Hydrodenitrogenation of Petroleum

Abstract

A high level of hydrodenitrogenation (HDN) is required to achieve a desirable conversion of other hydroprocessing reactions. This results from a strong adsorption of nitrogen‐containing compounds on catalytic sites that slows down the hydrogen activation process and hinders the adsorption of other reactants. Studies on model compounds and real feeds indicate that less than 50 ppm of nitrogen in the feed can poison catalytic sites. Kinetic studies determined adsorption constants of various nitrogen‐containing compounds and concluded that at least four different catalytic sites are required to interpret experimental observations in contrast with a dual site site≅concept, which only considered two sites. The advancements in experimental techniques allowed identification of products formed during very early stages of hydrodenitrogenation. These results confirmed that the removal of the amino group from saturated amines, as the last step in hydrodenitrogenation, is governed by the type of carbon to which the amino group is attached rather than the number of hydrogen atoms attached to carbon in α and β position to nitrogen Performance of conventional Co(Ni)Mo(W)/Al2O3 catalysts during hydrodenitrogenation was enhanced by combination with various additives and by replacing the traditionally used γ‐Al2O3 support with novel supports. Catalytic functionalities could be modified by using different precursors of active metals and varying conditions during preparation. Progress has been made in the development of catalysts possessing a high selectivity for hydrodenitrogenation. In this case, the nonconventional catalysts based on the carbides and nitrides of transition metals exhibited high activity and selectivity. Noble metal sulfides alone or supported on different supports were active for HDN as well. Feedstocks used for catalyst evaluation included model compounds and mixtures of model compounds as well as real feeds. The challenges in the development of catalysts for hydrodenitrogenation of heavy feeds containing asphaltenes and metals have been identified.