Study On The Pyrolysis Performance Of Waste Tire And The Migration Of Sulfur

With the rapid development of the transportation industry,the amount of waste tire is increasing rapidly,which causes serious pollution to the environment.Waste tire has become a kind of solid waste that needs to be treated on the principle of reducing quantity,resource and hazardous-free.Pyrolysis is considered to be one of the most thorough,efficient and low-polluting methods for waste tire treatment.However,the high content of sulfur is not conducive to the high value utilization of pyrolysis products of waste tires.Therefore,in this thesis the effects of pyrolysis temperature,heating rate,material particle size and catalyst on the properties of pyrolysis products of waste tires are explored.The transformation of sulfur in the process of pyrolysis and the influence of different pyrolysis conditions are discussed.Pyrolysis of waste tire by thermogravimetric analysis can be divided into three stages,the first stage（200 to 320°C）is the decomposition of plasticizers and additives,the second stage（320 to 500°C）is for natural rubber and synthetic rubber decomposition,while the third stage（500 to 750°C）is that some high thermal stability of macro molecules continue to decompose and release CH₄ and CO₂.The average activation energy of the three stages is 129.81 k J/mol.Waste tire rubber produces monomer free radicals through random chain breaking.The monomer further generates chain olefins,cyclolefins,and monocyclic aromatics through decomposition,binding and D-A cyclization.Cycloprees generate chain olefins through an inverse D-A cyclization.D-A cyclization and aromatheization of chain olefins and cycloolefins is the main generation path of polycyclic aromatic compounds.At low temperature pyrolysis in fixed bed experiment,the yield of cyclolefins and monocyclic aromatic hydrocarbons is higher.And at high temperature pyrolysis,more polycyclic aromatic hydrocarbons are produced in the way of D-A cyclization and aromatheization.The content of polar compounds decreases gradually with the increase of temperature.Compared to rapid pyrolysis,the slow pyrolysis time is longer,the yield of solid and gas were increased by 3%and 11%,while the liquid yield was decreased by 14%,and the yields of monocyclic aromatic hydrocarbons and indene,naphthalene were decreased,the yields of cycloolefins and polar compounds were increased.As the particle size of waste tyres increases,the production of monocyclic aromatic hydrocarbons,indene,and naphthalene increases first,then descreases,and achieves maximum yield at 0.8 mm.Small particle size is not only more conducive to the generation of cyclolefins,and polycyclic aromatic hydrocarbons,but also can fix more hybrid elements in solid-state products.ZSM-5 and SAPO-34 molecular sieve both increase the content of chain olefins,cycloolefins and reduce the content of monocyclic aromatic hydrocarbons.SAPO-34 has a better catalytic effect due to stronger acidic sites and more micropores,with higher selectivity for low-carbon chain olefins and cyclolefins.The content of 2-methyl propylene,2-acetylene and D-Limonene can reach 20.6%,22.5%and31.5%,respectively.The main migration and transformation path of sulfur in the pyrolysis process of waste tire is that aliphatic sulfide and thiophene sulfur are gradually decomposed and transformed into liquid and gas phases.Sulfoxide,sulfone,sulfate and inorganic sulfide mainly remain in solid-state products.Benzodiazepines,benzodiazepines,4,4’-Bis（tetrahydrothiopyran）and sulfur-containing compounds with high dew point migrate to liquid products.The sulfur-containing gases released are mainly H₂S and COS.In addition,the pyrolysis of waste tyres is accompanied by secondary reactions.Sulfur-containing compounds in the primary volatile matter was not only decomposed and produced H₂S and COS,but also can be absorbed and fixed in solid-state products.H₂S and COS are also involved in the generation of inorganic sulfide,sulfoxide and sulfone.Sulfoxide and sulfone can be further converted into sulfate at high temperature or over a long time.