A method and system for converting waste plastics into hydrogen based on microwave pretreatment and solar photo-reforming

Abstract

This invention discloses a method and system for converting waste plastics into hydrogen based on microwave pretreatment and solar photocatalytic reforming, belonging to the field of solid waste resource utilization and clean energy technology. The method includes: mixing waste plastics with water for microwave pretreatment to destroy their macromolecular structure and generate a liquid-phase product rich in small-molecule organic matter; performing solid-liquid separation on the liquid-phase product; and conveying the separated liquid to a flat-plate photocatalytic reactor for photocatalytic reforming under sunlight irradiation and the action of a catalyst supported on a 3D-printed substrate to produce hydrogen and high-value chemicals. The system includes a microwave pretreatment unit, a filtration unit, and a flat-plate photocatalytic reaction unit connected in sequence. This invention achieves efficient, low-carbon, and high-value conversion of waste plastics through the synergy of microwave pretreatment and solar photocatalytic reforming, effectively overcoming the problems of high energy consumption, poor product selectivity, and low photocatalytic efficiency in existing technologies.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and clean energy technology, specifically to a method and system for the co-processing of waste plastics into hydrogen and high-value chemicals. Background Technology

[0002] Plastics, as one of the most important synthetic materials of the 20th century, have permeated every corner of human society's production and daily life due to their excellent durability, plasticity, and low cost. However, this very advantage that gives them wide application has become the root of their environmental sustainability. Hundreds of millions of tons of plastic waste are generated globally each year, a large portion of which enters the natural environment through improper disposal. On land, plastic waste occupies land resources, affecting soil structure and microbial communities; after entering water bodies, it not only damages aquatic ecosystems but also forms microplastics through physical fragmentation and photodegradation. These particles, smaller than 5 millimeters in diameter, are widely distributed in oceans, rivers, and even drinking water, and through the food chain, they produce bioaccumulation effects, posing a potential threat to organisms and human health. Current mainstream plastic remediation technologies have significant limitations: landfill disposal not only permanently occupies scarce land resources, but its leachate can also pollute groundwater systems; while incineration power generation can achieve energy recovery, it may release persistent organic pollutants such as dioxins and inevitably produce large amounts of greenhouse gases; mechanical recycling, although successful in specific areas, has stringent requirements for the cleanliness of raw materials and inevitably suffers from "downgraded recycling," making it difficult to form a closed-loop cycle. These traditional methods, in essence, fail to truly achieve the efficient recycling of plastic resources, necessitating the development of a new generation of environmentally friendly resource recovery technologies.

[0003] Hydrothermal pretreatment technology, an emerging plastic treatment method in recent years, theoretically enables the rapid depolymerization of polymers by heat-treating plastics in a subcritical or supercritical water environment. This technology typically operates within a temperature range of 200–450°C and a pressure range of 2–25 MPa. The process involves multiple reaction mechanisms, including hydrolysis and thermal decomposition, and can convert plastics into liquid hydrocarbon mixtures or partially oxidized products. However, this technology faces several challenges in practical applications: First, maintaining high-temperature and high-pressure reaction conditions requires significant energy consumption and places extremely high demands on reactor materials, sealing structures, and safety systems, resulting in high equipment investment and operating costs. Second, the hydrothermal process exhibits poor product selectivity; under the same conditions, dozens of compounds, including alkanes, alkenes, aromatic hydrocarbons, and oxygen-containing organic compounds, may be produced simultaneously, and product distribution is highly susceptible to fluctuations in raw material composition and reaction parameters. This complexity makes subsequent separation and purification exceptionally difficult. Furthermore, coking and carbon buildup that may occur in the hydrothermal environment not only reduce heat transfer efficiency but also lead to reactor blockage, affecting continuous and stable operation. Although catalyst modification can improve product distribution to some extent, it is still difficult to fundamentally solve the core problems of complex product composition and low added value, which restricts the industrial promotion and economic feasibility of this technology.

