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.