Reactivity and product selectivity in FCC and hydrocracking

Abstract

There is a wide variation in the concentration distribution of various compound types (paraffins, mono- and poly-cyclo¬paraffins, mono- and poly-cyclic aromatics) in vacuum gas oils from various crude oils. This variation in the compound type distribution has a significant influence on the design and operation of secondary catalytic conversion processes such as FCC and Hydrocracking. Specifically, the reactivities of various compound types differ significantly from one another. The consequences of differing reactivities is highlighted by a kinetic analysis of available pilot plant data for FCC and Hydrocracking, both with amorphous catalysts. Paraffins, especially straight chain compounds, are shown to have a significantly lower reactivity than say cyclo-paraffins and, therefore, the overall reactivity of highly paraffinic feedstocks is lower than that for feedstocks with a low concentration of paraffins. The influence of lower reactivity of paraffinic feedstocks is highlighted by kinetic computer simulations of the product yields in a hydrocracking reactor processing Kuwait and Bombay High Vacuum Gas Oils. To achieve maximum middle distillates, operation with Bombay High (highly paraffinic) will require operation at higher severity (say with in¬creased catalyst holdup) than with Kuwait VGO (lower paraffin content). The rationale for using zeolite based catalysts for maximizing middle distillates, in both FCC and Hydrocracking operations, to cater for highly paraffinic feedstocks is underlined in the discussions.