Thermal stability of aqueous acetate and variations in product composition under different experimental conditions

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In order to obtain more knowledge of the temperature dependent reactions of water soluble organic acids with respect to catagenesis, the degradation of acetate is studied using confined pyrolysis in sealed gold tubes with a confinement pressure of 40 MPa and final temperatures of 380–430°C. The complete spectrum of products is analysed. The effects of water as reaction medium, salinity of water phase and presence of a potential mineral oxidant, the mineral hematite, is investigated. Methane is the single product found in the highest quantity, with molar yields slightly higher than the initial acatate. The carbon isotopic signature of the methane shows a typically thermogenic trend. A series of higher carbon-number products is generated, including n-alkanes up to C 34. CO 2 and CO are generated in low concentrations relative to the conversion of acetate. The carbon isotopic signature of the CO 2 is very different from that observed in natural samples. In the perspective of deep, hot reservoirs, the results imply that cracking of carboxylic acids may be a (minor) source for in situ hydrocarbon gas generation. Since the yields of CO 2 are small, the contribution to late carbonate cementation processes would be limited.