Method for continuously preparing green hydrogen through polyethylene waste gasification-catalytic reforming

Abstract

The invention provides a method for continuously preparing green hydrogen through polyethylene waste gasification-catalytic reforming, which comprises the following steps: a gasification process and a catalytic reforming process are included, the temperature of the gasification process is 450-650 DEG C, and the temperature of the catalytic reforming process is 750-850 DEG C. According to the method disclosed by the invention, the efficient catalyst is selected and prepared, and the adaptability to plastic wastes with different components is high; the continuous reaction can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection, in particular to the recycling of waste plastics. Background Art

[0002] With the continuous increase in global plastic production, the problem of plastic waste disposal is becoming increasingly serious. Polyethylene (PE), one of the most common plastics, has become a major issue in environmental protection and resource recycling. Due to its excellent chemical resistance, low-temperature resistance, and electrical insulation properties, PE is widely used in food packaging, pharmaceutical packaging, building materials, and other fields. However, PE is difficult to degrade in the natural environment, and long-term accumulation can cause soil and water pollution. Therefore, the development of efficient PE plastic recycling and reuse technologies is of great significance for environmental protection and resource conservation.

[0003] Traditional methods for disposing polyethylene plastics include landfill, incineration, and recycling. Landfilling consumes land resources, and plastics are difficult to degrade, posing a potential threat to soil and groundwater. While incineration can reduce the volume of plastic, it can produce toxic gases and solid waste, causing secondary environmental pollution. While recycling is an ideal treatment method, traditional recycling technologies suffer from low efficiency, high costs, and inconsistent product quality, limiting their widespread adoption.

[0004] In recent years, catalytic reforming technology has garnered widespread attention as an emerging plastics recycling and reuse technology. Using catalysts, catalytic reforming converts polyethylene plastics into high-value-added fuels and other chemicals, achieving resource recycling. While catalytic reforming technology demonstrates significant potential for polyethylene plastic recycling and reuse, current technology still faces several challenges that limit its widespread application.

[0005] The production of green, low-carbon hydrogen (also known as green hydrogen) is a key concern in the engineering community. Green hydrogen production produces virtually no carbon emissions. Green hydrogen production relies on renewable energy sources such as solar, wind, and hydropower. These energy sources are sustainable and are not consumed during use. Unlike traditional hydrogen produced by burning fossil fuels (such as coal, oil, and natural gas) (often referred to as "grey hydrogen"), the production of green hydrogen emits virtually no carbon dioxide.

[0006] The present invention provides a method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste. Summary of the Invention

[0007] The present invention provides a method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste, comprising the following steps: It includes gasification process and catalytic reforming process. The temperature of the gasification process is 450-650℃, and the temperature of the catalytic reforming process is 750-850℃.

[0008] Furthermore, the catalytic reforming process uses a NiAl2O4 spinel catalyst.

[0009] Furthermore, the preparation steps of the catalyst NiAl2O4 spinel are as follows: Step 1: Dissolve NiCl2∙6H2O, Al(NO3)3∙9H2O and citric acid in deionized water to obtain a uniform solution, and the molar ratio of citric acid to total metal ions is 0.8-2.0; Step 2: Slowly stir the uniform solution at 60-100ºC until a viscous gel is observed to form; Step 3: Transfer the gel to a drying oven at 120-180ºC and dry it for 3-5 hours until it is completely dry; Step 4: Calcinate the product of Step 3; Step 5: Crush the sample that is naturally cooled after calcination and sieve out 20-40 mesh particles.

[0010] Furthermore, the molar ratio of citric acid to total metal ions is 1.0.

[0011] Furthermore, the calcination temperature in step 4 is 750-850°C.

[0012] Furthermore, a fixed bed reactor system is used, including a gasification zone and a catalytic reforming zone.

[0013] Furthermore, the gasification step is to feed the polyethylene waste into the gasification zone, where the polyethylene waste is rapidly gasified at high temperature; and the catalytic reforming step is to react the volatile matter produced by the gasification with water vapor under the action of the catalyst in the catalytic reforming zone to undergo catalytic reforming reaction.

