ABSTRACT
This paper is a selective review of new approaches and emerging technologies for ultra-clean (ultra-low sulfur) diesel fuels. The issues of diesel deep desulfurization are becoming more serious because some crude oils are higher in sulfur contents, while the regulated sulfur limits are becoming lower and lower. Deep reduction of diesel sulfur (from 500 to < 15 ppmw sulfur) is dictated largely by 4,6-dimethyldibenzothiophene, which represents the least reactive sulfur compound that have substitutions on both 4- and 6- positions. The deep HDS problem of diesel streams is exacerbated by the inhibiting effects of co-existing polyaromatics and nitrogen compounds in the feed as well as, H2S in the product. New and more effective approaches and continuing catalysis and processing researches are needed for producing affordable ultra-clean diesel fuels, in order to meet the new government sulfur regulations in 2006-2010. Desulfurization research should also take into consideration the fuel-cell fuel processing needs, which will have stringent requirement on desulfurization.