Notes

Depending on the nature of the feed and the amount and type of the different heteroatoms (i.e., different reactivities compounds), specific hydro-treating processes have been developed. The reactions occurring during hydrotreating are hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodeoxygenation (HDO), hydrodearomatization (HDA), hydrodeme-tallization (HDM), and hydrodeasphaltenization (HDAs). In addition, the average molecular weight of the feed is lowered by hydrocracking (HDC), which can happen without a substantial loss in liquid product yield, as in the HDT of light distillates, or with moderate or severe reduction of molecular weight, such as in the case of heavy feeds. To accomplish the current and future stringent environmental regulations to produce clean fuels (e.g., ultralow sulfur fuel), the extent of each reaction needs to be maximized either to obtain the final product or to prepare feeds for subsequent processes. To do that, researchers have focused their attention on the optimization of catalyst properties and composition and also on hydrotreating reactor and process design (Rana et al., 2007). As for reactor and process design, each process is optimized individually according to the nature and boiling range (i.e., physical and chemical properties) of the feed to be hydrotreated, for which reaction conditions and reactor type and configuration are the most important features to be considered. The severity of reaction conditions depends on the type of feed and on the product quality desired. In general, the higher the boiling point of the feed, the higher the reaction severity.