Investigating the reaction mechanism of light tar for Shenfu bituminous coal pyrolysis

The generation mechanism of light tar during Shenfu bituminous coal pyrolysis was investigated in this work. TGA, Py-GC/MS, TGA-FTIR and reactive force field simulations (ReaxFF) were implemented to reveal the light tar reaction mechanism. The proposed coal structure model was C3198H3261N51O513S33, whose pyrolysis was simulated using the ReaxFF method. Simulation results showed that the pyrolysis process was divided into activation, pyrolysis, and condensation, which agreed well with TGA results. Based on evolutions of gases in the activation stage, it was discovered that coal pyrolysis was initiated by the cleavage of oxygen-containing groups. Simulated results with the coal unimolecular structure showed that the reaction mechanism of light tar was free radical addition reaction, where free radicals were mainly obtained from the cleavage of C–O chemical bond. Also, it was found that the temperature of 2400 K was the transition point, indicating the transition of dominating bond cleavage from C–O bond to C–C bond. The variation of chemical bond agreed well with TGA-FTIR and Py-GC/MS results, indicating that the simulated results are valid and convincing. Therefore, it was concluded that the free radical addition reaction that was mainly controlled by the rupture of C–O bond was the reaction mechanism of light tar.