Synergistic mechanism and radicals interaction of the co-pyrolysis of lignite and PE based on ReaxFF-MD and DFT

Co-pyrolysis is a clean and efficient strategy for utilizing coal and plastics to effectively manage plastic waste while improving valuable chemicals. Since coal and plastic belongs to organic macromolecules, the synergistic mechanism is insufficiently clear. In this paper, a kind of lignite and polyethylene (PE) were selected as representatives to study the synergistic effects of the main products during co-pyrolysis. The synergistic mechanism was elucidated at the microscopic level that radicals such as ·H and CnHm· fragments broken from PE broken combined with the tar fragments produced by lignite cleavage, which produces hydrocarbon products. As the temperature increases, the positive synergistic effect of the major liquid and gaseous products increases in a specific temperature range while weakens with a further increase in temperature. Increase of lignite can produce more oxygenated compounds while more hydrocarbons can be obtained by increasing the percentage of PE. The highest synergistic effect occurs at equal ingredients. The energy barriers of the reaction paths in the individual pyrolysis process were higher than those in the co-pyrolysis process, which indicates that the main products, such as aromatic hydrocarbons as well as ethylene are more easily formed in the co-pyrolysis process, thus a manifestation of positive synergistic effect.