Colloidal Structure of Asphaltene Solutions and Heavy-Oil Fractions Studied by Small-Angle Neutron and X-Ray Scattering

Abstract

ABSTRACT Asphaltene and heavy oil colloidal structure were studied by small angle X-ray and neutron scattering (SAXS – SANS). Different suspensions were analysed: *asphaltene after n-heptane precipitation; effect of different good solvents on the asphaltene macrostructure, effect of n-heptane on the state of molecular aggregation, temperature effect.*resins, after fractionation, in solution in toluene, and effect of the addition of a small amount of n-heptane,*in order to precise the effect of resins on asphaltenes in solution, we studied mixtures of the two kinds of molecules,*Safanya vacuum residuum (VR), we foccussed our attention on the effect of temperature. We have shown that asphaltene are flat aggregates whose size and molecular weight mainly depend on the solvent and the temperature. As temperature increases, we noticed a decrease of the molecular weight; then asphaltenes follow an aggregation equilibrium. The n-heptane addition induces an increase of the molecular weight. The resins behavior is singular; SANS experiments showed that resins suspensions are heterogeneous, exhibiting concentration fluctuations. As temperature increases, the system becomes more homogeneous. We observed a decrease of the asphaltene molecular weight when we added a small amount of resins. Scattering spectra of VR dilutions in toluene are quite similar to those of pure resins in the same solvent and at comparable concentrations. Pure VR exhibits a very strong scattering at small Q-values which suggest important density fluctuations in the medium. As temperature increases, the scattering decreases due to more homogeneous system.