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A new fully automated saturates, aromatics, resins, and asphaltenes (SARA) separation for asphalt bitumen and petroleum residua has been developed and optimized. This system performs separations on 2 mg sample portions utilizing four columns packed with different stationary phases. The direction of solvent flow is controlled by automated four-port and six-port switching valves. The asphaltenes precipitate out of solution within a ground polytetrafluoroethylene (PTFE) packed column in an excess of heptane. The heptane-soluble maltenes pass through glass beads, aminopropyl bonded silica, and activated silica packed columns where chromatographic separation of the maltenes occurs. The saturates material is not retained, and it passes through all three adsorption columns. The more highly polar and pericondensed aromatic resins are retained by the glass bead column, and the remaining resins are adsorbed on the aminopropyl silica column. The glass bead column minimizes irreversible adsorption of resins by preventing the more polar resins from reaching the aminopropyl silica column. The aromatics are adsorbed on the activated silica column. In the next step of the method, the asphaltenes are selectively redissolved from the PTFE column with cyclohexane, toluene, and methylene chloride:methanol (98:2 v/v), yielding highly alkyl substituted asphaltene components, less alkyl substituted pericondensed aromatic asphaltenes, and precoke pericondensed aromatic asphaltenes, respectively. In the final steps, the aromatics and resins are eluted from their respective columns. An evaporative light scattering detector is used to quantify the amounts of each fraction, and an optical absorbance detector set at 500 nm records the relative amounts of pericondensed aromatic material with extended π systems that absorb visible light contained within the eluting fractions. The entire system is regenerated to the original column activity with a toluene and heptane solvent flush sequence, prior to the next injection. An automated separation is performed every four hours compared to several days for a corresponding gravimetric manual method.

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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.

The tendency of the asphaltenes to form aggregates in hydrocarbon solution is one of their most characteristic features and has tended to complicate the determination of the structure of petroleum. In addition, if the composition and properties of the precipitated asphaltenes reflect those of the micelles in solution, the latter should be considered as mixed micelles. This is a reasonable assumption in view of the large quantities of soluble resins found in the precipitated solid.Empirical observations indicate that the resins play an important role in stabilizing asphaltenes in crude oil and under unfavorable solvent conditions the asphaltene species are prone to further aggregation into clusters that are unstable and precipitate from the crude oil. It is also suggested that the resins and the asphaltenes from a particular crude oil have points of structural similarity relative to the asphaltenes and resins from another crude oil. On a more localized scale, i.e. in one particular crude oil there are also structural differences within the constituents of asphaltenes and structural differences within the constituents of the resins are also anticipated.Therefore, the structure of the micelles within anyone crude oil must be expected to be varied and non-homogenous. From the evidence cited herein, it follows that the potential for graphite-type stacking by the asphaltene molecules in the center of a micelle might not be as great as the potential for the micelles forming by asphaltene-resin interactions rather than by asphaltene-asphaltene interactions.