Assessing compositional changes of nitrogen compounds during hydrotreatingof typical diesel range gas oils using a novel preconcentration technique coupled with gas chromatography and atomic emission detection

This paper describes the identification of nitrogen-containing compounds in a typical feed for diesel oil hydrotreating and how their individual conce ntrations change upon hydrotreating over a conventional sulfided CoMo/Al2O3 catalyst at commercial conditions. A preconcentration procedure followed b y gas chromatographic (GC) analysis utilizing a highly sensitive nitrogen-s pecific detector (atomic emission detector) allowed the quantitative analys is of individual nitrogen-containing compounds (N compounds) at levels as l ow as 0.05 mu g N/mL. The nitrogen compounds in the feed and products were identified by comparison with reference compounds as well as by high-resolu tion GC/mass spectrometric characterization. The relative reactivities of i ndividual compounds in the diesel fuel feed were determined and the most re fractory compounds identified. Alkyl-substituted carbazoles were found to b e the major compound class in the feed and to be among the least reactive N compounds in the feed. Just as in the case of alkyldibenzothiophene hydrod esulfurization, carbazoles having alkyl substituents at positions adjacent to the nitrogen atom were found to be the least reactive N compounds in the diesel fuel feed for hydrodenitrogenation.