CN115072659A - A kind of method for producing hydrogen from polyethylene plastic - Google Patents

Abstract

The invention belongs to the field of energy regeneration, and specifically discloses a method for producing hydrogen by using polyethylene plastic as a raw material. The method uses polyethylene plastic, especially polyethylene plastic waste as raw material, and includes continuous microwave thermal cracking and microwave catalytic treatment. The high-efficiency and low-carbon hydrogen production method based on microwave technology provided by the invention realizes high-selectivity and high-efficiency dehydrogenation treatment through the interaction of catalyst and microwave, and realizes the preparation of high-purity hydrogen from polyethylene plastics.

Description

A kind of method for producing hydrogen from polyethylene plastic

technical field

The invention belongs to the field of energy regeneration, and in particular relates to a method for producing hydrogen by using polyethylene plastic as a raw material.

Background technique

Polyethylene is a high molecular polymer and a plastic commonly used in life. Although there are many types of plastics, such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, etc., the use of polyethylene plastics accounts for about 30% of the daily commonly used plastic products, and the amount is large. We are familiar with polyethylene plastic products including widely used plastic bags, plastic films, plastic boxes and so on. Polyethylene plastic products have a short service life, and the general service cycle is 1 to 3 months, and then they are discarded. Polyethylene plastic waste produces a large amount, is difficult to be recycled and reused, and has low recycling value. At present, most of polyethylene plastic wastes are treated by incineration method. This traditional incineration treatment has the disadvantages of high emission and high pollution.

Polyethylene plastic is also a solid raw material rich in hydrogen element, and its hydrogen content is about 14.2%, which is a good hydrogen storage material. However, due to the stable polymer structure of polyethylene, it is difficult to achieve selective dehydrogenation. Therefore, there is an urgent need to develop a method for preparing hydrogen from polyethylene plastics for high-value utilization of polyethylene plastic wastes.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for producing hydrogen from polyethylene plastic, especially polyethylene plastic waste, which can prepare high-purity hydrogen, and the preparation process can be carried out continuously, and no harmful gas such as carbon dioxide is generated during the preparation process.

Specifically, the present invention provides a method for producing hydrogen from polyethylene plastics, wherein the method uses polyethylene plastics as a raw material to produce hydrogen, including two stages of continuous treatment; wherein:

The first stage of treatment is to carry out microwave thermal cracking of polyethylene plastics to generate thermal cracking products;

The second stage of treatment is that the thermal cracking product is subjected to microwave catalytic treatment to generate hydrogen-containing gas;

Wherein, the catalyst used in the microwave catalytic treatment is selected from carbon materials, transition metal materials or transition metal materials supported by carbon materials.

In some embodiments, the transition metal material is an iron-based metal material.

In some preferred embodiments, the transition metal material is selected from one or more of metallic iron, ferrous oxide, iron oxide, ferric oxide, and iron carbide.

In some embodiments, the carbon material is carbon black, activated carbon, or silicon carbide.

In some preferred embodiments, the carbon material is carbon black.

In some embodiments, the catalyst used in the present invention is a mixture of a carbon material and the transition metal material or a transition metal material supported by a carbon material.

In some embodiments, the catalyst includes a transition metal material and a carbon material in a mass ratio of (1-99):1, preferably a transition metal material and a carbon material in a mass ratio of (4-19):1.

According to a specific embodiment, the catalyst includes a transition metal material and a carbon material in a mass ratio of (2-9):1. According to a specific embodiment, the catalyst includes a transition metal material and a carbon material in a mass ratio of (3-9):1. According to a specific embodiment, the catalyst includes a transition metal material and a carbon material in a mass ratio of (4-9):1. According to a specific embodiment, the catalyst includes a transition metal material and a carbon material in a mass ratio of 4:1, 5:1, 6:1, 7:1, 8:1, 9:1.

In some embodiments, the catalyst used in the present invention is a mixture of carbon black and iron oxide, or a metal iron catalyst supported by carbon black.

