Synergistic effect and redistribution characteristics during co-pyrolysis of lignite and polypropylene based on ReaxFF molecular dynamic

Abstract

In this paper, the co-pyrolysis behavior of Zhundong coal and polypropylene (PP) was studied by reactive force field molecular dynamic (ReaxFF-MD) method combined with atomic labeling method to investigate the synergy evolution mechanism. Consistent product distribution and synergistic effect characteristics obtained from fixed-bed experiments (500–1000 °C) and ReaxFF MD (2000–3000 K) simulations at different temperatures suggesting that high temperatures promote the generation of tar products. The sources of the co-pyrolysis tar components were distinguished in detail, the results reveal that the components from coal migrated towards the tar fraction, whereas the components from plastics were confined to migration to heavy tar. The combination of free radicals generated stabilizing compounds categorized as heavy tar leading to an increase in tar yield. Moreover, co-pyrolysis promoted the macromolecular decomposition of both feedstocks at low temperature in the early stage, whereas labeling methods demonstrated that the H and hydrocarbon radicals were successively captured by the char with the extension of time to produce stabilized macromolecular intermediates. Furthermore, the inhibition of secondary reactions of coal tar at high temperatures result in the positive synergy of tar which overcomes the further decomposition behavior of PP tar into gas. The findings of the component migration perspective further enriched the theoretical information on the co-pyrolytic interaction between coal and plastics.