ReaxFF molecular dynamics study on nitrogen-transfer mechanism in the hydropyrolysis process of lignite

Abstract

Molecular dynamics simulations based on reactive force field (ReaxFF) and density functional theory (DFT) were performed to investigate the nitrogen-transfer mechanism in the pyrolysis and hydropyrolysis processes of lignite. Results showed that the nitrogen transfer in the hydropyrolysis system was a stepwise hydrogenation and dealkylation process. Their intermediates included tertiary/primary amines, imines and nitriles, which can mutually transform into each other. Especially, the major gas product HCN has diverse formation pathways in the pyrolysis and hydropyrolysis processes. Hydrogen favored to the decomposition reactions of the stable tertiary amine and heterocyclic nitrogen moieties in lignite, and accelerated transfer reactions of nitrogen atoms from the solid phase into the liquid and gas phases.