A method for catalyst-assisted microwave pyrolysis of waste plastic

Abstract

This invention discloses a method for catalytic-assisted microwave pyrolysis of waste plastics, the main steps of which include: step (1): crushing a large piece of waste plastic into a plurality of waste plastic sheets; step (2): placing the waste plastic sheets and a catalyst together into a microwave heating cavity and mixing them evenly; step (3): subjecting the waste plastic sheets to microwave high-temperature treatment in an oxygen-free atmosphere in the microwave heating cavity to form a plurality of solid carbon materials and gaseous volatiles; and step (4): the solid carbon materials enter a cooling container from the microwave heating cavity, and the gaseous volatiles enter a condenser pipe from at least one outlet of the microwave heating cavity and then form fuel oil in a collection container. By using catalytic-assisted microwave pyrolysis, this method achieves the recycling of high-value carbon materials from waste plastics at lower temperatures and atmospheric pressures, while simultaneously meeting the needs of improving the recovery rate of high-value carbon materials, shortening reaction time, simplifying the reaction process, saving energy, and protecting the environment, and also realizing the recycling of high-quality fuel oil.

Description

Technical Field

[0001] This invention relates to a method for treating waste plastics, and more particularly to a method for treating waste plastics using catalyst-assisted microwave pyrolysis. Prior Technology

[0002] Plastic is a petrochemical product that does not naturally exist in the environment and therefore cannot decompose naturally or be recycled back into nature. Without proper treatment, it becomes what is known as "perpetual waste." Waste plastic containers come in a variety of materials. To facilitate recycling, the general public does not need to sort them by material. Instead, they are sorted, compressed, and packaged by recyclers before being sent to recycling plants for processing. The processing flow of a plastic recycling plant mainly includes crushing, washing, flotation to remove impurities, and dehydration to produce plastic fragments of a single material. These fragments are then hot-melted and extruded to produce various recycled plastic materials. Polyethylene terephthalate (PET) can be directly transported to downstream recycling plants or textile mills for the production of recycled products such as yarn spinning and textiles. Other materials, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), etc., need to be sent to a granulation plant first. After granulation, they are made into secondary plastic raw materials. These recycled raw materials can then be injection molded or compression molded to produce various plastic products.

[0003] However, the value of physically recycled plastic products is currently low. Plastics are petrochemical products and can be further decomposed into their original material state using pyrolysis. Pyrolysis occurs under anaerobic or anaerobic conditions, heating long-chain organic compounds to break their molecular bonds, ultimately decomposing them into smaller molecular byproducts (such as fuel oil) and water. Traditional pyrolysis recycling involves feeding waste plastics into oiling equipment, where they undergo pyrolysis, vaporization, condensation, separation, and distillation to obtain plastic pyrolysis oil. To convert this into liquid or gaseous fuel oil, further distillation and condensation processes are required. This method can process waste plastics, waste engine oil, and waste solvents without pretreatment and is easy to operate. It can produce heavy oil fuel with a sulfur content of 1.0-1.3%, which can be refined into diesel and gasoline through fractionation technology. In addition, the gas from the vaporization of waste plastics can be desulfurized to produce medium-calorific-value fuel gas, which can be used for industrial processes or boilers. However, the pyrolysis temperature of waste plastics is very high, which is extremely energy-intensive, thus affecting the reuse of waste plastics.

[0004] Microwave heating has three key characteristics: Immediateness: High thermal efficiency and short heating time. Selectivity: Different materials exhibit significantly different heating characteristics in a microwave field due to their varying dielectric properties. Penetration: Electromagnetic waves can penetrate the interior of a medium, thus microwaves possess strong penetrating power. Numerous studies have demonstrated that microwave-assisted pyrolysis of waste can yield high-quality recyclable materials, achieving the concept of a regenerative circular economy. Compared to traditional heating, microwave heating offers shorter heating times and avoids direct contact with the heated material, overcoming the high energy consumption and low efficiency of traditional methods. Many studies have confirmed that adding a catalyst to waste plastics can effectively reduce the temperature of microwave pyrolysis and yield high-quality carbon materials and fuel oil. However, catalytic-assisted microwave pyrolysis of waste plastics is currently still in the laboratory scale. These laboratory methods are often complex and unsuitable for industrial-scale microwave pyrolysis of waste plastics for high-quality carbon materials and fuel oil recovery.

