Automated High-Performance Liquid Chromatography for SARA Analysis (SARA-HPLC)

Abstract

SARA analysis is widely used to separate crude oil components to saturate, aromatic, resin, and asphaltene fractions. Despite the continuous improvement of the current methods, they are still suffering from insufficiencies in providing fast, accurate, and repeatable results. In this study, an automated SARA high-performance liquid chromatograph (SARA-HPLC) is developed and evaluated to overcome the aforementioned limitations and enhance SARA analysis. The developed system is equipped with three columns packed with different stationary phases, including poly(tetrafluoroethylene) (PTFE), silica, and cyano, connected by automated six-port switching valves that can control the flow path of solvents. The system utilizes propane to sweep the primary carrier phase toward a flat and smooth baseline. A sample of 50 μL (bitumen dissolved in toluene) is passed through the columns where chromatographic separation of maltenes occurs. The asphaltene fraction precipitates on PTFE due to excess pentane, resins are adsorbed by the cyano column, and aromatics are retained on the activated silica column. After sweeping the primary carrier phase (n-pentane) using propane, the fractions are eluted from their columns by applying toluene and consequently sent to an ultraviolet light (UV) detector for analysis. The system can be run unattended and automatically, and each run needs 3 h, including system preparation. The obtained results verify that the developed analytical approach is fast, cost-effective, repeatable, and more precise than current SARA analysis methods.

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

“…In our previous study, the fully automated HPLC system was equipped with three columns that were preparative (manually packed) in our lab with silica, cyano, and PTFE to separate asphaltenes, resins, and aromatics, and the fraction that was not adsorbed by these three columns was quantified as saturates. 10 …”

“…In our previous study, the fully automated HPLC system was equipped with three columns that were preparative (manually packed) in our lab with silica, cyano, and PTFE to separate asphaltenes, resins, and aromatics, and the fraction that was not adsorbed by these three columns was quantified as saturates. 10 Silica has an active, hydrophilic surface that contains acidic silanol functional groups. The polarity of the silica surface can be transformed selectively by chemically bonding it to its less polar functional groups such as cyanopropylsilyl [CN], noctylsilyl [C8], and n-octadecylsilyl [C18, ODS] moieties on silica, in order of decreasing polarity.…”

“…For brevity, further details of UV−vis spectral results are explained elsewhere. 10 Automation: Pump and Valve Programs. A CLICK PLC (programmable logic controller) supplied by Automationdirect was programmed and utilized; therefore, timing can be set, and the analysis can be performed fully automatically.…”

“…Also, this method has been extensively criticized due to the requirement of excessive time and resources, poor reproducibility, and automation issues. 10 − 12 …”

“…Recently, we developed an automated SARA high-performance liquid chromatography (SARA-HPLC) method to improve the efficiency, accuracy, and reproducibility of the group-type characterization of heavy oil and bitumen where poly(tetrafluoroethylene) (PTFE), silica, and cyano columns were nonstandard preparative (packed manually). 10 However, preparative columns do not allow adequate replication of the developed analytical method by other researchers since the packing procedures may vary. To standardize the developed SARA-HPLC and make it reproducible by other researchers, in this work, we introduce standard commercially available packed columns.…”