ReaxFF molecular dynamics simulation of pyrolysis and combustion of pyridine

Abstract

The reactive molecular dynamics (ReaxFF MD) simulation was applied to investigate the initial reaction mechanism of pyrolysis and combustion of pyridine. By analyzing the dynamic change with time of intermediates and products formed during the simulation process, the underlying detailed chemical reactions of pyrolysis and combustion of pyridine for a variety of reaction conditions (temperature, pressure/density and heating rate) were revealed. We found that a raise in temperature, pressure/density and heating rate shortens the initiation time and accelerates the pyrolysis of pyridines, producing more species and numbers of products. Specifically, the free radicals of H and pyridyl were generated from the pyridine molecules at the early stage of pyrolysis simulation, and prominent products observed during these decompositions were H2, C2H2 and HCN, indicating the pyrolysis of pyridine is a chain process initiated principally by CH bond fission. And we investigated the dynamic transformation pathways of nitrogen during the pyrolysis process. As the pyrolysis temperature and pressure/density increase, the nitrogen transformation process from HCN and CN to NH3 and N2 will be promoted. In addition, for the simulation of the oxidation of pyridines, we found that increasing temperature promotes the combustion of pyridine but only has a limited effect on the oxidation process when it reached a higher range, and the initiation of oxidation is the unimolecular CH bond fission and bimolecular reaction with O2 to form the pyridyl radical, which can further react with oxygenated species to form the pyridoxy radical. The simulation results agreed reasonably well with previous experimental studies, implying that this paper offers a new and promising approach to systematically study the detailed and dynamic chemical reactions of thermal decomposition of nitrogen compounds.