More preferably, the catalyst used in the present invention is a carbon black supported metal iron catalyst.

In some embodiments, the temperature of the microwave thermal cracking is 450-800°C, preferably 500-750°C, more preferably 500-550°C.

In some embodiments, the power of the microwave catalytic treatment is 100-6000W, preferably 1000-4000W, such as 1000W, 2000W, 3000W or 4000W, more preferably 3000-4000W.

In some embodiments, the microwave frequency of the microwave thermal cracking and the microwave catalytic treatment is 2.45 GHz or 915 MHz, preferably 2.45 GHz.

In some embodiments, the duration of the microwave catalytic treatment is 20-60 minutes.

In some embodiments, the microwave thermal cracking and the microwave catalytic treatment employ a microwave thermal cracking reactor and a microwave catalytic dehydrogenation reactor in series.

Preferably, the catalyst in the microwave catalytic dehydrogenation reactor is preheated during microwave thermal cracking. The reaction product obtained by microwave thermal cracking is passed into the preheated microwave catalytic dehydrogenation reactor for microwave catalytic treatment.

According to some embodiments of the present disclosure, the mass ratio of the catalyst loaded in the microwave catalytic dehydrogenation reactor to the polyethylene plastic is 1:(5˜100). According to a specific embodiment, the mass ratio of the catalyst to the polyethylene plastic may be 1:(5-90), 1:(5-80), 1:(5-70), 1:(5-60 ), 1:(5~50), 1:(5~40), 1:(5~30), 1:(5~20), 1:(5~15). For example, the mass ratio of the catalyst to the polyethylene plastic may be 1:(10-15).

In some embodiments, the method for producing hydrogen from polyethylene plastic provided by the present invention further includes the operation of separating and purifying the hydrogen-containing gas, and the separation and purification method may adopt a known method in the art.

In some embodiments, the separation and purification includes gas scrubbing and/or pressure swing adsorption (PSA) treatment. Pressure swing adsorption usually refers to the method of adsorption under pressure and decompression (vacuum) or normal pressure desorption under the condition of constant temperature, that is, adsorption and desorption by changing the pressure. In the present disclosure, pressure swing adsorption especially refers to the use of periodic changes in pressure to perform adsorption and desorption based on different selective adsorption capacities of adsorbents for hydrogen and other gases under different pressures, thereby realizing the separation and purification of hydrogen.

According to some embodiments of the present disclosure, the adsorbent includes one or more of carbon, alumina, silica gel, molecular sieve, silica, and graphene.

Before the polyethylene plastic is subjected to the microwave thermal cracking treatment, the polyethylene plastic raw material may be pretreated according to the actual situation, and the pretreatment includes drying treatment and/or pulverization treatment.

According to some embodiments of the present disclosure, the microwave thermal cracking and/or microwave catalytic dehydrogenation treatment steps are performed under anaerobic or hypoxic conditions (eg, an inert environment with an oxygen content below 5000 ppm). According to a specific embodiment, in the process of the microwave thermal cracking and/or microwave catalytic dehydrogenation treatment, an inert gas, such as nitrogen or argon, is introduced.

The present invention also provides a device for preparing hydrogen, the device comprising:

The microwave thermal cracking reactor is used for microwave thermal cracking treatment to generate thermal cracking products;

a microwave catalytic dehydrogenation reactor for microwave-treating the thermal cracking product in the presence of a catalyst to generate a hydrogen-containing gas; and

The first gas collecting tank is used for collecting the hydrogen-containing gas product.

The microwave thermal cracking reactor and the microwave catalytic dehydrogenation reactor used in the present invention may be microwave reactors equipped with conventional microwave sources (including magnetrons or solid-state sources).

In some embodiments, the inner furnace wall of the microwave pyrolysis reactor is provided with a wave absorbing material, such as a silicon carbide-based wave absorbing material, and the maximum working temperature of the microwave pyrolysis reactor can reach 1600°C.

