Method for accelerating thermal decomposition of poorly-decomposable composite plastic waste material

Abstract

[Configuration] Provided is a method for thermally decomposing a poorly-decomposable composite plastic waste material containing a thermosetting plastic typified by a carbon fiber pipe, a GFRP, a solar panel, a printed circuit board, and a waste tire, the method comprising (A) adding, as a reaction accelerator, a PP- or PE-containing PS-free hydrogen-rich hydrocarbon-based plastic having a high Arrhenius factor into a thermal decomposition tank together with the poorly-decomposable composite plastic waste material containing the thermosetting plastic that is a material to be thermally processed, in an amount of 20 parts by weight or more and preferably in an equal amount or more with respect to 100 parts by weight of the material to be thermally processed; keeping the melting temperature of the reaction accelerator for 1 to 2 hours to perform a (liquid phase)-(solid phase) reaction; and subsequently raising the temperature to a thermal decomposition temperature to generate hydrogen radical or hydrocarbon radical from the reaction accelerator, thereby achieving the thermal decomposition by a (gas phase)-(solid phase) decomposition reaction. Examples of the reaction accelerator include random cleavage or decomposition type plastics each having a high Arrhenius factor, typified by PE (LDPE or HDPE) and PP.

Description

Method for accelerating the thermal decomposition of recalcitrant composite plastic waste

[0001] The present invention relates to a method for promoting thermal decomposition of recalcitrant composite plastic waste, such as waste tires, solar panels, printed circuit boards (PCBs), and fiber-reinforced plastics (FRP), by using a high hydrogen-containing hydrocarbon plastic with a high Aurenius factor as a decomposition accelerator, and converting the solid-phase reaction of the recalcitrant plastic into a liquid-phase-solid reaction and a gas-phase-solid reaction, thereby generating hydrogen radicals.

[0002] Polymer compounds 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 extremely strong compared to "thermoplastics," recycling is difficult when thermosetting plastics are used as a matrix in materials such as waste tires, circuit boards, and fiber-reinforced plastics (FRP), unlike with thermoplastics. In other words, due to the strong bonds known as cross-linking, they do not soften or melt even when heated again. Furthermore, because the resin contains additives, sorting and classification are not possible, and therefore, the recycling of thermosetting resins is often done by using them as fuel, which provides thermal energy. However, fiber-reinforced plastics (FRP) contain carbon fibers and glass fibers, and circuit boards contain metals, so they cannot be used as fuel. Therefore, if thermal decomposition is attempted, it requires high temperature and long processing time, resulting in high processing costs, while the composite materials such as carbon fibers deteriorate severely, making recycling and reuse difficult. For example, if waste tires are not managed and are landfilled or dumped, they can cause mosquito outbreaks, leading to malaria epidemics, and can also cause fires, thus negatively impacting human health and the environment, and cannot be left unattended. Therefore, a method has been proposed to recycle waste tires by dry distillation, in which waste tires are thermally decomposed in an oxygen-free environment to recover dry distillation gas, carbon black (carbide), iron scrap, etc. However, because the processing costs are high, most are crushed and landfilled or used as fuel. On the other hand, solar panels have a lifespan of 25 to 30 years, and those that rapidly spread in the 2000s will reach the end of their lifespan in the 2030s. It is predicted that approximately 170,000 to 250,000 tons of used solar panels will be discarded during this period. However, there is no effective recovery method, and coupled with the lack of established methods for treating hazardous substances, the main method of disposal is crushing and physical separation (Patent Documents 3 and 4).Furthermore, many electronic devices requiring control systems use printed circuit boards, but there is no effective recycling method, and much of it becomes industrial waste, generating approximately 200,000 to 500,000 tons of electronic waste annually. However, while precious metals are contained and only the metals are recovered electrolytically (Patent Document 5), other heavy metals are pollutants, and because decomposition and separation are difficult, the majority is currently disposed of by incineration or burial. In addition, for recalcitrant fiber-reinforced plastics (FRP), while methods such as alcohol dissolution at atmospheric pressure and subcritical water cracking have been proposed, laser irradiation (Patent Document 6) and hypochlorous acid contact (Patent Document 7) have also been proposed. However, these methods have poor processing efficiency, and since 50-70% is inorganic and difficult to burn, the majority is currently crushed and landfilled.

