Deep oxidative desulfurization with task-specific ionic liquids: An experimental and computational study

High Oxidation Desulfurization of Fuels Catalyzed by Vanadium-Substituted Phosphomolybdate@Polyaniline@Chitosan as an Inorganic-Organic Hybrid Nanocatalyst

From the environmental protection and human health perspectives, the design and synthesis of efficient and reusable oxidative desulfurization nanocatalysts has always been sought after by scientists and industries. In this regard, a new heterogeneous nanocatalyst (V-SPM@PANI@CH) was synthesized by immobilizing Keggin-type vanadium-substituted phosphomolybdate ([PVMo₁₁O₃₉]^4-) (named V-SPM) clusters on the surface of polyaniline (PANI) and chitosan (CH) polymers. The features of the assembled nanocatalyst were detected by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques in detail. The XRD studies indicated that the average crystallite size of V-SPM@PANI@CH was estimated to be about 36 nm. The catalytic performance of V-SPM@PANI@CH was investigated in the extractive and catalytic oxidation desulfurization (ECOD) procedure of real and thiophenic model gasoline by H₂O₂/AcOH (volume proportion of 2:1) as an oxidizing system. The optimal desulfurization conditions for ECOD reactions were as follows: 50 mL of model/real gasoline, 0.1 g of V-SPM@PANI@CH, reaction time of 60 min, and reaction temperature of 35 °C. Under the experimental conditions outlined above and the designed ECOD system, the content of sulfur in real gasoline could decline from 0.4985 to 0.0193 wt %, which corresponds to an efficiency of 96%. Moreover, the removal percentage of aromatic hydrocarbons, including thiophene (Th), benzothiophene (BT), and di-benzothiophene (DBT) as model fuels decreases in the order of DBT ≥ BT > Th under identical operating conditions. High catalytic activity was maintained with only a slight loss during five cycles. This work offers the ECOD system (V-SPM@PANI@CH/AcOH/H₂O₂) for the desulfurization of liquid fuels, which had a great repercussion on the ECOD efficiency.

Size-matched polyoxometalate encapsulated in UiO-66(Zr): an extraordinary catalyst with double active sites for the highly efficient ultra-deep oxidative desulfurization of fuel oil

In this study, for the first time, we selected a size-matched polyoxometalate α-Mo8O26, and successfully prepared Mo8-UiO-66(Zr) as a catalyst with double active sites for extractive and catalytic oxidative desulfurization systems (ECODS).

Deep Oxidative Desulfurization of Fuels in the Presence of Brönsted Acidic Polyoxometalate-Based Ionic Liquids

Polyoxometalate-based ionic liquid hybrid materials with a pyridinium cation, containing Brönsted acid sites, were synthesized and used as catalysts for the oxidation of model and real diesel fuels. Keggin-type polyoxometalates with the formulae [PMo12O40]3-, [PVMo11O40]4-, [PV2Mo10O40]4-, [PW12O40]3- were used as anions. It was shown that increasing the acid site strength leads to an increase of dibenzothiophene conversion to the corresponding sulfone. The best results were obtained in the presence of a catalyst, containing a nicotinic acid derivative as cation and phosphomolybdate as anion. The main factors affecting the process consisting of catalyst dosage, temperature, reaction time, oxidant dosage were investigated in detail. Under optimal conditions full oxidation of dibenzothiophene and more than a 90% desulfurization degree of real diesel fuel (initial sulfur content of 2050 ppm) were obtained (the oxidation conditions: NK-1 catalyst, molar ratio H2O2:S 10:1, molar ratio S:Mo 8:1, 1 mL MeCN, 70 °C, 1 h). The synthesized catalysts could be used five times with a slight decrease in activity.

Catalytic Oxidative/Extractive Desulfurization of Model Oil using Transition Metal Substituted Phosphomolybdates-Based Ionic Liquids

Polyoxometalates based ionic liquids (POM-ILs) exhibit a high catalytic activity in oxidative desulfurization. In this paper, four new POM-IL hybrids based on transition metal mono-substituted Keggin-type phosphomolybdates, [Bmim]5[PMo11M(H2O)O39] (Bmim = 1-butyl 3-methyl imidazolium; M = Co2+, Ni2+, Zn2+, and Mn2+), have been synthesized and used as catalysts for the oxidation/extractive desulfurization of model oil, in which ILs are used as the extraction solvent and H2O2 as an oxidant under very mild conditions. The factors that affected the desulfurization efficiency were studied and the optimal reaction conditions were obtained. The results showed that the [Bmim]5[PMo11Co(H2O)O39] catalyst demonstrated the best catalytic activity, with sulfur-removal of 99.8%, 85%, and 63% for dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and benzothiophene (BT), respectively, in the case of extraction combining with a oxidative desulfurization system under optimal reaction conditions (5 mL model oil (S content 500 ppm), n(catalyst) = 4 μmol, n(H2O2)/n(Substrate) = 5, T = 50 °C for 60 min with [Omim]BF4 (1 mL) as the extractant). The catalyst can be recycled at least 8 times, and still has stability and high catalytic activity for consecutive desulfurization. Probable reaction mechanisms have been proposed for catalytic oxidative/extractive desulfurization.

Sulfur removal from model fuel by Zn impregnated retorted shale and with assistance of design of experiments

There is global concern about acid rain and other pollution which is caused by the consumption of oil. By decreasing sulfur content in the oil, we can reduce unwanted emissions and acid rain. Shale was used which is a solid waste generated in the pyrolysis of shale, impregnated with Zn as an adsorbent which removes sulfur present in fuels from the hexane/toluene model solution. An influence of the agitation time (60-180 min), temperature (25-35 °C), adsorbent mass (0.1-0.25 g), and initial sulfur concentration (100-250 ppm) factorial 24 with three central points totaling 19 experiments was applied to investigate the effect of the variables on the efficiency of sulfur removal in fuels. The values of the parameters tested for maximum sulfur removal were obtained as follows: contact time = 180 min, temperature = 35 °C, adsorbent mass = 0.25 g, and initial sulfur concentration = 100 ppm. The mathematical model proposed with R² 99.97% satisfied the experimental data. This may provide a theoretical basis for new research and alternative uses for tailings of schist industrialization in order to evaluate its potential.

Oxidative Desulfurization of Fuels Using Ionic Liquids: A Review

Extractive oxidation, wherein aromatic sulfur compounds are extracted and subsequently oxidized to their corresponding sulfones, has proven to be one of the most effective desulfurization methods for producing ultra-low sulfur content fuels. As non-volatile and highly designable solvents, ionic liquids (ILs) have attracted considerable attention for the oxidative desulfurization of fuels. In this review, we systematically discuss the utility of ILs in catalytic extractive oxidation, including their roles as extractants, catalysts, or dual extracting/catalytic species for this application. We also discuss the challenges facing the use of ILs in this regard, including their relatively high costs and excessive viscosities, as well as the efficiencies and stabilities of catalysts presently being considered within them.