ReaxFF-molecular dynamics simulations of non-oxidative and non-catalyzed thermal decomposition of methane at high temperatures.

Incomplete combustion of carbon based materials produces fine, carbon rich particles. Controlled manufacturing of very pure carbon nanoparticles (Carbon Black) can be achieved by, for example, thermal decomposition of gaseous precursors like acetylene and methane. Molecular dynamics simulations of hydrocarbon growth after non-catalyzed thermal decomposition of methane were carried out in order to understand the impact of the thermal decomposition reaction of methane on the formation of large hydrocarbon molecules. A reactive force field (ReaxFF) was employed to model the interactions of the involved hydrocarbons. The decomposition of 150 methane molecules was investigated at different system temperatures and system densities. Formation of molecular hydrogen, a broad range of hydrocarbons and carbon dimers from decomposed methane was observed above a temperature of 2500 K. The basic reactions are in agreement with existing models of thermal decomposition of methane. An increasing variety of hydrocarbons is observed with increasing temperature. The largest molecules formed within 1 ns of simulation time at 3500 K contain enough carbon atoms to form ring structures. Ring formation is observed in one case.