[0014] Furthermore, the method comprises the following steps: the feeding mass ratio of polyethylene waste to water vapor is 1:2-15 within the same time.

[0015] Furthermore, the method comprises the following steps: the feeding mass ratio of polyethylene waste to water vapor is 1:12 within the same time.

[0016] Green hydrogen synthesis gas prepared according to the above method.

[0017] The method of the present invention has the following technical advantages: A highly efficient catalyst was selected and prepared, which has high adaptability to plastic waste of different components.

[0018] The method of the present invention can realize continuous reaction, and thus has strong application characteristics in actual production. DETAILED DESCRIPTION

[0019] To make the technical problems solved, the technical solutions adopted, and the technical effects achieved by the present invention more clearly understood, the technical solutions of the embodiments of the present invention will be described in further detail below. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0020] Catalytic reforming technology is an effective method for converting polyethylene plastic waste into high-value-added fuels and other chemicals. Its basic principles include the gasification of plastics, catalytic reforming reactions, and product separation and purification.

[0021] Gasification of plastics is the first step in catalytic reforming technology. Under the influence of high temperatures and catalysts, plastic waste undergoes a gasification reaction, converting solid plastics into gaseous products. Gasification reactions primarily include cracking, reforming, and oxidation.

[0022] Pyrolysis reactions break down long-chain polymers into shorter-chain hydrocarbons. Polyethylene plastic undergoes pyrolysis at high temperatures, breaking long polyethylene chains into shorter hydrocarbon molecules such as methane, ethane, and ethylene.

[0023] Reforming reactions recombine short-chain hydrocarbons to form higher-carbon hydrocarbons. Under the action of a catalyst, the short-chain hydrocarbon molecules produced by cracking undergo further chemical reactions to produce higher-carbon hydrocarbon molecules, such as aromatics and cycloalkanes.

[0024] Oxidation reactions convert organic matter into gaseous and liquid fuels. During the gasification process, some hydrocarbon molecules react with oxygen to produce gaseous products such as carbon dioxide, carbon monoxide, and water vapor. Oxidation reactions are a possible reaction.

[0025] The gasification reaction of plastics is a complex process involving multiple physical and chemical factors. The gasification reaction effect is affected by many factors, including the type of plastic, the type and amount of catalyst, the reaction temperature, pressure, and gas atmosphere.

[0026] After gasification, catalytic reforming is continued.

[0027] Catalytic reforming is the core step of catalytic reforming technology. Under the action of a catalyst, the hydrocarbon molecules produced by gasification undergo further chemical reactions to produce higher-value fuels and other chemicals.

[0028] The catalytic reforming reaction mainly includes the following steps: Adsorption. Hydrocarbon molecules produced by gasification are adsorbed on the catalyst surface. The pore structure and surface properties of the catalyst have a significant impact on the adsorption of hydrocarbon molecules.

[0029] Catalytic reaction. Under the action of a catalyst, hydrocarbon molecules adsorbed on the surface react with water vapor and other substances to produce other chemicals. The active centers of the catalyst play a key role in the occurrence of chemical reactions.

[0030] Desorption. The products generated by the reaction desorb from the catalyst surface and enter the gas or liquid phase. The desorption rate of the products is affected by many factors, including the surface properties of the catalyst, reaction temperature, and pressure.

[0031] The effect of catalytic reforming reaction is affected by many factors, including the type and amount of catalyst, reaction temperature, pressure, gas atmosphere, etc.

[0032] Generally speaking, industrial catalytic reforming technology also requires product separation and purification to obtain high-value-added fuels and other chemicals. Separation and purification technologies can be adapted to different purposes. Generally speaking, product separation and purification can include the following steps: Gas-liquid separation: The products generated by the catalytic reforming reaction include gas and liquid. The gas and liquid products are separated by gas-liquid separation equipment.

