Quantitative study of the carboxylic acids in Green River oil shale bitumen

Abstract

Bitumen fractions were extracted by a benzene/methanol reflux of Green River oil shale (GROS) before and after treatment with HCl, HF, and HCl/HF. Acid leaching released 80% more bitumen than could be extracted without acid treatment. This additional bitumen had greater concentrations of carboxylic acids and their salts than the untreated oil shale bitumen. The carboxylic acids were separated from all bitumen fractions (untreated, post HCI, post HF, and post HF/HCl) and individual acids were identified and quantified by gas chromatography—mass spectrometry and high resolution mass spectrometry. The same types of acids were present in all four bitumen fractions but showed significant differences in their relative abundances. These carboxylic acids and salts were present in the original GROS and were not formed during the treatment. The post-HCl bitumen fraction contained Mg and Fe salts of long-chain aliphatic carboxylic acids with carbon numbers in the range of 21–38. Significantly, even though calcium is the major cation in the carbonate minerals of GROS, no Ca was present in the ash of these carboxylic acid salts. These results indicate that there is a strong interaction between carboxylic acids present in GROS and its mineral matrix (especially carbonate minerals). These carboxylic acids are possible coupling agents that ‘glue’ mineral and organic material together. The treatment of the oil shale also resulted in the formation of highly purified kerogen, low in ash yield (2 wt %) which had undergone only very mild acid treatment.