[0004] Solar photocatalysis, as a crucial pathway for clean energy conversion, directly utilizes the inexhaustible power of sunlight as the driving force for the reaction, achieving a technological transformation from an "energy-consuming" to an "energy-input" process. Its life-cycle carbon emissions can be reduced by more than 70% compared to traditional thermochemical processes. However, when this technology is directly applied to virgin plastics, its efficiency is severely limited. The stable chemical structure, low light absorption efficiency, and limited contact interface between intact plastic macromolecules and solid catalysts lead to a significant reduction in the separation and migration efficiency of photogenerated carriers. Simultaneously, the high energy barrier of macromolecule adsorption and activation on the catalyst surface results in a slow interfacial reaction rate, ultimately causing the hydrogen production efficiency to fall far short of the requirements for practical applications.

[0005] Given the current technological bottlenecks, there is an urgent need to develop a new method for plastic treatment that can achieve high efficiency, environmental friendliness, and low energy consumption. This project innovatively proposes a new technological path of synergistic effect between "microwave pretreatment and photocatalytic reforming." Microwave pretreatment technology, through its unique molecularly selective heating mechanism, can break down the stubborn structure of plastics, efficiently converting them into small-molecule intermediates rich in activity. This process not only consumes far less energy than hydrothermal methods, but also has a rapid and uniform reaction. More importantly, it prepares "ideal substrates" for subsequent reactions. These active intermediates greatly enhance the reaction rate and selectivity of the target product (such as hydrogen) in the photocatalytic process, making high-value conversion driven by solar energy possible. This system successfully achieves low-carbon and high-efficiency conversion from waste plastics to green hydrogen energy and high-value chemicals, breaking through the limitations of single technologies. It provides an innovative solution with significant economic and environmental benefits for plastic pollution control and clean energy production, realizing the high-value conversion of waste plastics and clean energy production, fundamentally solving the problems of resource waste and secondary pollution in current technological routes. Summary of the Invention

[0006] In view of the problems of high energy consumption, low efficiency of direct photocatalytic treatment and low added value of products in existing waste plastic treatment technologies, the purpose of this invention is to provide a synergistic treatment method and integrated system that is low in energy consumption, high in efficiency, and can efficiently convert waste plastics into hydrogen and high-value chemicals.

[0007] To achieve the above objectives, the first aspect of this invention provides a waste plastic conversion system based on microwave pretreatment and solar reforming for hydrogen production, comprising a microwave pretreatment unit, a filtration unit, and a planar photocatalytic reaction unit connected in sequence. This system achieves continuous conversion from waste plastic to hydrogen through the synergistic cooperation between the units.

[0008] The waste plastic conversion system based on microwave pretreatment and solar reforming for hydrogen production is characterized by comprising a microwave pretreatment unit, a filtration unit, and a flat-plate photocatalytic reaction unit connected in sequence.

[0009] The microwave preprocessing unit includes:

[0010] A sealed reaction chamber with a metal outer shell and a polytetrafluoroethylene liner;

[0011] A microwave generator located outside a sealed reaction chamber;

[0012] A stirring device installed inside a closed reaction chamber;

[0013] Sensors used to monitor temperature and pressure inside a closed reaction chamber;

[0014] The filtering unit includes:

[0015] A basket filter connected to the outlet of the microwave pretreatment unit, wherein the basket filter is provided with a replaceable filter basket.

[0016] A storage tank connected to the liquid outlet of a basket filter;

[0017] The planar photocatalytic reaction unit includes:

[0018] A metering pump connected to a storage tank via a pipeline;

[0019] At least one flat-plate photocatalytic reactor, wherein the flat-plate photocatalytic reactor is connected to a metering pump via an inlet pipe;

[0020] The flat-plate photocatalytic reactor includes a transparent quartz panel and a 3D-printed substrate loaded with catalyst disposed inside the flat-plate photocatalytic reactor. The quartz panel is sealed on the flat-plate photocatalytic reactor and seals the 3D-printed substrate loaded with catalyst inside it. It is also equipped with a liquid outlet pipe and a gas outlet pipe.

