DEEP DESULFURIZATION AND AROMATICS SATURATION FOR AUTOMOTIVE GAS-OIL MANUFACTURING

The strive towards a cleaner environment has lead to low sulphur specifications for middle distillate fuels. In addition compositional specifications are presently debated, Thus, to meet future emission standards regarding, specifically, particulates emissions, the motor industry calls for improved automotive gasoil (AGO) quality. Although this gasoil quality clearly effects diesel engine emissions it must be considered that it is less influential then engine design and maintenance. Sulphur, density and cetane number are the fuel properties having the greatest influence on diesel engine emissions while also aromatics and endpoint specifications have been defined in environmentally adopted governmental initiatives. This paper reviews the options which are available to tackle these new requirements. The high severity single stage concept (using conventional mixed sulphides catalysts) will be discussed in its potential to meet more severe product requirements as well as in terms of its limitations, especially at the point of aromatics saturation and cetane upgrading. In addition newly developed technologies for aromatics saturation in AGO manufacturing will be reviewed and their potential to break the limitations of the single stage concept discussed. As the first example of commercial scale aromatics saturation for AGO production the new Shell Middle Distillate Hydrogenation (SMDH) technology, applying a (semi) two-stage approach based on the Shell proprietary hydrogenation catalyst S-704, is described. The new S-704 catalyst is crucial in this process and allows a highly integrated mode of operation. It is characterised by a high tolerance to S and N and a high stability. A number of applications of this novel process are discussed, especially the production of environmentally adapted AGO from straight run light gasoil (SR-LGO) in Sweden, and the upgrading of cycle oils in premium quality middle distillates.