Molecular Structure of Athabasca Asphaltene:  Sulfide, Ether, and Ester Linkages

Athabasca n-C5-asphaltene was fractionated into occluded maltene, low and high molar mass (LMA, HMA) asphaltene, and the latter fractions were subjected to Ni2B reduction to cleave the sulfide C−S bonds, basic hydrolysis to cleave the ester C−O bonds, and BBr3 treatment to cleave the ether C−O bonds. Ni2B reduction of asphaltenes yielded 5−18% n-pentane solubles, which were separated into saturates, aromatics, and polars, and the saturates were analyzed for biomarkers. The residual asphaltene underwent 40% desulfurization and a greater than 4-fold drop in the MW of HMA but no change in the MW of LMA. The decrease in the MW is attributed to sulfide-bound core segments in the structure of the asphaltene:  [core]-S-[core]-S-[core]-S-[core] + Ni2B → 4[core] + 3H2S. This is an important structural feature of Athabasca asphaltene and is responsible for its upgradability without excessive coke formation. The biomarkers of the asphaltene fractions were also characteristically different with regard to maturity sta...