tank 12, a pyrolysis receiver tank 14, a condenser 16, an absorption tower 18, a fuel gas receiver tank 19, a seal pot 20, and a chimney 22. The pyrolysis apparatus 10 also includes a pyrolysis oil tank 24, a valve device 26, a high-temperature circulation pump 28, a three-way valve device (also referred to as a valve device) 29, and a cooler 30. Among these, the pyrolysis tank 12 includes a receiver 32, a heating furnace 34, and a combustion burner 36.

[0017] The material regeneration method performed by the thermal decomposition apparatus 10 configured as described above includes a pyrolysis process in which the raw material to be heat-treated is introduced into the pyrolysis tank 12 and pyrolyzed; a cooling process in which the pyrolysis oil obtained by pyrolysis in the pyrolysis tank 12 is cooled; a storage process in which the cooled pyrolysis oil is stored in the pyrolysis oil tank 24; a condensation process in which the volatile components obtained by pyrolysis in the pyrolysis tank 12 are condensed; and a discharge process in which the condensed volatile components are purified and discharged. More specifically, in the pyrolysis process of the first embodiment, the raw material to be heat-treated, which has been sufficiently heated, is first introduced into the tray 32 of the pyrolysis tank 12. As shown in FIG. 2 , the raw material to be heat-treated (not shown) is introduced into the tray 32, which has been removed from the pyrolysis tank 12, and the tray 32 is then placed in the pyrolysis tank 12 as indicated by arrow B. A decomposition accelerator is also introduced into the pyrolysis tank 12. In the pyrolysis tank 12, a tray 32 is heated by a combustion burner 36 in a heating furnace 34. The raw material to be heat-treated is heated in the tray 32.

[0018] The raw material to be heat-treated is the waste targeted by the present invention. Examples of waste include scrap tires, solar panels, wiring boards, silicone packing, air conditioning piping, carbon fiber, reinforced glass fiber, and specific organic compositions (combinations of multiple substances including organic materials such as synthetic resins). At least one of these materials is washed (e.g., with water or steam) and then introduced into the pyrolysis tank 12.

[0019] In the case of scrap tires, for example, rubber and other components of the tires are thermally decomposed. Solar panels sometimes use thermosetting resin raw materials for sealing materials, backsheets, etc., and one or more of these materials are thermally decomposed. Examples of wiring boards include phenolic resin, epoxy resin, polyimide, or polyester, either alone or in combination with materials other than resin (such as copper or glass fiber, which form wiring), and the resin material contained therein is thermally decomposed. Examples of air conditioning piping include metal pipes coated with resin insulation (such as polyethylene foam), and the resin insulation is thermally decomposed. Carbon fiber and reinforced glass fiber are composites of fibers and resins (such as epoxy resins, including precursors of such resins before they harden), and these resins are thermally decomposed. Examples of the organic material include resins (including their precursors before they harden) and oil. Examples of the resin include silicone resins (thermosetting), epoxy resins, and urethane resins. The inorganic material is preferably an inorganic powder. Examples of the inorganic material include carbon such as carbon fiber, metals (such as silver), metal oxides (such as alumina), metal nitrides, metal oxynitrides, and metal sulfides. Note that the metals (including metals in metal oxides) may also be semimetals (such as silicon and boron).

[0020] The thermal decomposition accelerator used is one that is suitable for the type of raw material to be heat-treated. For any of the above-mentioned waste tires, solar panels, wiring boards, silicone packing, air conditioning piping, carbon fiber (carbon fiber-containing resin), and reinforced glass fiber (reinforced glass fiber-containing resin), PE (polyethylene) resin, PP (polypropylene) resin, alkaline substances, etc. can be used as the thermal decomposition accelerator. When PE resin and PP resin are added during heating of the raw material to be heat-treated, the PE resin and PP resin may be used in mixture.