[0003] Japanese Patent Publication No. 2003-286490, Japanese Patent Publication No. 2024-55873, Utility Model Registration No. 23245211, Patent No. 5509834, WO2009 / 087908, Patent No. 7378123, Japanese Patent Publication No. 2023-122265, Japanese Patent Publication No. 1997-104873

[0004] However, even though recyclable composite plastic waste, including thermosetting plastics, is difficult to recycle, if it is not recycled, it not only harms the environment as industrial waste but also wastes resources. Therefore, appropriate recycling methods should be applied to waste tires, solar panels, printed circuit boards (PCBs), and fiber-reinforced plastics (FRP) to recover resources. In particular, composite plastic waste, including thermosetting plastics, which is difficult to recycle, often contains metals, inorganic materials, and reinforcing fibers that require different recovery methods, making so-called chemical recycling difficult. As a result, incineration or landfill is the main methods of disposal. However, from the perspective of resource conservation, there is an urgent need to provide methods for the separate collection and recovery of its components. Therefore, in order to separate and effectively utilize components from recyclable composite plastic waste, including thermosetting plastics, considering that most plastic components decompose at around 400°C or below 500°C, as shown in Figure 3, the dry distillation method seems desirable for large-scale processing. However, such carbonization pyrolysis methods currently require significant processing costs and degrade the components of the recovered reinforcing fibers, so large-scale projects are not underway. In other words, the main reason for this is that the current carbonization pyrolysis method requires high temperature, high pressure, and long processing time. Therefore, the inventors have diligently researched ways to reduce the processing costs of carbonization pyrolysis and have found that, although the thermal decomposition reaction of plastics during carbonization pyrolysis is mainly a solid-phase reaction, if a high hydrogen-containing hydrocarbon plastic with a high Aurenius factor is used as the reaction solvent for the thermosetting plastic to be carbonized, a liquid-solid-phase reaction is initiated under carbonization pyrolysis. The high hydrogen-containing hydrocarbon penetrates the matrix of the thermosetting plastic, and then, as hydrogen radicals or hydrocarbon radicals are generated in the atmosphere due to the thermal decomposition of the solvent, these begin a gas-solid-phase reaction with the thermosetting plastic components in the waste, thus promoting the decomposition of the thermosetting plastic matrix, which is originally a solid-phase reaction. High-hydrogen-containing plastics such as PE and PP, used as decomposition accelerators, have high levels of Arrhenius factor A (frequent factor), which governs the reaction rate K, and it is thought that this accelerates the reaction rate.Further research revealed that while prior literature 8 proposes a method for obtaining high-boiling-point oil from thermosetting plastics by using polystyrene (PS), polypropylene (PP), and polyethylene (PE), collectively known as the 3Ps, as oil-forming materials for thermal decomposition of thermosetting plastics, polystyrene is an aromatic hydrocarbon and, unlike other oil-forming materials, exhibits a different effect in promoting thermal decomposition. Specifically, although polystyrene is classified as an oil-forming material along with polyethylene and polypropylene, it has a lower hydrogen content compared to other hydrocarbons, and is an aromatic hydrocarbon that does not undergo random cleavage or decomposition like PP and PE. Looking at the Arrhenius factor, the aromatic hydrocarbon PS has a factor of 9.24 × 10 at 50°C. １３ And, randomly cleaving HDPE yields 4.44 × 10⁻¹⁴ at 50°C. ２９ The results were overwhelmingly small (see Table 6 in "Study on the thermal decomposition characteristics of waste plastics"), indicating that the involvement of hydrogen radical generation, which promotes resin decomposition, is extremely small (see Figure 10(a)(b)).

[0005] Based on the novel finding that a large Arrhenius factor indicates a hydrocarbon with a high hydrogen content that is prone to generating hydrogen radicals, the present invention aims to provide a method for the thermal decomposition of recalcitrant composite plastic waste, including thermosetting plastics, in a short time under atmospheric pressure.

