Study On The Characteristics Of Waste Tire Pyrolysis Char And Its Catalytic Pyrolysis Effect On Waste Tires

China is the big country producing waste tires.The output of waste tires is increasing year by year.The waste tires have the characteristics of high thermal stability and poor biodegradability,which will lead to occupying land,spreading diseases,causing fires and other environmental problems,seriously endangering environmental health and human life and health.Treatment and disposal are urgently needed for waste tires.Pyrolysis is an effective method to treat waste tires.Pyrolysis char is the main product of pyrolysis of waste tires,which comes from commercial carbon black and additives added in tire production process.Pyrolysis char has become a potential catalyst because of its low price,porous structure and the presence of weak alkaline metal elements on its surface.In this paper,the effects of pyrolysis temperature on the physical and chemical properties of pyrolysis char,the catalytic performance of pyrolysis char on pyrolysis of waste tires under different conditions and the catalytic performance of supported metal catalysts modified with iron,nickel and nickel-iron binary metals were discussed.The main conclusions are as follows:?1?With the increase of pyrolysis temperature,the aromaticity and polarity of pyrolysis char of waste tires gradually increase,and the oxygen-containing functional groups gradually decrease,which helps to improve the stability of pyrolysis char.The nitrogen adsorption and desorption curve of pyrolysis char is of type II,indicating that pyrolysis char is a mesoporous material with mesopores as the main and macropores as the auxiliary,with an average pore diameter of 34.36 nm,which is conducive to the adsorption of pyrolysis char on macromolecular substances.The surface of pyrolytic carbon is rough,and it has aggregated particle structure.There are weak alkaline metal elements such as Al and Ca which can provide active catalytic sites.All of this indicates that pyrolysis char can be used as catalyst and carrier of catalyst.?2?The addition of pyrolysis char promoted the conversion of waste tire pyrolysis oil to pyrolysis gas,and reduced energy consumption to a certain extent.At the same time,the content of CH₄ and CO₂ in pyrolysis gas increased significantly,resulting in a significant increase in the calorific value of pyrolysis gas,reaching a maximum of 34.56 MJ/m³ at 20 wt.%.In the process of catalytic pyrolysis,the pyrolytic oil molecules are adsorbed on the surface of pyrolysis char and catalytically cracked into light combustible gas at the active site.The content of olefins,polycyclic aromatic hydrocarbons and heteroatom compounds containing oxygen,nitrogen and sulfur in pyrolysis oil decreases while the content of monocyclic aromatic hydrocarbons increases.Pyrolysis char improves the quality of pyrolysis oil.In the catalytic pyrolysis process of waste tires,the material balance error is 8.2%.The theoretical minimum external heating is 106 48.76 kJ/kg by energy balance analysis and the energy output is 46278.90 kJ per kilogram waste tires.?3?The catalytic performance of four pyrolysis char catalysts is as follows:nickel-loaded pyrolysis char>nickel-iron binary metals pyrolysis char>iron-loaded pyrolysis char>pyrolysis char.The catalytic performance of nickel-loaded pyrolysis char is the best,because the pyrolytic intermediates have higher activation ability on the surface of nickel metal,and the catalytic mechanism of iron-loaded pyrolysis char is more inclined to co-catalysis.The role of pyrolysis char in supported metal catalysts is mainly working as the substrate of metal catalysts,while adsorbing pyrolytic intermediates to pyrolysis char to provide chances for catalytic reaction.Although the catalytic performance of nickel-loaded pyrolysis char is the best,considering the economic factors,it is more suitable to load nickel-iron binary metal in pyrolysis char.