[0021] Furthermore, the microwave pretreatment unit also includes a control panel integrated with temperature and pressure sensors for setting and adjusting microwave power, reaction temperature, reaction time, and stirring rate.

[0022] Furthermore, the filtration unit includes a basket filter and a liquid storage tank.

[0023] Furthermore, the basket filter is equipped with a pressure sensor for monitoring the pressure difference across the basket.

[0024] Furthermore, the storage tank is equipped with a level gauge.

[0025] Furthermore, the planar photocatalytic reaction unit includes a metering pump and at least one planar photocatalytic reactor equipped with a 3D-printed substrate loaded with a catalyst.

[0026] Furthermore, the cavity of the plate-type photocatalytic reactor is set at an angle of 30° to 60° with the horizontal plane, and the quartz panel is set above the cavity of the plate-type photocatalytic reactor and faces the sunlight, and seals the cavity of the plate-type photocatalytic reactor.

[0027] Furthermore, the 3D printing substrate loaded with the catalyst is loaded with the photocatalyst onto the three-dimensional porous printing substrate by impregnation or in-situ growth.

[0028] This invention uses the above-mentioned system for a waste plastic conversion method, characterized by comprising the following steps:

[0029] S1. Microwave pretreatment: The crushed waste plastic and water are added to the microwave pretreatment unit in proportion, and microwave irradiation is carried out under stirring to obtain a pretreated slurry containing small molecule organic matter.

[0030] S2. Solid-liquid separation: The pretreated slurry obtained in step S1 is transported to the filtration unit, where solid-liquid separation is performed by a basket filter, and the liquid phase product is collected into a storage tank.

[0031] S3. Photocatalytic reforming: The liquid phase product in the storage tank is quantitatively delivered to the flat-plate photocatalytic reactor by a metering pump. Under the irradiation of sunlight through the quartz panel, it comes into contact with the catalyst loaded on the 3D printed substrate to undergo a photocatalytic reforming reaction. The liquid and hydrogen-rich gas after the reaction are collected from the liquid outlet pipe and the gas outlet pipe, respectively.

[0032] Further, in step S1, the conditions for microwave pretreatment are: microwave power 300~1500W, reaction temperature 150~250℃, and reaction time 5~30min.

[0033] Furthermore, in step S1, the microwave pretreatment unit adopts a metal sealed cavity with a polytetrafluoroethylene liner, combined with a microwave generator and a stirring device, to achieve rapid and uniform depolymerization of waste plastics.

[0034] Furthermore, in step S2, the filtration unit adopts a basket filter with differential pressure monitoring to achieve efficient solid-liquid separation and early warning of filter residue blockage.

[0035] Furthermore, in step S3, the hydraulic residence time of the liquid product in the flat-plate photocatalytic reactor is controlled by adjusting the flow rate of the metering pump.

[0036] Furthermore, in step S3, the catalyst used in the photocatalytic reforming reaction is a composite catalyst selected from one or more noble metals selected from Pt, Pd, Ru, and Rh, supported on TiO2, g-C3N4, or CdS semiconductor materials.

[0037] Furthermore, the planar photocatalytic reaction unit adopts an inclined planar reactor, with a 3D-printed substrate loaded with catalyst inside, in order to maximize light energy utilization and liquid-solid mass transfer efficiency.

[0038] The beneficial effects of this invention are:

[0039] 1. Synergistic and efficient: Microwave pretreatment rapidly depolymerizes recalcitrant plastic macromolecules into small molecule intermediates that are easy to photocatalyze, greatly improving the rate and efficiency of subsequent photocatalytic hydrogen production and solving the core bottleneck of low efficiency of direct photocatalysis of plastics.