In some embodiments, the furnace body of the microwave catalytic dehydrogenation reactor is made of quartz or stainless steel, and no wave absorbing material is provided in the furnace wall.

In some embodiments, the device for preparing hydrogen provided by the present invention further comprises:

a pressure swing adsorption unit for performing pressure swing adsorption purification on the hydrogen-containing gas to generate high-purity hydrogen; and

The second gas collecting tank is used to collect the high-purity hydrogen.

According to a specific embodiment, the method of the present disclosure may include: loading the catalyst in a microwave catalytic dehydrogenation reactor, setting the microwave power to be 500-4000 W, 2.45 GHz, and under the condition of an inert gas (nitrogen or argon), Heat the catalyst to ≥350°C and maintain it stably; put the crushed polyethylene plastic fragments into the microwave thermal cracking furnace, set the thermal cracking temperature to 450-800°C, and introduce inert gas (nitrogen or argon) to carry out the plasticization process. Thermal cracking; the hydrocarbons obtained by thermal cracking are introduced into the microwave catalytic dehydrogenation reactor through an inert gas (carrier gas), and the hydrocarbons are subjected to catalytic dehydrogenation treatment through the interaction of the catalyst and the microwave. , to achieve high-selectivity in-situ pyrolysis-catalytic dehydrogenation; the obtained gas product (which can be washed through a gas cylinder) is collected into the first gas collecting tank.

According to a specific embodiment, the gas product in the first gas collection tank enters the pressure swing adsorption unit to purify the hydrogen to obtain the final hydrogen product, which is collected into the second gas collection tank.

In the present disclosure, the microwave thermal cracking reactor utilizes microwaves to rapidly heat polyethylene plastics to achieve rapid cracking and gasification of polyethylene plastics; microwave catalytic dehydrogenation achieves selective carbon-hydrogen bonds through the interaction of microwaves and catalysts Fragmentation, the preparation of high-purity hydrogen.

The present disclosure provides a brand-new method for processing polyethylene plastic waste, which can quickly and efficiently produce high-purity hydrogen from polyethylene plastic. In the method, a microwave reactor is used as a reaction furnace, and crude hydrogen with high hydrogen content is prepared from polyethylene plastic through microwave pyrolysis and microwave catalytic dehydrogenation, which can be further purified by pressure swing adsorption to obtain high-purity hydrogen with a purity of more than 99%. . In the method of the present disclosure, the polyethylene plastic polymer is firstly cracked into small molecular gas-liquid mixed intermediate products through rapid pyrolysis under microwave; then these intermediate products are passed into the microwave catalytic dehydrogenation reaction furnace through the carrier gas, and the Under standard atmospheric pressure and an oxygen-free/low oxygen environment, the mixed product obtained by microwave thermal cracking is subjected to microwave catalytic dehydrogenation treatment through the interaction of microwave and catalyst to obtain high-purity hydrogen-containing gas. Microwave thermal cracking is mainly based on the rapid heating characteristics of microwaves to achieve thermal cracking of polyethylene plastics, and obtain small molecular hydrocarbons that are conducive to subsequent catalytic dehydrogenation. In the process of microwave catalytic dehydrogenation treatment, the in-situ high-selective carbon-hydrogen bond cleavage is achieved by instantaneous heating of the catalyst under microwave, thereby improving the catalytic dehydrogenation treatment of hydrocarbons. The hydrogen production method of the present disclosure effectively improves the yield and purity of hydrogen. The hydrogen production method of the present disclosure can fully decompose polyethylene plastic to prepare hydrogen gas without generating carbon dioxide gas, and is an energy-saving, environmentally-friendly and efficient process for processing plastic waste and hydrogen production. In addition, the method of the present invention can continuously prepare high-purity hydrogen, which is of great significance for industrial continuous production.

Description of drawings

Fig. 1 is a device diagram used in a method for producing hydrogen from polyethylene plastic provided by the present invention.

