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Coal Cascade Utilization

MD Simulation of Pyrolysis Reaction


The heterogeneous nature of coal and the complexity of its pyrolysis process have made it very difficult to determine the mechanisms of coal pyrolysis both with thestate-of-the-art experimental approaches and quantum mechanics (QM) modeling. QM allows for prediction of energy barrier and getting detailed knowledge ofchemical bonding and reaction mechanism, but its limitation in practical model scale(100 atoms) prevents it from being used in more meaningful and larger coal modelcontaining 10,000 atoms. Classical molecular dynamics (MD) has been very helpfulin generating 3D structures of coal model for more ‘realistic’ molecular view of a coalmolecular model, but it is not feasible for exploring chemical reactions in coalpyrolysis because it only describes physical elastic collision between atoms with staticbonds and fixed charges.


As a bridge of QM and MD, the reactive molecular dynamics (ReaxFF MD) approachthat combines MD with an empirical reactive force field (ReaxFF) proposed by vanDuin et a1, is an option for studying the complex chemistry in coal pyrolysis. ReaxFFis a bond order potential permitting much faster ReaxFF MD simulations than densityfunctional theory (DFT, fast and widely used QM approach) for large and complexmolecular systems involving chemical reactions at closer accuracy of DFT. Particularly, no pre-defined reactive sites or reaction pathways are required becauseits potential functions would deal with the coordination changes automatically that areassociated with reactions. Therefore it is promising to investigate the complexchemistry of coal pyrolysis directly with ReaxFF MD simulation for a comprehensive prior knowledge on the multiple reaction pathways of coal thermolysis.