Hydrotreating and deep hydrodesulfurization (HDS) have attacted increased attention recently due to the introduction of new legislation regarding fuel specifications.In order to meet these challenges,there is a need to modify and imporve existing reactors and processes and to introduce more active and selective catalysts.The removal of hte so-called sterically hindered sulfur-containing molecules,like 4,6 dimethyldibenzothiophene,is observed to be a key issue for deep HDS.Also the choice of reactor internals plays an important role for deep HDS.In order to guide rational catalyst developments,structure-activity relationships are desired and the Co-Mo-S model and the Bond Energy Model have been useful for describing many activity parameters for promoted catalysts and transition metal sulfides.It has also recently been shown that important new insight may be gained from density functional theory (DFT) calculations.The present article will focus on some of the current practicla and theoretical issues.
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