Colloidal macrostructure of crude oil studied by neutron and X-ray small angle scattering techniques

The asphaltenes and heavy oils are known to have a colloidal structure. We used small angle neutron and X-ray scattering in order to analyse different suspensions as : * asphaltenes in different solvents, and at different temperatures (same conditions for resins) * mixture of resins and asphaltenes * vacuum residu (noted VR) at different temperatures and from different origins. We obtained that asphaltenes are flat aggregates whose size and molecular weight mainly depend on the solvent and on the temperature. In fact by increasing the temperature, the molecular weight decreases, or by adding n-heptane in solution, the molecular weight increases. We noticed the same effects on resins suspensions, and by using SANS experiments, we remarked that the resins suspensions are heterogeneous. By mixing the two solutions, we saw a solvent effect which corresponds to a smaller asphaltene entity. The more we add resins, the smaller is the asphaltene molecular weight. We noticed also that the curve of the VR in solvent is the same as the resins in the same conditions. Pure VR curves demonstrate an important concentration fluctuation which desappears when temperature increases ; the system becomes more homogeneous