Microscopic pyrolysis mechanisms of superfine pulverized coal based on TG-FTIR-MS and ReaxFF MD study

Abstract

Current studies on coal pyrolysis characteristics mainly focus on macroscopic aspects. Here, the structural properties of coal residues were well characterized based on HRTEM, XPS, and 13C NMR etc., and the macromolecule models were constructed. Combining the small molecule compositions of extracts and the macromolecule models of residues, the multi-component models of raw coals with different particle sizes were successfully constructed. Thus, the microscopic pyrolysis mechanisms of raw coals were obtained by combining TG-MS-FTIR and ReaxFF MD analysis. More importantly, the evolution of chemical bonds and carbon-containing products was discussed. The effect of particle size on microscopic pyrolysis characteristics was focused on. The results show that for smaller particles, the abundant alkylated aromatic and aromatic bridgehead carbon enhances the pyrolysis process. During the primary thermal depolymerization, the conversion of C100+ to C14–C40 and C41–C100 and the generation of pyrolysis gases collectively govern the thermochemical process. For the secondary thermal depolymerization, the release of massive pyrolysis gases is dominant, and most oxygen-containing intermediate groups transform into CO and CO2. In the thermal polymerization stage, the C100+ mainly evolves into C41–C100 and C14–C40, accompanied by the evolution of substantial H2. The microscopic pyrolysis mechanisms shed light on further developing new low-NOx combustion technologies.