[0040] 2. Low carbon and energy saving: The pretreatment stage uses efficient microwave heating, and the reaction stage directly utilizes solar energy. The entire system does not require external fossil energy heating, which significantly reduces process energy consumption and carbon emissions.

[0041] 3. High-value products: The target products are high-purity green hydrogen and potentially high-value oxygen-containing chemicals, realizing the targeted conversion of waste plastics into clean energy and high-value chemicals, which is significantly more economical than traditional recycling methods.

[0042] 4. Systematization and Safety: This invention provides an integrated, modular system solution, enabling continuous operation from feed to product. The system incorporates multi-parameter monitoring and early warning (temperature, pressure, differential pressure, liquid level), and gaseous products are collected separately, ensuring operational safety and stability.

[0043] 5. Flexible operation: By adjusting microwave parameters, filter specifications, catalyst type and liquid residence time, it can adapt to different types and compositions of waste plastic raw materials and optimize the yield and selectivity of the target product. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the overall process of the waste plastic conversion system of the present invention.

[0045] Figure 2 This is a schematic diagram of the structure of the microwave preprocessing unit of the present invention.

[0046] Figure 3 This is a schematic diagram of the structure of the filter unit of the present invention.

[0047] Figure 4 This is a schematic diagram of the structure of the planar photocatalytic reaction unit of the present invention.

[0048] Labels in the diagram: 1. Microwave pretreatment unit; 2. Microwave generator; 3. Basket filter; 4. Storage tank; 5. Metering pump; 6. Flat-plate photocatalytic reactor; 7. Stirring device; 8. Metal shell; 9. Polytetrafluoroethylene liner; 10. Filter basket; 11. Liquid inlet pipe; 12. Liquid outlet pipe; 13. Gas outlet pipe; 14. 3D printed substrate for catalyst support; 15. Quartz panel; 16. Single-stage flat-plate photocatalytic reaction unit. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] 1. A waste plastic conversion system based on microwave pretreatment and solar reforming for hydrogen production, characterized in that it comprises a microwave pretreatment unit, a filtration unit, and a flat-plate photocatalytic reaction unit connected in sequence;

[0051] The microwave preprocessing unit includes:

[0052] A sealed reaction chamber with a metal outer shell 8 and a polytetrafluoroethylene liner 9;

[0053] Microwave generator 2 is located outside the sealed reaction cavity;

[0054] Stirring device 7 is installed in a closed reaction chamber;

[0055] Sensors used to monitor temperature and pressure inside a closed reaction chamber;

[0056] The filtering unit includes:

[0057] A basket filter 3 is connected to the discharge port of the microwave pretreatment unit, and the basket filter 3 is provided with a replaceable filter basket 10 inside.

[0058] A storage tank 4 connected to the liquid outlet of the basket filter 3;

[0059] The planar photocatalytic reaction unit includes:

[0060] Metering pump 5 is connected to storage tank 4 via a pipeline;

[0061] At least one single-stage flat-plate photocatalytic reaction unit 16, wherein the single-stage flat-plate photocatalytic reaction unit 16 is connected to the metering pump 5 through the liquid inlet pipe 11;

[0062] The single-stage flat-panel photocatalytic reaction unit 16 includes a transparent quartz panel 15 and a 3D-printed substrate 14 loaded with catalyst disposed inside the reactor, and is provided with a liquid outlet pipe 12 and a gas outlet pipe 13.

