Heating-rate-dependent pyrolysis mechanism of Dayan lignite: Integrating experimental studies and ReaxFF-MD

Coal pyrolysis technology serves as a critical pathway for achieving clean and efficient coal utilization. To elucidate the pyrolysis mechanisms of lignite, this study systematically investigated the heating-rate-dependent pyrolysis behavior of Dayan lignite through an integrated approach combining experimental characterization and reactive force field molecular dynamics (ReaxFF-MD) simulations. Thermogravimetric (TG) analysis revealed three distinct pyrolysis stages, with the primary decomposition occurring between 300–600 °C. Furthermore, increased heating rates were found to correspondingly elevate the maximum pyrolysis temperature (T max ), demonstrating more pronounced thermal hysteresis effects. ReaxFF-MD simulations similarly identified three pyrolysis stages: the initial pyrolysis stage (300–1300 K), the primary pyrolysis stage (1300–2700 K), and the secondary reactions stage (2700–3000 K). Reaction pathway analysis indicated that pyrolysis was primarily governed by cleavage and formation of C–C and C–O bonds. Furthermore, the influence of varying heating rates on pyrolysis mechanisms was investigated. The results demonstrated significant heating-rate dependence on product distribution, attributable to tar secondary reactions. Secondary reactions required sustained high temperatures, thus proceeding more extensively at slower heating rates. Moreover, gas product distributions varied significantly across heating rates. The number of molecules of gas products (CO 2 , H 2 O, C 2 H 2 O) exhibited decreasing trends with increasing heating rates. Finally, the formation pathways of characteristic gas products (H 2 O, C 2 H 4 , C 2 H 2 O) were analyzed at 2 K/ps. In general, by combining experimental and ReaxFF-MD approaches, this work elucidates the complete reaction pathways and product evolution during lignite pyrolysis. The findings provide critical insights for optimizing pyrolysis conditions to enhance tar and gas yields in industrial applications.