CN116688984B - Microwave-assisted process for catalyzing and cracking polyethylene based on double-layer iron-based catalyst - Google Patents

Microwave-assisted process for catalyzing and cracking polyethylene based on double-layer iron-based catalyst Download PDF

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CN116688984B
CN116688984B CN202310548439.7A CN202310548439A CN116688984B CN 116688984 B CN116688984 B CN 116688984B CN 202310548439 A CN202310548439 A CN 202310548439A CN 116688984 B CN116688984 B CN 116688984B
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王松
张斌
胡艳兵
李三喜
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Shenyang University of Technology
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Abstract

The invention relates to a microwave-assisted process for catalytic cracking of polyethylene based on a double-layer iron-based catalyst. Comprising the following steps: 1) Preparing an iron-based catalyst FeMO; 2) Preparing composite carbon nano-tubes; 3) Preparation of FeMO/CNT composite catalyst; 4) Microwave-assisted catalytic cracking of polyethylene: (1) Uniformly mixing polyethylene and FeMO/CNT composite catalyst in a mass ratio of 1:1, forming a first layer of material at the bottom of the reactor, wherein the height of the first layer of material is H1, and then adding a second layer of material FeMO/CNT composite catalyst on the first layer of material; (2) After purging with nitrogen to purge air, a microwave pyrolysis reaction was performed using a method of gradually increasing microwave power. The invention has the advantages that: 1. the catalyst treatment method is simple. 2. The whole process is simple. 3. The yield of hydrogen obtained by cracking polyethylene is obviously increased.

Description

Microwave-assisted process for catalyzing and cracking polyethylene based on double-layer iron-based catalyst
Technical Field
The invention relates to a process for catalytically cracking polyethylene by microwave assistance, in particular to a process for catalytically cracking polyethylene by microwave assistance based on a double-layer iron-based catalyst.
Background
Polyethylene is widely used in many industries because of its durability, robustness, water resistance, light weight, strong corrosion resistance, good insulation, and the like. However, polyethylene brings convenience and also brings the problem of environmental pollution caused by white garbage. Therefore, how to effectively recycle the waste polyethylene becomes an important problem today. The development of high value-added products from waste polyethylene is identified as a promising approach to polyethylene waste disposal compared to direct landfill or incineration.
The hydrogen energy is used as a clean secondary energy carrier, the energy density is up to 142.82 kilojoules per kilogram, the hydrogen energy can be converted into electric energy and heat energy, the conversion efficiency is high, and the hydrogen energy has good application prospect. Conversion of polyethylene to hydrogen is therefore a research hotspot in the field of polyethylene waste utilization. During the cracking of polyethylene, solid carbon materials, liquid hydrocarbon compounds and gaseous substances may be produced. Wherein, the gaseous substance is mainly hydrogen and also comprises carbon monoxide, carbon dioxide and the like. Thus, from the molecular structure of the polyethylene, the maximum hydrogen yield theoretically produced by cracking the polyethylene is about 71.4 millimoles per gram of polyethylene. However, the current efficient polyethylene cracking technology still has problems, and the hydrogen yield of polyethylene cracking is far less than the theoretical maximum value. As in document (nature catalysis,2020.3: p902-912.DOI:10.1038/s 41929-020-00518-5), a process for the microwave-assisted catalytic cracking of polyethylene is described which gives hydrogen yields of only 55.6 mmoles per gram of polyethylene. The catalysts used in this process were further optimized in the literature (Journal of Hazardous Materials,2023.445:p130609.DOI:10.1016/j. Jhazmat. 2022.130609.) and the hydrogen yield obtained by the reaction was only 59.28 mmoles per gram of polyethylene using plasma combined technology. For another example, patent (CN 115779904 a) describes the preparation of an iron-aluminum catalyst. With this catalyst, the hydrogen yield can only reach 42.84 millimoles per gram of polyethylene. This is because the current process for cracking polyethylene still has the problems of low hydrogen yield, higher proportion of oily byproducts, and the like. At present, the catalyst is mainly an iron catalyst, the temperature of the catalyst is rapidly increased under microwave irradiation, and the catalyst and polyethylene at the contact position of the polyethylene are subjected to cracking reaction to generate hydrogen and carbon nanotubes. In order to increase the hydrogen yield of polyethylene cracking and to produce high-quality carbon nanotubes, there is a strong need for a polyethylene cracking process that stably and efficiently produces hydrogen in addition to searching for a more efficient catalyst.
Disclosure of Invention
In order to solve the technical problems, the invention provides a microwave-assisted process for catalytic cracking of polyethylene based on a double-layer iron-based catalyst, and aims to solve the problem of low hydrogen yield.
