Impact of Feedstock Properties on the Deactivation of a Vacuum Gas Oil Hydrocracking Catalyst

Abstract

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.

Impact of Metal Content on the Deactivation of a Bifunctional Hydrocracking Catalyst

“…Since no meaningful differences were observed in sintering or depromotion between the spent samples (Supporting Information Table S1, TEM analysis), this behavior was attributed to a higher coke buildup with the reference catalyst. In ref , we had already observed a strong correlation between the amount of coke formation and the loss of hydrogenation activity. The coke deposition is determined by the metal/acid (M/A) balance.…”

“…It seems that the nitrogen in the coke is the main cause of the decrease in residual cracking activity. We had already pointed out in our previous work that the residual acidity of the catalyst was decorrelated from the total coke content and specifically related to nitrogen compounds.…”

“…Unsaturated coke precursors produced on the acid sites undergo polymerization reactions before being hydrogenated, and successive dehydrogenation reactions occurred on metal sites leading to partially hydrogenated intermediates that combine to form coke. The formed coke deactivates both functions, but in a more significant way for the hydrogenation function, 51 since the cracking function is mainly affected by the nitrogen compounds. This phenomenon leads to a negative feedback loop, which is illustrated in Figure 15.…”

Effect of Phosphorus and Zinc on the Catalytic Performance of CoMo/Al₂O₃ for Mild Hydrocracking of VGO

“…The coke content of the catalyst gradually increased with depth in the catalyst bed, as hydrogen has been consumed by the reaction resulting in lower hydrogen pressure at the bottom of the catalyst bed 5) . Feed content of nitrogen and aromatic com- pounds also affects the amount of hydrogen consumption 17) . Experiments with different operating conditions such as reaction temperature or hydrogen pressure and measurement of the coke precursor asphaltene removal ratio indicated that effective utilization of limited hydrogen contributed to coke suppression 21) .…”

Enhancing the Performance of a Ptpd/Hy Catalyst for Hdpe/Vgo Hydrocracking Through Zeolite Desilication

“…Besides, to obtain a pure bifunctional behavior, these functions must be well-balanced to provide an appropriate cracking/hydrogenation balance [19,20]. The composition of the catalysts has been tuned to maximize the formation of fractions with commercial interest, such as naphtha and diesel, from secondary refinery streams like VGO (vacuum gasoil) [21,22]. However, for hydrocracking neat plastics or plastics blended with secondary refinery streams it is necessary to develop new catalysts specifically designed for this purpose.…”