[0033] Gas purification: The gas product contains impurities such as unreacted hydrocarbon molecules, carbon dioxide, carbon monoxide, etc. These impurities are removed through gas purification equipment to obtain pure gas fuel.

[0034] Liquid refining: Liquid products contain impurities such as unreacted hydrocarbon molecules, tar, and coke. These impurities are removed through liquid refining equipment to obtain pure liquid fuels or other chemicals.

[0035] In the present invention, in order to realize industrial application, continuous gasification of plastic to produce hydrogen is to be achieved, and a NiAl2O4 spinel catalyst is used for the catalytic reaction.

[0036] The metal ions (such as nickel ions) in spinel catalysts act as active centers in the catalytic reforming reaction. The metal ions form active sites on the catalyst surface, adsorbing hydrocarbon molecules and promoting the chemical reaction.

[0037] Oxygen vacancies in spinel catalysts can promote the adsorption and activation of hydrocarbon molecules, while participating in chemical reactions and improving the efficiency and selectivity of catalytic reforming reactions.

[0038] The specific steps of the present invention are as follows: Raw materials: polyethylene plastic (PE), NiAl2O4 spinel catalyst, distilled water.

[0039] Equipment: Tube furnace (for heating and reaction), injection pump (injects water into the steam generator at a certain rate), steam generator (used to control the water injected into the steam generator to produce water vapor), gas flow meter (used to control the carrier gas flow rate, and bring water vapor into the reaction system through the carrier gas), feed valve (used to control the feed rate), gas chromatograph (for product analysis), electronic balance (used to weigh catalysts and other materials).

[0040] step: Catalyst Preparation: First, the required amounts of NiCl₂∙6H₂O, Al(NO₃)₃∙9H₂O, and citric acid were dissolved in deionized water to obtain a homogeneous solution. The molar ratio of citric acid to total metal ions was 0.8–2.0. The homogeneous solution was then slowly stirred at 60–100°C until a viscous gel formed. The gel was then transferred to a drying oven at 120–180°C for 3–5 hours to ensure complete dryness. The samples were then calcined in a muffle furnace at various temperatures (ranging from 500–900°C) for 4 hours. Finally, the naturally cooled samples were pressed and sieved to a particle size of approximately 20–40 mesh for use in catalytic reforming experiments on plastic waste.

[0041] Reactor Preheating: Preheat a dual-zone tubular furnace to the set temperature (600°C for the gasification section and 800°C for the catalytic section). Load the NiAl2O4 spinel catalyst into the center of the reactor to form a catalyst bed. Inject distilled water into the steam generator at a rate of 36 mL / h via a water injection pump to generate steam. This steam is then delivered into the reactor using a carrier gas, maintaining a controlled steam injection rate of 36 mL / h.

[0042] Feeding and Reaction: Polyethylene plastic or waste is formed into strips and fed through a feed valve. 0.5 g (3 g / h) of polyethylene plastic (prefabricated into strips) is fed into the top of the reactor through the feed valve at a fixed rate. Feeding begins when the catalyst bed and steam reach the desired temperature. 0.5 g of polyethylene plastic is fed every 10 minutes, for a total reaction time of 40 minutes and a total feed rate of 2 g. The steam injection rate and feed rate are maintained constant throughout the reaction.

[0043] Product Collection and Analysis: After the reaction is complete, gaseous and liquid products are collected. Gaseous products are analyzed using a gas chromatograph to determine their composition and content. Liquid products are further processed and analyzed to obtain pure fuels or other chemicals.

[0044] The present invention utilizes catalytic reforming technology to convert polyethylene plastic into high-value-added fuels and other chemicals, based on the steps of plastic gasification, catalytic reforming reaction, and product separation and purification.

[0045] The present invention adopts a method for producing hydrogen by continuous gasification of plastics. Example

[0046] In the catalytic gasification process, the performance of the catalyst plays a vital role in gasification efficiency and product distribution. Among them, the calcination temperature of the catalyst is one of the key factors affecting its performance.

[0047] Raw materials: polyethylene (PE) waste, as raw material for gasification reaction; water.