[0006] The present invention is based on the above-mentioned knowledge regarding high hydrogen-containing hydrocarbon plastics, and is a method for accelerating thermal decomposition of recalcitrant composite plastic waste, including thermosetting plastics. This method involves adding a high hydrogen-containing hydrocarbon plastic containing PE or PP and not PS, with a high Arrhenius factor, to the thermal decomposition tank along with the recalcitrant composite plastic waste, which is the raw material to be heated, and then maintaining the temperature from the melting start temperature of the reaction accelerator to the decomposition start temperature for 1 to 2 hours to carry out a liquid-solid phase reaction, and then raising the temperature to the thermal decomposition temperature to generate hydrogen radicals or hydrocarbon radicals from the decomposition accelerator, thereby causing thermal decomposition by a gas-solid phase decomposition reaction. Here, examples of high hydrogen-containing hydrocarbon plastics include random cleavage or decomposition type plastics represented by PE (LDPE and HDPE) and PP, which have a high Arrhenius factor. These have a high Arrhenius factor in the thermal decomposition reaction, and it is thought that hydrogen radicals are involved in promoting the thermal decomposition reaction. Resistant composite plastic waste includes waste tires, solar panels, printed circuit boards (PCBs), and fiber-reinforced plastics (FRP), and refers to waste containing thermosetting plastics as the matrix plastic. Typical 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.

[0007] According to the present invention, when a high-hydrogen-content hydrocarbon plastic is added to a pyrolysis vessel as a decomposition accelerator, the high-hydrogen-content hydrocarbon plastic melts and surrounds the thermosetting plastic, which is originally a solid-phase reaction, causing a liquid-solid-phase reaction. Subsequently, when the temperature is increased, hydrogen radicals and hydrocarbon radicals are generated in the atmosphere by thermal decomposition, and it has been found that this improves the rate of the carbonization decomposition reaction under a gas-solid-phase reaction. Considering this phenomenon, the phenomenon of accelerated reaction rate in the carbonization pyrolysis reaction can be thought to be as follows: The thermal decomposition of thermosetting plastics is usually dominated by solid-phase decomposition reactions, but the decomposition accelerator has a high hydrogen content, and the thermal decomposition pattern is classified as a random cleavage type in which the cleavage of the main chain proceeds in an undisordered manner, resulting in a high Aurenius factor, which is thought to promote the thermal decomposition reaction. Therefore, it is thought that a liquid-solid-phase reaction accompanies the thermal decomposition reaction, which is mainly a solid-phase reaction, and when hydrogen radicals or hydrocarbon radicals are generated in the furnace atmosphere thereafter, they are influenced by the secondary gas-solid-phase reaction and promote the decomposition reaction. The method of adding a decomposition accelerator to the solid-phase reaction of such thermosetting plastics, thereby accelerating the thermal decomposition of the thermosetting plastics through a liquid-phase-solid-phase reaction followed by a gas-phase-solid-phase reaction, is novel. Incidentally, the Arrhenius factor (K) in the thermal decomposition reaction of PP and PE is... ｒ０When the Arrhenius factor of waste plastics is investigated (Research on the thermal decomposition characteristics of waste plastics: Nippon Steel Technical Report No. 360), it is found to be overwhelmingly larger than that of other plastics. Furthermore, its thermal decomposition pattern involves main chain severance, making it easy to generate gas. Moreover, it is a random decomposition type hydrocarbon plastic with a high hydrogen content, so it is presumed that the generation of hydrogen radicals and hydrocarbon radicals improves the decomposition reaction rate. As a result, according to the present invention, the reaction time for the carbonization thermal decomposition reaction can be reduced to less than a quarter of the original time, provided that all other conditions are the same. In the present invention, high hydrogen-containing hydrocarbon plastics, such as PP and PE, are selected as decomposition accelerators in the thermal decomposition reaction of plastics. This is because 1) they have a high Arrhenius factor that promotes the reaction, and 2) they are random decomposition type hydrocarbon plastics with a high hydrogen content that easily generate hydrogen radicals and hydrocarbon radicals. The reason for this is thought to be that after the reaction accelerator melts and undergoes a liquid-solid phase reaction, the hydrocarbon radicals and hydrogen radicals formed by thermal decomposition undergo a gas-solid phase reaction, promoting the cleavage of carbon bonds in the raw material being heated. Figure 3 shows the decomposition curves of various resins, but PE is given by the formula [-CH ２ -CH ２ It is represented by [-CH], the monomer molecular weight is 28, and PP is represented by the formula [-CH]. ２ -CH(CH ２ It is represented as )-] and the monomer molecular weight is 44.

