FT-ir and XRD analysis of sapropelitic coals

Sapropelitic coals of various coalification stages were examined using FT-i.r. spectroscopy and X-ray diffraction (XRD). The FT-i.r. spectra showed that the main constituent of low-rank sapropelitic coals is aliphatic chains. The evolution of carbonyl groups is more likely to be related to rank changes from peat to anthracite than that of aliphatic groups. The XRD analysis showed great differences between the low-rank sapropelitic coals and humic coals, although bituminous coals have a structure similar to that of humic coals of the same degree of coalification. The method of function of radial distribution of atoms (FRDA) was applied to low-rank sapropelitic coals. Maxima at 0.5 and 1 nm in the FRDA curves of these coals were established, indicating the parallel orientation of aliphatic chains in sapropelitic coals. The sapropelitic structure is probably determined by preservation of algal cell membranes, because it is known that the aliphatic parts of fatty acids of algal cell membranes have a parallel orientation. Copyright (C) 1996 Elsevier Science Ltd.