Dynamic trends for char/soot formation during secondary reactions of coal pyrolysis by large-scale reactive molecular dynamics

Abstract Coal char formation depends on its precursor properties and pyrolysis time-temperature history that has a significant impact on subsequent coal conversion processes and desired tar products. With the intention for getting comprehension of char/soot formation in coal pyrolysis, a simulation strategy combining the pyrolysis simulation for raw coal model and the secondary pyrolysis simulation for nascent tar radical model with ReaxFF MD method was employed. The models around 100,000 atoms were used in order to describe the large char/soot precursors formed and their chemical structure transformation statistically that is only accessible by large-scale model and long-time simulation. The simulations revealed that an optimal condition (1700–1800 K in this case) exists during coal pyrolysis process to produce high yields of light tar and few char/soot formation. The char precursors of C100+ are mostly originated from heavy tar (C14–C40) of recombination of methylene and Car–Car bonds with significant aromaticity increasing at high temperature. The obtained overall competitive spectrum among condensation, stabilization and decomposition reactions at different typical conditions provides a more complete understanding for char/soot formation from the pyrolysis reaction perspective.