Detailed ways

The following examples and figures are provided to assist the understanding of the present invention. However, it should be understood that these embodiments and accompanying drawings are only used to illustrate the present invention, but do not constitute any limitation. The actual scope of protection of the invention is set forth in the claims. It should be understood that any modifications and changes may be made without departing from the spirit of the invention.

The catalyst used in the present invention can be prepared by chemical preparation methods such as impregnation method, precipitation method, and combustion method known in the art. For transition metal materials supported by carbon materials or iron-based metal materials supported by carbon materials, metals can be mixed with the support materials in the form of precursors, including but not limited to nitrates, Chlorates, organometallic compounds, etc. In order to better ensure the effect of the catalyst to absorb microwaves, the particle size of the catalyst used in the present invention is less than 50 μm, and preferably the particle size of the catalyst is 50 nm˜10 μm.

Fig. 1 exemplarily shows a device for producing hydrogen from polyethylene plastic, including a microwave thermal cracking reactor (1), a microwave catalytic dehydrogenation reactor (2), a first gas collecting tank, a pressure swing Adsorption unit and second gas collection tank. In the process of preparing hydrogen, the polyethylene plastic is put into the microwave thermal cracking reactor (1) for microwave thermal cracking; the obtained gas-liquid mixture enters the microwave catalytic dehydrogenation reactor (2) along with the carrier gas, and the microwave thermal cracking is carried out. Catalytic dehydrogenation treatment to obtain a hydrogen-containing product; the obtained hydrogen-containing product flows into the first gas collection tank; then enters the pressure swing adsorption unit for separation and purification to obtain high-purity hydrogen, which is collected into the second gas collection tank middle.

Example 1

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) 100g polyethylene plastic is crushed and put into microwave thermal cracking reactor (1), nitrogen (50mL/min) is introduced, the heating rate is set to 20°C/min, the temperature is raised to 500°C and kept, polyethylene plastic is thermally cracked generate thermal cracking products;

(2) Take 10g of catalyst (the catalyst is prepared by mixing 325 mesh iron oxide powder and carbon black powder in a mass ratio of 9:1) and load it into the microwave catalytic dehydrogenation reactor (2), set the microwave power to 1000W, the frequency At 2.45GHz, the microwave catalytic dehydrogenation reactor (2) is opened while the microwave thermal cracking reactor (1) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 1000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected and sampled for analysis after washing, the results are shown in Table 1; the gas product was further subjected to pressure swing adsorption (PSA) treatment, the gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 1. Gas Product Analysis Results

Element molar ratio H₂ 72.3% CH₄ 5.7% C₂₊ 2.9% CO 15.6% CO₂ 3.5%

The iron oxide powder in the catalyst in this example was prepared by the following method: after mixing ferric nitrate and citric acid in a mass ratio of 1:1, calcined at 350° C. for 3 hours to obtain orange iron oxide powder.

Example 2

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) Pulverize 100g polyethylene plastic and put it into the microwave thermal cracking reactor (1), feed nitrogen (50mL/min), set the heating rate to 20°C/min, heat up to 550°C and maintain, the polyethylene plastic is thermally cracked generate thermal cracking products;

(2) Take 10g of catalyst (the catalyst is prepared by mixing 325 mesh iron oxide powder and carbon black powder in a mass ratio of 9:1) and load it into the microwave catalytic dehydrogenation reactor (2), set the microwave power to 2000W, the frequency At 2.45GHz, the microwave catalytic dehydrogenation reactor (2) is opened while the microwave thermal cracking reactor (1) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through the carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 2000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected and sampled for analysis after washing, the results are shown in Table 2; the gas product was further subjected to pressure swing adsorption (PSA) treatment, the gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 2. Gas product analysis results

Element molar ratio H₂ 76.6% CH₄ 4.3% C₂₊ 0.8% CO 13.8% CO₂ 4.5%

Example 3

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) Pulverize 100g polyethylene plastic and put it into the microwave thermal cracking reactor (1), feed nitrogen (50mL/min), set the heating rate to 20°C/min, heat up to 550°C and maintain, the polyethylene plastic is thermally cracked generate thermal cracking products;

