Solvent and Concentration Effects Governing the Hierarchical Organization of Asphaltenes: A Small-Angle X-Ray Scattering Study

Asphaltenes are a group of planar molecules found in crude oil and are prone to aggregation which causes blockage of pipes along the oil production stream. The solution-state nanostructure of various asphaltene solutions was studied using small-angle x-ray scattering (SAXS) (over a Q-range of 0.008 - 0.4 Å^-1) in order to understand solvent and concentration effects on asphaltene hierarchical organization. The fractal aggregate structure of asphaltenes was characterized as a function of concentration in toluene (1-50 mg/ml), tetrahydrofuran (1-500 mg/ml), and benzene (1-100 mg/ml). In toluene, the varying cutoff length, primary radius parameters, and the growing mass fractal dimension, all suggest that at a certain chain length, asphaltene nano-aggregates (NA) begin to collapse onto themselves to form a larger and denser aggregate. The experimental data has also been fit with several models including the Unified Power Law and the Ellipsoidal/Spherical Hayter Mean Spherical Approximation models to compare their characteristic parameters such as the ‘Guinier Radius’ and ‘Porod Slope’ to develop a consistent view of the hierarchical structure of asphaltene which will aid as a valuable input to develop strategies to mitigate the effects of asphaltene aggregation.