Effect of Chemical Composition on Asphaltenes Aggregation

1 H DOSY NMR experiments were used to investigate the macrostructure of the asphaltenes of Maya, Athabasca, and Buzurgan feedstocks in toluene- d 8 at 20 °C. The influence of the concentration of asphaltenes on their diffusion coefficients is presented for the three asphaltenes. A separation between two classes of aggregates—one diffusing quickly and one diffusing more slowly—was observed at an onset concentration that is dependent upon the origin of the sample. This illustrates that the chemical interactions (and, hence, the chemical structures) are different for the three asphaltenes. Because asphaltenes are a continuum of both archipelago and continental asphaltenes, the interactions in the solutions differ, depending on the repartition between archipelago- and continental-type asphaltenes in the feed. Maya and Buzurgan asphaltenes show similar diffusion properties in the dilute regime, while Athabasca asphaltenes diffuse more slowly. Results obtained from DOSY experiments data seem to indicate that Buzurgan asphaltenes show a more continental character than the two other asphaltenes, while Athabasca asphaltenes seem to contain more archipelago asphaltenes. 1 H and 13 C NMR experiments were also performed to determine the average structural parameters of asphaltenes. Average sizes and molecular weights were determined from the 1 H-DOSY NMR diffusion coefficients and compared to size exclusion chromatography (SEC) data.