Insight into the influence of calcium on the co-pyrolysis of coal and polystyrene

In this paper, the influence of calcium on the co-pyrolysis of coal and polystyrene (PS) is investigated by reactive molecular dynamics (ReaxFF MD) method. The experimental results show the same trend of products variation as the pyrolysis simulation. The results show that the presence of calcium in the coal sample significantly promotes the co-pyrolysis process. The addition of calcium greatly enhances the rapid cracking of coal/PS into small molecular fragments within 2000-2600 K, leading to the high yield of light tar. The slow weight loss of oxygen -containing char and high CO yield, as well as the sharp rise of oxygen-free tar, suggest the promotion of calcium on the conversion of tar to char in coal pyrolysis and the positive effect on PS pyrolysis. Moreover, the delayed release of OH radicals in coal and early release of H radicals in PS during coal(Ca)/PS co-pyrolysis present the strong binding effect of Ca-containing species on free radicals in coal and the promotion effect of calcium on PS pyrolysis. Furthermore, the low C8H8 yield in the early stage during coal(Ca)/PS co-pyrolysis, along with the phenomenon that H radicals are released early, proves that calcium-containing compounds enhance benzene ring dehydrogenation or the breaking of C--C bonds in PS. By using the first-order reaction model, the kinetic pa-rameters for the co-pyrolysis of coal/PS and coal(Ca)/PS are quantitatively determined.