Oxidative Desulfurization of Heavy Gas Oil over a Ti–TUD-1-Supported Keggin-Type Molybdenum Heteropolyacid

Abstract

Catalytic oxidative desulfurization (ODS) is emerging as a potential alternative to deep hydroprocessing as a result of its milder operating conditions and no hydrogen requirements. In this study, ODS catalysts based on a mesoporous TUD-1 support were developed to overcome the diffusion limitation of zeolite-based catalysts in oxidizing large-size organosulfur compounds present in real petroleum feedstocks. Different mesoporous oxidation catalysts were formed by substituting Ti in the TUD-1 framework and impregnating Keggin molybdenum heteropolyacid (HPA) on the TUD-1 support. The mesoporosity of TUD-1 and the presence of Ti(IV) and Mo Keggin units in the prepared catalysts were confirmed from the characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption near edge structure, and Brunauer−Emmett−Teller N 2 surface area analyses. The ODS performance of catalysts was studied using a mild hydrotreated bitumen-derived heavy gas oil feedstock. The HPA-dispersed Ti−TUD-1 catalyst was found to be most active for desulfurizing the heavy gas oil feedstock as a result of a strong synergy effect of Ti and Mo Keggin ions on catalyzing oxygen transfer from an oxidant to a substrate. Oxidants, such as hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and molecular oxygen, were screened in this study. The first two oxidants were better than others and equally efficient. The HPA/Ti−TUD-1 catalyst was found to be suitable for ODS and oxidative denitrogenation (ODN) in both the batch stirred-tank reactor and continuous fixed-bed reactor systems.

Oxidative Desulfurization of Tire Pyrolysis Oil over Molybdenum Heteropolyacid Loaded Mesoporous Catalysts

“…In both series, the promotion effect of Ti reaches its optimum when the Ti/Si(Al) ratio is 0.025. A similar promotional effect of Ti on the ODS activity of HPMo with heavy gas oil was observed in our earlier study [37]. The optimum catalysts of both series, which were identified in ODS of LGO were tested for ODS of tire pyrolysis oil.…”

“…The optimum catalysts of both series, which were identified in ODS of LGO were tested for ODS of tire pyrolysis oil. As shown in Figure 7 promotional effect of Ti on the ODS activity of HPMo with heavy gas oil was observed in our earlier study [37]. The optimum catalysts of both series, which were identified in ODS of LGO were tested for ODS of tire pyrolysis oil.…”

“…Textural properties such as the BET surface area, pore volume, and BJH pore diameter of the supports and their respective catalysts as determined by N2 physisorption are given in Table 3. The loading of the phosphomolybdic acid reduces the surface area and pore volume of supports significantly due to the filling of mesopores by the Keggin anion (large cluster of twelve MO6 octahedra), which has a kinetic diameter of around 1.2 nm [37]. The NH 3 temperature-programmed desorption study was carried out to quantify the total acidity of HPMo/Ti-TUD-1 and HPMo/Ti-Al 2 O 3 catalysts.…”

“…Generally, TBHP is a stronger oxidant than H 2 O 2 . However, the efficiency of an oxidant in an ODS reaction over a mesoporous catalyst depends on its diffusion rate through mesopores and its ability to interact with the Mo = O of heteropoly acid to form hydroperoxymolybdate [37]. Since TBHP is bulkier than H 2 O 2 , its diffusion ability through its mesoporous structure and its rate of hydroperoxymolybdate formation are expected to be slower than H 2 O 2 .…”

“…The ODS reaction is shown in Figure 10, where the transfer of oxygen from hydrogen peroxide to sulfur compounds is facilitated by a catalyst to form sulfone and sulfoxide. The reaction mechanism of ODS over HPMo/Ti-TUD-1 was discussed in detail in our previous publication [37]. Since hydrogen peroxide is used in excess for ODS, the reaction kinetic is assumed as the zero-order to an oxidant [41,42].…”