Improved class separation by GC x GC of volatile hydrocarbons with an unconventional increase in the second dimension plate number

Abstract

Light petroleum fractions are produced during crude and synthetic oil refining processes and are upgraded to useful products in various markets. These fractions are upgraded using various refining processes, and the characterization of these fractions is essential for process control and ensuring final product specifications. These light fractions can be very complex and multidimensional gas chromatography (GC × GC) is used to characterise these complex samples. ASTM method D1319, Fluorescent Indicator Adsorption (FIA), is used routinely for the determination of the total volume percent of saturates, olefins and aromatics in petroleum fractions and is used in the certification of final gasoline products. There would be several advantages if chemical group-type separation for gasoline can be achieved on GC × GC. Even though excellent GC × GC chemical group-type separation has been achieved, the separation of ≤C6 aliphatics (alkanes, alkenes and cyclic alkanes) in light fuels like gasoline remains a challenge with insufficient resolution between these compounds. In this study, the GC × GC parameters for the optimum separation of the ≤C6 aliphatics were determined with group-type separation of light fuels in mind. The study showed that it is possible to achieve this separation under GC × GC wrap-around conditions whereby two modulations of analytes are moving through the second dimension column at any time, allowing for the use of 2 - 4 times longer second dimension columns. For the first time the optimum separation of the ≤C6 aliphatics were determined while maintaining good separation for the heavier hydrocarbons. Good GC × GC chemical group-type separation for gasoline samples was obtained with this method. Quantitative results, combined with bromine number analysis, compared well with the results obtained by the FIA method.

HIGHLIGHTS • GC × GC parameters for the optimum separation of the ≤C6 aliphatics were determined. • Separation under GC × GC wrap-around conditions, allowing longer 2nd dimension columns. • GC × GC chemical group-type separation for gasoline samples obtained with this method. • This method potentially provides an alternative to the FIA method.