Study On The Formation Mechanism Of Gas Products From The Co-pyrolysis Of SBR And NR

With the development of economy,the output of waste rubber is increasing year by year,which has become an important environmental problem.Styrene-butadiene rubber?SBR?and natural rubber?NR?are the most widely used rubbers.The research on them should not be ignored.Because the common waste disposal methods can cause the problems of occupying land and polluting the environment,through pyrolysis,not only the pollution is small,but also the products with high utility value can be produced,which is a good way to deal with rubber.In this paper,the molecular dynamics simulation of Materials Studio software,pyrolysis and thermogravimetry experiments were used to study the micro formation mechanism of gas products from the co-pyrolysis of SBR and NR,which provided a theoretical basis for the recovery and utilization of rubber.Firstly,the micro simulation of the pyrolysis process of SBR,NR and their mixed rubber?NR-SBR?was studied.All kinds of rubber models were built by Amorphous cell and optimized to make the model reasonable.The periodic boundary conditions,ReaxFF force field and NVT ensemble were used to simulate the change of micro structure at different temperatures.The results show that in the pyrolysis process,the number of long chains decreases,the number of monomers increases first and then decreases,and the number of small molecule gases increases continuously.It can be seen that the pyrolysis process is divided into two stages:the generation of monomers by chain-breaking and the pyrolysis of monomers into small molecules.The end gas products of these three rubbers are hydrogen?H2?Methane?CH4?and ethylene?CH2=CH2?.Compared with the pyrolysis temperature range of different SBR content model,we can find that the continuous addition of SBR makes the pyrolysis temperature range move to high temperature.Secondly,the reaction paths of the pyrolysis of SBR and the co-pyrolysis of SBR and NR were simulated and analyzed by Density functional theory?DFT?.After analysis,it was seen that 1,3-butadiene and styrene are the main monomers of SBR,and the gas products produced by further pyrolysis are mainly H₂,followed by CH₄;styrene has a more stable structure,which is not conducive to the generation of free radicals,thus inhibiting the subsequent reaction of free radicals attacking1,3-butadiene;in the co-pyrolysis,with the addition of SBR,new paths conducive to the production of H2,resulting in the increase of H2;the new paths are not conducive to the production of CH4,resulting in the decrease of CH4;for the production process of CH₂=CH_2,there are both promotion and inhibition effects,so CH₂=CH₂ increases first and then decreases.Then,three kinds of rubber samples were studied by fixed bed reactor,gas chromatograph and thermogravimetric analyzer to verify simulation results.In the pyrolysis experiment of SBR,it was found that the main gas product of SBR pyrolysis is H₂,followed by CH₄,and then CH₂=CH₂,which is consistent with the path analysis conclusion of SBR pyrolysis;in the co-pyrolysis,with the increase of SBR,the yield of H₂ increases,the yield of CH₄ decreases,and the yield of CH₂=CH₂ first increases and then decreases,which is consistent with the path analysis of co-pyrolysis.The results of thermogravimetric analysis showed that with the increase of SBR,the pyrolysis range moves to high temperature,which was consistent with the simulation results of pyrolysis process.Finally,the mechanism of Fe₂O₃ catalytic pyrolysis of NR-SBR was studied by molecular dynamics simulation.It is found that Fe₂O₃ could reduce the energy barrier of chain-breaking,free radical formation and H-capture reaction,thus reducing the pyrolysis temperature and promoting the reaction.