In order to achieve the above object, the microwave-assisted process for catalytic cracking of polyethylene based on a double-layer iron-based catalyst of the present invention comprises:
1) Preparation of iron-based catalyst FeMO:
Mixing Fe (NO 3)3 and M (NO 3)y and citric acid according to the molar ratio of Fe 3+:My+ to citric acid of 1:n (1+n) (n=1-2), adding deionized water to dissolve and uniformly mix to obtain a mixed solution, heating the mixed solution at 60 ℃ for 2-4 hours, cooling to room temperature to obtain gel, and preserving the temperature of the obtained gel at 350 ℃ for 3 hours in a certain atmosphere in an atmosphere furnace to obtain FeMO catalyst powder;
2) Preparation of composite carbon nano tube:
(1) Uniformly mixing polyethylene with a mass ratio of 1:1 with FeMO catalyst, pouring the mixture into a microwave reactor, purging the mixture with nitrogen until air is exhausted, and performing microwave pyrolysis reaction by using a method of gradually increasing microwave power until the polyethylene is completely cracked;
(2) After the reaction is finished, uniformly mixing the residual solid with polyethylene according to the mass ratio of 1:1, and then loading the mixture into a microwave reactor again; repeating the step (1), and carrying out microwave pyrolysis again until the polyethylene is completely cracked;
(3) Repeating the step (2) for 1-13 times to obtain the self-made composite carbon nano tube;
3) Preparation of FeMO/CNT composite catalyst
Mixing an iron catalyst FeMO, a composite carbon nano tube and absolute ethyl alcohol according to the mass ratio of (0.01-0.05): 10, performing ultrasonic mixing treatment on the mixture by using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture, stirring and evaporating the mixture at 60 ℃, then placing the mixture in a 120 ℃ oven, and drying for 3 hours to obtain the FeMO/CNT composite catalyst;
4) Microwave-assisted catalytic cracking polyethylene
(1) Uniformly mixing polyethylene and FeMO/CNT composite catalyst in a mass ratio of 1:1, forming a first layer of material at the bottom of the reactor, wherein the height of the first layer of material is H1, and then adding a second layer of material FeMO/CNT composite catalyst on the first layer of material;
(2) After purging with nitrogen to purge air, a microwave pyrolysis reaction was performed using a method of gradually increasing microwave power.
M in the step 1) is one or a mixture of two of Ni, al, co, mn, cu, mg, zn, ce, pd, yb, la, zr; in the case of mixing two metal elements M, the molar ratio of the two metal elements is 1:1.
The atmosphere in the step 1) is nitrogen, air or argon.
The method for gradually increasing the microwave power to carry out the microwave pyrolysis reaction refers to firstly adjusting the power of a microwave reactor to 200-300 watts and maintaining for 5-10 seconds; then adjusting the microwave power to 650-700W for 20-30 seconds; and then adjusting the power to 850-900W for 20-30 seconds, and finally adjusting the microwave power to 1000W for 3-5 minutes until the polyethylene is completely cracked.
The ratio of the height of the first layer material to the height of the second layer material in the step 4) is H1:H2=1 (0.5-2).
A microwave-assisted double-layer iron-based catalyst-based catalytic cracking process for polyethylene, comprising:
1) Preparation of iron-based catalyst FeO:
mixing Fe (NO 3)3 and citric acid according to a molar ratio of 1:1, adding deionized water to dissolve and uniformly mix to obtain a mixed solution, heating the mixed solution at 60 ℃ for 2-4 hours, cooling to room temperature to obtain gel, and preserving the temperature of the obtained gel at 350 ℃ for 3 hours in a certain atmosphere in an atmosphere furnace to obtain FeO catalyst powder;
2) Microwave-assisted catalytic cracking polyethylene
(1) Uniformly mixing polyethylene and FeO catalyst powder in a mass ratio of 1:1, forming a first layer of material at the bottom of a reactor, wherein the height of the first layer of material is H1, and then adding a second layer of material FeO catalyst on the first layer of material;
(2) After purging with nitrogen to purge air, a microwave pyrolysis reaction was performed using a method of gradually increasing microwave power.
The method for gradually increasing the microwave power carries out the microwave pyrolysis reaction as follows: the method of gradually increasing the microwave power for the microwave pyrolysis reaction is to firstly adjust the power of a microwave reactor to 200-300 watts and maintain for 5-10 seconds; then adjusting the microwave power to 650-700W for 20-30 seconds; and then adjusting the power to 850-900W for 20-30 seconds, and finally adjusting the microwave power to 1000W for 3-5 minutes until the polyethylene is completely cracked.