[0021] The raw materials to be heat-treated may contain PE or PP, which act as hydrogen-donating solvents. Therefore, the PE or PP contained in the raw materials to be heat-treated is also used as a pyrolysis accelerator. Any shortage of pyrolysis accelerator is added to the pyrolysis tank 12 along with the raw materials to be heat-treated (by being added to the raw materials to be heat-treated).

[0022] When the raw material to be heat-treated is an organic composition, PE, PP, etc. can be used as the thermal decomposition accelerator. Examples of the specific organic composition include compositions containing silicone (thermosetting), alumina, CF (carbon fiber), etc.

[0023] Slaked lime (calcium hydroxide) is also charged into the pyrolysis tank 12 as an alkaline substance. The alkaline substance is used to neutralize any acidic substances contained in the raw material to be heat-treated. Examples of acidic substances include PVC (polyvinyl chloride) and nitrogen compounds. Slaked lime is used to neutralize chlorine contained in the raw material to be heat-treated. Although slaked lime can be charged midway through the piping, it is usually charged into the pyrolysis tank 12 together with the raw material to be heat-treated to prevent clogging of the piping. An inorganic base other than slaked lime may also be used as the alkaline substance. For example, an alkaline earth metal hydroxide (such as magnesium hydroxide) or an alkali metal hydroxide may also be used.

[0024] The conditions for thermal decomposition in the thermal decomposition tank 12 preferably satisfy, for example, the following: Temperature: 350 to 550°C Pressure: normal pressure Time: 1 to 3 hours Accelerator: the amount of PE and PP after mixing (total amount added) is 20 to 200 wt % of the weight of the raw material to be heat-treated Slaked lime: the amount added is 1 to 3 wt % of the total weight of the raw material to be heat-treated

[0025] PE and PP are substances with a high hydrogen content. Therefore, as described above, in the pyrolysis device 10, the PE and PP contained in the various raw materials to be heat-treated function as pyrolysis accelerators. It is believed that substances other than PE and PP can also function as pyrolysis accelerators as long as they contain a high hydrogen content. The hydrogen content of various resins will be described later.

[0026] In the pyrolysis tank 12, the water content of the raw material to be heat-treated evaporates. When the raw material to be heat-treated is further heated, the resin (waste plastic) in the raw material to be heat-treated melts and liquefies. Melting of the waste plastic generates pyrolysis oil gas and other volatile components, and pyrolysis oil is obtained by cooling the pyrolysis oil gas (cooling process).

[0027] The pyrolysis fuel oil is transferred to the pyrolysis receiving tank 14 as indicated by arrow A using, for example, a transfer device (not shown) and stored therein (storage process). Volatile components generated by pyrolysis are condensed by a condenser 16. Unreacted acid gases are absorbed by an absorption tower 18 (purification process), and the fuel gas is accumulated in a fuel gas receiving tank 19. The remaining gas is prevented from backflowing by a seal pot 20 (safety device) and is released into the outside air from a chimney 22 (discharge process). Specific gases not absorbed by the absorption tower 18 (hydrogen, methane, ethane, propane gas, etc.) pass through the fuel gas receiving tank 19 and are used in a combustion burner 36.

[0028] A valve device 26, a circulating high-temperature pump 28, a three-way valve device 29, etc. are installed along the piping 40 (indicated by an arrow in FIG. 1 ) connected to the pyrolysis receiving tank 14. The pyrolysis fuel oil in the pyrolysis receiving tank 14 is sent to the pyrolysis tank 12 and the pyrolysis oil tank 24 via the valve device 26, the circulating high-temperature pump 28, and the three-way valve device 29. The pyrolysis fuel oil sent to the pyrolysis tank 12 is reused as a pyrolysis accelerator. The pyrolysis fuel oil transferred to the pyrolysis oil tank 24 is passed through a cooler 30. The pyrolysis fuel oil in the pyrolysis oil tank 24 is transferred to the combustion burner 36 via a circulation pump 42 and used by the combustion burner 36.

