Divergent pyrolytic evolution of vitrinite and inertinite aggregate structures from tar-rich coal revealed by ReaxFF MD simulations

Northern Shaanxi’s tar-rich coal possesses significant hydrocarbon potential, yet the maceral-specific mechanisms governing its conversion remain poorly understood. We developed aggregate models for vitrinite-enriched (DBDV) and inertinite-enriched (DBDI) macerals by integrating XPS and 13C-NMR data, followed by ReaxFF molecular dynamics simulations to elucidate their divergent pyrolysis behaviors. Microscopic pathway tracking reveals that product evolution is fundamentally governed by dynamic transitions between synchronous and asynchronous dehydrogenation. Results show DBDI suffers premature, localized synchronous H2 elimination below 2000 K. This renders its aromatic matrix hydrogen-deficient before primary devolatilization, forcing intensive radical cross-linking. Conversely, DBDV achieves a 15.41% peak tar yield via a synergistic radical-capping mechanism. Its oxygenated functional groups serve as effective hydrogen transfer hubs, facilitating a robust asynchronous migration network driving 68.55% of H2 generation. This kinetic control ensures hydrogen radicals effectively cap nascent fragments, maximizing liquid tar formation. These microscopic insights are substantiated by macroscopic yield predictions, which show high phenomenological consistency with experimental data, notably the tar yield peak at 600°C. Consequently, vitrinite-rich coal is optimal for low-temperature fast pyrolysis, while inertinite-rich coal excels in high-temperature gasification or metallurgical coke production.