THE EFFECTS OF OXIDATION ON THE MACROMOLECULAR STRUCTURE OF COAL

The effect of oxidation on the macromolecular structure of four coals of rank 902 to 204 in the British Coal classification scheme was inves tigated. Various particle size ranges of the coals were oxidized in ai r at 200 degrees C for 24 h. Oxidation led to an increase in the exten t of swelling in pyridine, which indicates a decrease in the covalent cross-link densities of the coals. Unlike that of the initial coals, w hich can be described by Fickian diffusion and relaxation processes, t he swelling of the oxidized coals occurred by a two-stage process. Thi s behaviour was attributed to the differences in extent of oxidation w ith increasing depth in the coal particles. A two-stage swelling proce ss was observed regardless of whether a well-defined oxidation front w as observed by optical microscopy. FT-i.r. spectra indicated that oxid ation reduced the aliphatic:aromatic ratio, increased the hydroxyl:aro matic ratio and increased the carbonyl functionality in the coals. The results are consistent with breaking of the cross-links in the coal b y severe oxidation.