Abstract
Oxidation with alkaline cupric oxide has been combined with solid-state 13C-n.m.r. spectroscopy to evaluate the cellulose and lignin input to the formation of low rank coals. Model studies carried out on lignin-cellulose mixtures, carbonified cellulose, synthetic coals and synthetic humic acids (melanoidins) have established m-hydroxybenzoic acid as a source indicator for cellulose. This product has been found specifically in the oxidation of bio- and geo-macromolecules containing cellulose and/or thermally altered cellulosic material and is chemically distinct from the characteristic oxidation products of lignin-derived materials. Systematic changes in the distribution of the major oxidation products from lignin provide a chemical fingerprint which, in general, can be utilized to trace the thermal history of the sample. Analysis of two lignite coals from the northern hemisphere has demonstrated their predominantly lignitic origin. On the other hand, a Victorian brown coal (pale lithotype) sample is shown to contain a significant amount of highly transformed carbohydrate materials which are presumably incorporated into the macromolecular structure as humic acid derivatives.
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