(685a) Asphaltene-Solid Co-Aggregation Mechanism Investigated By Ultra-Small Angle X-Ray Scattering and in Situ Titration

Athabasca bitumen contains over 10% asphaltenes and around 1% inorganic solids following the froth extraction process. The previous results showed that the asphaltene precipitation rate increased significantly when inorganic solids were present in the mixture [1]. However, the co-aggregation mechanism is still unknown. Our preliminary results indicated there might exist two competitive mechanisms. Heterogeneous precipitation dominates at low insoluble asphaltene concentration, as more solids were found in precipitated asphaltenes. Homogeneous precipitation becomes the majority at high insoluble asphaltene concentration, as fewer solids are in precipitated asphaltenes. We aim to investigate the asphaltene-solid co-aggregation at low and high concentrations of insoluble asphaltenes. To profoundly understand the co-aggregation, ultra-small angle X-ray scattering (USAXS) was used to observe the interaction between nanometer-scale insoluble asphaltenes and solids. USAXS effectively probes the structural information, size, internal structure, overall shape, and surface morphology of clusters from 5 nm to 5 microns. Heptane was used as an anti-solvent and titrated into an asphaltenes-toluene solution at a different flow rate for precise control of the rate of asphaltene destabilization. The fast heptane titration rate leads to a high concentration of insoluble asphaltene in a short time, which is supposed to be an ideal condition for homogeneous precipitation in terms of the preliminary results. We are able to observe the homogeneous precipitation. Slowly heptane titration created an ideal condition for heterogeneous precipitation, propitious to exploring heterogeneous precipitation. This study has the potential to assistant us in controlling asphaltene-solid co-aggregation for more efficient removal of solids from bitumen during naphthenic froth treatment.

[1] Rapid Heterogeneous Asphaltene Precipitation with Dispersed Solids W Chaisoontornyotin, J Zhang, S Ng, MP Hoepfner - Energy & fuels, 2018