[0029] <Hydrogen content of various resins> For thermosetting resins, the hydrogen content of UPE (unsaturated polyester, in one example, molecular weight 158 ​​per unit) is 8.9 wt% in one example, both "per unit" and "hydrocarbon only". The hydrogen content of PR (phenolic resin, in one example, molecular weight 198 per unit) is 5.1 wt% in one unit and 6.0 wt% in "hydrocarbon only".

[0030] <Examples of Resin Thermal Decomposition Curves> Of the various resins mentioned above, thermal decomposition curves for PE, PP, PET, acrylic resin (PMMA (methacrylic resin)), ABS resin, and PVC are shown in FIG. 3. In addition to these resins, FIG. 3 also shows thermal decomposition curves for UF (urea resin), UR (polyurethane), PF (phenolic resin), and PS (polystyrene).

[0031] According to Figure 3, for example, weight loss is observed for PE from around 375°C, and the weight loss reaches 100% (weight is 0%) at around 500°C. For PP, weight loss is observed from around 340°C, and the weight loss reaches 100% at around 500°C. Furthermore, for PVC, weight loss is observed in two stages, and the weight loss stops at about 60% (weight is about 40%) between 300 and 450°C. For PS, weight loss is observed from around 290°C, and the weight loss reaches 100% (weight is 0%) at around 450°C.

[0032] Advantages of the Pyrolysis Apparatus 10 The pyrolysis apparatus 10 and material recycling method of the first embodiment utilize the differences in melting points and hydrogen contents of various resins. The pyrolysis characteristics illustrated in FIG. 3 are utilized to selectively pyrolyze the resin to be recycled contained in the raw material to be heat-treated. Unnecessary volatile components then evaporate at the target temperature, and the various liquefied resins are recovered and recycled. For many raw materials to be heat-treated, the residue remaining after pyrolysis is primarily valuable metals, fillers, and carbon.

[0033] For example, if the raw material to be heat treated is waste tires, fuel oil, metal, and filler are recycled. In the case of solar panels, glass, metal, and fuel oil are recycled. In the case of wiring boards, copper, glass fiber, and fuel oil are recycled. In the case of silicone packing, filler, fuel oil, etc. are recycled. In the case of glass fiber reinforced plastic (GFRP), glass, filler, and fuel oil (including unsaturated polyester) are recycled. In the case of carbon fiber reinforced plastic (CFRP), rCF (recycled carbon fiber) and fuel oil (including epoxy) are recycled.

[0034] Furthermore, rapid pyrolysis is carried out in the pyrolysis tank 12, making it possible to separate the raw materials to be heated in a short time. For example, conventionally, it took 15 hours to decompose a solar panel in the pyrolysis tank 12. However, with the pyrolysis device 10 and material recycling method of the first embodiment, the time required to decompose a solar panel in the pyrolysis tank 12 has been reduced to 2 hours. The pyrolysis device 10 and material recycling method capable of such rapid pyrolysis are suitable for small, regionally distributed recycling facilities. Furthermore, the pyrolysis device 10 and material recycling method of the first embodiment reuse a portion of the pyrolysis fuel oil, and therefore CO2 is generated by the thermal circulation of PE and PP. ２ Contribute to reduction.

[0035] <Pyrolysis Apparatus 50 According to Second Embodiment> Next, a pyrolysis apparatus 50 according to a second embodiment will be described. Note that descriptions of the same configuration and decomposition conditions (pyrolysis conditions) as those of the first embodiment will be omitted where appropriate. The pyrolysis apparatus 50 is a continuous version of the pyrolysis apparatus 10 according to the first embodiment, and is equipped with two pyrolysis tanks 12A and 12B. Hereinafter, the pyrolysis tanks 12A and 12B will be referred to as the first pyrolysis tank 12A and the second pyrolysis tank 12B.