[0008] This is a schematic diagram showing the configuration of a first embodiment for carrying out the method of the present invention. This is a schematic diagram showing the configuration of a pyrolysis tank according to the first embodiment of the method of the present invention. This is a graph showing examples of pyrolysis curves for various resins. This is a schematic diagram showing the configuration of a second embodiment for carrying out the method of the present invention. This is a photograph showing the recovered crude rCF and rCF after washing (b), epoxy decomposition products (c), epoxy decomposition oil, and separated epoxy decomposition products (d) after pyrolysis of a thick-walled carbon fiber pipe (a) using the method of the present invention. This is a photograph showing the recovered polyester powder (b), GFRP pyrolysis oil (c), and glass fibers (d) after pyrolysis of a thick-walled GFRP carbon piece (a) using the method of the present invention. This is a photograph showing the recovered coke (b), waste tire pyrolysis oil (c), and metal (d) after pyrolysis of a waste tire (a) using the method of the present invention. This is a photograph showing the recovered pyrolysis oil (b), glass, aluminum, and silicon (c) after pyrolysis of a solar panel (a) using the method of the present invention. This photograph shows the copper foil (b), glass fiber (c), pyrolysis oil (d), and IC chip (e) recovered after thermal decomposition of a printed circuit board (a) using the method of the present invention. This photograph compares the results when HDPE was used as the decomposition accelerator in Example 1 (a) and the results when polystyrene was used instead of HDPE in the comparative example (b).

[0009] The present invention provides a thermal decomposition method for thermally decomposing a recalcitrant composite plastic containing a thermosetting plastic, comprising: A) a thermal decomposition step in which a high hydrogen-containing hydrocarbon plastic, such as PP and PE, is added as a reaction accelerator to a thermal decomposition tank along with the recalcitrant composite plastic waste containing the thermosetting plastic, which is the raw material to be heated, in an amount of 20 parts by weight or more per 100 parts by weight of the raw material to be heated, preferably equal to or greater than the amount by weight of the thermosetting plastic; holding the tank at the melting temperature of the reaction accelerator for 1 to 2 hours to carry out a liquid-phase-solid-phase reaction; then raising the temperature to the thermal decomposition temperature to generate hydrogen radicals or hydrocarbon radicals from the reaction accelerator, and thermal decomposition by a gas-phase-solid-phase decomposition reaction; B) a recovery step in which the thermal decomposition oil obtained by thermal decomposition in the thermal decomposition tank is cooled and recovered; and, if necessary, C) a separation step in which metals, inorganic materials or reinforcing fibers remaining in the thermal decomposition tank are washed with a glycol-based solvent and separated and recovered. The present invention provides a thermal decomposition method for carbon fiber pipes, GFRP, solar panels, printed circuit boards, and waste tires, and its effects have been confirmed.

[0010] (Example 1) Thermal decomposition of carbon fiber pipe with epoxy resin matrix 1) Step 1: 74.3 g of HDPE resin and 1.9 g of caustic soda were added to 61.9 g of carbon fiber pipe (wall thickness 20 mm) shown in Figure 5(a). The mixture was gradually heated in a thermal decomposition tank from 350°C to 420°C under atmospheric pressure and held for 1.5 hours to melt the HDPE resin. After the liquid-solid phase reaction, the temperature was raised from 420°C to 500°C in half an hour to thermally decompose the HDPE resin. After the gas-solid phase reaction, the mixture was collected and cooled to recover it as thermal decomposition oil. The amount of thermal decomposition oil was 60 g. On the other hand, 53.8 g of crude rCF shown in Figure 5(b) and 8.8 g of epoxy decomposition products shown in Figure 5(c) remained in the thermal decomposition tank. 2) Step 2: The crude rCF shown in Figure 5(b) above was washed with TEG as a separating agent at 280°C (below its boiling point) for 0.5 hours under stirring, and then washed with water to obtain the rCF shown in Figure 5(b). In the conventional atmospheric pressure dissolution method (Hitachi Chemical), when no decomposition accelerator was used, it took 10 hours to process a carbon fiber pipe with a wall thickness of 10 mm, whereas with the present invention, a pipe with a wall thickness of 20 mm could be processed in 2.5 hours. A pipe with a wall thickness of 40 mm can be processed under the same conditions. (Comparative Example) When PS resin was used as a decomposition accelerator instead of HDPE resin, and the thermal decomposition method was applied in the same manner as in Example 1, there was no epoxy resin residue on the carbon fiber surface in the case of HDPE (Figure 10(a)), but when PS resin was used, epoxy resin remained on the carbon fiber surface (Figure 10(b)).