The invention has the advantages that: 1. the catalyst treatment method is simple. In the current research of microwave assisted processes, the catalyst essentially needs to be activated before use, as in literature (MATERIALS TODAY CHEMISTRY,2022.26: p101166.DOI: 10.1016/j.mtchem.2022.101166.) the catalyst needs to be mixed with activated carbon for 2 hours at 500 degrees celsius under nitrogen protection before use. Whereas the catalysts in the literature (Journal of ANALYTICAL AND APPLIED Pyrolysis,2022.165: p105577.DOI:10.1016/j. Jaap. 2022.105577.) require activation at 800℃for 4 hours under an atmosphere of 10% hydrogen mixed with nitrogen. The catalyst of the invention can keep activity for a long time after preparation, and does not need to be activated before use.
2. The whole process is simple. The current method for microwave cracking polyethylene has the hydrogen yield basically lower than 60
Millimoles per gram of polyethylene. In order to increase the hydrogen production, the literature (Journal of Hazardous Materials,2023.445:p130609.DOI:10.1016/j.jhazmat. 2022.130609.) uses the plasma-plasma combination technique, and the final hydrogen production also reaches only 59.28 millimoles per gram of polyethylene. Whereas the present invention uses only microwave technology, the hydrogen production exceeds 60 millimoles per gram of polyethylene. The whole process is obviously simple.
3. The yield of hydrogen obtained by cracking polyethylene is obviously increased, the invention adopts a double-layer catalytic reaction process, and the novel composite catalyst can greatly reduce oily byproducts generated by the cracking reaction. The composite catalyst used in the invention improves the wave-absorbing performance of the catalyst and greatly improves the reaction efficiency because FeMO/CNT composite catalyst is added. More importantly, the invention adopts a double-layer catalytic reaction process, and when a large amount of hydrocarbon gas carried by the lower reaction zone is blown into the upper reaction zone, the upper catalyst can carry out dehydrogenation reaction on the hydrocarbon again, so that the hydrogen yield is greatly improved. The hydrogen production using the present technology is greater than 60 millimoles per gram of polyethylene.
Drawings
FIG. 1 is a schematic illustration of the placement of a first layer of material and a second layer of material according to the present invention.
FIG. 2 is a graph showing the morphology of the carbon material after the microwave pyrolysis reaction of the first layer of material according to the present invention.
FIG. 3 is a graph showing the morphology of the carbon material after the microwave pyrolysis reaction of the second layer material according to the present invention.
Detailed Description
The method for preparing hydrogen and carbon nano tubes by microwave-assisted double-layer catalytic cracking of polyethylene according to the invention is further described below by way of examples and with reference to the accompanying drawings. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the invention, are within the scope of the invention.
Example 1
FeAlO catalyst preparation
Fe (NO 3)3:Al(NO3)3: citric acid) is weighed according to a molar ratio of 1:1:2 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is subjected to heat preservation at 350 ℃ for 3 hours in an atmosphere furnace to obtain FeAlO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing the microwave power, wherein the power of a microwave reactor is firstly adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) And (3) repeating the step (2) 13 times to obtain the self-made composite carbon nanotube.
3. Preparation of FeAlO/2wt% CNT composite catalyst
The catalyst FeAlO, the composite carbon nanotube and the absolute ethyl alcohol are weighed and mixed according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. Finally, a composite catalyst of FeAlO/2wt% CNT is obtained.
4. Microwave-assisted FeAlO/2wt% CNT double-layer catalytic cracking polyethylene (H1: H2=1:0.5)
(1) The polyethylene and FeAlO/2wt% CNT catalyst are weighed and mixed uniformly according to the mass ratio of 1:1, and are placed at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then a second layer of material FeAlO/2wt% CNT catalyst is added on the first layer of material, and the height of the second layer of material is H2, as shown in figure 1. The height ratio of the two layers of materials is H1:H2=1:0.5.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 850 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked. The hydrogen (H 2) yield was 66.38 mmoles per gram of polyethylene.
Figures 2 and 3 show the morphology of the first and second layers of carbon material, respectively, after cracking, and the presence of longer carbon nanotubes in the first layer is seen. Some short, irregular carbon nanotube-like carbon material is present in the second layer, which demonstrates that the lower cracking gas undergoes further cracking to produce hydrogen and carbon material as it passes over the upper catalyst layer.
Example 2
FeAlO catalyst preparation
Fe (NO 3)3:Al(NO3)3: citric acid) is weighed according to a molar ratio of 1:1:2 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is subjected to heat preservation at 350 ℃ for 3 hours in an atmosphere furnace to obtain FeAlO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing the microwave power, wherein the power of a microwave reactor is firstly adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) Repeating the step (2) for 2 times to obtain the self-made composite carbon nano tube.
