Gaining a better understanding of the properties of heavy products

Heavy crudes and oil residues produced by successive distillations have the specific characteristic of containing a high concentration of heavy, aromatic species called asphaltenes. Their aggregation properties are the source of their high viscosity and low mobility in catalytic networks.

Joëlle Eyssautier PhD student Applied Chemistry and Physical Chemistry	Loïc Barré Applied Chemistry and Physical Chemistry loic.barre@ifpen.fr	Didier Espinat Expert Director Products Analysis and Characterization didier.espinat@ifpen.fr

Hierarchized aggregation mechanisms govern the association of asphaltene molecules.
A detailed description of these mechanisms — on a nanometric lengthscale, in particular — would help to improve our understanding of the transport and refining steps.

To this end, IFPEN is using radiation small-angle scattering (neutrons, SANS and X-rays, SAXS), enabling observation of colloidal systems over a broad range of scales, from the nanometric to the micron lengthscale. In addition, each type of radiation “sees” matter differently, making the methods complementary. Hence, combination of SANS and SAXS measurements on large facilities instruments (LLB, ILL, ESRF), combined with variation of experimental conditions, led to identification of a fine organization of matter over regions with distinct chemical compositions. These asphaltene nanoaggregates are best depicted by a disc structure composed of a dense, aromatic core, surrounded by an aliphatic shell. The average size is around 32 Å radius, whereas the height corresponds to a stacking of 3 aromatic molecules.

Knowledge of the small-scale structure of these materials is the basis for description and modeling of their functions. On the basis of this characterization, the mechanisms governing viscosity, temperature behavior and diffusion properties can be explained.

Diagramdepicting an asphaltene nanoaggregate described by SANS contrast variation and SAXS.

Publications

• L. Barre, S. Simon, T. Palermo, Solution properties of asphaltenes, Langmuir, 24 (2008), p.3709–3717. DOI: 10.1021/la702611s
• J. Eyssautier, P. Levitz, D. Espinat, J. Jestin, J. Gummel, I. Grillo, L. Barré, Insight into Asphaltene Nanoaggregate Structure Inferred by Small Angle Neutron and X-ray Scattering, J. Phys. Chem. B, 115 (2011), p.6827–6837. DOI: 10.1021/jp111468d

>> See also IFPEN Publications database