[0048] Catalyst: NiAl2O4 spinel was used as the catalyst, and catalysts with different performances were prepared by changing the calcination temperature (500℃, 600℃, 700℃, 750℃, 800℃, 850℃, 900℃).

[0049] Experimental setup and process: The experiment uses a fixed bed reactor system, including a gasification zone and a catalytic reforming zone. The details are as follows: Catalyst loading: NiAl2O4 catalysts with different calcination temperatures were loaded on the catalyst bed in the catalytic reforming zone.

[0050] System preheating: Preheat the gasification zone and catalytic reforming zone to the set temperature (600℃ for gasification zone and 800℃ for catalytic reforming zone) respectively.

[0051] Feeding and Reaction: Polyethylene plastic or waste is formed into strips and fed through a feed valve. 0.5g (3g / h) is fed into the polyethylene at a fixed rate. At 3g / h, the water vapor injection rate is controlled at 36mL / h (ml is the water vapor equivalent).

[0052] Gasification reaction: The polyethylene waste is sent to the gasification zone for rapid gasification at high temperature. The generated volatile matter enters the catalytic reforming zone, where a catalytic reforming reaction occurs under the action of the catalyst.

[0053] Product collection and analysis: Condensable tar is collected through a condensation system, and non-condensable gases are analyzed by gas chromatography to determine their composition and yield.

[0054] Experimental results and analysis: The effect of catalyst calcination temperature on gasification products is shown in Table 1 below.

[0055]

[0056] Table 1 According to the experimental results (see Table 1), the catalysts calcined at different temperatures had a significant effect on the yield and composition of the gasification products.

[0057] Hydrogen Yield: As the catalyst calcination temperature increased, hydrogen yield showed a trend of first decreasing, then increasing, and then decreasing again. Hydrogen yields were relatively high for catalysts calcined at 500°C and 700°C, reaching 239.96 mmol / g and 235.49 mmol / g, respectively. However, hydrogen yields decreased for catalysts calcined at 600°C and 900°C, reaching 213.17 mmol / g and 219.87 mmol / g, respectively. The highest hydrogen yield was reached on the catalyst calcined at 800°C, at 244.42 mmol / g.

[0058] Carbon Monoxide Yield: The variation trend of carbon monoxide yield with catalyst calcination temperature is similar to that of hydrogen, but the fluctuation range is smaller. On the catalyst calcined at 800℃, the carbon monoxide yield reaches a maximum of 12.46 vol%.

[0059] Methane and carbon dioxide production: The production of methane and carbon dioxide does not change significantly with the catalyst calcination temperature, but generally shows a trend of slightly decreasing with increasing temperature.

[0060] Effect of catalyst calcination temperature on gasification efficiency Gasification efficiency is one of the important indicators to measure the performance of the gasification process, which can be evaluated by carbon conversion efficiency (CCE). Experimental results show that: Carbon Conversion Efficiency (CCE): As the catalyst calcination temperature increases, the carbon conversion rate shows a trend of first increasing and then decreasing. The carbon conversion rate reaches its highest value, approaching 100%, on the catalyst calcined at 800°C, indicating that the plastic feedstock is almost completely converted into gaseous products under these conditions.

[0061] From Example 1, we can see the effect of catalyst calcination temperature on catalyst performance.

[0062] The calcination temperature of a catalyst is a key factor influencing its crystal structure, specific surface area, pore structure, and surface chemical properties. Generally speaking, an appropriate calcination temperature can increase the catalyst's crystallinity, surface area, and pore volume, thereby enhancing its catalytic activity. However, excessively high calcination temperatures can lead to grain growth, a decrease in specific surface area, and a collapse of the pore structure, thereby reducing catalytic performance.

[0063] In this embodiment, the NiAl2O4 catalyst calcined at 800°C exhibited the best catalytic performance, and exhibited excellent performance between 750°C and 850°C.

