A comparison of the NaOH-HCl and HCl-HF methods of extracting kerogen from two different marine oil shales

The organic matter (kerogen, defined as including the organic material soluble and insoluble in organic solvents at room temperature) from two marine oil shales, El-Lajjun (Jordan) and Julia Creek (Queensland, Australia), has been extracted by the commonly used HCl-HF method and the resulting products compared with those obtained using the NaOH-HCl method, i.e. with initial strong alkali extraction. The elemental analyses on a dry ash-free basis of the solids obtained by the two methods were similar to each other and to that of the original oil shale. The pyrolysis-gas chromatography-total ion chromatograms were also similar for the kerogens obtained by the two methods and for the original oil shale, showing regular n-alkene/alkane series, as would be expected from the high atomic H/C ratio, and series of alkyl substituted thiophenes and benzothiophenes. The solid state C-13 NMR spectra showed similar trends. The Fe contents of the solids obtained by the HCl-HF treatment were much higher than for the solids from NaOH-HCl treatment, which could have implications for reactivity studies. XPS showed depletion of the sulfur and oxidation near the surface and confirmed that some aliphatic sulfur was present. However, in general, both methods gave organic products with similar characteristics, allowing isolation of organic matter by a method not involving HF, whose use is restricted in many countries.