The air-oxidation reactions of Taiheiyo coal were carried out under the relatively high temperatures (130, 170 and 213°C). The roles of hydrogen bond in terms of humic acid formation in the structure of oxidized coal were investigated from the pyridine and benzene extractabilities and the changes of IR spectra of the solvent extracts.
At 213°C, strong hydrogen bonds are formed within 10 hours from the beginning of oxidation, which is due to production of humic acids. Then, the elimination of the hydrogen bondings by the decomposition of carboxyls begins also immediately to release cluster between humic acid molecules and degraded coal structure. The apparent network structures linked ether oxygens are considerably difficult to be formed below 200°C.