[0005] In view of this, it is necessary to propose a rapid and environmentally friendly catalytic-assisted microwave pyrolysis method for plastic waste on an industrial scale. Summary of the Invention

[0006] To address the aforementioned problems, the main objective of this invention is to provide a catalytic-assisted microwave pyrolysis method for waste plastics, specifically addressing the shortcomings and deficiencies of existing technologies. This method efficiently pyrolyzes waste plastics using microwaves at relatively low temperatures and atmospheric pressures, recovering high-value carbon materials and fuel oil. Through catalytic assistance, this method enables waste plastics to undergo low-temperature pyrolysis at appropriate microwave power densities and in a suitable atmosphere, thereby improving the recovery rate of high-value carbon materials, shortening reaction time, simplifying the reaction process, saving energy, and protecting the environment, while simultaneously achieving the recycling of high-quality fuel oil.

[0007] To achieve the objectives of this invention, a method for catalyst-assisted microwave pyrolysis of waste plastics is provided, the main steps of which include: Step (1): Crush a large piece of waste plastic into multiple pieces of waste plastic. The length of these pieces is between 0.2 cm and 10 cm, and the width is between 0.2 cm and 10 cm. Step (2): The waste plastic sheets and a catalyst are placed together in a microwave heating cavity and mixed evenly. The microwave heating cavity has at least one air inlet and at least one air outlet. The air outlet is connected to an external air extraction device through a pipe. Step (3): An oxygen-free atmosphere containing inert gas is introduced into the microwave heating cavity through at least one air inlet. The waste plastic sheets undergo a microwave high-temperature treatment to form a plurality of solid carbon materials and gaseous volatiles. The microwave high-temperature treatment temperature is between 300 and 600°C, and the time is between 0.1 and 1 hour. Step (4): The solid carbon materials enter a cooling container from the microwave heating cavity, and the gaseous volatiles enter a condensation pipe from at least one outlet of the microwave heating cavity to form fuel in a collection container.

[0008] According to one feature of the present invention, the microwave heating cavity is mainly a ceramic container with an outer metal shell, the at least one air inlet is located in the lower half of the ceramic container, and the at least one air outlet is located in the upper half of the ceramic container.

[0009] According to one feature of the present invention, in step (2), the catalyst material is selected from carbon-containing materials, metal particles or metal oxide powders.

[0010] According to one feature of the present invention, in step (2), the catalyst is a carbon-containing substance, and the amount of the catalyst added to the waste plastic sheets is between 1% and 20% of the weight percentage of the waste plastic sheets.

[0011] According to one feature of the present invention, in step (2), the catalyst is metal particles, and the amount of the catalyst added to the waste plastic sheets is between 0.5% and 5% of the weight percentage of the waste plastic sheets.

[0012] According to one feature of the present invention, in step (2), the catalyst is a metal oxide powder, and the amount of the catalyst added to the waste plastic sheets is between 1% and 10% of the weight percentage of the waste plastic sheets.

[0013] According to one feature of the present invention, in step (3), the microwave power density of the microwave high-temperature treatment is between 0.1 kW / kg and 1 kW / kg, where kg is the unit weight of the waste plastic sheets.

[0014] According to one feature of the present invention, in step (3), the inert gas system introduced into the microwave high-temperature treatment is nitrogen gas, and its flow rate is between 1 LPM / kg and 10 LPM / kg, where LPM is liters per minute [L / min] and kg is the unit weight of the waste plastic sheets.

[0015] According to one feature of the present invention, in step (3), during the microwave high-temperature treatment, the external air extraction device extracts the gas generated by the waste plastic from the microwave heating cavity at a speed greater than or equal to that of the gas generated by the microwave high-temperature treatment, so as to keep the microwave heating cavity in the oxygen-free atmosphere.

[0016] According to one feature of the present invention, in step (4), the condenser pipeline is a pipeline with a reflux structure having a heat preservation module.

[0017] The advantages of the catalyst-assisted microwave waste pyrolysis method for plastics of the present invention are: (1) By adding a catalyst, the waste plastic is rapidly heated by microwave heating, which shortens the overall processing time, reduces microwave power consumption, and significantly saves energy. (2) Inert gas is introduced under normal pressure, and a certain microwave power density and temperature are controlled to degrade the organic materials in the waste plastic, thereby improving the recycling efficiency and effect of carbon materials and fuel. (3) The recycled fuel obtained by microwave treatment can be used again to synthesize new plastic materials and applied to different fields. It can also be used directly as fuel for vehicles, which is a green and environmentally friendly recycling method. Simple Explanation of the Diagram

