Studies on asphaltenes through analysis of polar fractions

Asphaltenes from Mobil crude oil were characterized by fractionation into components of different polarities. The fractions, varying from dense, shiny black particles that displayed a relative amount of order and crystallinity in their structure (the most polar fraction) to light, dull brown powder of a completely amorphous nature (the least polar fraction), revealed no significant differences in structure or content when analyzed by gel permeation chromatography and FTIR spectroscopy, yet displayed significantly different rates of dissolution in a differential reactor using an amphiphile/alkane solution of 10 wt % dodecylbenzenesulfonic acid in heptane. Further analysis suggested that the metal element content, especially iron, nickel, and vanadium, differentiates the most polar and the least polar fractions from each other. The effect of the presence of ferric (Fe3+) iron in an acidic medium during asphaltene precipitation from another crude oil (Chaguaramal) was then systematically studied. The results from these studies corroborate the earlier inference that the presence of metal ions such as Fe3+ plays a primary role in determining asphaltene polarity.