Asphaltene Determinator Method for Automated On-Column Precipitation and Redissolution of Pericondensed Aromatic Asphaltene Components^†

Abstract

The new on-column precipitation and redissolution separation technique developed at Western Research Institute (WRI) uses a continuous flow system to precipitate and redissolve various chemical species from oil. Although high-performance liquid chromatography (HPLC) equipment is used, the separation does not involve chromatographic adsorption mechanisms. Separations are conducted using a ground polytetrafluoroethylene (PTFE)-packed column, and they are strictly solubility-based. The asphaltene determinator method based on the new technique involves precipitation of asphaltene components from residua on the column using a heptane mobile phase. The precipitated material is redissolved at 30 °C in three steps using solvents of increasing solubility parameter: cyclohexane, toluene, and methylene chloride/methanol (98:2, v/v). This method has been optimized with rigorous daily quality control (QC) checks, and it is now in routine use. Several new applications for the method were demonstrated. These include monitoring pyrolysis severity during cracking reactions, determining total pericondensed aromatic (TPA) content, and providing profiles of the solubility distributions of the pericondensed aromatic components, including a new detailed characterization approach for asphaltene component molecules.