[0064] Example 1.1 Experimental conditions: Catalyst: NiAl2O4 spinel catalyst calcined at 800°C (based on the best results of Example 1) Gasification process temperature: 450℃ Catalytic reforming process temperature: 750℃ Experimental process: The experimental apparatus and process are the same as those in Example 1. The catalyst is loaded on the catalytic bed in the catalytic reforming zone, and the gasification zone and catalytic reforming zone are preheated to 450°C and 750°C, respectively. The polyethylene waste is fed into the gasification zone for gasification, and the generated volatile matter then enters the catalytic reforming zone, where a catalytic reforming reaction occurs under the action of a NiAl2O4 catalyst calcined at 800°C. The polyethylene feed rate is controlled at 3g / h, and the water vapor injection rate is 36mL / h. Condensable tar is collected by a condensation system, and non-condensable gases are analyzed by gas chromatograph.

[0065] Example 1.2 Experimental conditions: Catalyst: NiAl2O4 spinel catalyst calcined at 800℃ Gasification process temperature: 650℃ Catalytic reforming process temperature: 750℃ Experimental process: The experimental procedure was similar to that of Example 1.1, except that the temperature of the gasification zone was increased to 650° C. This would increase the degree of polyethylene gasification, while the temperature of the catalytic reforming zone remained unchanged to observe the effect of different gasification temperatures on product distribution.

[0066] Example 1.3 Experimental conditions: Catalyst: NiAl2O4 spinel catalyst calcined at 800℃ Gasification process temperature: 450℃ Catalytic reforming process temperature: 850℃ Experimental process: The experimental procedure was similar to that of Example 1.1, but the temperature of the catalytic reforming zone was increased to 850°C.

[0067] Example 1.4 Experimental conditions: Catalyst: NiAl2O4 spinel catalyst calcined at 800℃ Gasification process temperature: 650℃ Catalytic reforming process temperature: 850℃ Experimental process: The experimental procedure combined the conditions of Examples 1.2 and 1.3, that is, the temperature of the gasification zone was 550°C and the temperature of the catalytic reforming zone was 850°C.

[0068] The technical effects of the above embodiments are shown in Table 1.1.

[0069]

[0070] Table 1.1 Example

[0071] For the NiAl2O4 spinel catalyst calcined at 800°C in Example 1, Example 2 preliminarily observed the performance of the NiAl2O4 spinel catalyst in five consecutive cycles. The specific results are shown in Table 2 below:

[0072] Table 2 Gas production: The experimental results show that gas yield (mmol / g) initially increases and then slightly decreases with increasing cycle number. During the first cycle, gas yield reached 244.42 mmol / g, then increased to 262.28 mmol / g and 265.63 mmol / g in the second and third cycles, reaching peak values. Subsequently, gas yield decreased slightly in the fourth and fifth cycles, reaching 260.04 mmol / g and 252.23 mmol / g, respectively.

[0073] This change reflects the initial activation time required for the catalyst. As the reaction proceeds, the catalyst's active sites are gradually fully utilized, and gas production reaches its maximum. However, as the number of cycles increases, the catalyst may begin to deactivate or carbonize, resulting in a slight decrease in gas production.

[0074] Hydrogen production: The trend of hydrogen production (mmol / g) was similar to that of total gas production, initially increasing and then slightly decreasing. During the first cycle, hydrogen production reached 200.95 mmol / g, then increased to 220.58 mmol / g and 221.30 mmol / g in the second and third cycles. In the fourth and fifth cycles, hydrogen production decreased slightly to 217.22 mmol / g and 207.90 mmol / g, respectively.

[0075] The change in hydrogen production further confirms that the catalyst activity increases after initial activation, followed by a slight decrease due to possible deactivation or carbon deposition. Nevertheless, hydrogen production remains at a relatively high level throughout the cycle, indicating that the NiAl2O4 spinel catalyst has good catalytic stability and hydrogen selectivity.

