Chemical Composition of Athabasca Bitumen: The Saturate Fraction

Presented is an account of the bulk and molecular composition of the saturate fraction of Athabasca bitumen. It is shown that, for a clean isolation, it is necessary to subject the column-chromatography-separated crude saturates to molecular distillation followed by a silver ion chromatography step. Upon field ionization mass spectrometry (FIMS) analysis, the molecular distribution of the purified saturates exhibits a pulsating character with near trace concentration at hexa- and heptacyclics and varying concentrations of mono- to pentacyclics, with bi-, tri-, and tetracyclic dominance. The overall distribution is bimodal and, in contrast to conventional gas chromatography (GC) or GC-mass spectrometry (MS) results, extends to m/z similar to 750, having maxima at m/z similar to 400 and 600, with a total concentration of 15.1% of the bitumen. A gamut of biomarker molecules has been identified, including drimanes, cheilanthanes, tetracyclic terpanes, 17,21- and 8,14-secophanes, steranes and diasteranes, hopanes, gammaceranes, hexahydrobenzohopanes, etc. GC-FIMS results indicate that over half a dozen isomers accompany nearly each of the identified biomarkers. Although biomarker chemistry lies outside the scope of the present paper (an item that will be dealt with in detail in a forthcoming paper), we briefly remark here that the overall distribution of the biomarkers detected is consistent with and thus lends support to the notion that Athabasca bitumen is the residue of the secondary microbiological degradation of mature/(early mature) marine carbonate oils formed in a strongly reducing depositional environment. Additionally, a useful novel method for the extraction of biomarkers from oil sands is reported.