| After entering the 21st century,with the surge in the use of plastics in China,the output of waste plastics is also increasing,which causes great pressure on the environment.In order to realize the resource utilization of waste plastics,this paper adopts the microwave pyrolysis method,selects waste polypropylene（PP）as the pyrolysis raw material,and uses granular activated carbon as the microwave absorbent.In order to realize the resource utilization of waste plastics,this paper adopts the microwave pyrolysis method,selects waste polypropylene（PP）as the pyrolysis raw material,and uses granular activated carbon as the microwave absorbentto explore the microwave power,raw material quality,and the quality of activated carbon without adding catalyst,and the effect of adding different kinds of metal oxides as catalysts on the pyrolysis gas,pyrolysis oil,and solid carbon residues obtained from plastic microwave pyrolysis.On this basis,two metal oxides Mg O and Zn O were selected to study the effects of catalyst addition,power and catalyst morphology on the microwave pyrolysis products of waste plastics in detail.For the consideration of economical practicability,the reuse performance of the microwave absorbent is also studied in this paper,and the research conclusions are as follows:1.Under the condition of no catalyst,the total content of H2 and CH4 in the pyrolysis gas obtained from PP pyrolysis increases with the increase of the mass of activated carbon,and decreases with the increase of the mass of PP plastics.When the mass of activated carbon and PP plastic is 20g,and the power is 700W,the microwave pyrolysis effect is the best.At this time,the yield of pyrolysis gas is 41.75%,the yield of pyrolysis oil is 44.20%,and the yield of solid carbon residue is 14.05%.The content of monocyclic aromatic hydrocarbons in pyrolysis oil is the largest,accounting for 40%of the total organic content in pyrolysis oil,and the total content of alkanes,olefins and monocyclic aromatic hydrocarbons can reach more than 90%.When adding different metal oxides such as Ca O,Ti O2,Fe2O3,Al2O3,Mg O,Zn O,Mo O3 as catalysts,in addition to Mo O3,other metal oxides can promote the cyclization of carbon chains in polypropylene pyrolysis oil,as well as increase the content of monocyclic aromatic hydrocarbons in pyrolysis oil,and further increase the calorific value of pyrolysis oil.Based on the yield of pyrolysis gas,pyrolysis oil and solid carbon obtained from PP pyrolysis,and the content of H2 and CH4 in pyrolysis gas,the pyrolysis effect of adding Ca O and Ti O2 is the worst,followed by Mo O3and Al2O3,Fe2O3 is better,Mg O and Zn O has the best catalytic effect,after adding Mg O and Zn O,the yield of pyrolysis gas can reach more than 50%.2.Using Zn O and Mg O as catalysts,it is found that Mg O and Zn O can enhance the intensity of the reaction.Among them,when Mg O is used as catalyst,it is found that Mg O can increase the content of CH4 in the pyrolysis gas,when Zn O is used as catalyst,it is found that Zn O can increase the content of H2 in the pyrolysis gas.After adding Mg O,the total content of H2 and CH4 in the pre-cracking gas can approximately reach more than 45%,and the post-pyrolysis gas can approximately reach more than 65%;after adding Zn O,the total content of H2 and CH4 in the pre-cracking gas can approximately reach more than 50%,and the post-pyrolysis gas can reach more than 60%approximately.Mg O and Zn O can further increase the content of monocyclic aromatic hydrocarbons in pyrolysis oil,and can significantly increase the content of short carbon chain organics in pyrolysis oil,the content of organic matter with carbon chain length less than C11 after adding Mg O is 81.44%,the content of organic matter with carbon chain length less than C11 after adding Zn O is 82.43%,the specific gravity of cracked oil is between 0.7 and 0.8,which belongs to light pyrolysis oil.According tothe response surface analysis,the optimal pyrolysis conditions for PP are as follows:the power is 660W-720W and the catalytic dose is 0.6-1g with the addition of Mg O;the power680-740Wand the catalytic dose 0.4-1g with the addition of Zn O.In the study of Zn O with two different morphologies,granular and flaky,it was found that the morphology of Zn O had a significant effect on the yield of PP pyrolysis products and the content of H2 and CH4 in the pyrolysis gas,but it has little effect on the composition of cracked oil obtained from PP microwave pyrolysis.3.The activated carbon has positive reusability.It is found that with the increase of the number of reuses of activated carbon,under the condition of no catalyst,the yield of pyrolysis gas and solid carbon residue obtained by microwave pyrolysis of PP decreases,and the yield of pyrolysis oil increases.After repeated microwave pyrolysis six times,the yield of pyrolysis gas decreased to 32.2%,the yield of solid carbon residue decreased to 6.4%,and the yield of pyrolysis oil increased to 61.1%.With the increase of microwave pyrolysis times,the content of H2 and CH4 in the pyrolysis gas decreased.After adding Zn O,from the second microwave pyrolysis,with the increase of microwave pyrolysis times,the yield of PP microwave pyrolysis products and the content of H2 and CH4 in the pyrolysis gas have the same regularity as those without catalyst.To sum up,the use of microwave pyrolysis method can more effectively recover the chemical components and energy in waste plastics,which greatly improves the use of waste plastics,and is important for reducing the harm of plastic waste to the environment.It also provides new ideas and new methods for the treatment and resource utilization of waste plastics. |
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