Identification of Refractory Weakly Basic Nitrogen Compounds in a Deeply Hydrotreated Vacuum Gas Oil and Assessment of the Effect of Some Representative Species over the Performance of a Ni–MoS₂/Y-Zeolite–Alumina Catalyst in Phenanthrene Hydrocracking

Abstract

Heavy crude oil processing leads the way in current refining. These crudes yield larger amounts of distillable heavy fractions such as vacuum gas oil (VGO). VGO must be treated in at least two refining units: a hydrotreating unit where sulfur, nitrogen, and other heteroatoms are removed, and a hydrocracking unit where suitable fuels are obtained. Removal of heteroatoms during hydrotreating, particularly, nitrogen, dictates the efficiency of hydrocracking. In the first part of this work, the nature of refractory nitrogen-containing compounds on the performance of a hydrotreating catalyst was evaluated. To achieve this goal, both a VGO and its hydrotreated counterpart were studied using electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Weakly basic N-containing compounds, namely, heavy pyrrolic-like compounds and their partially hydrogenated derivatives, were found to be the most refractory to hydrotreating. These compounds are weakly basic compared to most nitrogen compounds present in VGO. Considering this finding, the second part of the work was devoted to assessing the effect of pyrroles on the reactivity of phenanthrene over a Ni–MoS2/Y-zeolite–alumina two-stage hydrocracking catalyst. Tests were carried out in a fixed-bed reactor using mixtures of carbazole and tetrahydrocarbazole. Results showed that these compounds can affect the catalytic performance of Ni–MoS2/Y-zeolite–alumina by reducing its activity and inhibiting its selectivity to hydrocracking products. These findings draw attention to the possible role of weakly basic nitrogen compounds in the catalytic performance of materials employed for two-stage hydrocracking units.

In Situ IR‐ATR Study of the Interaction of Nitrogen Heteroaromatic Compounds with HY Zeolites: Experimental and Theoretical Approaches

“…Such interactions should also alter the surface chemistry of these materials and thus block the Brønsted acid sites. These findings draw attention to the possible role of weakly basic nitrogen compounds that can modify the catalytic performance of zeolitic materials employed for hydrocracking units …”

“…[10][11][12] Nonetheless, the effect of nitrogen heteroaromatics such as indoles (pKa Indole-H + /Indole = À 3.6), carbazoles, benzocarbazole over hydrocracking catalysts has only been recently put in evidence. [4,9] Indeed, a previous work confirmed that weakly basic nitrogenates are the most abundant nitrogenates in a hydrotreated vacuum gas oil (ca. 20 ppm of total nitrogen content).…”

“…Understanding the interaction of nitrogen heteroaromatic compounds over zeolite‐catalysts is a key to improve their design and enhance their application in the chemical industries . The interaction of nitrogen heteroaromatics with zeolites has been amply studied within the frame of refining processes such as hydroprocessing and hydrocracking . Among these compounds, pyridine and indole‐type molecules are commonly present in the petroleum feedstocks of the refineries .…”

“…Indeed, a previous work confirmed that weakly basic nitrogenates are the most abundant nitrogenates in a hydrotreated vacuum gas oil (ca. 20 ppm of total nitrogen content) . Even at such a low concentration level, these compounds reduced the catalytic activity and influenced the selectivity of the employed catalyst .…”

“…[1] The interaction of nitrogen heteroaromatics with zeolites has been amply studied within the frame of refining processes such as hydroprocessing and hydrocracking. [2][3][4][5][6] Among these compounds, pyridine and indole-type molecules are commonly present in the petroleum feedstocks of the refineries. [7] They are recognized to exert inhibitory or poisoning effects over the activity and selectivity of zeolite-based catalysts employed in hydrocracking units.…”