| Waste rubber has become a kind of macromolecular material next only to waste plastics.And simplified treatment?landfill and combustion?not only causes a waste of resources,but also poses a threat to the environment and human health.Therefore,it is extremely urgent to use waste rubber effectively.Pyrolysis of waste rubber is an efficient thermo-chemical recovery method,which can produce energy and products with high value.In this study,the pyrolysis of natural rubber,a kind of most commonly used rubber,was studied by molecular dynamics simulation.And the composition and formation mechanism of gaseous products during pyrolysis were discussed by the combination of reaction molecular dynamics?RMD?simulations,process simulation and thermogravimetry-infrared spectroscopy?TG-FTIR?experiments.Then the effects of different heating rates and gas atmosphere on the pyrolysis process and gas products were further discussed by TG-FTIRexperiments.This will play a theoretical guiding role in improving the gas yield and obtaining the required gaseous products by selecting appropriate pyrolysis conditions.Firstly,the pyrolysis process of natural rubber model with a degree of polymerization of 10 was simulated based on AMBER force field in Hyperchem software.The simulation results show that the pyrolysis process of natural rubber includes low-temperature heating process and high-temperature fracture process.When the temperature is lower than 600K,only some physical changes occur in the molecular internal structure.When the temperature reaches about 600K,a small number of macromolecular fragments are generated due to the bond breaking.With temperature increasing,macromolecular fragments further generate more small molecules fragments,including-CH2-?-CH3?H?-C2H3 and-C4H5.The pyrolysis law was consistent with the results of TG experiments.Then,considering its bond formation,the pyrolysis process of natural rubber model with three chains was simulatedby RMD in Materials studio software.The results show that the pyrolysis gases includeCH4,C2H4 and a small amountof C3H6and C4H6.The TG-FTIR also shows the presence of CH4 and functional groups?-C-H,-CH2,-CH3 and–C=C-?in C2H4,C3H6 and C4H8.Then the reaction models of isoprene monomer,dimer and short chain were constructed,and the reaction path of gas products was obtained based on density functional theory and Aspen plus process simulation.The simulation results show that CH3 abstracts H from other molecules to generate CH4,whileC2H4is mainly generated by the breaking of C-C bonds on long chains.C3H6 and C4H6 are generated by the breaking up of large olefins or free radicals.Finally,the effects of different heating rates and gas atmosphere on the pyrolysis process and gas products were further discussed by TG-FTIR experiments.Through thermogravimetric analysis,it is found that the initial pyrolysis temperature and the maximum weight loss rate temperature will be slightly increased with the increase of heating rate.Pyrolysis is a two-step reaction under air atmosphere,while only a one-step reaction under nitrogen.Through infrared analysis,it is found that the heating rate has almost no influence on its components.The higher the heating rate is,the higher the gas product yield will be.Under the air atmosphere,the moisture and CO2will increase significantly,and the small molecular olefins will decrease. |
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