[0063] Example 1: System Structure and Connections

[0064] like Figure 1As shown, the waste plastic conversion system provided by this invention has the following core process: microwave pretreatment unit 1 → basket filter 3 + storage tank 4 → flat-plate photocatalytic reaction unit (metering pump 5 + flat-plate photocatalytic reactor 6). Each unit is connected sequentially via pipes and valves. The microwave pretreatment unit 1 has an inlet at the top and an outlet at the bottom connected to the inlet of the basket filter 3 via a pipe. The liquid outlet of the basket filter 3 is connected to the storage tank 4 via a pipe and a water pump. The outlet of the storage tank 4 is connected to the inlet pipe 11 of the flat-plate photocatalytic reactor 6 via the metering pump 5. The outlet pipe 12 of the flat-plate photocatalytic reactor 6 can be connected to a subsequent liquid collection or circulation unit, and the gas outlet pipe 13 of the flat-plate photocatalytic reactor 6 is connected to a gas collection device (such as a gas collection bag or gas chromatograph).

[0065] Example 2: Working process of the microwave preprocessing unit

[0066] like Figure 2 As shown, the microwave pretreatment unit 1 is one of the core components of this system. Its metal outer shell 8 serves as a metal shielding layer, and a polytetrafluoroethylene (PTFE) liner 9 is installed inside the metal outer shell 8. The PTFE liner 9 is made of corrosion-resistant and microwave-permeable PTFE material. The cavity within the PTFE liner 9 is a sealed reaction chamber. A microwave generator 2 is located outside the sealed reaction chamber, and the microwave energy from the microwave generator 2 penetrates the PTFE liner 9 to irradiate the material inside the sealed reaction chamber. During operation, pre-crushed waste plastics (such as PE, PET, PP, etc.) and deionized water are fed into the sealed reaction chamber through the top inlet at a specific solid-liquid ratio (e.g., 1:5 to 1:20). The microwave power (e.g., 800W), target temperature (e.g., 200℃), reaction time (e.g., 15min), and stirring rate are set via the control panel of the microwave pretreatment unit 1. After startup, microwave generator 2 operates, and stirring device 7, which can be a stirring rod, is installed inside the sealed reaction chamber. Its rotation ensures uniform mixing of the materials. The microwave energy from microwave generator 2 directly acts on the material molecules within the sealed reaction chamber, causing them to heat up rapidly and undergo bond breaking and depolymerization. Built-in temperature and pressure sensors monitor the reaction status in real time. After the reaction is complete, the reaction slurry in the sealed reaction chamber automatically cools. Once it is safe to proceed, the bottom valve of microwave pretreatment unit 1 opens, and the reaction slurry flows into the next unit under gravity or pressure difference.

[0067] Example 3: Separation and Monitoring of Filter Units

[0068] like Figure 3As shown, the filtration unit includes a basket filter 3 connected to the outlet of the microwave pretreatment unit, with a replaceable filter basket 10 inside. The filtration unit receives the reaction slurry from the microwave pretreatment unit. After the slurry enters the basket filter 3, solid residues are trapped in the removable filter basket 10, while the filtrate passes through the filter screen of the filter basket 10. A differential pressure sensor installed on the basket filter monitors the pressure difference across the filter screen. When the pressure difference rises to a set threshold (indicating a large amount of filter residue and increased filtration resistance), the system issues an alarm, prompting the replacement or cleaning of the filter basket 10. The filtrate is promptly transferred to a storage tank 4 for temporary storage by a water pump. A level gauge on the storage tank 4 displays the liquid volume in real time, providing data for subsequent feeding.

[0069] Example 4: Configuration and reaction of a planar photocatalytic reaction unit

