Behavior of Nitrogen Compounds during Hydrotreatment of Khafji Atmospheric Residuum

Abstract

Khafji atmospheric residuum was hydrotreated over a NiO-MoO₃-Al₂O₃ catalyst to effect 82 and 48% removals of sulfur and nitrogen, respectively. Hydrocarbons and organic nitrogen compounds in the feed and the hydrotreated, product were characterized. After the hydrotreatment, the amount of asphaltenes was reduced by half, but its nitrogen content remained practically unchanged. The nitrogen content of maltenes in the hydrotreated product decreased to a half of that in the feed, whereas nitrogen in the light fractions greatly increased. Nitrogen type analyses by USBM-API 60 methods have revealed that the nitrogen compounds in the maltene of the feed mostly consist of pyrroles, amides, and pyridines and that the basic nitrogen compounds such as pyridines are easily removed by hydrotreatment. Pyrrole type nitrogen compounds were more refractory probably due to the adsorption of pyridines on the acidic catalyst surface in preference to pyrroles. When the contents in the produced distillate relative to those in the feed were compared, an increase in pyrrole type compounds and a great increase in basic nitrogen concentrations were observed. The trend should have resulted from hydrocracking of nitrogen compounds which were present in the maltene fraction of the feed. In contrast, amide compounds in the maltene were readily hydrocracked into hydrocarbons directly and thus without contamination of the distillate.