(2) Take 10g of catalyst (the catalyst is prepared by mixing 325 mesh iron oxide powder and carbon black powder in a mass ratio of 4:1) and load it into the microwave catalytic dehydrogenation reactor (2), set the microwave power to 2000W, the frequency At 2.45GHz, the microwave catalytic dehydrogenation reactor (2) is opened while the microwave thermal cracking reactor (1) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through the carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 2000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected and sampled for analysis after washing, the results are shown in Table 3; the gas product was further subjected to pressure swing adsorption (PSA) treatment, the gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 3. Gas Product Analysis Results

Element molar ratio H₂ 74.2% CH₄ 8.9% C₂₊ 3.6% CO 10.2% CO₂ 3.1%

Example 4

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) 100g polyethylene plastic is crushed and put into microwave thermal cracking reactor (1), nitrogen (50mL/min) is introduced, the heating rate is set to 20°C/min, the temperature is raised to 500°C and kept, polyethylene plastic is thermally cracked generate thermal cracking products;

(2) Take 10g of catalyst (the catalyst is prepared by mixing 325 mesh iron oxide powder and carbon black powder in a mass ratio of 4:1) and load it into the microwave catalytic dehydrogenation reactor (2), set the microwave power to 3000W, the frequency At 2.45GHz, the microwave catalytic dehydrogenation reactor (2) is opened while the microwave thermal cracking reactor (1) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 3000W and frequency 2.45GHz to generate hydrogen-containing gas products , collected and sampled for analysis after washing, the results are shown in Table 4; the gas product was further subjected to pressure swing adsorption (PSA) treatment, gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 4. Gas Product Analysis Results

Example 5

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) Pulverize 100g polyethylene plastic and put it into the microwave thermal cracking reactor (1), feed nitrogen (50mL/min), set the heating rate to 20°C/min, heat up to 550°C and maintain, the polyethylene plastic is thermally cracked generate thermal cracking products;

(2) get 10g catalyst (catalyst is the metallic iron catalyst supported by carbon black, and the mass ratio of metallic iron and carbon black is 4:1) is loaded in the microwave catalytic dehydrogenation reactor (2), and the microwave power is set as 2000W , frequency 2.45GHz, when opening the microwave thermal cracking reactor (1), the microwave catalytic dehydrogenation reactor (2) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through the carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 2000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected and sampled for analysis after washing, the results are shown in Table 5; the gas product was further subjected to pressure swing adsorption (PSA) treatment, the gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 5. Gas Product Analysis Results

Element molar ratio H₂ 84.5% CH₄ 6.8% C₂₊ 3.9% CO 3.1% CO₂ 1.7%

The catalyst in this example was prepared by the following method: fully mixing carbon black and ferric nitrate in distilled water; calcining at 350°C for 3 hours in an inert atmosphere of argon; after calcining, at 5% H ₂ /Ar The catalyst was subjected to reduction treatment in the environment, and the reduction treatment temperature was 650° C. for 6 hours. Finally, the black powder of the metal iron catalyst supported by carbon black was collected, and the mass ratio of iron and carbon was 4:1.

Example 6

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) Pulverize 100g polyethylene plastic and put it into the microwave thermal cracking reactor (1), feed nitrogen (50mL/min), set the heating rate to 20°C/min, heat up to 550°C and maintain, the polyethylene plastic is thermally cracked generate thermal cracking products;

(2) get 10g catalyst (catalyst is the metal iron catalyst supported by carbon black, and the mass ratio of metal iron and carbon black is 4:1) is loaded in microwave catalytic dehydrogenation reactor (2), and the microwave power is set as 1000W , frequency 2.45GHz, when opening the microwave thermal cracking reactor (1), the microwave catalytic dehydrogenation reactor (2) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 1000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected and sampled for analysis after washing, and the results are shown in Table 6; the gas product was further subjected to pressure swing adsorption (PSA) treatment, collected gas, and sampled for analysis. The purity of hydrogen reached 99.9%.

