COMPARATIVE GEOCHEMICAL STUDY OF 3 MACERAL GROUPS FROM A HIGH-VOLATILE BITUMINOUS COAL

Three maceral concentrates (vitrinite, fusinite, and sporinite, over 90% pure) from the same high-volatile bituminous coal (Vouters, Lorraine Basin, France; 0.84% R(o)) have been analyzed for their organic solvent soluble (bitumen) and insoluble (macromolecular network) fractions in the scope of a comparative geochemical study. Molecular marker distributions in the saturated and aromatic hydrocarbon fractions from the bitumen of vitrinite and fusinite were almost identical, whereas they were rather different for sporinite, probably due to a difference of origin. Hopanoid compounds were much more abundant in fusinite than in vitrinite, giving evidence for a major bacterial input in the former. The macromolecular networks have been oxidized with ruthenium tetroxide, a reagent known for its selectivity toward aromatic rings. Oxidation products reflect the high aliphatic character of sporinite (which yields essentially linear mono- and dicarboxylic acids) and the highly aromatic characters of vitrinite and fusinite (which yield essentially aromatic acids). Both oxidative degradation and Rock-Eval pyrolysis showed sporinite to be easily degradable and fusinite very resistant, at this level of maturity. Covalently bound hopanes are present in the matrix of sporinite; they appear less mature than the free hopanes in the bitumen, probably due to a protection of the macromolecular network. Hopanoids seem to have been incorporated in the matrix of fusinite. New coal rank parameters based on oxidation products of aromatic structural entities belonging to the macromolecular network have been proven to be more discriminating than rank parameters from the bitumen. They enabled the quantification of the level of condensation of the polyaromatic subunits of the macerals (fusinite > vitrinite > sporinite). Moreover, fusinite seems to behave like a 2% R(o) vitrinite-rich coal. These new parameters could find useful applications in the coking industry since they are able to differentiate between inert and reactive inertinites.