(451c) Small-Angle Scattering Investigation of the Fractal Structure of Petroleum Asphaltenes

Asphaltene fractal clusters can be destabilized by changes in the composition, pressure, and/or temperature of a petroleum mixture [1,2]. It is well known that asphaltenes self-assemble into large-scale and thermodynamically stable fractal clusters [1,2]; however, the mechanism of this assembly and why the size terminates on the nanometer length scale is currently unclear. In order to better understand the effect of solvent environment on the fractal structure and interaction of asphaltenes, small angle scattering (SAXS) and ultra-small angle x-ray scattering (USAXS) experiments were performed to identify the fractal clusterâ??s size, shape, and molecular weight in various solvents and mixtures. This talk will first present SAXS results of asphaltenes as a function of concentration in various solvents and anti-solvents generated on beamline 12-ID-C at the Advanced Photon Source at Argonne National Lab. Understanding how solvents and anti-solvents influence the fractal dimension and dissociation of asphaltene clusters is critical in understanding the asphaltene destabilization mechanism. The SAXS experiments were designed to understand the thermodynamics of the asphaltene nanoaggregate and cluster association/dissociation process. USAXS results generated on beamline 9-ID-C will also be presented to explore the asphaltene precipitation process. Because USAXS is able to detect a wider range of scattering vectors (q), both soluble and precipitating asphaltenes with larger length scales can be observed. Overall, this study can provide an improved understanding of the solventâ??s influence on the structure and association of asphaltenes.

[1] Hoepfner, M. P., Fávero, C. V. B., Haji-Akbari, N., and Fogler, H. S, â??The fractal aggregation of asphaltenes,â? Langmuir, vol. 29, 2013, pp. 8799â??808.

[2] Hoepfner, M. P., and Fogler, H. S., â??Multi-scale Scattering Investigations of Asphaltene Cluster Breakupâ?, Langmuir, vol. 29, 2013, pp. 15423â??15432