3. Preparation of FeAlO/2wt% CNT composite catalyst
The catalyst FeAlO, the composite carbon nanotube and the absolute ethyl alcohol are weighed and mixed according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. Finally, a composite catalyst of FeAlO/2wt% CNT is obtained.
4. Microwave-assisted FeAlO/2wt% CNT bi-layer catalytic cracking polyethylene (H1:H2=1:0.5)
(1) Uniformly weighing and mixing polyethylene and FeAlO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeAlO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.5.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 850 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked. The reaction is not carried out until the power is increased to 850 watts, and a small amount of oil exists on the inner surface of the reactor after the reaction is finished. The H 2 yield was 63.46 mmoles per gram of polyethylene.
Comparative example 1
Step2 of step 4 in example 1 is: (2) purging with nitrogen to purge air. The microwave cracking reaction is carried out by directly increasing the microwave power to 1000 watts, namely, the microwave power is adjusted to 1000 watts and the polyethylene is completely cracked within 5 minutes. Otherwise, the same as in example 1 was conducted.
The gas production rate at the initial stage of the reaction can be seen to be extremely high, the white fog can be seen to flow out from the reactor, the oily matters and the catalyst powder are accumulated in the gas path, a large amount of oily matters are attached in the gas collecting device, and the gas quantity is small. The H 2 yield was 56.53 mmoles per gram of polyethylene.
Comparative example 2
Step 3 of step2 in example 1 is: (3) Repeating the step (2) 17 times to obtain the composite carbon nano tube. Otherwise, the same as in example 1 was conducted.
Wherein the H 2 yield was 66.34 millimoles per gram of polyethylene.
Comparison of cleavage reaction results:
the cleavage reaction results of examples 1-2 and comparative examples 1-2 were compared.
TABLE 1 microwave assisted catalytic cracking polyethylene product ratio Table
Numbering device Solid (wt%) Oil quality (wt%) Gas (wt%) Hydrogen yield (mmol/gPE)
Example 1 46.21 0.47 53.32 66.38
Example 2 47.32 0.75 51.93 63.46
Comparative example 1 51.04 2.05 46.91 56.53
Comparative example 2 46.70 0.48 52.82 66.34
As shown in table 1, example 1, which reacted at a stepwise increase in microwave power, resulted in a hydrogen yield of 66.38 millimoles per gram of polyethylene. Whereas in comparative example 1, where the reaction was carried out by directly increasing the microwave power to 1000 watts, the hydrogen production was reduced to only 56.53 millimoles per gram of polyethylene (mmol/gPE). Therefore, the method of increasing the microwave power stepwise should be a more stable reaction process. The composite carbon nanotube obtained after 17 times of cyclic reaction was used in the FeAlO/2wt% CNT composite catalyst in comparative example 2, and the hydrogen yield was 66.34 mmol/g polyethylene. Comparison with examples 1 and 2 is sufficient to demonstrate that the number of cyclic reactions for the preparation of the composite catalyst is limited to 1-13 times, while exceeding this range does not allow further improvement in hydrogen production while increasing the complexity of the process.
Example 3
FeNiAlO catalyst preparation
Fe (NO 3)3:Ni(NO3)2:Al(NO3)3: citric acid is weighed according to a molar ratio of 1:1:1:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 4 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under nitrogen to obtain FeNiAlO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing the microwave power, wherein the power of a microwave reactor is firstly adjusted to 300 watts and maintained for 5 seconds; then adjusting the microwave power to 680 watts for 25 seconds; the power was again adjusted to 900 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 3 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) And (3) repeating the step (2) for 8 times to obtain the self-made composite carbon nanotube.
3. Preparation of FeNiAlO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeNiAlO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeNiAlO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FeNiAlO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FeNiAlO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeNiAlO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 250 watts and maintained for 8 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The H 2 yield was 66.85 mmoles per gram of polyethylene.
Example 4
FeNiAlO catalyst preparation
Fe (NO 3)3:Ni(NO3)2:Al(NO3)3: citric acid is weighed according to a molar ratio of 1:1:1:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 4 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under nitrogen to obtain FeNiAlO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing the microwave power, wherein the power of a microwave reactor is firstly adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) And (3) repeating the step (2) for 9 times to obtain the self-made composite carbon nanotube.
3. Preparation of FeNiAlO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeNiAlO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeNiAlO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FeNiAlO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:2)
(1) Uniformly mixing polyethylene and FeNiAlO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeNiAlO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:2.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 250 watts and maintained for 8 seconds; then adjusting the microwave power to 700 watts for 15 seconds; the power was again adjusted to 850 watts for 25 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked. The H 2 yield was 61.86 mmoles per gram of polyethylene.
