posted on 2021-07-09, 18:42authored byJuly C. Vivas-Báez, Gerhard D. Pirngruber, Alberto Servia, Anne-Claire Dubreuil, David J. Pérez-Martínez
The
aim of this study was to understand the impact of vacuum gas
oil (VGO) properties on the deactivation rate of a hydrocracking catalyst
(nickel–molybdenum sulfide dispersed on a carrier containing
USY zeolite). For this purpose, two hydrotreated feeds of different
densities, organic nitrogen (∼120–150 ppmw) and aromatic
content, were hydrocracked under operating conditions that favor catalyst
deactivation, that is, high temperature (T = 418
°C) and high space velocity (LHSV = 3 h–1).
The catalyst performance was followed by measuring the VGO conversion
(370 °C+ petroleum cut) and determining the apparent
kinetic constants for the main hydrocracking reactions (cracking,
hydrodenitrogenation, hydrodesulfurization, and aromatics hydrogenation).
The experiments were stopped after different times on stream (either
6 or 30 days) in order to assess the evolution of the catalyst as
a function of time. The spent catalysts, obtained from three different
reactor locations, were characterized by elemental and textural analyses
and by thermogravimetry to investigate the quantity and nature of
the coke formed. Catalytic tests with different model compounds (toluene
and n-heptane) were carried out to determine the
residual activity of the hydrogenating and acid catalyst functions.
It was found that, at the evaluated conditions, both the nature and
the content of organic nitrogen and aromatics compounds of the feedstock
have a determinant role in the deactivation rate. Organic nitrogen
determines the ratio between available metal and acid sites. The aromatics
generate coke precursors on the available acid sites. Both factors
play a coupled role that promotes coke deposition on the catalyst
surface, which leads to an increase in the deactivation rate on top
of the end boiling point of the feed.