EPR STUDIES ON PETROGRAPHIC CONSTITUENTS OF BITUMINOUS COALS, CHARS OF BROWN COALS GROUP COMPONENTS, AND HUMIC ACIDS 600 DEGREES-C CHAR UPON OXYGEN AND SOLVENT ACTION
F. Czechowski et A. Jezierski, EPR STUDIES ON PETROGRAPHIC CONSTITUENTS OF BITUMINOUS COALS, CHARS OF BROWN COALS GROUP COMPONENTS, AND HUMIC ACIDS 600 DEGREES-C CHAR UPON OXYGEN AND SOLVENT ACTION, Energy & fuels, 11(5), 1997, pp. 951-964
Free radicals were characterized in petrographic constituents of bitum
inous coals and in chars from brown coal components by EPR. The change
in free radical concentration on oxidation of humic acid 600 degrees
C char from humodetritous brown coal with gaseous 10% oxygen at 330 de
grees C was evaluated. Spin concentration in the petrographic constitu
ents from a bituminous coal increases in the order liptinite < vitrini
te << inertinite. Increasing maturity of each petrographic constituent
correlates with an increase in spin concentration and decrease in g-v
alue. Heat treatment of brown coal group components (bitumens, cellulo
se, lignin, humic acids, and residual coal) leads to the formation of
free radicals up to a temperature of about 550 degrees C and to their
sharp disappearance at higher temperatures. Strongly marked maxima in
the spin concentration of the chars are observed at atomic H/C ratios
in the range 0.40-0.42 and O/C ratios in the range 0.08-0.10. Increasi
ng heat treatment temperature causes a steady decrease in g-value from
about 2.0040 to 2.0025. Treatment of the 600 and 700 degrees C chars
with organic solvents resulted in an increase in their spin concentrat
ion. This effect was particularly strong in the case of treatment with
tetralin and naphthalene. Burning off humic acid 600 degrees C char w
ith 10% oxygen at 330 degrees C leads to a decrease in spin concentrat
ion in oxidized products. Structural units associated with elevated ch
ar free radicals density were more prone to oxidation and presumably a
re peripheral polyaromatic skeletons of lower structural ordering.