Investigation of the rank dependence of tar evolution

Despite its high nitrogen concentration levels relative to the parent coal samples, 7.2% vs. 1.4 - 2.0%, little volatile nitrogen evolution is observed until decomposition temperatures of 600[degree]C or greater are obtained. Due to the lack of decomposition via tar evolution and as contrasted to parent coals, no significant bound nitrogen is evolved with heavy hydrocarbons at particle temperatures less than 600[degree]C. Similar to virgin'' chars and tars formed during rapid devolatilization, the polyimide samples begin to evolve significant fractions of bound nitrogen as IR-active light gases at particle temperatures between 650 and 750[degree]C. Unlike coal samples, however, relatively large fractions of the light gases are observed to be ammonia. The IR-active, nitrogen-containing light gas evolution rapidly declines at polyimide char temperatures greater than 750[degree]C, again in contrast to observed behavior in virgin coal char samples. It is not certain if the nitrogen evolution kinetics changes from selectively forming ammonia and hydrogen cyanide to benzonitriles or free nitrogen at these temperatures. The light gas evolution pattern with decomposition temperature of polymide could contribute to our understanding of the low conversion efficiencies observed for bound nitrogen to NO[sub x] conversion in the char combustion phase of pfc combustion.