Ruthenium tetroxide oxidation of natural organic macromolecules: Messel kerogen

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Molecular characterisation of Messel kerogen was undertaken using selective chemical degradation with ruthenium tetroxide (RuO 4). Eight degradation experiments were performed utilising co-oxidant/substrate (c/s) ratios (weight for (weight for weight (w/w) based upon a Total Organic Carbon (TOC) content of 53.5% for the kerogen concentrate) of 4:1, 8:1, 12:1, 16:1, 20:1, 30:1, 40:1, and 50:1 at a temperature of 25°C. Two further experiments were executed using a temperature of 35°C and c/s ratios (w/w based on TOC) of 4:1 and 16:1; the products were extracted from the former reaction and more co-oxidant added (16:1) to continue the oxidation. It was discovered that a high (20:1 and above) c/s ratios yields a high percentage of organic solvent extract and an increase in temperature liberates more products from the lower c/s ratio reaction mixtures more rapidly. For these reasons, ruthenium tetroxide completely oxidises (> 95%) the kerogen matrix at elevated (> 20:1) co-oxidant concentrations. Affects of time on the reaction (with an excess (50:1) of cooxidant and a temperature of 25°C) were also investigated; temperature and time appear to be inversely proportional to each another and directly affect reaction rates without significantly altering the products. Solvent-soluble extracts were dominated by two homologous series of acids: straight chain monocarboxylic acids (mono' acids) and α,ω-dicarboxylic acids (di' acids) (C 4C 30) indicating that polymethylene chains are important constituents of Messel kerogen. Of lesser importance was a series of acyclic isoprenoid acids (C 13C 17) and C 19C 21), and minor series of branched mono' (C 13C 17), branched di' (C 5C 11) and hopanoic' (C 30C 32) acids. This method provides valuable compositional information about the aliphatic and alicyclic portions of the kerogen. From these results, Messel kerogen appears to be a mixed type I and type II kerogen which can then be definitely classified as a type II on a van Krevelen diagram.