[0070] like Figure 4As shown, the flat-plate photocatalytic reaction unit includes: a metering pump 5 connected to the storage tank 4 via a pipeline; and at least one flat-plate photocatalytic reactor 6. The flat-plate photocatalytic reactor 6 is connected to the metering pump 5 via an inlet pipe 11. The flat-plate photocatalytic reactor 6 includes a transparent quartz panel 15 and a 3D-printed substrate 14 loaded with catalyst disposed inside the reactor, and is provided with an outlet pipe 12 and an outlet pipe 13. The flat-plate photocatalytic reactor 6 is the key to the solar energy conversion of this system. When one flat-plate photocatalytic reactor 6 is used, the flat-plate photocatalytic reaction unit is a single-stage flat-plate photocatalytic reaction unit 16. The main body of the flat-plate photocatalytic reactor is a flat cavity placed at an incline (e.g., at a 45° angle to the horizontal plane). The high-transmittance quartz panel 15 covers the flat cavity of the flat-plate photocatalytic reactor, and is generally placed at the same incline angle as the flat cavity of the flat-plate photocatalytic reactor 6 (e.g., at a 45° angle to the horizontal plane) to maximize the reception of sunlight. A 3D-printed substrate 14 loaded with catalyst is placed within the flat cavity of a planar photocatalytic reactor. This 3D-printed substrate can be fabricated using 3D printing technology to create objects with high specific surface area and specific flow channel structures (such as honeycomb or mesh structures) (e.g., using resin, ceramic, etc.). Then, a photocatalyst (e.g., Pt / TiO2) is loaded onto it using an impregnation method. During operation, a metering pump 5 pumps the filtrate from the storage tank 4 into the inlet pipe 11 at the bottom of the planar photocatalytic reactor at a constant flow rate (e.g., 10 mL / min). The filtrate flows upward within the flat cavity of the reactor, fully impregnating the 3D-printed substrate 14 loaded with catalyst. Sunlight (or simulated sunlight) shines through a quartz panel 15 onto the catalyst within the flat cavity, exciting electron-hole pairs that drive a photocatalytic reforming reaction between water and small organic molecules, producing hydrogen gas. The generated gas accumulates at the top of the flat cavity and is collected through the outlet pipe 13. The reacted liquid flows out from the lower outlet pipe 12. By adjusting the flow rate of the metering pump 5, the residence time of the filtrate in the flat-plate photocatalytic reactor can be precisely controlled, thereby optimizing the reaction conversion rate.

[0071] Example 5: A specific process

[0072] Taking the treatment of waste polyethylene (PE) plastic as an example:

[0073] a) Pretreatment: Add 10g of crushed PE particles and 100g of water to the microwave pretreatment unit and react for 20 minutes at a microwave power of 600W and a temperature of 160℃ to obtain slurry.

[0074] b) Filtration: After cooling, the slurry is filtered through a filtration unit to separate a small amount of solid carbon residue, yielding approximately 95 mL of clear to slightly turbid liquid.

[0075] c) Photoreforming: ZnCdS and Ni MOF were synthesized via a hydrothermal method, mixed, and then hydrothermally sulfided to form a ZnCdS / NiS catalyst. A porous catalyst support was printed using 3D printing technology, and the active components were then loaded onto the support surface using an impregnation deposition method to prepare a ZnCdS / NiS@3D printed matrix. The filtered liquid was pumped into a flat-plate photocatalytic reactor containing the ZnCdS / NiS@3D printed matrix, and the residence time of the liquid in the flat-plate photocatalytic reactor was controlled to be 2 hours under simulated sunlight (AM 1.5G).

[0076] d) Results: Gas discharged from the outlet pipe 13 of the flat-plate photocatalytic reactor was detected by gas chromatography, and the hydrogen content in the gas was significant, proving that this method can effectively convert waste PE into hydrogen.

[0077] Example 6: A specific process

[0078] Taking the treatment of waste polyethylene terephthalate (PET) plastic as an example:

[0079] a) Pretreatment: Add 10g of crushed PET particles and 100g of water to the microwave pretreatment unit and react for 20 minutes at a microwave power of 800W and a temperature of 200℃ to obtain a slurry.

[0080] b) Filtration: After cooling, the slurry is filtered through a filtration unit to separate a small amount of solid carbon residue, yielding approximately 95 mL of clear to slightly turbid liquid.

