Oxidation studies of high fluidity coals

Abstract Highly fluid fresh bituminous coals were oxidised and four techniques (cross-link measurement, chloroform extraction, proton magnetic resonance thermal analysis (PMRTA) and FT-i.r. diffuse reflectance spectroscopy) were used to correlate Gieseler fluidity changes with chemical differences between the fresh and oxidised samples. The oxidised samples were found to have a depleted concentration of aliphatic CH bonds. During slow heating through the plastic temperature range, they developed less molecular mobility, and generated smaller amounts of chloroform extracts but underwent cross-link formation to the same extent and at the same rate as the fresh samples. The addition of a radical stabiliser greatly inhibited fluidity loss and restored fluidity to some oxidised samples. The results suggest that for Geiseler fluidity development, the capping of radicals derived from the coal structure during heating is a far more important factor than variations in cross-link formation.