Characterization of nitrogen-containing compounds in heavy gas oil petroleum fractions using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry

Nitrogen (N)-containing compounds are naturally present in petroleum, and they are responsible for several deleterious effects that reduce the quality of products and negatively affect the processes involved in the upgrading of feedstock. The speciation of such compounds in petroleum heavy fractions is still a challenge. In the present work, N-containing compounds were characterized in heavy gas oil (HGO) fractions using a solid-liquid fractionation scheme and comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry. Classification and identification of compounds were carried out based on seven different categories of analytical information viz. retention times in first and second dimensions, analytical standards co-injection, the structured pattern of the separation space, the structured pattern of the separation space with the selection of specific m/z values, the library mass spectra match factor, and the characteristic deconvoluted mass spectra. All of these interpretations were available from a single analytical run followed by a standard injection. Compounds were extracted from the sample using an ion-exchange resin method to separate neutral and basic N-containing compounds, after a pre-fractionation step, using neutral aluminum oxide. This methodology allowed for the identification of 120 N-containing compounds and tentative identification of a further 108 compounds using their deconvoluted characteristic mass spectra as a basis for identification. Identified components included alkyl-indols, alkyl-carbazols, alkyl-benzocarbazols, alkyl-quinolines, alkyl-indene-pyridines, alkyl-benzoquinolines, and alkyl-dibenzoquinolines.