Reactive molecular dynamics simulation of the pyrolysis and combustion of benzene: ultrahigh temperature and oxygen-induced enhancement of initiation pathways and their effect on carbon black generation

Abstract

The pyrolysis and combustion mechanisms of benzene under different chemical environments and temperatures were investigated by a reactive force field based molecular dynamics (ReaxFF MD) simulation using two systems, pure benzene and a mixture of benzene and oxygen gas. The chemical behaviors of this system were investigated under an ultrahigh temperature that can be induced by a high-energy density laser and compared to those at high temperature. According to some experimental data, we assume that an ultrahigh temperature can be used to mimic laser irradiation. The conclusions of this simulation are as follows. First, the ReaxFF MD simulations showed that the decomposition rates of benzene were significantly accelerated by laser irradiation or in the presence of oxygen. Second, additional initiation pathways were opened up by these two factors. The primary initiation pathway involves only the hydrogen atom loss in the pyrolysis of benzene at 3000 K, and the initiation pathways become much more complicated after laser irradiation or the involvement of oxygen. Third, the ReaxFF MD simulations formed a reasonable carbon black (CB) texture of various sizes in the pyrolysis of benzene, and we also focused on the evolution of the texture of CB. The calculation results of the final gaseous products, hydrocarbons, and the formation of CB are in a good agreement with the literature. This study provides a better understanding of the initiation mechanisms of the pyrolysis and combustion of benzene under extreme conditions.