Macromolecular and chemical changes induced by air-oxidation of a medium volatile bituminous coal

Abstract

A medium volatile bituminous coal was oxidized in air at 200 °C. The oxidized coal was characterized by its swelling properties, infrared spectra, thermogravimetric analysis, and optical microscopy. Examination of the oxidized coal indicated that carboxyl and hydroxyl groups are formed during oxidation of alkyl and cycloalkyl cross-linkages which have been identified as largely responsible for the macromolecular structure of coal. Treatment of the oxidized coal with pyridine broke weak hydrogen bonds, but bases with higher pK b values were needed to attack stronger hydrogen bonds. Extraction of the oxidized coal with dilute sodium hydroxide yielded characteristic coal humic acids that contained no pyrite. Yields of humic acids, rates of humic acid formation, some properties of the humic acids and results of examination under optical microscopy of the acids and the oxidized coal are reported.