[0018] To make the above and other objects, features and advantages of the present invention more apparent and understandable, several preferred embodiments are described below in detail with reference to the accompanying drawings. Figure 1 shows a flowchart of a method for catalyst-assisted microwave pyrolysis of waste plastics according to the present invention. Figure 2 shows a photograph of an embodiment of the present invention: (a) waste plastic sheet before microwave heat treatment, (b) recycled carbon black after microwave pyrolysis, and (c) recycled metal wire after microwave pyrolysis. Implementation

[0019] While the present invention may be embodied in various forms, those shown in the accompanying drawings and described herein are preferred embodiments of the invention. Those skilled in the art will understand that the apparatus and methods specifically described herein and illustrated in the drawings are intended as examples of the invention, not limiting illustrative embodiments, and the scope of the invention is defined only by the claims. Features illustrated or described in connection with an illustrative embodiment may be combined with features of other embodiments. Such modifications and variations are included within the scope of the invention.

[0020] Thermal pyrolysis is a thermochemical reaction process that decomposes organic matter into solid substances, condensed liquids, and combustible gases under high temperature, oxygen-free, or low-oxygen conditions. To achieve the objectives of this invention, a method for catalyst-assisted microwave pyrolysis of waste plastics is provided. Please refer to Figure 1, which shows a flowchart of a method for catalyst-assisted microwave pyrolysis of waste plastics according to this invention.

[0021] To achieve the objectives of this invention, a method for catalyst-assisted microwave pyrolysis of waste plastics is provided, the main steps of which include: Step (1): Crush a large piece of waste plastic into multiple pieces of waste plastic. The length of these pieces is between 0.2 cm and 10 cm, and the width is between 0.2 cm and 10 cm. Step (2): The waste plastic sheets and a catalyst are placed together in a microwave heating cavity and mixed evenly. The microwave heating cavity has at least one air inlet and at least one air outlet. The air outlet is connected to an external air extraction device through a pipe. Step (3): An oxygen-free atmosphere containing inert gas is introduced into the microwave heating cavity through at least one air inlet. The waste plastic sheets undergo a microwave high-temperature treatment to form a plurality of solid carbon materials and gaseous volatiles. The microwave high-temperature treatment temperature is between 300 and 600°C, and the time is between 0.1 and 1 hour. Step (4): The solid carbon materials enter a cooling container from the microwave heating cavity, and the gaseous volatiles enter a condensation pipe from at least one outlet of the microwave heating cavity to form fuel in a collection container.

[0022] Waste plastic materials include: polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyethylene terephthalate (PET). In step (1), since waste plastics are not homogeneous materials, different shapes and structures will affect heat transfer and thus the thermal decomposition effect. Therefore, larger waste plastics can be crushed mechanically. The dimensions of these waste plastic sheets are between 0.2 cm and 10 cm in length and between 0.2 cm and 10 cm in width. Preferably, the dimensions of these waste plastic sheets are between 0.2 cm and 1 cm in length and between 0.2 cm and 1 cm in width, which can increase the reaction rate.

[0023] In step (2), the microwave heating cavity system is mainly a ceramic container with an outer metal shell. At least one air inlet is located in the lower half of the ceramic container, and at least one air outlet is located in the upper half. The at least one air inlet at the bottom effectively provides airflow to the entire microwave processing. A plurality of microwave power sources are arranged around the metal shell to provide microwave power to the waste plastic sheets inside the ceramic container of the microwave heating cavity. The required microwave power is related to the capacity of the heating cavity and the weight of the carbon black composite material being processed. The power of these microwave power sources is adjustable, providing an appropriate power density based on the weight of the heated carbon black composite material. Microwaves are electromagnetic waves, using a microwave power at a frequency of 915MHz or 2450MHz. Microwave heating utilizes the principle of radiation, penetrating the surface of the medium to enter the interior of the waste plastic sheets. The waste plastic sheets convert the absorbed microwave energy into heat to achieve the purpose of heating and decomposition. These waste plastic sheets are placed into the microwave heating cavity from above, and they occupy about one-third to two-thirds of the space of the ceramic container in the microwave heating cavity.