Comparative example 3
Uniformly mixing polyethylene and FeNiAlO/2wt% of CNT catalyst in a mass ratio of 1:1 in the step (1) of the step 4 in the example 3, and placing the mixture at the bottom of a reactor;
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 250 watts and maintained for 8 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked. Otherwise, the same as in example 3 was conducted.
The gas production rate is slower at the initial stage of the reaction, and a large amount of white mist is generated in the reactor along with the increase of the gas production rate, flows into the gas circuit and the gas collecting device along with the gas, and a large amount of oil is accumulated in the gas circuit and the gas collecting device. The H 2 yield was 50.33 mmoles per gram of polyethylene.
Comparative example 4
Uniformly mixing polyethylene and FeNiAlO/2wt% of CNT catalyst in a mass ratio of 1:1 in step (1) in the embodiment 3, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeNiAlO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H1:H2=1:2.5;
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 250 watts and maintained for 8 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked. Otherwise, the same as in example 3 was conducted. Wherein the H 2 yield is 58.85 mmoles per gram of polyethylene.
Comparison of cleavage reaction results:
the cleavage reaction results of examples 3-4 and comparative examples 3-4 were compared.
TABLE 2 microwave assisted catalytic cracking polyethylene product ratio Table
Numbering device Solid (wt%) Oil quality (wt%) Gas (wt%) Hydrogen yield (mmol/gPE)
Example 3 46.53 0.33 53.14 66.85
Example 4 47.20 0.43 52.37 61.86
Comparative example 3 48.53 6.40 45.07 50.33
Comparative example 4 48.31 0.37 51.32 58.85
As shown in Table 2, comparative example 3, which reacted in a monolayer process, had only a hydrogen yield of 50.33 millimoles per gram of polyethylene. While the hydrogen production in comparative example 4, h1:h2=1:2.5, was also slightly reduced compared to examples 3-4. It is thus sufficient to demonstrate that the height ratio H1:H2 of the bilayer process should be controlled between 1 (0.5-2) to be more advantageous for improving the yield of hydrogen.
Example 5
Preparation of FeZnZrO catalyst
Fe (NO 3)3:Zn(NO3)2:Zr(NO3)4: citric acid is weighed according to a molar ratio of 1:1:1:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 2 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under nitrogen to obtain FeZnZrO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing microwave power, wherein the power of a microwave reactor is firstly adjusted to 250 watts and maintained for 10 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) Repeating the step (2) 11 times to obtain the self-made composite carbon nano tube.
3. Preparation of FeZnZrO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeZnZrO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeZnZrO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FeZnZrO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FeZnZrO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeZnZrO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 250 watts and maintained for 8 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 900 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The H 2 yield was 66.32 mmoles per gram of polyethylene.
Example 6
In example 5, step 3 is to weigh and mix the catalyst FeZnZrO, the composite carbon nanotube and the absolute ethanol in a mass ratio of 1:0.01:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeZnZrO/1wt% CNT composite catalyst was obtained.
Otherwise, the same as in example 5. The yield of H 2 was 63.88 mmoles per gram of polyethylene.
Example 7
Preparation of FeMgLaO catalyst
Fe (NO 3)3:Mg(NO3)2:La(NO3)3: citric acid is weighed according to a molar ratio of 1:1:1:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under nitrogen to obtain FeMgLaO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing microwave power, wherein the power of a microwave reactor is firstly adjusted to 250 watts and maintained for 10 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) Repeating the step (2) for 10 times to obtain the self-made composite carbon nano tube.
3. Preparation of FeMgLaO/5wt% CNT composite catalyst
And weighing and mixing the catalyst FeMgLaO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.05:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeMgLaO/5wt% CNT composite catalyst was obtained.
4. Microwave-assisted FeMgLaO/5wt% cnt double-layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FeMgLaO/5wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeMgLaO/5wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 250 watts and maintained for 8 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 900 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The yield of H 2 was 62.23 mmoles per gram of polyethylene.
Comparative example 5
In example 5, step 3 is to weigh and mix the catalyst FeZnZrO, the composite carbon nanotube and the absolute ethanol in a mass ratio of 1:0.08:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeZnZrO/8wt% CNT composite catalyst was obtained.
Otherwise, the same as in example 5. The yield of H 2 was 59.89 mmoles per gram of polyethylene.
Comparison of cleavage reaction results:
The cleavage reaction results of examples 5 to 7 and comparative example 5 were compared.
TABLE 3 microwave assisted catalytic cracking polyethylene product ratio Table
Numbering device Solid (wt%) Oil quality (wt%) Gas (wt%) Hydrogen yield (mmol/gPE)
Example 5 46.35 0.45 53.20 66.32
Example 6 47.80 0.76 51.44 63.88
Example 7 47.82 0.36 51.82 62.23
Comparative example 5 47.51 0.52 51.97 59.89
As shown in Table 3, the present invention gave a range of (1 to 5 wt%) with respect to the amount of self-made composite carbon nanotubes in the catalyst, and the results were shown in examples 5 to 7, whereas exceeding this range, as in comparative example 5, the hydrogen production was significantly reduced to 59.89 mmol per g of polyethylene.
