Atomic-scale insights into soot formation and gasification during pyrolysis and combustion of furan and benzofuran

Furan groups play significant roles in the combustion of low-rank coal. We employed ReaxFF MD to investigate the pyrolysis and oxidation processes of furan (FR) and benzofuran (BFR) under various oxygen contents and temperatures. The results show that the initial reaction of FR groups pyrolysis is FR/BFR → R-unstable carbon chain + CO, with all oxygen-containing components converting to CO during pyrolysis. The aggregation of numerous unstable carbon chains leads to the formation of soot particles. Decreasing temperature and increasing oxygen content both reduce the size of the soot particles. We discovered a new mechanism for the formation of PAHs from FR molecules or unstable carbon chains, termed recombination cyclization of the unsaturated carbon chains from ring-opening (RCCRO). Soot particle evolution tends from 5-membered-carbon-ring to 6-membered-carbon-ring structures. During oxidation, oxygen-containing radicals attack carbon chains to extract carbon components, forming hydroxyl and aldehyde groups at the molecular ends. With increasing oxygen content, H₂O, CO, and CO₂ production increases. Hydrogen is an important product during the oxidation and pyrolysis processes, with higher temperatures and lower oxygen content leading to increased hydrogen production. The similarities in the pyrolysis and oxidation mechanisms of FR and BFR further emphasize the effectiveness of studying FR group reactions in coal.