The Automated Asphaltene Determinator Coupled with Saturates, Aromatics, and Resins Separation for Petroleum Residua Characterization

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.