Multiple mechanisms for the loss of coking properties caused by mild air oxidation

Abstract

Evidence is presented for the existence of at least three different mechanisms by which low temperature oxidation (weathering) destroys coal's coking properties. Lithium aluminium hydride reduction of Bruceton coal oxidized for 28 days restores the FSI to its initial value of 8 from a value of 3. After 220 days oxidation, reduction raises the FSI from 0.5 to 2. Clearly, two different processes are responsible for the FSI decrease. The pyridine solvent swelling change during this time is quite small, much smaller than observed by Liotta. Thus the oxidative increase in cross-link density observed by Liotta is a third mechanism of thermoplasticity loss. The initial FSI decrease, that reversible by reduction, is tentatively ascribed to oxidative loss of readily donatable hydrogen from the coal. The second mechanism remains uncharacterized. © 1986.