[0036] In FIG. 4, the rotary kiln is designated by the reference numeral 52. The rotary kiln 52 is provided upstream of the first pyrolysis tank 12A and the second pyrolysis tank 12B. The raw material to be heat-treated is introduced into the inlet 54 of the rotary kiln 52, as indicated by arrow C. Hot gas (Hot Gas In) is introduced into the rotary kiln 52, as indicated by arrow N-1. In the second embodiment, the flow path diameter of the hot gas indicated by arrow N-1 is 600 mm (φ600), and the temperature is 550°C. Arrows C, N-1, N-3, and N-4 indicated for the rotary kiln 52 indicate the transport direction of the raw material to be heat-treated. The raw material to be heat-treated is continuously transported from the left side (upstream side) to the right side (downstream side) in the figure.

[0037] Hot gas (Hot Gas In) is introduced downstream of the rotary kiln 52 (the interrupted portion downstream of arrow C) as shown by arrow N-3. In the second embodiment, the diameter of the hot gas flow path indicated by arrow N-3 is 600 mm (φ600), and the temperature is 550°C.

[0038] Arrow N-4 in the figure indicates the flow of high-temperature gas (Hot Gas Out) discharged upstream of the rotary kiln 52 (in the example of FIG. 4, the location downstream of the input position of arrow C and upstream of arrow N-3). The flow path diameter of the high-temperature gas indicated by arrow N-4 is 600 mm (φ600), and the temperature is 240°C.

[0039] The raw material to be heat-treated that has been heated in the rotary kiln 52 is discharged downstream from the rotary kiln 52. The raw material to be heat-treated that is discharged from the rotary kiln 52 is a molten material that has become a fluid (a fluid molten material) or a solid such as a metal (a solid such as a metal).

[0040] The raw material to be heat-treated discharged from the rotary kiln 52 is transferred to the first pyrolysis tank 12A or the second pyrolysis tank 12B via the open discharge rotary valve device 56. The transfer of the raw material to be heat-treated from the rotary kiln 52 to the first pyrolysis tank 12A or the second pyrolysis tank 12B is alternately performed by intermittently opening and closing the valve devices 58, 60.

[0041] The pyrolysis fuel oil obtained in the first pyrolysis tank 12A and the second pyrolysis tank 12B is alternately transferred to the pyrolysis receiving tank 14 by intermittently switching the opening and closing of the valve devices 62, 64 (arrow A).

[0042] The high-temperature gas generated in the first thermal decomposition tank 12A and the second thermal decomposition tank 12B is introduced into the rotary kiln 52 as the high-temperature gas (Hot Gas In) indicated by the arrow N-3. In the example of Figure 4, a valve device 66 is provided in the high-temperature gas (Hot Gas In) flow path connecting the first thermal decomposition tank 12A to the rotary kiln 52 (and from the second thermal decomposition tank 12B to the rotary kiln 52). Combustion waste gas is transported through the flow path N-3 from the first thermal decomposition tank 12A and the second thermal decomposition tank 12B.

[0043] The pyrolysis fuel oil in the pyrolysis receiving tank 14 is delivered to the first pyrolysis tank 12A, the second pyrolysis tank 12B, and the pyrolysis oil tank 24 via a valve device 26, a circulating high-temperature pump 28, and a three-way valve device 29. The pyrolysis fuel oil in the pyrolysis oil tank 24 is delivered by a pump 68 to the combustion burners 36 of the first pyrolysis tank 12A and the second pyrolysis tank 12B, respectively.

[0044] In the thermal decomposition apparatus 50 according to the second embodiment, the first thermal decomposition tank 12A and the second thermal decomposition tank 12B are operated by intermittent switching, while the other components, such as the rotary kiln 52, the condensation system including the condenser 16, and the chimney 22, are operated continuously. The fluid in the rotary kiln 52 is a plastic melt or a solid such as a metal. The rotary kiln 52 generates a small amount of decomposition gas, and the water is vaporized.

