ReaxFF simulations of the synergistic effect mechanisms during co-pyrolysis of coal and polyethylene/polystyrene

In this paper, the co-pyrolysis behaviors of Zhundong coal with polyethylene (PE) and polystyrene (PS) are investigated using reactive molecular dynamics (ReaxFF MD) simulation. The individual pyrolysis simulation results are in good agreement with experimental results. The co-pyrolysis simulation results show that coal promotes the primary decomposition of PE at low temperatures, but shows little effect on PE pyrolysis at high temperatures. It is also found that coal has little effect on PS pyrolysis during coal/PS co-pyrolysis at all given temperatures. PE and PS have no effects on coal pyrolysis at low temperatures, but significantly promote coal char decomposition and inhibit the secondary reactions of coal tar at high temperatures. The promoting effect of PS on coal pyrolysis is more pronounced than that of PE. The interaction mechanisms between coal and plastics are revealed by analyzing the distributions of H and OH radicals. The kinetic parameters for the individual pyrolysis of coal, PE and PS, as well as the co-pyrolysis of coal and PE/PS are determined using the first-order reaction model. The results suggest that the synergistic effect significantly reduces the activation energy for coal/PE co-pyrolysis, while has little effect on the activation energy for coal/PS co-pyrolysis.