The solubility and three-dimensional structure of asphaltenes

The tendency of the asphaltenes to form aggregates in hydrocarbon solution is one of their most characteristic features and has tended to complicate the determination of the structure of petroleum. In addition, if the composition and properties of the precipitated asphaltenes reflect those of the micelles in solution, the latter should be considered as mixed micelles. This is a reasonable assumption in view of the large quantities of soluble resins found in the precipitated solid. Empirical observations indicate that the resins play an important role in stabilizing asphaltenes in crude oil and under unfavorable solvent conditions the asphaltene species are prone to further aggregation into clusters that are unstable and precipitate from the crude oil. It is also suggested that the resins and the asphaltenes from a particular crude oil have points of structural similarity relative to the asphaltenes and resins from another crude oil. On a more localized scale, i.e. in one particular crude oil there are also structural differences within the constituents of asphaltenes and structural differences within the constituents of the resins are also anticipated. Therefore, the structure of the micelles within any one crude oil must be expected to be varied and non-homogenous. From the evidence cited herein, it follows that the potential for graphite-type stacking by the asphaltene molecules in the center of a micelle might not be as great as the potential for the micelles forming by asphaltene-resin interactions rather than by asphaltene-asphaltene interactions.