Insight into hydrogen migration and redistribution characteristics during co-pyrolysis of coal and polystyrene

Abstract

The hydrogen migration and redistribution features in products during co-pyrolysis of coal and polystyrene (PS) were explored using the reactive molecular dynamics (ReaxFF MD) simulations. The weight loss parameters of coal and PS pyrolysis derived by ReaxFF MD simulations agreed well with thermogravimetric (TG) experimental data. The hydrogen transfer route in the co-pyrolysis products was investigated and the hydrogen synergy mechanisms were also elucidated. The results show that the synergistic effect of coal and PS co-pyrolysis can promote char conversion to volatiles, but this effect diminishes from 20.7% to 5.3% (seen from the char yield) as the proportion of PS increases. It is discovered that a large amount of hydrogen migrates from char to volatile in coal, whereas hydrogen migrates from heavy tar to light tar in PS. The content of total hydrogen in heavy tar decreases from 21.47% to 14.06% as PS content increases, whereas hydrogen in light tar increases from 40.27% to 77.76%, indicating an improvement in co-pyrolysis tar quality. The variation of H and O in co-pyrolysis char demonstrates that char formation is highly dependent on the hydrogen/oxygen content. Different levels of hydrogen content cause changes in the dominant reaction and its reaction time in the various char reaction stages, affecting the formation of volatiles.