| Abstract
| - Volumetric changes of crude oils and derived fractions can cause phase separation. Crude oilasphaltene swelling has been recently reported in the open literature. Solvent swelling processeshave been formerly studied in greater detail for coal samples. Important structural and chemicalinformation on coals have been gathered through the use of swelling as a characterizationtechnique. In this study, crude oil isolated asphaltenes were successfully characterized by solventswelling, employing polar as well as nonpolar solvents. Operationally stable and unstable crudeoils, virgin and hydrocracked vacuum residua, and solid deposits from oil production tubingswere the selected matrices for asphaltene isolation and characterization. The main factor thatgoverns swelling appears to be dispersive forces, since swelling maxima were observed for alkanetype solvents. Consistently, compositional asphaltene parameters like elemental hydrogen andaliphatic chain content significantly influenced the solvent swelling process. However, solventdonor properties and asphaltene acceptor properties also played an important role in the swellingphenomenom. Asphaltene swelling in nonpolar solvents was successfully fitted using the Flory−Rehner equation. This procedure allows to estimate the solubility parameters for the samples,which turned out relatively low. The former results allowed us to present a structural model forsolid asphaltenes. This model proposes the solids to be composed of inner aromatic cores thatare impermeable to solvents, surrounded by aliphatic moieties capable of incorporating solventsand swell. Kinetic dissolution experiments carried out with solvent swollen asphaltenes showconsistency with the proposed model.
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