Effect of low-temperature oxidation of coal on hydrogen-transfer capability

Coal oxidation with molecular oxygen at low temperatures is a process that can lead to spontaneous combustion. In this study, four Colombian coals were oxidized in a stove at temperatures between 30 and 150°C. The oxidized samples were heat-treated in an autoclave under nitrogen pressure at 420°C in the presence of anthracene. The main hydrogenated product was 9,10-dihydroanthracene. The amount of hydrogen transferred to the aromatic solvent was drastically reduced by oxidation of the sample and this varies with the coal rank. Fourier transform infra-red analysis, solvent swelling and coal conversion to soluble products in tetrahydrofuran were carried out for all of the samples. The mechanism by which coal reacts with molecular oxygen is strongly dependent on temperature. The initial stage of coal oxidation was apparently the same for all coals studied, i.e. the attack by molecular oxygen on the hydrogen in the α position. However, the path followed thereafter depends on the chemical functionality to which the α CH2 group is attached. In this way it is possible to differentiate the products from low- and high-rank coals.