Oxidation studies on coking coal related to weathering. 4. Oxygen linkages influencing the dilatometric properties and the effect of cleavage of ether linkages

Abstract

Samples of a vitrinite concentrate of Balmer 10, medium-volatile bituminous coal (433) and high-volatile Moss 3 coal (535) were oxidized in air at 85°C for four days to partially destroy the swelling characteristics as measured by the Ruhr dilatometer. Similar samples were oxidized at 100°C for three days to completely destroy the swelling properties. These artificially weathered coals were then treated with reagents to remove peroxides, keto and aldehyde groups. The hydroxyl groups were also blocked to prevent condensation reactions. The result of the removal of these functional groups and the blocking of the hydroxyl groups had little influence in restoring the swelling properties. This suggested that the swelling properties were largely destroyed by ether-type cross-links which form at low temperature. The cleavage of these ether linkages in the Balmer coal using potassium in tetrahydrofuran resulted in the lowering of the melting point and a large increase in dilatation. The values of these properties after cleavage were essentially the same for the fresh and oxidized coal indicating that no significant amount of polymerization through carbon-carbon bond formation occurred during the low-temperatureoxidation step. Indications were obtained that the large increase in dilatation after cleavage was due to steam formation resulting from condensation reactions occurring at the temperature of the dilatation measurements. After the cleavage of the ether linkages, the dilatation could be reduced by blocking the hydroxyl groups or removing water by heat treatment under vacuum.