[0076] Gas composition: In terms of gas composition, hydrogen (H2) is the primary product, with a volume fraction exceeding 70% and remaining relatively stable throughout the cycle. The volume fraction of carbon monoxide (CO) fluctuates between 10% and 12%, while the volume fraction of methane (CH4) is lower, below 1%. The volume fraction of carbon dioxide (CO2) fluctuates between 15% and 17%.

[0077] The stability of the gas composition indicates that the NiAl2O4 spinel catalyst effectively promotes the gasification and reforming of polyethylene during the catalytic reforming process, generating hydrogen-rich syngas. Furthermore, the low methane volume fraction and relatively stable carbon dioxide volume fraction also reflect the catalyst's good selectivity for the reaction pathway.

[0078] Cyclic stability analysis: Results from five consecutive cycles show that the NiAl2O4 spinel catalyst exhibits excellent cyclic stability. Although total gas and hydrogen production decrease slightly in the later stages of the cycle, they remain at high levels overall. The stability of the gas composition further confirms the catalyst's cyclic stability. Example

[0079] Four common plastic wastes, namely agricultural films, ziplock bags, Wahaha bottles and medicine bottles, were selected as raw materials, and continuous gasification experiments were carried out using NiAl2O4 spinel catalysts. During the experiment, each type of plastic waste was rapidly gasified at 600°C, and the generated volatile matter was catalytically reformed by the catalyst at 800°C. 0.5g of plastic waste was fed every 10 minutes, the water vapor injection rate was 36mL / h, the total reaction time was 40 minutes, and the total feed amount was 2g. By comparing the gasification performance of different plastic wastes under the same conditions, the feasibility and efficiency of their catalytic steam reforming can be evaluated. The specific reaction data are shown in Table 3 below:

[0080] Table 3 From Table 3, we can observe the performance differences of different plastic wastes in the continuous gasification process. Specifically: Gas production and hydrogen production: Polyethylene (PE) was used as a reference, and its gas and hydrogen yields were relatively high, at 244.42 mmol / g and 201.87 mmol / g, respectively.

[0081] In contrast, the gas and hydrogen production of agricultural film, ziplock bags, Wahaha bottles, and pharmaceutical bottles all decreased. The gas production of agricultural film was 223.21 mmol / g, and the hydrogen production was 185.85 mmol / g; the gas production of ziplock bags was 217.63 mmol / g, and the hydrogen production was 180.27 mmol / g; the gas production of Wahaha bottles was 214.29 mmol / g, and the hydrogen production was 178.25 mmol / g; and the gas production of pharmaceutical bottles was 239.96 mmol / g, and the hydrogen production was 200.10 mmol / g.

[0082] These differences may stem from the varying chemical structures and pyrolysis characteristics of different plastic wastes. For example, polyethylene, composed primarily of carbon and hydrogen, readily produces hydrogen-rich volatiles during pyrolysis. Meanwhile, some plastic waste containing additives or complex chemical structures may produce more tar and other byproducts during pyrolysis, thus affecting both gas and hydrogen production.

[0083] Gas composition: The gas composition produced during the continuous gasification process varies among different types of plastic waste. However, overall, hydrogen (H2) is the primary product, with a volume fraction exceeding 69%. The volume fractions of carbon monoxide (CO), methane (CH4), and carbon dioxide (CO2) vary depending on the type of plastic.

[0084] These differences may be related to the pyrolysis mechanism of plastic waste and the selectivity of the catalyst. In the catalytic steam reforming process, the catalyst not only promotes the gasification reaction of plastic waste, but also affects the gas composition by selectively catalyzing the reforming reaction pathway.

[0085] Based on Example 1, in order to further compare the effects of different catalysts on the catalytic gasification reaction, we selected another catalyst, Co3O4, and followed an experimental process similar to that of Example 1, but made necessary adjustments to the catalyst calcination temperature and loading details based on the characteristics of Co3O4.

[0086] Raw materials and catalysts: Raw materials: Polyethylene (PE) waste is used as gasification raw material.

[0087] Catalyst: Co3O4 catalyst was used, and four calcination temperature points of 550℃, 650℃, 750℃ and 850℃ were selected.