[0045] The pyrolysis apparatus 50 according to the second embodiment, like the first embodiment, can regenerate various materials from raw materials to be heated, including synthetic resin materials and metal materials. Furthermore, the use of the rotary kiln 52, the first pyrolysis tank 12A, and the second pyrolysis tank 12B allows for more effective material regeneration. Furthermore, the risk of fire due to blockage of piping, etc., that may occur when pyrolysis residue is discharged outside the system is eliminated.

[0046] In the second embodiment, the first pyrolysis tank 12A and the second pyrolysis tank 12B may be switched intermittently without providing the rotary kiln 52. In this case, the raw material to be heat-treated is fed into the first pyrolysis tank 12A and the second pyrolysis tank 12B, respectively.

[0047] 10, 50: Pyrolysis apparatus 12: Pyrolysis tank 12A: First pyrolysis tank 12B: Second pyrolysis tank 14: Pyrolysis receiving tank 16: Condenser 18: Absorption tower 19: Fuel gas receiving tank 20: Seal pot 22: Chimney 24: Pyrolysis oil tank 26: Valve device 28: Circulating high-temperature pump 30: Cooler 32: Receiving tray 34: Heating furnace 36: Combustion burner 40: Piping

Claims

1. A method for thermally decomposing difficult-to-decompose composite plastic waste containing thermosetting plastics, comprising: A) a thermal decomposition step in which a high-hydrogen-containing hydrocarbon plastic with a high Arrhenius factor is added as a decomposition accelerator to a thermal decomposition tank together with the difficult-to-decompose composite plastic waste, which is the raw material to be heat-treated, and the difficult-to-decompose composite plastic waste is subjected to a liquid-solid phase reaction at the melting temperature of the decomposition accelerator, and then the temperature is raised to the thermal decomposition temperature to generate hydrogen radicals or hydrocarbon radicals from the decomposition accelerator, causing the difficult-to-decompose composite plastic waste to undergo a gas-solid phase decomposition reaction and thermal decomposition; and B) a recovery step in which the pyrolysis oil obtained by thermal decomposition in the pyrolysis tank is cooled and recovered.

2. A method for pyrolysis of difficult-to-decompose composite plastic waste containing thermosetting plastics as described in claim 1, wherein the difficult-to-decompose composite plastic waste contains one selected from the group consisting of carbon fiber pipes, GFRP, solar panels, printed circuit boards, and waste tires.

3. A method for thermally decomposing difficult-to-decompose composite plastic waste containing thermosetting plastics according to claim 1, wherein the high-hydrogen-containing hydrocarbon plastics with high Arrhenius factors contain polyethylene or polypropylene.

4. A method for thermally decomposing difficult-to-decompose composite plastic waste containing thermosetting plastics as described in claim 1, in which the high-hydrogen-containing hydrocarbon plastic with a high Arrhenius factor is added in an amount equal to or greater than the thermosetting plastic content of the difficult-to-decompose composite plastic waste.

5. The method for pyrolysis of persistent composite plastic waste containing thermosetting plastics according to claim 1, wherein the liquid-solid phase reaction is carried out in a molten state of the high-hydrogen-containing hydrocarbon-based plastic with a high Arrhenius factor in a temperature range of 350°C to 420°C by stepwise heating, and the gas-solid phase reaction is carried out in a thermal decomposition state of the high-hydrogen-containing hydrocarbon-based plastic with a high Arrhenius factor in a temperature range of 420°C to 500°C by stepwise heating.

6. The pyrolysis method according to claim 1, further comprising a separation step C) of washing and recovering metals, inorganic substances or reinforcing fibers remaining in the pyrolysis tank with a glycol-based solvent.

7. The thermal decomposition method according to claim 6, wherein the glycol solvent comprises one or more selected from the group consisting of EG, DEG and TEG.

Images