[0081] c) Photoreforming: ZnCdS and Ni MOF were synthesized via a hydrothermal method, mixed, and then hydrothermally sulfided to form a ZnCdS / NiS catalyst. A porous catalyst support was printed using 3D printing technology, and the active components were then loaded onto the support surface using an impregnation deposition method to prepare a ZnCdS / NiS@3D printed matrix. The filtered liquid was pumped into a flat-plate photocatalytic reactor containing the ZnCdS / NiS@3D printed matrix, and the residence time of the liquid in the flat-plate photocatalytic reactor was controlled to be 2 hours under simulated sunlight (AM 1.5G).

[0082] d) Results: The gas discharged from the outlet pipe 13 of the flat plate photocatalytic reactor was detected by gas chromatography, and the hydrogen content in the gas was significant, proving that the method can effectively convert waste PET into hydrogen.

[0083] 2. The present invention employs the above-mentioned waste plastic conversion system based on microwave pretreatment and solar-powered reforming for hydrogen production, as well as the waste plastic conversion method described in Examples 1-6, characterized by comprising the following steps:

[0084] S1. Microwave pretreatment: The crushed waste plastic and water are added to the microwave pretreatment unit in proportion, and microwave irradiation is carried out under stirring to obtain a pretreated slurry containing small molecule organic matter.

[0085] S2. Solid-liquid separation: The pretreated slurry obtained in step S1 is transported to the filtration unit, and solid-liquid separation is performed through the basket filter 3. The liquid phase product is collected into the storage tank 4.

[0086] S3. Photocatalytic reforming: The liquid phase product in the storage tank 4 is quantitatively transported to the flat-plate photocatalytic reactor 6 by the metering pump 5. Under the irradiation of sunlight through the quartz panel 15, it comes into contact with the catalyst loaded on the 3D printed substrate 14 to undergo a photocatalytic reforming reaction. The liquid and hydrogen-rich gas after the reaction are collected from the liquid outlet pipe 12 and the gas outlet pipe 13, respectively.

[0087] In step S1 above, the conditions for microwave pretreatment are: microwave power 300~1500W, reaction temperature 150~250℃, and reaction time 5~30min.

[0088] In step S3 above, the hydraulic residence time of the liquid product in the flat-plate photocatalytic reactor 6) is controlled by adjusting the flow rate of the metering pump 5.

[0089] In step S3 above, the catalyst used in the photocatalytic reforming reaction is a composite catalyst selected from one or more noble metals of Pt, Pd, Ru, and Rh, supported on TiO2, g-C3N4, or CdS semiconductor materials.

[0090] It should be noted that this invention is not limited to the specific embodiments described above. Those skilled in the art can make various modifications and variations within the scope of the claims regarding the microwave pretreatment conditions (such as adding alkaline or acidic additives), filtration methods (such as centrifugal filtration), the structure and material of the 3D printing substrate, the type and loading method of the catalyst, and the series / parallel arrangement of the flat-plate reactor. All such modifications and variations are considered to fall within the protection scope of this invention.

Claims

1. A waste plastic conversion system based on microwave pretreatment and solar-powered reforming for hydrogen production, characterized in that, It includes a microwave pretreatment unit, a filtration unit, and a flat-plate photocatalytic reaction unit connected in sequence; The microwave preprocessing unit includes: A closed reaction chamber with a metal shell (8) and a polytetrafluoroethylene liner (9); A microwave generator (2) is located outside the sealed reaction chamber; A stirring device (7) is installed in a closed reaction chamber; Sensors used to monitor temperature and pressure inside a closed reaction chamber; The filtering unit includes: A basket filter (3) connected to the outlet of the microwave pretreatment unit, wherein the basket filter (3) is provided with a replaceable filter basket (10) inside; A storage tank (4) connected to the liquid outlet of the basket filter (3); The planar photocatalytic reaction unit includes: A metering pump (5) connected to the storage tank (4) via a pipeline; At least one flat-plate photocatalytic reactor (6), said flat-plate photocatalytic reactor (6) is connected to a metering pump (5) via an inlet pipe (11); The flat-plate photocatalytic reactor (6) includes a transparent quartz panel (15) and a 3D-printed substrate (14) loaded with catalyst disposed inside the flat-plate photocatalytic reactor. The quartz panel (15) is sealed on the flat-plate photocatalytic reactor and seals the 3D-printed substrate (14) loaded with catalyst inside it. It is also provided with a liquid outlet pipe (12) and a gas outlet pipe (13).