[0024] In step (2), the catalyst material is selected from carbon-containing materials, metal particles, or metal oxide powders, and mixtures thereof. The catalyst material can absorb microwave energy, and by uniformly mixing it with the waste plastic sheets, the waste plastic sheets can be uniformly heated, accelerating the reaction rate. Among them, the carbon-containing materials can be carbon black, stone mill, activated carbon, and carbon fiber, etc., and mixtures thereof; the metal particles can be carbon iron, nickel copper zinc ferrite magnets, nickel zinc ferrite magnets, manganese zinc ferrite magnets, or related metal materials or nano metal materials, or mixtures thereof; the metal oxide powder can be magnesium oxide, calcium oxide, strontium oxide, barium oxide, aluminum oxide, silicon oxide, iron oxide, zirconium oxide, vanadium oxide, iron oxide, titanium oxide, manganese oxide, cobalt oxide, nickel oxide, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, aluminum carbonate, etc., oxides or carbon oxide materials with high dielectric constants, and mixtures thereof.

[0025] Preferably, in step (2), the catalyst is a carbon-containing substance, and the amount of the catalyst added to the waste plastic sheets is between 1% and 20% of the weight percentage of the waste plastic sheets. Preferably, in step (2), the catalyst is metal particles, and the amount of the catalyst added to the waste plastic sheets is between 0.5% and 5% of the weight percentage of the waste plastic sheets. Preferably, in step (2), the catalyst is metal oxide powder, and the amount of the catalyst added to the waste plastic sheets is between 1% and 10% of the weight percentage of the waste plastic sheets. It should be noted that the catalyst can be added before, during, or after the waste plastic sheets are crushed, that is, before step (3).

[0026] In step (3), the microwave power density of the microwave high-temperature treatment is between 0.1 kW / kg and 1 kW / kg, where kg is the unit weight of the waste plastic sheets. In step (3), the inert gas system introduced into the microwave high-temperature treatment is nitrogen, and its flow rate is between 1 LPM / kg and 10 LPM / kg, where LPM is liters per minute [L / min], and kg is the unit weight of the waste plastic sheets. In step (3), during the microwave high-temperature treatment, the external exhaust device extracts the gas generated by the waste plastic from the microwave heating cavity at a speed greater than or equal to the gas speed generated by the microwave high-temperature treatment, so that the microwave heating cavity is kept in an oxygen-free atmosphere. The oxygen-free condition means that there is almost no oxygen during the microwave heat treatment process. By continuously introducing an inert gas, such as nitrogen or argon, the oxygen in the microwave heating cavity is consumed, and there is no subsequent oxygen replenishment to achieve the limited air intake design. The inert gas flow rate is proportional to the capacity of the heating cavity.

[0027] In step (3), the waste plastic sheets undergo microwave high-temperature treatment to form a plurality of solid carbon materials and gaseous volatiles. The microwave high-temperature treatment temperature is between 300 and 600°C, and the time is between 0.1 and 1 hour. To increase the recovery rate of liquid fuel oil, in step (4): the solid carbon materials enter a cooling container from the microwave heating cavity, and the gaseous volatiles enter a condensing pipe from at least one outlet of the microwave heating cavity and then form fuel oil in a collection container. The condensing pipe is a pipe with a reflux structure and a heat preservation module. The gaseous volatiles are extracted from the microwave heating cavity by the external air extraction device, and after subsequent condensation, they will separate into liquid products, i.e., fuel oil, and gaseous products, i.e., syngas (mainly hydrogen, methane, and carbon monoxide). Both liquid and gaseous products can be used as energy fuels.

[0028] In step (4), the solid carbon materials enter the cooling container from the microwave heating cavity and are cooled to below 200°C before being removed by a conveyor belt. Once cooled to below 200°C, the solid carbon materials are fed from the bottom of the microwave heating cavity, preventing oxidation and combustion, thus accelerating the cooling to room temperature.

[0029] This catalytic-assisted microwave heat treatment involves controlling different catalysts and their amounts, different microwave power densities, different heating temperatures, different heating times, different gas compositions and flow rates, and different extraction conditions, effectively obtaining high-quality recycled carbon materials and fuel oil. The advantages of this catalytic-assisted microwave waste pyrolysis method for plastics are:

[0030] The advantages of the catalyst-assisted microwave waste pyrolysis method for plastics of the present invention are: (1) By adding a catalyst, the waste plastic is rapidly heated by microwave heating, which shortens the overall processing time, reduces microwave power consumption, and significantly saves energy. (2) Inert gas is introduced under normal pressure, and a certain microwave power density and temperature are controlled to degrade the organic materials in the waste plastic, thereby improving the recycling efficiency and effect of carbon materials and fuel. (3) The recycled fuel obtained by microwave treatment can be used again to synthesize new plastic materials and applied to different fields. It can also be used directly as fuel for vehicles, which is a green and environmentally friendly recycling method.

