FORMATION OF FREE-RADICALS DURING DRYING AND OXIDATION OF A LIGNITE AND A BITUMINOUS COAL

The changes in radical concentrations and species brought about by vac uum and gas flow drying of New Vale lignite and Stockton bituminous co al samples were studied. Vacuum drying produces a sudden increase in c oncentration, flow drying a more gradual but ultimately greater one. F or both coals the changes depend on a balance between decarboxylation, which produces new radical sites, and removal of moisture from hetero atomic sites within the coal macrostructure. This balance is influence d by the drying method used. Exposure of dried samples to dry air prod uces changes in radical concentration consistent with the findings of previous oxidation studies of these coals.