Athabasca asphaltenes were characterized using small-angle X-ray scattering (SAXS). Two methods were used to separate asphaltenes from the Athabasca bitumen: namely, chemical separation by precipitation with n-pentane and physical separation by nanofiltration using a zirconia membrane with a 20 nm average pore size. The permeate and chemically separated samples were diluted in 1-methylnaphtalene and n-dodecane prior to SAXS measurements. The temperature and asphaltene concentration ranges were 50À310 °C and 1À10.4 wt %, respectively. Model-independent analysis of SAXS data provided the radius of gyration and the scattering coefficients. Model-dependent fits provided size distributions for asphaltenes assuming that they are dense and spherical. Model-independent analysis for physically and chemically separated asphaltenes showed significant differences in nominal size and structure, and the temperature dependence of structural properties. The results challenge the merits of using chemically separated asphaltene properties as a basis for asphaltene property prediction in hydrocarbon resources. While the residuals for model-dependent fits are small, the results are inconsistent with the structural parameters obtained from modelindependent analysis.
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