New developments in hydrocracking: low pressure high-conversion hydrocracking.

Abstract

Hydrogen partial pressure is a key parameter for distillate hydrocracking processes. There are two types of distillate hydrocracking processes. Mild hydrocracking is an improved vacuum gas oil hydrotreatment process with a relatively low conversion, which operates at hydrogen pressures usually less than 50 bars. Total conversion hydrocracking operates at hydrogen pressures of more than 100 bars. It is thus obvious that hydrogen pressure is a key parameter for hydrocracking performances. By looking at the different reactions taking place in the hydrocracking process, we try to explain this effect from thermodynamic and kinetic standpoints. For instance the hydroconversion of n-heptane has a negative order with respect to hydrogen pressure, when this order is positive for the conversion of a vacuum gas oil. We present pilot data showing the great influence of a first step hydrotreatment of a VGO on the second hydrocracking step. We demonstrate also the possibility of achieving very high conversion when operating at “medium pressure” (i.e. around 70 bars) with a recently developed zeolite hydrocracking catalyst.