The proposition of the hypothesis-relating structure with properties of asphaltenes is a very important endeavor. In view of their complexity, being an intricate mixture of high-molecular-mass compounds, experimental and theoretical procedures must be designed to check whether the structures proposed are consistent with expected and found behavior. During recent years, a structural characteristic of asphaltene, whereby the several polycyclic systems present in them are joined by flexible aliphatic chains, has been proposed by several authors. For simplicity, we will refer to this as the rosary-type structure. In this paper, using both reported as well as new experimental and theoretical results, an attempt is made to show how asphaltene properties, such as molecular-mass distribution, molecular fragmentation, solubility, adsorption, trapping of molecules, solvent swelling, and aging, could be accounted for in terms of the above rosary-type structures.

The Sphere method developed by Hansen (Hansen, C. M. Hansen Solubility Parameters: A User's Handbook; CRC Press: Boca Raton, FL, 1999) to calculate components of solubility parameters (SP), δ D , δ P , and δ H , where D, P, and H stand for dispersion, polar, and hydrogen bonding respectively, have been applied to resins, to asphaltenes, and fractions A1 and A2. Mean values for these compounds in MPa 0.5 were asphaltenes (19.5 ( 0.1, 4.7 ( 0.2, 4.2 ( 0.1); A2 (19.6 ( 0.1, 5.8 ( 0.1, 4.4 ( 0.2); A1 (20.9 ( 0.2, 5.6 ( 0.3, 6.8 ( 0.2); resins (18.6 ( 0.2, 3.6 ( 0.3, 3.2 ( 0.3). Also, the SP components of the asphaltene sample (AsH-NS), denuded from acidic natural surfactant (NS), were determined affording values equal to A2. These values were obtained after using 57 solvents, and the method is consistent with all known solubility properties of asphaltenes and confirm the expected solubility behavior of A1 and A2, with A1 being the less soluble material in all solvent examined. Excellent affinity between asphaltene with resins was predicted as well as affinity between samples examined. These results are coherent with a colloidal model whereby fraction A1 is in not contact with the solvent, being within a core shielded from the media by a periphery composed by fraction A2 and NS. Flocculation results measured in n-C 7 -1-methylnaphthalene mixtures correlate with the above SP showing the following order of flocculation tendency: A1 . A2 > asphaltenes (AsH). We also observed that flocculation points of A2 and AsH-NS were very close, and this strongly supports the colloidal model above. SP were helpful in analyzing other properties such as adsorption, vaporization, affinity, and molecular mass and paraffin's properties.

Here, the concept of suppression of phase separation is proposed to account for the solubility behavior of asphaltenes at high dilution in toluene under ambient conditions. Nuclei formation at concentrations near 90 mg L–1 is the consequence of reaching A1 fraction solubility, and phase separation is suppressed by the intercalation of sufficient A2 in these nuclei or nanoaggregates. Presumably, such intercalation leads to media penetration of the nuclei periphery, hindering the growth and allowing for nuclei dispersion as a kinetic unit. Trapped compounds (TCs) or compounds trapped by asphaltene clusters were isolated, and their elemental analysis showed that they were neither resins nor asphaltenes. The information available regarding the A1 and A2 asphaltene subfractions is revised and complemented with new thermogravimetric analysis, simulation distillation (SimDis) curves, microcarbon Conradson, softening points, and nanoparticle results involving size-exclusion microchromatography. In general, physical results, such as solubility, SimDis, aggregation, and the softening point, differ substantially, whereas structural results, such as elemental analysis, DBE, and 13C nuclear magnetic resonance spectra, are similar. These results suggest that minor structural differences strongly affect the solubility, softening point, and other physical characteristics.

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