[0088] Experimental apparatus and process (similar to Example 1, but with adjustments to the catalyst type and calcination temperature): The steps of catalyst loading and preheating were carried out as described in Example 1, except that the catalyst type was replaced with Co3O4, and the preheating temperature of the catalytic reforming zone was appropriately adjusted according to the calcination temperature of Co3O4.

[0089] Experimental results and analysis: The gasification product data of Co3O4 catalyst at different calcination temperatures are shown in Table 3. Compared with the data in Example 1, the difference in technical effects can be clearly seen.

[0090]

[0091] Table 4 From Table 4 we can see that: Hydrogen production: Although the hydrogen production increased with increasing calcination temperature of the Co3O4 catalyst, it was still much lower than that of the NiAl2O4 catalyst in Example 1. The highest hydrogen production was only 200.11 mmol / g, which occurred on the catalyst calcined at 750°C.

[0092] Carbon monoxide production: The production trend of carbon monoxide is similar to that of hydrogen, but it is also much lower than that of NiAl2O4 catalyst.

[0093] Methane and carbon dioxide production: The methane production was relatively high, while the carbon dioxide production also showed a higher ratio, which indicated that the selectivity of gasification products was not as good as that of NiAl2O4 catalyst when using Co3O4 catalyst.

[0094] Gasification efficiency evaluation: Carbon conversion efficiency (CCE): When using Co3O4 catalyst, the carbon conversion efficiency is generally low. With the increase of calcination temperature, its change trend is similar to that of Example 1, but there is a significant difference in the absolute value.

[0095] in conclusion: The experimental results and analysis of Comparative Example 1 clearly show that while the Co3O4 catalyst exhibits some catalytic activity at different calcination temperatures, its overall catalytic effect and technical performance are significantly inferior to those of the NiAl2O4 catalyst in Example 1. This further emphasizes the critical influence of catalyst type and calcination temperature on the performance of the catalytic gasification process.

[0096] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste, characterized in that: The steps include: It includes gasification process and catalytic reforming process. The temperature of the gasification process is 450-650℃, and the temperature of the catalytic reforming process is 750-850℃.

2. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 1, characterized in that: The catalytic reforming process uses NiAl2O4 spinel catalyst.

3. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 2, characterized in that: The preparation steps of the catalyst NiAl2O4 spinel are as follows: Step 1: Dissolve NiCl2∙6H2O, Al(NO3)3∙9H2O and citric acid in deionized water to obtain a uniform solution, and the molar ratio of citric acid to total metal ions is 0.8-2.0; Step 2: Slowly stir the uniform solution at 60-100ºC until a viscous gel is observed to form; Step 3: Transfer the gel to a drying oven at 120-180ºC and dry it for 3-5 hours until it is completely dry; Step 4: Calcinate the product of Step 3; Step 5: Crush the sample that is naturally cooled after calcination and sieve out 20-40 mesh particles.

4. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 3, characterized in that: The molar ratio of citric acid to total metal ions was 1.

0.

5. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 3, characterized in that: The calcination temperature in step 4 is 750-850°C.

6. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 1, characterized in that: A fixed bed reactor system is used, including a gasification zone and a catalytic reforming zone.

7. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 1, characterized in that: The method comprises the following steps: a gasification step: feeding polyethylene waste into a gasification zone, where the polyethylene waste is rapidly gasified at high temperature; a catalytic reforming step: volatile matter generated by gasification and water vapor undergo catalytic reforming reaction under the action of a catalyst in the catalytic reforming zone.

8. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 1, characterized in that: The method comprises the following steps: the feeding mass ratio of polyethylene waste to water vapor is 1:2-15 within the same time.

9. The method for continuously preparing green hydrogen by gasification-catalytic reforming of polyethylene waste according to claim 1, characterized in that: The method comprises the following steps: the feeding mass ratio of polyethylene waste to water vapor is 1:12 within the same time.

10. Green hydrogen synthesis gas prepared by the method according to any one of claims 1 to 9.

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