Early maturation processes in coal. Part 2: Reactive dynamics simulations using the ReaxFF reactive force field on Morwell Brown coal structures

This paper reports reactive dynamics (RD) simulations of a macro-model of Morwell Brown coal using the ReaxFF reactive force field. We find that these reactive MD simulations successfully reproduce thermal decomposition processes of defunctionalization, depolymerization and rearrangement of the residual structure observed in various experimental studies. For example, our simulations indicate that the decarboxylation and dehydroxylation of the lignin side chain of the Morwell model involves the formation of double bonds conjugated with the aromatic rings. The process of defunctionalization of the methoxy functions involving the formation of phenolic structures in the residue has been confirmed. We also observe that gaseous hydrocarbons are generated by cleavage of C-C bonds of the lignin side chain. The success in using ReaxFF RD to describe the molecular processes underlying the kinetics in pyrolysis of this model of coal plus the success of a similar previous study on the algaenan of Botryococcus braunii race L biopolymer model of kerogens suggests that such computation can be useful in providing molecular based kinetic models for other pyrolysis processes underlying the organic transformations in sedimentary materials.