[0011] (Example 2) Thermal decomposition of GFRP 1) Step 1: 63.8 g of GFRP piece (10 mm thick) with unsaturated polyester resin as the matrix as shown in Figure 6(a) is mixed with 95.8 g of HDPE resin and slaked lime (Ca(OH) ２) 2.9 g was placed in a pyrolysis tank and gradually heated from 372°C to 420°C under atmospheric pressure to melt the HDPE resin. This was maintained for 1.5 hours, and after the liquid-solid phase reaction, the temperature was raised from 420°C to 500°C in half an hour to pyrolyze the HDPE resin. After the gas-solid phase reaction, this was collected and cooled to recover as pyrolysis oil (see Figure 6(c)). The amount of pyrolysis oil was 110 g. On the other hand, polyester powder and crude glass fibers as shown in Figure 6(b) remained in the pyrolysis tank. 2) Step 2: The crude rCF shown in Figure 6(a) above was washed with TEG as a separating agent at 200°C below the boiling point for 0.5 hours under stirring, and then washed with water to obtain the glass fibers shown in Figure 6(d). In the conventional method (without a decomposition accelerator), it took 10 hours to process GFRP with a wall thickness of 10 mm, whereas in the present invention, the same GFRP could be processed in 2.5 hours.

[0012] (Example 3) Thermal decomposition of a solar panel 1) Step 1: 83.7 g of HDPE resin and 2.5 g of slaked lime were added to 64.4 g of the solar panel shown in Figure 7(a). The panel was gradually heated in a thermal decomposition tank from 359°C to 420°C over 2 hours under atmospheric pressure to melt the HDPE resin and undergo a liquid-solid phase reaction. The temperature was then raised from 420°C to 500°C over 0.5 hours to cause thermal decomposition. After a gas-solid phase reaction, the material was collected and cooled to recover it as thermal decomposition oil (see Figure 7(b)). The amount of thermal decomposition oil was 73 g. On the other hand, glass, aluminum, and silicone resin remained in the thermal decomposition tank. 2) Step 2: The residue was washed with TEG at 100°C to obtain 57 g of glass, aluminum, and silicone resin as shown in Figure 7(c). Note that thermosetting plastics are used as adhesives and sealants in solar panels.

[0013] (Example 4) Pyrolysis of waste tires 1) Step 1: 69.4 g of HDPE resin and 2.1 g of slaked lime were added to 53.4 g of waste tires shown in Figure 8(a), and the mixture was gradually heated in a pyrolysis tank from 360°C to 420°C over 2 hours under atmospheric pressure to melt the HDPE resin and allow a liquid-solid phase reaction to occur. The temperature was then raised from 420°C to 500°C over half an hour to allow for pyrolysis and a gas-solid phase reaction to occur. This was collected and cooled to recover as pyrolysis oil (see Figure 7(b)). The amount of pyrolysis oil was 85 g. 2) Step 2: On the other hand, the residue remaining in the pyrolysis tank was washed at 200°C using a TEG to obtain coke shown in Figure 8(c) and metal shown in Figure 8(d).

[0014] (Example 5) Thermal decomposition of printed circuit board 1) Step 1: 35 parts by weight of LDPE resin and 3 parts by weight of slaked lime were added to 62 parts by weight of the printed circuit board shown in Figure 9(a). The mixture was heated in a thermal decomposition chamber at atmospheric pressure from 370°C to 430°C for 1 hour to melt the LDPE resin, and held for 1 hour. After the liquid-solid phase reaction, the temperature was raised to 420°C to 480°C and thermal decomposition was carried out for 0.5 hours, followed by a gas-solid phase reaction. This was collected and cooled to recover as thermal decomposition oil (see Figure 9(d)). There were 10 parts by weight of thermal decomposition gas and 25 parts by weight of thermal decomposition oil. On the other hand, residual circuit board IC chips remained in the thermal decomposition chamber. 2) Step 2: The residue was washed with TEG at 270°C to obtain 20 parts by weight of copper foil shown in Figure 9(b), 15 parts by weight of glass fiber shown in Figure 9(c), and 20 parts by weight of IC chips. Note that thermosetting plastics are used as adhesives and sealants in printed circuit boards.

