Initial Chemical Reaction Simulation of Coal Pyrolysis via ReaxFF Molecular Dynamics

Mechanisms investigation of coal pyrolysis will aid efficient and clean coal conversion and utilization. However, coal pyrolysis is a complex process involving myriad coupled reaction pathways such that the deeper understanding of its mechanism is still limited even with state-of-the-art experimental approaches. In this paper, ReaxFF molecular dynamics simulation was employed to perform simulation of chemical reactions in pyrolysis of a bituminous coal model with 4976 atoms to examine the nascent decomposition mechanisms and product profiles at temperatures from 1000 to 2000 K over a 250 ps simulation period. It is found that more than 900 reactions may occur at the temperature 2000 K within the simulation period with a trajectory output interval of 12.5 ps, and a detailed chemical reaction network was obtained by further analysis of the trajectory using a newly created C++ program. The product profile evolution tendency with temperature observed in the simulation agrees well with what was obtained experimentally in the literature. In addition, the sequence of gas generation was H2O, CO2, CO, C2H6, and then CH4 consistent with experimental observations. We believe that the methodology presented in this paper offers a new and promising approach to systematically build understanding of the complex chemical reactions in thermolysis of very complicated molecular systems.