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 H 2 O, CO 2, CO, C 2 H 6, and then CH 4 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.