[0015] As is clear from the experiments in Examples 1 to 4 above, HDPE was used as the decomposition accelerator, and LDPE was used in Example 5. It can be seen that the thermosetting plastic is converted from a solid-phase reaction to a liquid-solid-phase reaction by the decomposition accelerator, and then a secondary reaction of gas-solid-phase reaction occurs, resulting in a thermal decomposition reaction in about two hours. This allows for the thermal decomposition of difficult-to-decompose composite plastic waste using thermosetting plastics in a short time, and the thermal decomposition oil can be recovered. Even if PP is used instead of HDPE or LDPE, the Aurenius factor is equivalent (see Research on the Thermal Decomposition Characteristics of Waste Plastics: Nippon Steel Technical Report No. 360), and since it is a random-fracture type plastic, equivalent effects can be obtained. In the above examples, the thermal decomposition was performed on thermosetting plastics, but there is no problem even if thermoplastics are included. The amount of decomposition accelerator used relative to the raw material to be heated should be about 20% of the amount of thermosetting plastic in the raw material to start the gas-solid-phase reaction after the liquid-solid-phase reaction, but it is preferable to use an equal amount to more than twice the amount. If the raw material to be heat-treated contains PE or PP, their proportions can be taken into consideration.

[0016] The apparatus configuration for carrying out the method of the present invention will be described below with reference to the drawings. Figure 1 shows a pyrolysis apparatus 10 according to the first embodiment. The pyrolysis apparatus 10 according to the first embodiment includes a pyrolysis tank 12, a pyrolysis receiving tank 14, a condenser 16, an absorption tower 18, a fuel gas receiving 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 circulating high-temperature pump 28, a three-way valve device (also called a valve device) 29, and a cooler 30. Of these, the pyrolysis tank 12 includes a receiving tray 32, a heating furnace 34, and a combustion burner 36.

[0017] The material regeneration method performed by the pyrolysis apparatus 10 with this configuration comprises a pyrolysis step of introducing the raw material to be heated into the pyrolysis tank 12 and pyrolyzing it, a cooling step of cooling the pyrolysis oil obtained by pyrolysis in the pyrolysis tank 12, a storage step of storing the cooled pyrolysis oil in the pyrolysis oil tank 24, a condensation step of condensing the volatile components obtained by pyrolysis in the pyrolysis tank 12, and a discharge step of purifying and discharging the condensed volatile components. More specifically, first, in the pyrolysis step of the first embodiment, the raw material to be heated, which has been sufficiently heated, is introduced into the receiving tray 32 of the pyrolysis tank 12. As shown in Figure 2, the raw material to be heated (not shown) is introduced into the receiving tray 32, which has been withdrawn from the pyrolysis tank 12, and the receiving tray 32 is placed back into 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, the receiving tray 32 is heated by the combustion burner 36 inside the heating furnace 34. The raw material to be heated is heated in the receiving tray 32.

[0018] The raw materials to be heat-treated are the waste materials covered by this invention. Examples of waste materials include used tires, solar panels, circuit boards, silicone gaskets, air conditioning pipes, carbon fibers, reinforced glass fibers, and specific organic compositions (substances that combine multiple substances containing organic materials such as synthetic resins). At least one of these is put into the pyrolysis tank 12 after being washed (for example, by washing with water or steam).

[0019] In the case of waste tires, for example, the rubber that makes up the tire is thermally decomposed. In solar panels, thermosetting resin raw materials may be used for encapsulants, sealants, backsheets, etc., and one or more of these are thermally decomposed. Examples of wiring boards include materials in which phenolic resin, epoxy resin, polyimide, or polyester is used alone or in combination with materials other than resin (such as metals that make up the wiring, such as copper, or glass fibers), and the resin material contained in these is thermally decomposed. Examples of air conditioning piping include materials in which metal pipes are covered with resin insulation material (such as polyethylene foam), and the resin insulation material is thermally decomposed. Carbon fibers and reinforced glass fibers are, for example, composites of fibers and resin (such as epoxy resin, and also including precursors before such resins harden), and these resins are thermally decomposed. Examples of the above organic materials include resin (including its precursor before hardening) and oil. Examples of the above resins include silicone resin (thermosetting), epoxy resin, and urethane resin. The above inorganic materials are preferably inorganic powders. Examples of the inorganic materials mentioned above include carbon such as carbon fibers, metals (silver, etc.), metal oxides (alumina, etc.), metal nitrides, metal oxynitrides, and metal sulfides. Note that the term "metal" here (including metals in metal oxides, etc.) may also refer to metalloids (silicon, boron, etc.).

