Transformation simulation of N-containing functional groups in coal pyrolysis and combustion processes by using ReaxFF

In order to explore the formation mechanism of NOx precursors and NOx during coal pyrolysis and combustion, four typical N-containing functional groups in coal, including pyridine-N (N-6), pyrrole-N (N-5), protonation-N (N-Q) and oxidized pyridine-N (N-X), were taken for study. Firstly, the thermal reaction processes of N-containing functional groups under different conditions were simulated via ReaxFF, then the transformation processes of N-containing functional groups to NOx precursors were obtained via Ovito, finally the reaction networks of NOx precursors and NOx were built via ReacNetGenerator. According to the study results, we speculated that the transformation process of N-containing functional groups to NOx precursors involved 4 steps, including the ring opening of N-6 and N-5, the shift of N atom to the edge, the shortening of carbon chain and the formation of NOx precursors. Besides, we found that the increasing of temperature greatly promoted the transformation processes of NO to HNO and HO₂N.