[0031] Although the present invention has been disclosed with reference to the foregoing preferred embodiments, it is not intended to limit the invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention. As explained above, various modifications and variations can be made without destroying the spirit of the invention. Therefore, the scope of protection of this invention shall be determined by the claims outlined in the appended patent claims.

Claims

1. A method for catalyst-assisted microwave pyrolysis of waste plastic, comprising the following main steps: Step (1): crushing a large piece of waste plastic into a plurality of waste plastic sheets, wherein the length of the waste plastic sheets is between 0.2 cm and 10 cm and the width is between 0.2 cm and 10 cm; Step (2): placing the waste plastic sheets and a catalyst material together into a microwave heating cavity and mixing them evenly, wherein the microwave heating cavity has at least one air inlet and at least one air outlet, wherein the air outlet is connected to an external air extraction device via a pipe; Step (3): introducing an oxygen-free atmosphere containing inert gas into the microwave heating cavity through the at least one air inlet, wherein the waste plastic sheets undergo microwave high-temperature treatment to form a plurality of solid carbon materials and gas volatilization. The microwave high-temperature treatment of the waste plastic sheets is carried out at a temperature between 300 and 600°C for 0.1 to 1 hour, with a microwave power density between 0.1 kW / kg and 1 kW / kg, where kg is the unit weight of the waste plastic sheets. The inert gas system introduced into the microwave high-temperature treatment is nitrogen, with a flow rate between 1 LPM / kg and 10 LPM / kg, where LPM is liters per minute (L / min) and kg is the unit weight of the waste plastic sheets. Step (4) involves the solid carbon material entering a cooling container from the microwave heating cavity, and the volatile gas entering a condensing pipe through at least one outlet of the microwave heating cavity to form fuel oil in a collection container. In step (2), the catalyst material is selected from carbon-containing materials, metal particles, or metal oxide powders. The carbon-containing material can be carbon black, stone mill, activated carbon, carbon fiber, etc., mixed with it. The metal particles can be carbon iron, nickel copper zinc ferrite magnet, nickel zinc ferrite magnet, manganese zinc ferrite magnet, or related metal materials or nano metal materials, or mixtures thereof. The metal oxide powder can be magnesium oxide, calcium oxide, strontium oxide, barium oxide, aluminum oxide, silicon oxide, iron oxide, zirconium oxide, vanadium oxide, iron oxide, titanium oxide, manganese oxide, cobalt oxide, nickel oxide, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, aluminum carbonate, etc., oxides or carbon oxide materials with high dielectric constant, mixed with it.

2. The method for catalytic-assisted microwave pyrolysis of waste plastics as described in claim 1, wherein the microwave heating cavity is mainly a ceramic container with an outer metal shell, the at least one air inlet is located in the lower half of the ceramic container, and the at least one air outlet is located in the upper half of the ceramic container.

3. The method for catalyst-assisted microwave pyrolysis of waste plastics as described in claim 1, wherein in step (2), the waste plastic sheets occupy approximately one-third to two-thirds of the space of the ceramic container in the microwave heating cavity.

4. The method for catalyst-assisted microwave pyrolysis of waste plastics as described in claim 1, wherein in step (2), the catalyst is a carbon-containing substance, and the amount of the catalyst added to the waste plastic sheets is between 1% and 20% of the weight percentage of the waste plastic sheets.

5. The method for catalyst-assisted microwave pyrolysis of waste plastics as described in claim 1, wherein in step (2), the catalyst is metal particles, and the amount of the catalyst added to the waste plastic sheets is between 0.5% and 5% of the weight percentage of the waste plastic sheets.

6. The method for catalyst-assisted microwave pyrolysis of waste plastics as described in claim 1, wherein in step (2), the catalyst is a metal oxide powder, and the amount of the catalyst added to the waste plastic sheets is between 1% and 10% of the weight percentage of the waste plastic sheets.

7. The method for catalyst-assisted microwave pyrolysis of waste plastic as described in claim 1, wherein in step (3), during the microwave high-temperature treatment, the external air extraction device extracts the gas generated by the waste plastic from the microwave heating cavity at a speed greater than or equal to the gas speed generated by the microwave high-temperature treatment, so as to keep the microwave heating cavity in the oxygen-free atmosphere.

8. The method for catalyst-assisted microwave pyrolysis of waste plastics as described in claim 1, wherein in step (4), the condenser pipeline is a pipeline with a reflux structure having a heat preservation module.

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