[0020] As a thermal decomposition accelerator, one suitable for the type of raw material to be heat-treated is used. For any of the above-mentioned waste tires, solar panels, circuit boards, silicone gaskets, air conditioning pipes, carbon fibers (carbon fiber-containing resins), and reinforced glass fibers (reinforced glass fiber-containing resins), PE (polyethylene) resin, PP (polypropylene) resin, and alkaline substances can be used as thermal decomposition accelerators. 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 form.

[0021] Some of the raw materials to be heat-treated contain PE and PP, and the PE and PP contained in the raw materials act as hydrogen-donating solvents. For this reason, the PE and PP contained in the raw materials to be heat-treated are also used as thermal decomposition accelerators. Any insufficient thermal decomposition accelerator is added to the thermal decomposition tank 12 along with the raw materials to be heat-treated (added to the raw materials).

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

[0023] In the pyrolysis tank 12, slaked lime (calcium hydroxide) is also added as an alkaline substance. The alkaline substance is used to neutralize acidic substances in the raw material to be heated. 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 heated. Although it is possible to add slaked lime in the middle of the piping, it is added to the pyrolysis tank 12 together with the raw material to be heated to prevent blockage of the piping. As the alkaline substance, inorganic bases other than slaked lime may be used, for example, alkaline earth metal hydroxides (magnesium hydroxide, etc.) or alkali metal hydroxides may be used.

[0024] The conditions for pyrolysis in the pyrolysis tank 12 are preferably as follows: 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 heated Slaked lime: The amount added is 1 to 3 wt% of the total weight of the raw material to be heated

[0025] PE and PP are substances with a high hydrogen content. Therefore, in the pyrolysis apparatus 10, as mentioned above, the PE and PP contained in the various raw materials to be heated function as pyrolysis accelerators. It is thought that substances other than PE and PP, as long as they have a high hydrogen content, can also function as pyrolysis accelerators. The hydrogen content of various resins will be discussed later.

[0026] In the pyrolysis tank 12, the water in the raw material to be heated evaporates. When the raw material is heated further, the resin (waste plastic) in the raw material melts and liquefies. The 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 step).

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

[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 Figure 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, etc. 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 the circulation pump 42 and used in the combustion burner 36.

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

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

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

[0032] <Advantages of the Pyrolysis Apparatus 10> According to the pyrolysis apparatus 10 and material regeneration method of the first embodiment, the differences in melting points and hydrogen content of various resins are utilized. Then, the pyrolysis characteristics exemplified in Figure 3 are utilized, and the resins to be regenerated contained in the raw material to be heated are selectively pyrolyzed. Then, unwanted volatile components evaporate at the target temperature, and the liquefied various resins are recovered and regenerated. For many raw materials to be heated, the residues remaining after pyrolysis are mainly high-value 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 circuit boards, copper, glass fiber, and fuel oil are recycled. In the case of silicone gaskets, 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, high-speed pyrolysis is performed in the pyrolysis tank 12, and it is possible to separate the raw material to be heat-treated in a short time. For example, conventionally, for a solar panel, it took 15 hours to decompose in the pyrolysis tank 12. However, according to the pyrolysis apparatus 10 and the material recycling method of the first embodiment, for the solar panel, the time required for decomposition in the pyrolysis tank 12 was shortened to 2 hours. The pyrolysis apparatus 10 and the material recycling method capable of such high-speed pyrolysis are suitable for small-scale regional distributed recycling facilities. In addition, the pyrolysis apparatus 10 and the material recycling method of the first embodiment reuse a part of the pyrolysis fuel oil, so by the heat circulation of PE and PP, CO ２ contributes to the reduction.