Table 6. Gas Product Analysis Results

Element molar ratio H₂ 83% CH₄ 7.8% C₂₊ 5.2% CO 2.8% CO₂ 1.2%

Example 7

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) Pulverize 100g polyethylene plastic and put it into the microwave thermal cracking reactor (1), feed nitrogen (50mL/min), set the heating rate to 20°C/min, heat up to 550°C and maintain, the polyethylene plastic is thermally cracked generate thermal cracking products;

(2) get 10g catalyst (catalyst is the metallic iron catalyst supported by carbon black, the mass ratio of metallic iron and carbon black is 4:1) is loaded in the microwave catalytic dehydrogenation reactor (2), and the microwave power is set as 3000W , frequency 2.45GHz, when opening the microwave thermal cracking reactor (1), the microwave catalytic dehydrogenation reactor (2) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 3000W and frequency 2.45GHz to generate hydrogen-containing gas products , collected and sampled for analysis after washing, the results are shown in Table 7; the gas product was further subjected to pressure swing adsorption (PSA) treatment, the gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 7. Gas Product Analysis Results

Element molar ratio H₂ 90.1% CH₄ 3.4% C₂₊ 2.8% CO 2.3% CO₂ 1.4%

Example 8

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) 150g polyethylene plastic is crushed and put into microwave thermal cracking reactor (1), nitrogen (50mL/min) is introduced, the heating rate is set to 20°C/min, the temperature is raised to 550°C and kept, polyethylene plastic is thermally cracked generate thermal cracking products;

(2) get 10g catalyst (catalyst is the metallic iron catalyst supported by carbon black, the mass ratio of metallic iron and carbon black is 4:1) is loaded in the microwave catalytic dehydrogenation reactor (2), and the microwave power is set as 3000W , frequency 2.45GHz, when opening the microwave thermal cracking reactor (1), the microwave catalytic dehydrogenation reactor (2) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 3000W and frequency 2.45GHz to generate hydrogen-containing gas products , collected and sampled for analysis after washing, the results are shown in Table 8; the gas product was further subjected to pressure swing adsorption (PSA) treatment, gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 8. Gas Product Analysis Results

Element molar ratio H₂ 88.7% CH₄ 4.8% C₂₊ 3.1% CO 2.7% CO₂ 0.7%

Example 9

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) 150g polyethylene plastic is crushed and put into microwave thermal cracking reactor (1), nitrogen (50mL/min) is introduced, the heating rate is set to 20°C/min, the temperature is raised to 550°C and kept, polyethylene plastic is thermally cracked generate thermal cracking products;

(2) get 10g catalyst (catalyst is the metal iron catalyst supported by carbon black, and the mass ratio of metal iron and carbon black is 4:1) is loaded in the microwave catalytic dehydrogenation reactor (2), and the microwave power is set as 4000W , frequency 2.45GHz, when opening the microwave thermal cracking reactor (1), the microwave catalytic dehydrogenation reactor (2) is opened, and the loaded catalyst is preheated;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through the carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 4000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected and sampled for analysis after washing, the results are shown in Table 9; the gas product was further subjected to pressure swing adsorption (PSA) treatment, the gas was collected, sampled for analysis, and the purity of hydrogen reached 99.9%.

Table 9. Gas Product Analysis Results

Element molar ratio H₂ 92.3% CH₄ 3.2% C₂₊ 2.1% CO 1.3% CO₂ 1.1%

Example 10

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) Pulverize 100g polyethylene plastic and put it into the microwave thermal cracking reactor (1), feed nitrogen (50mL/min), set the heating rate to 20°C/min, heat up to 550°C and maintain, the polyethylene plastic is thermally cracked generate thermal cracking products;

(2) take 10g of catalyst and load it in the microwave catalytic dehydrogenation reactor (2), set the microwave power to 2000W, the frequency of 2.45GHz, and open the microwave catalytic dehydrogenation reactor while opening the microwave thermal cracking reactor (1). (2), preheating the loaded catalyst;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through the carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 2000W and frequency 2.45GHz to generate a hydrogen-containing gas product , collected after washing and sampled for analysis, the results are shown in Table 10.

