Complete elution of vacuum gas oil resins by comprehensive high-temperature two-dimensional gas chromatography.

The development of efficient conversion processes requires extended knowledge on vacuum gas oils (VGOs). Among these processes, hydrocracking is certainly one of the best suited to meet the increasing demand on high quality diesel fuels. Most of refractory and inhibiting compounds towards hydrocracking and especially nitrogen containing compounds are contained in a fraction of the VGO called the resin fraction, which corresponds to the most polar fraction of a VGO obtained by liquid chromatography (LC) fractionation on a silica column. However, the lack of resolution observed through existing analytical methods does not allow a detailed characterization of these fractions. A recent study showed that comprehensive high temperature two-dimensional gas chromatography (HT-GC×GC) methods could be optimized in order to elute heavy compounds. This method was implemented for the analysis of VGO resin fractions and complete elution was reached. Firstly, the method was validated through repeatability, accuracy, linearity and response factors calculations. Four VGO resin fractions were analyzed and their HT-GC×GC simulated distillation curves were compared to their GC simulated distillation (GC-SimDist) curves. This comparison showed that the method allows complete elution of most of the analyzed VGO resin fractions. However, a detailed characterization of these fractions is not yet obtained due to the very large number of heteroatomic and aromatic species that a flame ionization detector can detect. Current work aims at increasing the selectivity of GC×GC by using heteroatom selective detectors in order to improve the characterization of such products.

Overcoming the high-temperature two-dimensional gas chromatography limits to elute heavy compounds.

Overcoming high-temperature (HT) two-dimensional gas chromatography (GC × GC) limits is critical for the analysis of heavy hydrocarbons, particularly those contained in heavy petroleum fractions. To reach this goal, HT-GC × GC analysis was adapted from HT-GC Simulated Distillation (HT-GC SimDist) operating conditions as this analysis embraces compounds whose boiling point ranges from 35 °C to 700 °C and from a previous study that enabled the elution of linear alkane nC(60) and tetraaromatic compounds by HT-GC × GC. This paper shows that HT-GC × GC analysis using CO(2) cryogenic modulator and short wide bore columns with a thin film of stationary phase allows the elution of linear alkanes up to nC(68) (641 °C) as well as of highly aromatic hydrocarbons like coronene. Furthermore, compared to previous studies, an on-column injector was used to reduce discrimination of high boiling point compounds.