[0035] <Pyrolysis apparatus 50 according to the second embodiment> Next, the pyrolysis apparatus 50 according to the second embodiment will be described. Regarding the same configurations and decomposition conditions (pyrolysis conditions) as those of the first embodiment, the description will be omitted as appropriate. The pyrolysis apparatus 50 is obtained by changing the pyrolysis apparatus 10 according to the first embodiment into a continuous type, and includes two-stage 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] What is indicated by reference numeral 52 in FIG. 4 is a rotary kiln. The rotary kiln 52 is provided in the front stage of the first pyrolysis tank 12A and the second pyrolysis tank 12B. As shown by arrow C, the raw material to be heat-treated is charged into the charging port 54 of the rotary kiln 52. High-temperature gas (Hot Gas In) is introduced into the rotary kiln 52 as shown by arrow N-1. In the second embodiment, the flow path diameter of the high-temperature gas related to arrow N-1 is 600 mm (φ600), and the temperature is 550°C. Arrows C, N-1, N-3, and N-4 indicating the rotary kiln 52 represent the transfer direction of the raw material to be heat-treated. The raw material to be heat-treated is continuously transferred from the left side (upstream side) to the right side (downstream side) in the figure.

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

[0038] The arrow N-4 in the figure indicates the flow of the hot gas (Hot Gas Out) discharged at the upstream side of the rotary kiln 52 (in the example of FIG. 4, the part downstream of the input position of arrow C and upstream of arrow N-3). The flow path of the hot gas related to arrow N-4 is 600 mm (φ600), and the temperature is 240 °C.

[0039] The raw material to be heat-treated heated in the rotary kiln 52 is discharged from the rotary kiln 52 on the downstream side. The raw material to be heat-treated discharged from the rotary kiln 52 is a fluid melt (fluid melt) or a solid such as metal (metal and other solids).

[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 through 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 switching the opening and closing of the valve devices 58 and 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 (arrow A) by intermittently switching the opening and closing of the valve devices 62 and 64.

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

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

[0044] In such a pyrolysis device 50 according to the second embodiment, intermittent switching processing is performed on the first pyrolysis tank 12A and the second pyrolysis tank 12B, and continuous processing is performed on the other rotary kiln 52, the condensation system including the condenser 16, the chimney 22, etc. And the fluid in the rotary kiln 52 is a plastic melt or a solid such as metal. The decomposition gas generated in the rotary kiln 52 is small, and the moisture is vaporized.

[0045] And according to the pyrolysis device 50 according to the second embodiment, similar to the first embodiment, it is possible to regenerate various materials from the heat-treatment raw material including the synthetic resin material and the metal material. Also, since the rotary kiln 52, the first pyrolysis tank 12A, and the second pyrolysis tank 12B are used, it is possible to perform material regeneration more effectively. Also, when discharging the pyrolysis residue out of the system, there is a risk of fire due to blockage of pipes, etc., but such a problem is solved.

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

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

Claims

1. A method for accelerating the thermal decomposition of recalcitrant composite plastic waste, including thermosetting plastics, characterized by adding a high hydrogen-containing hydrocarbon plastic containing PE or PP and not PS, along with the recalcitrant composite plastic waste to be heated, as a decomposition accelerator to a thermal decomposition tank; allowing a liquid-solid phase reaction to occur in the recalcitrant composite plastic waste at the melting temperature of the decomposition accelerator; then raising the temperature to the thermal decomposition temperature to generate at least hydrogen radicals from the decomposition accelerator, causing a gas-solid phase decomposition reaction to occur in the recalcitrant composite plastic waste, thereby thermally decomposing it.

2. A method for accelerating the thermal decomposition of recalcitrant composite plastic waste according to claim 1, wherein the recalcitrant composite plastic waste includes one selected from the group consisting of carbon fiber pipes, GFRP, solar panels, printed circuit boards, and waste tires.

3. The method for accelerating the thermal decomposition of recalcitrant composite plastic waste according to claim 1, wherein an equal or greater amount by weight of a high hydrogen-containing hydrocarbon plastic with a high Arrhenius factor is added to the thermosetting plastic component of the recalcitrant composite plastic waste.

4. The method for accelerating the thermal decomposition of recalcitrant composite plastic waste according to claim 1, wherein the liquid-solid phase reaction is carried out in a molten state of the high hydrogen-containing hydrocarbon plastic with a high Arrhenius factor at a temperature range of 350°C to 420°C where the reaction is heated in stages, and the gas-solid phase reaction is carried out in a thermal decomposition state of the high hydrogen-containing hydrocarbon plastic with a high Arrhenius factor at a temperature range of 420°C to 500°C where the reaction is heated in stages.

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