Example 8
FeO catalyst preparation
Fe (NO 3)3: citric acid) is weighed according to a molar ratio of 1:1 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is subjected to heat preservation at 350 ℃ for 3 hours in an atmosphere furnace under argon to obtain FeO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing microwave power, wherein the power of a microwave reactor is firstly adjusted to 250 watts and maintained for 10 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) Repeating the step (2) for 10 times to obtain the self-made composite carbon nano tube.
Preparation of FeO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. Finally, a composite catalyst of FeO/2wt% CNT is obtained.
4. Microwave-assisted FeO/2wt% CNT double-layer catalytic cracking polyethylene (H1:H2=1:0.9)
(1) Uniformly mixing polyethylene and FeO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 900 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The H 2 yield was 63.23 mmoles per gram of polyethylene.
Example 9
FeCoCeO catalyst preparation
Fe (NO 3)3:Co(NO3)2:Ce(NO3)3: citric acid is weighed according to a molar ratio of 1:1:1:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under argon to obtain FeCoCeO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing microwave power, wherein the power of a microwave reactor is firstly adjusted to 250 watts and maintained for 10 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) Repeating the step (2) for 10 times to obtain the self-made composite carbon nano tube.
3. Preparation of FeCoCeO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeCoCeO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeCoCeO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FeCoCeO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FeCoCeO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeCoCeO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 900 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The yield of H 2 was 68.02 mmoles per gram of polyethylene.
Example 10
Preparation of FeCuLaO catalyst
Fe (NO 3)3:Cu(NO3)2:La(NO3)3: citric acid is weighed according to a molar ratio of 1:1:1:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under argon to obtain FeCuLaO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing microwave power, wherein the power of a microwave reactor is firstly adjusted to 250 watts and maintained for 10 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) And (3) repeating the step (2) for 9 times to obtain the self-made composite carbon nanotube.
3. Preparation of FeCuLaO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeCuLaO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeCuLaO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FeCuLaO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FeCuLaO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeCuLaO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 900 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The reaction did not occur too much oil, but the total gas production was relatively low. The yield of H 2 was 61.54 mmoles per gram of polyethylene.
Example 11
Preparation of FeYbO catalyst
Fe (NO 3)3:Yb(NO3)3: citric acid is weighed according to a molar ratio of 1:2:3 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under argon to obtain FeYbO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing the microwave power, wherein the power of a microwave reactor is firstly adjusted to 300 watts and maintained for 5 seconds; then adjusting the microwave power to 680 watts for 25 seconds; the power was again adjusted to 900 watts for 30 seconds and finally the microwave power was adjusted to 1000 watts for 3 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) And (3) repeating the step (2) for 9 times to obtain the self-made composite carbon nanotube.
3. Preparation of FeYbO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FeYbO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FeYbO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FeYbO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FeYbO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeYbO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 900 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The H 2 yield was 64.35 mmoles per gram of polyethylene.
Example 12
FeO catalyst preparation
Fe (NO 3)3: citric acid) is weighed according to a molar ratio of 1:1 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is subjected to heat preservation at 350 ℃ for 3 hours in an atmosphere furnace under argon to obtain FeO catalyst powder.
2. Microwave-assisted FeO double-layer catalytic cracking polyethylene (H1:H2=1:0.9)
(1) Uniformly mixing polyethylene and FeO catalyst in a mass ratio of 1:1, and placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeO catalyst on the first layer of material, the height of the second layer of material is H2, and the height ratio of the two layers of material is H1:H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 900 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The H 2 yield was 62.33 mmoles per gram of polyethylene.
Comparative example 6
Preparation of FePdMnO catalyst
Fe (NO 3)3:Pd(NO3)2:Mn(NO3)2: citric acid is weighed according to a molar ratio of 1:2:2:5 and poured into a beaker, deionized water is added for dissolving and mixing uniformly, the mixed solution is heated at 60 ℃ for 3 hours and cooled to room temperature to obtain gel, and the obtained gel is kept at 350 ℃ for 3 hours in an atmosphere furnace under argon to obtain FePdMnO catalyst powder.
2. And (3) preparing the composite carbon nano tube.
(1) Polyethylene and FeO catalyst in the mass ratio of 1:1 are evenly mixed and then poured into a microwave reactor, and nitrogen is used for purging until air is exhausted. The microwave cracking reaction is carried out by using a method of gradually increasing microwave power, wherein the power of a microwave reactor is firstly adjusted to 250 watts and maintained for 10 seconds; then adjusting the microwave power to 700 watts for 20 seconds; the power was again adjusted to 850 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 5 minutes until the polyethylene was completely cracked.