Wherein in step (2), the catalyst used is prepared by mixing 325 mesh iron oxide powder and carbon black powder, and the influence of catalysts under different ratios on generating hydrogen-containing gas products is investigated, wherein iron oxide powder and carbon black powder The mixing mass ratios are shown in the table below.

Table 10. Gas Product Analysis Results

Element 9:1 4:1 10:1 3:1 2:1 1:1 0.5:1 H₂ 76.6% 74.2% 71.9% 69.5% 68.2% 54.2% 47.7% CH₄ 4.3% 8.9% 6.9% 8.1% 8.6% 17.9% 19.4% C₂₊ 0.8% 3.6% 6.1% 9.4% 9.9% 14.1% 24.8% CO 13.8% 10.2% 12.4% 10.9% 11% 9.7% 5.4% CO₂ 4.5% 3.1% 2.7% 2.1% 2.3% 4.1% 2.7%

From the comparison of the data in Table 10, it can be seen that the composition of the catalyst has a significant effect on the composition of the produced hydrogen-containing gas product. The mass ratio of iron oxide powder and carbon black powder in the catalyst is in the range of (4-10): 1, and the content of hydrogen in the obtained gas product is greater than 70%; as the amount of iron oxide powder in the mixture of iron oxide powder and carbon black powder increases, decreased, the hydrogen content in the obtained gas product decreased significantly.

Example 11

The present embodiment uses polyethylene plastic waste as a raw material to carry out the hydrogen production reaction, and the process flow is shown in Figure 1, which specifically includes the following steps:

(1) 150g polyethylene plastic is crushed and put into microwave thermal cracking reactor (1), nitrogen (50mL/min) is introduced, the heating rate is set to 20°C/min, the temperature is raised to 550°C and kept, polyethylene plastic is thermally cracked generate thermal cracking products;

(2) take 10g of catalyst and load it in the microwave catalytic dehydrogenation reactor (2), set the microwave power to 3000W, the frequency of 2.45GHz, and open the microwave catalytic dehydrogenation reactor while opening the microwave thermal cracking reactor (1). (2), preheating the loaded catalyst;

(3) the thermal cracking product obtained in step (1) is passed into the microwave catalytic dehydrogenation reactor (2) through carrier gas nitrogen, and the microwave catalytic reaction is carried out for 30 minutes under the conditions of microwave power 3000W and frequency 2.45GHz to generate hydrogen-containing gas products , collected after washing and sampled for analysis, the results are shown in Table 11.

Wherein in step (2), the catalyst adopted is a metal iron catalyst supported by carbon black, and the influence of catalysts under different proportions on generating hydrogen-containing gas products has been investigated, and the mass ratio of metal iron and carbon black is respectively as follows surface.

Table 11. Gas Product Analysis Results

Element 4:1(Fe:C) 0.5:1(Fe:C) 1:1(Fe:C) 2:1(Fe:C) 3:1(Fe:C) 5:1(Fe:C) H₂ 88.7% 77.6% 79.1% 80.6% 83.7% 85.3% CH₄ 4.8% 11.1% 10.5% 7.5% 6.7% 5.2% C₂₊ 3.1% 9.2% 7.9% 6.6% 4.2% 4.5% CO 2.7% 1.3% 1.6% 3.3% 3.5% 3.9% CO₂ 0.7% 0.8% 0.9% 2% 1.9% 1.1%

As can be seen from the comparison of the data in Table 11, the composition of the catalyst has a significant effect on the composition of the produced hydrogen-containing gas product. Compared with the mixed catalyst of iron oxide powder and carbon black powder, the effect of metal iron catalyst supported by carbon black is better. Especially when the mass ratio of metallic iron and carbon black in the catalyst is in the range of (2 to 5): 1, the hydrogen content in the obtained gas product is greater than 80%; when the mass ratio of metallic iron and carbon black in the catalyst is 4:1 , the hydrogen content in the obtained gas product is the highest, which is 88.7%.

