Research On Pyrolysis And Combustion Characteristics And Substance Transition Law Of Base Asphalt

With the rapid development of Chinese economy,China has been the country with the most highway tunnels in the world.However,since the tunnel is a semi-enclosed space,When fire occurs,the asphalt will be ignited and release a large amount of toxic smoke,which seriously endangers the safety of human life and property.Asphalt is a complex compound,and its combustion characteristic is largely affected by the composition of asphalt.Therefore,research on pyrolysis and combustion characteristics based on the composition of asphalt has become an urgent topic.This research was sponsored by the National Natural Science Foundation of China of "All-Phase Materials Transition Law of Asphalt Combustion and Targeted Flame Retardant System"(51808521)and Zhejiang Natural Science Foundation of "Optimization of Flame Retardancy of Asphalt Based on its Composition "(LQ17E080011).Firstly,the Shuanglong No.70 asphalt was separated to four components,which were analyzed through the infrared spectrum and gel permeation chromatography technology in combination with elemental analysis.Secondly,the release characteristics of gaseous products and functional groups during the pyrolysis and combustion of asphalt were researched.Finally,the mass loss processes of asphalt combustion at different heating rates and different oxygen concentration were analyzed by thermogravimetry coupled with Fourier transform infrared spectrometer.The effects of reaction conditions on the products of gaseous and condensed were analyzed.Using the thermal analysis kinetics method,the kinetic parameters of the asphalt pyrolysis combustion process were calculated.The pyrolysis and combustion mechanism of the asphalt under the actual fire conditions was revealed.The main research results are as follows:(1)The main components in the based asphalt are aliphatic and aromatic compounds,with aromatic rings,long-chain alkanes,sulfoxide groups,and methoxy groups,among which,the saturates contain the least kinds of substances.The aromatics,resins,asphaltenes,compared with the saturate,the degree of aromatization increases,with more unsaturated bonds such as carbonyl,ether,sulfone and sulfoxide groups,etc.With the order of saturates,aromatics,resins and asphaltenes,the molecular weight distribution width index and the maximum molecular weight increase gradually.(2)The combustion of asphalt can be divided into two stages.The first stage is the aerobic pyrolysis.In the early stage of the first stage,the compounds such as aliphatic hydrocarbons in the saturates and aromatics pyrolyzed,which corresponds to the first and second mass loss peaks and the first half of the third mass loss peak in the pyrolysis process,generating compounds containing aromatic rings,ethers,esters that similar resins.In the late stage of the first stage,the resins convert to char,corresponding to the second half of the third mass loss peak.During this process,esters,benzene rings and sulfoxide groups increased,aliphatic hydrocarbons decreased,and the residue aromaticity increases,eventually forming a stable charring structure.The second stage is heavy components combustion,which is mainly the combustion of the char generated during the aerobic pyrolysis stage.(3)As heating rate increases,the three mass loss peaks of asphalt pyrolysis stage overlap,the maximum mass loss rate increased significantly,and the intensity of the infrared spectrum absorption peak increases gradually.At the combustion stage of heavy components,the intensity of infrared spectrum absorption does not change much with the heating rate.In addition,the combustion mechanisms of the two stages are different.In the first stage,the activation energy of the saturates,aromatics,and resins gradually increases,and the activation energy of the combustion phase of the heavy component is lower than that of resins.(4)When the oxygen concentration is less than 15%,residue remains after the asphalt is burned.The mass of the residue gradually increases with the decrease of the oxygen concentration.The oxygen concentration has a more significant effect on the combustion stage of the heavy components.Among the gas production releasing,the concentration of CH4 is basically not affected by the concentration of oxygen,while products such as SO2,CO2,CO,and aldehydes are greatly affected by the concentration of oxygen.Higher oxygen concentration will accelerate the dehydrogenation reaction in the pyrolysis stage,and the pyrolysis condensed products have higher saturation.