OVERVIEW

The conversion of large molecules to distillate fractions can also be achieved thermally without gaseous H ₂ being present as the reactant. For this purpose, both catalytic and non-catalytic processes have been used commercially. The former processes have been dominated by various modifications of the fluid catalytic cracking (FCC) process. In this process, H ₂ is being produced as the unwanted by-product rather than being used as reactant. Initially, the virgin VGO was the predominant feed for the FCC process. The main objective was the conversion of such feeds to a high octane number gasoline. This could be achieved by increasing the content of aromatics during FCC. Gradually, DAO has been introduced as the feed, either without or with pretreatment. In some cases, pretreatment of the feed was necessary to extend catalyst life in the FCC units. It usually involved hydroprocessing to remove asphaltenes and metals, as well as to decrease the content of aromatics and heteroatoms. Detailed accounts of the conventional FCC process, with emphasis on the feeds such as virgin VGO and pretreated DAO, was given by Venuto and Habib (800).

Frequent references to the FCC process over the preceding chapters were made with regard to testing and development of the catalysts for hydroprocessing of VGO, HGO, DAO and other heavy feeds to produce feeds which can be subsequently processed using the conventional FCC process. So, hydroprocessing was usually conducted to avoid extensive modifications of the conventional FCC process without which the direct utilization of...