ABSTRACT
The crude oils that are being rened for the production of transportation fuels have become heavier and heavier. Because of this, many topping reneries have shut down because of their inability to process these heavier crude oils. In comparison, the total capacity of those processes that is intended for upgrading high-boiling distillates (such as residua) and heavy crude oils has increased (Speight and Ozum, 2002; Parkash, 2003; Hsu and Robinson, 2006; Gary et al., 2007; Speight, 2013, 2014). Furthermore, the growing dependence on high-heteroatom heavy feedstocks has emerged as a result of the continuing decreasing availability of conventional crude oil through the depletion of reserves in various parts of the world. Thus, the ever growing tendency to convert as much as possible of lower-grade feedstocks to liquid products is causing an increase in the total sulfur content in rened products. Reners must, therefore, continue to remove substantial portions of sulfur from the lighter products; however, residua and heavy crude oil poses a particularly difcult problem. Indeed, it is now clear that there are other problems involved in the processing of the heavier feedstocks and that these heavier feedstocks, which are gradually emerging as the liquid fuel supply of the future, need special attention.
