QUANTITATIVE C-13 NMR-STUDY OF STRUCTURAL VARIATIONS WITHIN THE VITRINITE AND INERTINITE MACERAL GROUPS FOR A SEMIFUSINITE-RICH BITUMINOUS COAL

To determine the structural variation within vitrinite and inertinite maceral groups, fractions with purities over 90% in vitrinite and semi fusinite were obtained by density gradient centrifugation from a mediu m volatile Australian bituminous coal and the bulk structural composit ions of the maceral concentrates were determined by the quantitatively reliable single pulse excitation (SPE) solid state C-13 NMR technique . As previously reported for coals and chars, the aromaticities determ ined by cross polarisation are often lower than those by SPE, due to t he unfavourable spin dynamics. As expected, the aromaticities of the v itrinite fractions are significantly lower than those of the semifusin ite ones, but the aromaticity, the fraction of non-protonated aromatic carbon and the number of rings per cluster all increase with density within both the maceral groups. The vitrinite and semifusinite fractio ns contain 3-6 and 9 to over 15 aromatic rings, respectively. Methyl g roups account for greater proportions of the aliphatic carbon with inc reasing density. These structural trends are consistent with the varia tions evident in random reflectance. (C) 1998 Elsevier Science Ltd. Al l rights reserved.