The radical and bond cleavage behaviors of 14 coals during pyrolysis with 9,10-dihydrophenanthrene

The pyrolysis of 14 coals with carbon contents (C%) of 67.5–94.9% are studied in the presence of 9,10-dihydrophenanthrene (DHP) at 440 °C. The amounts of stable radicals in the coals and that generated in the pyrolysis are quantified by electron spin resonance (ESR). The amounts of active radicals generated in the pyrolysis are quantified by the amounts of hydrogen donated by DHP. The changes in quantity of these radicals during the pyrolysis are correlated with the parameters representing the coal rank (C%, the amounts of aromatic and aliphatic carbon). It is found that the quantity of stable radicals of the coals in the pyrolysis increases with an increase in C%. The lignites and bituminous coals break up significantly in the first 2 min in the pyrolysis. All the coals contain some rigid structures that do not break at 440 °C and the structure can be categorized to fusinite. The quantities of active radicals generated in the pyrolysis are approximately 3 orders of magnitude higher than that of the stable radicals in the coals. The total amounts of cleavable bonds in the coals and the rate constants of the bond cleavage are determined by the first order kinetics.