Standardized High-Performance Liquid Chromatography to Replace Conventional Methods for Determination of Saturate, Aromatic, Resin, and Asphaltene (SARA) Fractions

Abstract

One of the main approaches for compositional analysis of crude oils is SARA fractionation in which the sample is separated into saturate, aromatic, resin, and asphaltene fractions based on their polarity. A fully automated standardized SARA analysis for bitumen and heavy crudes has been developed and optimized using three commercial columns packed with different stationary phases based on the combination of adsorption and partition chromatography. The system is equipped with automated six-, eight-, and ten-port switching valves that control the flow direction. In this analytical technique, a bitumen (or heavy oil) sample diluted in toluene is swept through the column by pentane as the primary carrier phase. The sample is separated into four fractions by selective retention through interactions with the solvent mobile phases and the column stationary phases. The poly(tetrafluoroethylene) (PTFE) column filters asphaltenes, ZORBAX CN absorbs resins, and ZORBAX RX-SIL retains aromatics. Three samples of bitumen and heavy oils were fractionated to their SARA fractions by the developed method. Consistent results were obtained, proving the applicability of the new analytical technique to a wide range of crude oil samples. In addition, the performance of the developed SARA high-performance liquid chromatography (HPLC) method was compared with the conventional method, which demonstrates that it is more efficient, cost-effective, and consistent.