2. The waste plastic conversion system according to claim 1, characterized in that, The microwave pretreatment unit also includes a control panel with integrated temperature and pressure sensors for setting and adjusting microwave power, reaction temperature, reaction time, and stirring rate.

3. The waste plastic conversion system according to claim 1, characterized in that, The filtration unit includes a basket filter (3) and a liquid storage tank (4). The basket filter (3) is equipped with a pressure sensor for monitoring the pressure difference across the filter basket (10); The storage tank (4) is equipped with a level gauge.

4. The waste plastic conversion system according to claim 1, characterized in that, The flat-plate photocatalytic reaction unit includes a metering pump (5) and a flat-plate photocatalytic reactor (6) equipped with at least one 3D-printed substrate (14) loaded with catalyst. The cavity of the plate photocatalytic reactor (6) is set at an angle of 30° to 60° with the horizontal plane. The quartz panel (15) is set above the cavity of the plate photocatalytic reactor (6) and faces the sunlight and seals the cavity of the plate photocatalytic reactor (6). The catalyst-loaded 3D printing substrate (14) is formed by loading the photocatalyst onto the three-dimensional porous printing substrate using an impregnation method or an in-situ growth method.

5. A waste plastic conversion method using the waste plastic conversion system as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Microwave pretreatment: The crushed waste plastic and water are added to the microwave pretreatment unit in proportion, and microwave irradiation is carried out under stirring to obtain a pretreated slurry containing small molecule organic matter. S2. Solid-liquid separation: The pretreated slurry obtained in step S1 is transported to the filtration unit and subjected to solid-liquid separation by the basket filter (3). The liquid phase product is collected into the storage tank (4). S3. Photocatalytic reforming: The liquid phase product in the storage tank (4) is quantitatively transported to the flat-plate photocatalytic reactor (6) by the metering pump (5). Under the irradiation of sunlight through the quartz panel (15), it comes into contact with the catalyst loaded on the 3D printed substrate (14) to carry out a photocatalytic reforming reaction. The liquid and hydrogen-rich gas after the reaction are collected from the liquid outlet pipe (12) and the gas outlet pipe (13), respectively.

6. The method according to claim 5, characterized in that, In step S1, the conditions for microwave pretreatment are: microwave power 300~1500W, reaction temperature 150~250℃, and reaction time 5~30min; The microwave pretreatment unit adopts a metal sealed cavity structure with a polytetrafluoroethylene liner, combined with a microwave generator and a stirring device, to achieve rapid and uniform depolymerization of waste plastics.

7. The method according to claim 5, characterized in that, In step S2, the filtration unit adopts a basket filter with differential pressure monitoring to achieve efficient solid-liquid separation and early warning of filter residue blockage.

8. The method according to claim 5, characterized in that, In step S3, the hydraulic residence time of the liquid phase product in the flat-plate photocatalytic reactor (6) is controlled by adjusting the flow rate of the metering pump (5).

9. The method according to claim 5, characterized in that, In step S3, the catalyst used in the photocatalytic reforming reaction is a composite catalyst selected from one or more noble metals selected from Pt, Pd, Ru, and Rh, supported on TiO2, g-C3N4, or CdS semiconductor materials.

10. The method according to claim 5, characterized in that, In step S3, the flat-plate photocatalytic reaction unit adopts a tilted flat-plate reactor, which contains a 3D-printed substrate loaded with catalyst to maximize light energy utilization and liquid-solid mass transfer efficiency.

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