In situ EPR studies of coal pyrolysis

Abstract

A systematic in situ electron paramagnetic resonance (EPR) study of the effects of minerals and iron on the formation of free radicals during coal pyrolysis has been carried out. The results show that when pyrite is added to Pittsburgh No. 8 raw coal, an enhancement in the radical yield is observed in the presence of other inherent minerals. An attempt has been made to isolate the specific mineral which is responsible for the observed catalytic effect. The raw coal has been treated with HCl to remove the inherent mineral matter. EPR data shows strong evidence of the removal of pyrite and clays. When pyrite is added in various concentrations to the demineralized coal, no increase in free radical yield is observed. However, the addition of a mixture of pyrite and calcite produces higher free radical yields than are observed for acid treated coal (ATC) or any other ATC/mineral combination. These results indicate that pyrite alone is apparently not solely responsible for an enhancement of the free radical yield in the pyrolysis of raw coal, but suggests rather, that the combination of pyrite and another mineral, possibly calcite, is the active catalytic agent. The mixture of pyrite and calcite not only produces the highest radical yield in the shortest period of time, but also produces the most residual, stable, free radicals. This study also suggests that metallic iron may also play a catalytic role in the formation of free radicals. An iron concentration of approximately 0.1% appears to have an optimal effect on the radical yield.