Trends in aromatic ring number distributions of coal tars during secondary pyrolysis

To characterize the ring number distribution of coal tars throughout secondary pyrolysis, tar samples from two coal types were fractionated via gravity flow column chromatography (GFCC), and the polycyclic aromatic compounds (PAC) in the toluene fraction were analyzed via high performance liquid chromatography (HPLC) to quantify ring number distributions. During the early stages of secondary pyrolysis, the measured ring number distributions reflect prominent features of the parent coals, but the influence of original coal structure on the ring number distribution diminishes as pyrolysis conditions become more severe. Based on the trends observed for the various ring groups, insights are gained regarding the orchestration among neutralization, polymerization, and ring rupture, as well as the predominance of various sooting pathways. During the early stages of secondary pyrolysis, neutralization represents a major mass transformation mechanism among PAC, while direct conversion of PAC to soot also appears to be a dominant pathway. As secondary pyrolysis proceeds, polymerization and ring rupture become significant, while the addition of acetylene appears to be important in contributing to soot growth. By the end of secondary pyrolysis, ring rupture appears to be the dominant mass transformation mechanism.