Inhibition and Deactivation of Hydrodenitrogenation (HDN) Catalysts by Narrow-Boiling Fractions of Athabasca Coker Gas Oil

Abstract

The hydrodenitrogenation (HDN) of quinoline in the presence of narrow-boiling fractions of Athabasca bitumen coker gas oil was studied over a commercial NiMo/γ-Al2O3 hydrotreatment catalyst. The study was conducted to determine whether trends in HDN activity with increasing boiling point were the result of the increased molecular weight of the Athabasca coker gas oil (i.e., changes in hydrocarbon structure) or due to the nitrogen species contained in the feedstocks. In each boiling-point range, the components in the gas oils demonstrated, to a varying degree, both reversible inhibition and deactivation of catalyst activity. The low-boiling gas oil fraction (bp. 343−393 °C) was more inhibitory and deactivated the catalyst to a greater degree than intermediate- (bp. 433−483 °C) or high-boiling (bp. 524 °C+) fractions for the HDN of quinoline. Nitrogen speciation analysis suggested that alkyl-carbazoles and tetrahydrobenzocarbazoles were the primary species responsible for the higher inhibition and deactivation observed in the lightest fraction. In addition, the HDN activity of the narrow-boiling fractions varied with hydrogen partial pressure and sulfur concentration, although these effects were independent of molecular weight. This study suggests that, although Athabasca coker gas oils have higher concentrations of polyaromatics, compared to conventional distillates, non-nitrogen-containing species are insignificant in inhibiting catalyst activity, in comparison to the organonitrogen compounds. Consequently, the resistance of the Athabasca coker gas oils to HDN can be attributed to the organonitrogen compoundsparticularly, alkyl-carbazoles and tetrahydrobenzocarbazolesrather than the aromaticity of the gas oils.