Study of the pyrolysis of group components of coal combined experiments and ReaxFF molecular dynamics

Coal pyrolysis is one such area in which additional insights would be beneficial for utilization improvements and pollution control. Here, coal is divided into four components by the full component classification method. Those components are the dense medium component (DMC), loose medium component (LMC), heavy component (HC), and light component. Reactive molecular dynamics simulations and thermogravimetric experiments were used to determine the pyrolysis mechanism and examine the differences in the thermal behavior and contribution of raw coal pyrolysis. The previously constructed molecular model of group components of coal was used in pyrolysis simulations from 100 to 3000 K with a heating rate of 10 K ps-1 and at higher temperatures for 500 ps. This high temperature enabled chemical reactions to occur within a practical simulation time. The results showed that the pyrolysis process of group components of coal begins with the shedding of small molecules and then undergoes thermal decomposition of the skeleton and pyrolytic fragments. The simulation results of ReaxFF molecular dynamics in the temperature range of 100-3000 K are in good agreement with the experimental results in the temperature range of 303-1073 K according to the comparison between the pyrolysis thermogravimetric curve and nonvolatile yield curve. This result shows that the molecular model of the group components of coal is reasonable and that the ReaxFF reactive force field is suitable for exploring group components of coal pyrolysis. The pyrolysis process of coal is inversely related to the pyrolysis process of group components. In the whole rapid decomposition stage, the gas mainly comes from LMC and DMC. When the temperature is approximately 2200 K, coal coke mainly comes from HC and DMC, and asphaltene and tar mainly comes from LMC. This work demonstrates a new methodology for investigating the overall behaviors and underlying complex mechanisms of the pyrolysis of different group components in coal.