(2) After the reaction, uniformly mixing the residual solid and polyethylene according to the mass ratio of 1:1, and then loading the mixture into a reactor again. Repeating the step (1), and carrying out microwave pyrolysis reaction again.
(3) And (3) repeating the step (2) for 9 times to obtain the self-made composite carbon nanotube.
Preparation of FePdMnO/2wt% CNT composite catalyst
And weighing and mixing the catalyst FePdMnO, the composite carbon nanotube and the absolute ethyl alcohol according to the mass ratio of 1:0.02:10. The mixture was subjected to ultrasonic mixing treatment using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture. The mixture was stirred at 60 degrees celsius and evaporated to dryness and then dried in a 120 degrees celsius oven for a further 3 hours. A FePdMnO/2wt% CNT composite catalyst was obtained.
4. Microwave assisted FePdMnO/2wt% cnt double layer catalytic cracking polyethylene (h1:h2=1:0.9)
(1) Uniformly mixing polyethylene and FePdMnO/2wt% of CNT catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FePdMnO/2wt% of CNT catalyst on the first layer of material, wherein the height of the second layer of material is H2, and the height ratio of the two layers of material is H2=1:0.9.
(2) After purging with nitrogen to exhaust air, performing microwave pyrolysis reaction by gradually increasing microwave power, wherein the power of the microwave reactor is adjusted to 200 watts and maintained for 10 seconds; then adjusting the microwave power to 650 watts for 30 seconds; the power was again adjusted to 900 watts for 20 seconds and finally the microwave power was adjusted to 1000 watts for 4 minutes until the polyethylene was completely cracked. The H 2 yield was 57.23 mmoles per gram of polyethylene.
Comparison of cleavage reaction results:
The cleavage reaction results of examples 8-12 were compared with those of comparative example 6.
TABLE 4 microwave assisted catalytic cracking polyethylene product ratio Table
Numbering device Solid (wt%) Oil quality (wt%) Gas (wt%) Hydrogen yield (mmol/gPE)
Example 8 45.35 0.81 53.84 63.23
Example 9 46.28 0.24 53.46 68.02
Example 10 46.64 1.18 52.18 61.54
Example 11 46.35 0.75 52.90 64.35
Example 12 45.24 0.85 53.91 62.33
Comparative example 6 49.80 1.12 48.68 57.23
As shown in Table 4, the hydrogen yields obtained from the reactions with catalysts prepared by adding different metals were also different, and the reaction was carried out with FeCoCeO/2wt% CNT composite catalyst as in example 9 to give a hydrogen yield increase of 68.02 mmoles per gram of polyethylene. However, when the iron content of the catalyst was too small, the hydrogen production was reduced to 57.23 mmol per g of polyethylene as shown in comparative example 6, which shows the effect of the iron content on the excellent performance of the iron-based catalyst.

Claims (4)

1. The microwave-assisted process for catalytic cracking of polyethylene based on a double-layer iron-based catalyst is characterized by comprising the following steps:
1) Preparation of iron-based catalyst FeMO:
Mixing Fe (NO 3)3 and M (NO 3)y and citric acid according to the molar ratio of Fe 3+:My+ to citric acid of 1:n (1+n), wherein n=1-2, adding deionized water to dissolve and uniformly mix to obtain a mixed solution, heating the mixed solution at 60 ℃ for 2-4 hours, cooling to room temperature to obtain gel, and preserving the temperature of the obtained gel at 350 ℃ for 3 hours in a certain atmosphere in an atmosphere furnace to obtain FeMO catalyst powder, wherein M is one or two of Ni, al, co, mn, cu, mg, zn, ce, pd, yb, la, zr;
2) Preparation of composite carbon nano tube:
(1) Uniformly mixing polyethylene with a mass ratio of 1:1 with FeMO catalyst, pouring the mixture into a microwave reactor, purging the mixture with nitrogen until air is exhausted, and performing microwave pyrolysis reaction by using a method of gradually increasing microwave power until the polyethylene is completely cracked;
(2) After the reaction is finished, uniformly mixing the residual solid with polyethylene according to the mass ratio of 1:1, and then loading the mixture into a microwave reactor again; repeating the step (1), and carrying out microwave pyrolysis again until the polyethylene is completely cracked;
(3) Repeating the step (2) for 1-13 times to obtain the self-made composite carbon nano tube;
3) Preparation of FeMO/CNT composite catalyst
Mixing an iron catalyst FeMO, a composite carbon nano tube and absolute ethyl alcohol according to the mass ratio of (0.01-0.05): 10, performing ultrasonic mixing treatment on the mixture by using an ultrasonic pulverizer for 20 minutes to obtain a uniform mixture, stirring and evaporating the mixture at 60 ℃, then placing the mixture in a 120 ℃ oven, and drying for 3 hours to obtain the FeMO/CNT composite catalyst;
4) Microwave-assisted catalytic cracking polyethylene
(1) Uniformly mixing polyethylene and FeMO/CNT composite catalyst in a mass ratio of 1:1, placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeMO/CNT composite catalyst on the first layer of material, and the ratio of the height of the first layer of material to the height of the second layer of material is H2=1 (0.5-2);
(2) After nitrogen is purged to exhaust air, a method of gradually increasing microwave power is used for carrying out microwave pyrolysis reaction; the method of gradually increasing the microwave power for the microwave pyrolysis reaction is to firstly adjust the power of a microwave reactor to 200-300 watts and maintain for 5-10 seconds; then adjusting the microwave power to 650-700W for 20-30 seconds; and then adjusting the power to 850-900W for 20-30 seconds, and finally adjusting the microwave power to 1000W for 3-5 minutes until the polyethylene is completely cracked.
