Construction of a Multicomponent Molecular Model of Fugu Coal for ReaxFF-MD Pyrolysis Simulation

Proper description of chemical structure diversity is necessary for a coal model in exploring the coal pyrolysis mechanism by reactive molecular dynamics (ReaxFF-MD) simulation. This paper presents a strategy for constructing large and reasonable coal models manually with varied chemical structures. A multicomponent molecular model containing 23,898 atoms was constructed for Fugu subbituminous coal following the proposed strategy on the basis of characterization data obtained from the proximate and ultimate analysis, ¹³C NMR, and solvent extraction experiments. The model consists of 75 macromolecules of 20 varied average structures for structural diversity and 29 varied small compounds to capture the mobile phase. The elemental composition and key structural parameters of the multicomponent model agree with the analytical data of Fugu coal sample on the whole. The weight loss profile obtained from slow heat-up (2 K/ps) ReaxFF-MD simulations agrees fairly with the observations from thermogravimetric experiments reported in the literature. The temporal evolution of a representative product (C₂H₄) from long-time (2000 ps) isothermal ReaxFF-MD simulations shows qualitative agreement with the results of the synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry (SVUV-PI-TOF-MS) pyrolysis experiments. These examinations indicate the applicability of the constructed model in ReaxFF-MD simulations to explore the coal pyrolysis mechanism. The proposed strategy suggests a feasible approach for manually constructing reasonable large coal models based on limited conventional characterization data.