The migration and transformation of sodium carboxylate during Zhundong coal pyrolysis and combustion: A ReaxFF simulation study

In this paper, the migration and transformation of sodium carboxylate during Zhundong coal pyrolysis and combustion was studied by using the reactive molecular dynamic simulation (ReaxFF MD) method. By using the elemental analysis, XPS and 13C NMR spectroscopy, the Zhundong coal model containing sodium carboxylate was constructed. Pyrolysis simulations on the Zhundong coal model were studied at different temperatures ranging from 1200 K to 3000 K. The results show that sodium was mainly released in the form of atom and inorganic substance in the pyrolysis. Atomic sodium were mainly released directly by the H free radicals attacking in the pyrolysis. Furthermore, the nascent char model was constructed to study the migration and transformation of sodium in char combustion stage. Oxygen increased the bonding opportunities between sodium atoms and oxygen atoms. Sodium was first released in the form of atom, and then migrated to the inorganic substance. By using the Arrhenius expression, the kinetic parameter for the release of sodium into various species during pyrolysis and char combustion stages were quantitatively determined. This provides a basis for understanding the migration and transformation of sodium in coal at the atomic level.