Experimental Study On Process And Product Distribution Of Waste Tire Microwave Pyrolysis

With the development of the automobile industry and the deterioration of the ecological environment,idle and stacked of waste tires caused by tire scrapped have become an important social and environmental problem.The main problem of waste tire conventional pyrolysis is coking and low thermal efficiency,the fundamental reason is that the temperature field is not uniform,while microwave heating can fully heat the material,significantly improve the material temperature distribution,and considering the coupling effect between microwave and carbon black,steel,this paper proposed a method of rapid pyrolysis of waste tires by microwave irradiation,which mainly explored the microwave pyrolysis process and the distribution characteristics of pyrolysis products.Firstly,the microwave pyrolysis process of waste tires was studied,in order to master the dynamic evolution characteristics of pyrolysis products with pyrolysis time.It was found that the yield of pyrolysis gases increased gradually with pyrolysis time increasing,as the time increased from 10 min to 20 min,the yields of pyrolysis liquids and pyrolysis solids changed obviously,the yield of solids reduced from 54 wt%to 44.8%,while that of oils increased from 37.7%to 44.2%.According to the variation law of pyrolysis gas,the pyrolysis process is roughly divided into three stages;With the pyrolysis time increasing,the yield of pyrolysis oils increased obviously,the proportion of small molecule oils increased,while that of macromolecule oils decreased,as the time increased to 30min,the proportion of small molecule oils decreased slightly,and the content of polycyclic material increased;the pyrolysis degree of pyrolytic carbon gradually increased with time going,and compared to the edge portion,the sample in the central part of the reactor pyrolyzed preferentially.In addition,experiments were done to compare the microwave pyrolysis and conventional pyrolysis process,it was found that the final weight loss rate of microwave pyrolysis was about 12 percentage points higher than that of conventional pyrolysis,and the activation energy(44.38kJ/mol)of microwave pyrolysis is lower than the conventional pyrolysis(58.75kJ/mol),which reflects the advantages of microwave pyrolysis of waste tires.Which was also discussed is the influence of different factors on the distribution of pyrolysis products.On the one hand,the experiments of waste tire powder pyrolysis under different power were conducted,with the power increasing,the yield of pyrolysis solids gradually decreased from 48.8%at 270W to 41%at 720W,the yield of pyrolysis oils was the highest at 450W,and the yield of pyrolysis gases increased significantly at higher power,reached 18%at 720W.And as the power increased,the proportion of small molecules such as H2 and CH4 in the pyrolysis gases increased,the BTX species in the pyrolysis oils showed an increasing trend,and the volatiles in the solids gradually reduced,illustrating the degree of pyrolysis was deepened.On the other hand,considering that the microwave pyrolysis is not limited to rubber powder,the pyrolysis effect and mechanism of tire block were also explored.It was found that the pyrolysis gas yield of the tire block was about 4 percentage points higher compared with that of the powder at the same power,and the H2 content in the pyrolysis gases was relatively low.The products and proportions of pyrolysis liquids and solids were similar between tire block and powder.In addition,the distribution characteristics of pyrolysis products under the addition of steel wire were investigated and then compared with those without steel wire.It was found that after adding wire,with the power increasing,the yields of the pyrolysis gases and the pyrolysis oils increased obviously,the yield of pyrolysis gases was up to 35.3%,the proportion of small molecules in oil and gas products increased,and the proportion of polycyclic aromatic hydrocarbons(PAHs)in pyrolysis oil also showed an increasing trend,meanwhile,the pyrolysis carbon volatile content and H element content decreased and the pyrolysis degree depeen.Besides,compared with the pyrolysis products of the tire block,it was found that the content of H2 in the pyrolysis gases of the tire block was still low,and the proportions of benzene,toluene and limonene in the pyrolysis oil were obviously reduced,while the difference between pyrolysis solids were relatively small.Compared with the product without steel wire,it was found that the addition of steel wire was beneficial to deepen the degree of pyrolysis and improve the content of small molecules,but it was not conducive to the production of high temperature sensitive substances,such as limonene.Finally,in connection with the high concentration-added product,limonene,which is the most abundant in the pyrolysis oils,experiments were conducted to explore the effects of microwave power,carrier gas flow rate,tire particle size and steel wire on its output characteristics,it was found that the low microwave power(450W),higher carrier gas flow rate(1.5L/min),smaller tire particle size(0.6mm)and no wire addition were found to be beneficial for the production of limonene,the total yield of limonene of the raw material samples was up to 5.97%,and the yield of limonene in pyrolysis oils was up to 15.16%in the experiments.