Suppression of Phase Separation as a Hypothesis to Account for Nuclei or Nanoaggregate Formation by Asphaltenes in Toluene
Résumé
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.