Analysis of Tars Produced in Pyrolysis of Four Coals under Various Conditions in a Viewpoint of Radicals

Many studies tried to correlate coal pyrolysis conditions with reactivity of tars produced, but few analyzed the radical concentration of tars. This work studies pyrolysis of four coals, with carbon contents in a range of 74–82 wt %, in a fixed-bed tubular reactor at three heating rates and three N2-purging rates. The changes in the radical concentration of tars under various conditions, such as in solvents (hexane or tetrahydrofuran) or at high temperatures (300, 350, 400, and 450 °C), are analyzed. The effect of pyrolysis conditions on the radical concentration of tars is ascribed to the temperature difference between the gas phase and the coal in the reactor, which results in further cracking of tars. The difference in the radical concentration in tars obtained from pyrolysis of different coals is elaborated in a viewpoint of the coal structure and pyrolysis mechanism.