2. The process for the catalytic cracking of polyethylene based on a double-layer iron-based catalyst according to claim 1, characterized in that in step 1) the molar ratio of the two metal elements is 1:1 when it is a mixture of M two metal elements.
3. The microwave-assisted process for the catalytic cracking of polyethylene based on a double-layer iron-based catalyst according to claim 1, characterized in that the atmosphere in step 1) is nitrogen, air or argon.
4. The microwave-assisted process for catalytic cracking of polyethylene based on a double-layer iron-based catalyst is characterized by comprising the following steps:
1) Preparation of iron-based catalyst FeO:
mixing Fe (NO 3)3 and citric acid according to a molar ratio of 1:1, adding deionized water to dissolve and uniformly mix to obtain a mixed solution, heating the mixed solution at 60 ℃ for 2-4 hours, cooling to room temperature to obtain gel, and preserving the temperature of the obtained gel at 350 ℃ for 3 hours in a certain atmosphere in an atmosphere furnace to obtain FeO catalyst powder;
2) Microwave-assisted catalytic cracking polyethylene
(1) Uniformly mixing polyethylene and FeO catalyst powder in a mass ratio of 1:1, and placing the mixture at the bottom of a reactor to form a first layer of material, wherein the height of the first layer of material is H1, then adding a second layer of material FeO catalyst on the first layer of material, the height of the second layer of material is H2, and the ratio of the height of the first layer of material to the height of the second layer of material is H2=1 (0.5-2);
(2) After nitrogen is purged to exhaust air, a method of gradually increasing microwave power is used for carrying out microwave pyrolysis reaction; the method for gradually increasing the microwave power carries out microwave cracking reaction as follows: the method of gradually increasing the microwave power for the microwave pyrolysis reaction is to firstly adjust the power of a microwave reactor to 200-300 watts and maintain for 5-10 seconds; then adjusting the microwave power to 650-700W for 20-30 seconds; and then adjusting the power to 850-900W for 20-30 seconds, and finally adjusting the microwave power to 1000W for 3-5 minutes until the polyethylene is completely cracked.
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CN111153384A (en) * 2019-12-31 2020-05-15 四川天采科技有限责任公司 Direct methanol cracking preparation of H2Catalytic and permeable integrated membrane reactor and application thereof
CN115072659A (en) * 2022-07-19 2022-09-20 武汉新碳科技有限公司 Method for preparing hydrogen by polyethylene plastic
CN115432663A (en) * 2021-06-04 2022-12-06 南京工程学院 Method and device for preparing hydrogen and multi-walled carbon nanotubes by microwave pyrolysis of waste plastics
CN115537220A (en) * 2022-09-20 2022-12-30 广州博能能源科技有限公司 Method for microwave heat-assisted catalytic pyrolysis of polymer material

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111153384A (en) * 2019-12-31 2020-05-15 四川天采科技有限责任公司 Direct methanol cracking preparation of H2Catalytic and permeable integrated membrane reactor and application thereof
CN115432663A (en) * 2021-06-04 2022-12-06 南京工程学院 Method and device for preparing hydrogen and multi-walled carbon nanotubes by microwave pyrolysis of waste plastics
CN115072659A (en) * 2022-07-19 2022-09-20 武汉新碳科技有限公司 Method for preparing hydrogen by polyethylene plastic
CN115537220A (en) * 2022-09-20 2022-12-30 广州博能能源科技有限公司 Method for microwave heat-assisted catalytic pyrolysis of polymer material

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