Abstract
Wettabilities of five kinds of original coals and of coals extracted with methanol have been studied in terms of a critical wetting concentration and a heat of wet-ting.
The critical wetting concentration of original coal in methanol/water mixtures, which is obtained from wetting rates, decreased with increase in the carbon content. The heats of wetting for original coals in methanol and/or in water decreased as carbon content in-creased up to C85.2% (Miike), and beyond the point it remained constant. The changes of the heats of wetting with volume ratio of methanol/water mixtures were dependent on various ranks of original coal.
From these results, it was found that the wettabilities of original coals in methanol, water, and methanol/water mixtures were influenced by surface-chemical structures of coals, especially, by surface acidic functional groups of coals. Moreover, surface-chemical structures for low ranks of coals were found to be different between the original coals and the coals extracted with methanol.
