Asphaltene Precipitation from Heavy Oil Diluted with Petroleum Solvents

Heavy oils are sometimes diluted with petroleum solvents for pipeline transportation, and it is necessary to ensure that the selected solvent does not precipitate asphaltenes from the oil. The modified regular solution (MRS) model can predict asphaltene precipitation from heavy oil diluted with pure n-alkanes but has not yet been applied to petroleum solvents. To do so, asphaltene precipitation data were measured for bitumen diluted with petroleum solvents including gas condensates, diesels, kerosene, and naphtha and their blends with n-heptane. The petroleum solvents were characterized into single carbon number (SCN) fractions on the basis of gas chromatography assays. New correlations were proposed for the molecular weight, density, and solubility parameters of the SCN fractions. The MRS model with the characterization and correlations matched asphaltene precipitation data with an average absolute deviation of 0.7 wt % for petroleum solvents with relatively low contents of pure aromatic and cyclic components (<3 wt %), that is, condensates, diesels, and kerosenes. The model failed to match asphaltene precipitation data from the naphtha which contained a significant fraction of pure aromatic and cyclic components (>10 wt %). Hence, the proposed model is currently limited to solvents similar to condensates, diesels, and kerosenes.

Automated summary

The study demonstrates that the modified regular solution (MRS) model can successfully predict asphaltene precipitation from heavy oil, but currently only applicable to petroleum solvents with relatively low contents of pure aromatic and cyclic components. For petroleum solvents with a higher proportion of pure aromatic and cyclic components, such as naphtha, the model fails to fully match experimental data.