The percentages in the above gas product analysis tables are all mole percentages.

Although the present invention has been described in detail above with general description, specific embodiments and tests, some modifications or improvements can be made on the basis of the present invention, which is obvious to those skilled in the art . Therefore, these modifications or improvements made without departing from the spirit of the present invention fall within the scope of the claimed protection of the present invention.

Claims (10)

1. a method for producing hydrogen from polyethylene plastics, characterized in that the method takes polyethylene plastics as raw material for producing hydrogen, comprising two stages of continuous processing; wherein: The first stage of treatment is to carry out microwave thermal cracking of polyethylene plastics to generate thermal cracking products; The second stage of treatment is that the thermal cracking product is subjected to microwave catalytic treatment to generate hydrogen-containing gas; Wherein, the catalyst used in the microwave catalytic treatment is selected from carbon materials, transition metal materials or transition metal materials supported by carbon materials. 2. The method according to claim 1, wherein the transition metal material is an iron-based metal material, preferably selected from the group consisting of metallic iron, ferrous oxide, iron oxide, ferric oxide, and iron carbide or more; And/or, the carbon material is carbon black, activated carbon or silicon carbide, preferably carbon black. 3. The method according to claim 1 or 2, wherein the catalyst is a mixture of a carbon material and the transition metal material or a transition metal material supported by a carbon material; Preferably, the catalyst includes a transition metal material and a carbon material in a mass ratio of (1-99):1, further preferably includes a transition metal material and a carbon material in a mass ratio of (4-19):1, more preferably includes a mass ratio of (4-19):1 A transition metal material and a carbon material with a ratio of (4 to 9):1. The method according to any one of claims 1 to 3, wherein the catalyst is a mixture of carbon black and iron oxide or metal iron supported on carbon black, preferably metal iron supported on carbon black. 5 . The method according to claim 1 , wherein the temperature of the microwave pyrolysis is 450-800° C., preferably 500-750° C., and more preferably 500-550° C. 6 . 6. The method according to any one of claims 1-5, wherein the power of the microwave catalytic treatment is 100-6000W, preferably 1000-4000W, more preferably 3000-4000W; And/or, the microwave frequency of the microwave thermal cracking and the microwave catalytic treatment is 2.45GHz or 915MHz, preferably 2.45GHz. 7. The method according to any one of claims 1 to 6, wherein the microwave thermal cracking and the microwave catalytic treatment use a microwave thermal cracking reactor and a microwave catalytic dehydrogenation reactor in series; During thermal cracking, the catalyst in the microwave catalytic dehydrogenation reactor is preheated. 8. The method according to any one of claims 1 to 7, characterized in that the method further comprises purifying the hydrogen-containing gas, preferably by a pressure swing adsorption treatment. 9. A device for preparing hydrogen, wherein the device comprises: The microwave thermal cracking reactor is used for microwave thermal cracking treatment to generate thermal cracking products; a microwave catalytic dehydrogenation reactor for microwave-treating the thermal cracking product in the presence of a catalyst to generate a hydrogen-containing gas; and a first gas collection tank for collecting the hydrogen-containing gas product; Preferably, the inner furnace wall of the microwave thermal cracking reactor is provided with a wave absorbing material; and/or, the furnace body of the microwave catalytic dehydrogenation reactor is made of quartz or stainless steel. 10. The apparatus of claim 9, wherein the apparatus further comprises: a pressure swing adsorption unit for performing pressure swing adsorption purification on the hydrogen-containing gas to generate high-purity hydrogen; and The second gas collecting tank is used to collect the high-purity hydrogen.

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