PRODUCTION OF ULSD: CATALYSTS, KINETICS AND REACTOR DESIGN

摘要

This paper presents an overview of the critical factors governing the production of ultra low sulfur diesel (ULSD) i.e. diesel fuel with less than 50 ppm sulfur. To produce ULSD it is necessary to remove the most refractive sulfur compounds, which are certain alkyl-substituted dibenzothiophenes. Alkyl-substituted dibenzothiophenes are desulfurized via one of two routes: by direct extraction of the sulfur atom, or by hydrogenation of one of the aromatic rings followed by sulfur extraction. Factors affecting the relative rates of reaction for the two routes are discussed, in particular the inhibiting effect of certain nitrogen containing components of diesel oils on the hydrogenation route. CoMo catalysts are generally more active for the direct desulfurization route, whereas NiMoP catalysts show relatively higher activity for the hydrogenation route. The consequences for ULSD are demonstrated through a number of cases studies, which serve to illustrate the effect of catalyst choice on required catalyst volume, hydrogen consumption and product properties. The case studies are used to discuss the merits of revamps versus grassroots units. Many diesel hydrotreaters suffer from poor liquid distribution resulting in poor catalyst efficiency. Examples are given from industrial operation of how the application of state-of-the-art reactor internals improves reactor performance.