Deep Oxidative Desulfurization of Fuels Using Peroxophosphomolybdate Catalysts in Ionic Liquids

Synthesis, characterization, and application of N-CNT/1-(2-Hydroxyethyl)-3-methylimidazolium dicyanamide as a green nanocatalyst for the sulfur removal from light oils

Adsorptive desulfurization of light fuels is sustainable due to its ambient operation and reusability of exhausted adsorbents. In this study, 1-(2-hydroxyethyl)-3-methylimidazolium dicyanamide [HEMIM][DCA] IL was synthesized and utilized to modify N-doped carbon nanotubes (CNTs) to produce N-CNT/[HEMIM][DCA] as a green hybrid adsorbent. The adsorbent was characterized using XRD, FE-SEM, FTIR, BET, and TGA. It was indicated that the N-CNT treatment with [HEMIM][DCA] IL resulted in decreased crystallinity with the cubic and rod-shaped morphology and harsh surfaces and curved edges. The absence of shifts or variations in FTIR peaks of starting materials and N-CNT/[HEMIM][DCA] suggested that neither component was affected by chemical interactions. The adsorption capacity of N-CNT and N-CNT/[HEMIM][DCA] was 54.3 mg/g and for 83.6 mg/g for 50 ppm BT, respectively. Saturated with BT, the adsorbent's performance was decreased at high BT concentrations. The adsorption isotherms provided an understanding of interactions of BT with sorbent surface which follows the Langmuir model for N-CNT/[HEMIM][DCA] and N-CNT. The kinetics of BT adsorption on N-CNT/[HEMIM][DCA] was fitted with second-order kinetic model with the decreased adsorption ratio over time due to pore saturation. 25 % reduction of the adsorption capacity was obtained after two recycling cycles of the adsorbent (62.5 mg/g). N-CNT/[HEMIM][DCA] showed good recyclability and potential as a promising BT adsorbent.

Defective silicotungstic acid-loaded magnetic floral N-doped carbon microspheres for ultra-fast oxidative desulfurization of high sulfur liquid fuels

Highly active Keggin-type silicotungstic acid (SiW12) with oxygen vacancy (Ov) defects was encapsulated into the magnetic floral N-doped carbon microspheres (γ-Fe2O3@NC-300) through the facile one-step air pyrolysis of the precursor comprising core-shell Fe3O4@polydopamine (Fe3O4@PDA) and SiW12 to prepare γ-Fe2O3@NC@SiW12-300. The fabricated catalysts were systematically characterized and subsequently employed for the oxidation desulfurization (ODS) of the model fuel. The magnetic floral γ-Fe2O3@NC@SiW12-300 catalyst exhibited nearly perfect catalytic activity, which under mild conditions could remove 100% amount of 4000 ppm DBT in model fuel within 20 min (0.03 g catalysts and n(H2O2)/n(S) of 2). The catalyst activity is mainly attributed to the high activity SiW12 with the Ov defect and its outstanding dispersibility in γ-Fe2O3@NC, along with the high number of exposed active sites. A selected catalyst, γ-Fe2O3@NC@SiW12-300, showed a noticeable turnover frequency (TOF) (110.07 h-1) and lower activation energy (38.79 kJ mol-1) in oxidative desulfurization (ODS) with good recyclability. HO˙ radical was found to be the active species involved in ODS as confirmed by the EPR and scavenger experiments. Additionally, the fabricated catalyst can be conveniently separated and recycled within an externally applied magnetic field.

An overview of conventional and alternative technologies for the production of ultra-low-sulfur fuels

Environmental concerns have given a great deal of attention for the production of ultra-low-sulfur fuels. The conventional hydrodesulfurization (HDS) process has high operating cost and also encounters difficulty in removing sulfur compound with steric hindrance. Consequently, various research efforts have been made to overcome the limitation of conventional HDS process and exploring the alternative technologies for deep desulfurization. The alternative processes being explored for the production of ultra-low-sulfur content fuel are adsorptive desulfurization (ADS), biodesulfurization (BDS), oxidative desulfurization (ODS), and extractive desulfurization (EDS). The present article provided the comprehensive information on the basic principle, reaction mechanism, workability, advantages, and disadvantages of conventional and alternative technologies. This review article aims to provide valuable insight into the recent advances made in conventional HDS process and alternative techniques. For deep desulfurization of liquid fuels, integration of conventional HDS with an alternative technique is also proposed.

Oxidative Desulfurization of Heavy Oils with High Sulfur Content: A Review

The demand for clean fuels is increasing throughout the world, with more stringent environmental regulations for transportation fuels including marine fuels, particularly regarding their sulfur content. Moreover, the quality of crude oil and derived petroleum cuts is getting lower while fossil fuels are still in high demand. Heavy oils are characterized by high sulfur content where most sulfur is found in bulky thiophenic structures difficult to remove using conventional high pressure hydrodesulfurization process. However they appeared more reactive in oxidative desulfurization (ODS) process, carried out at mild conditions without hydrogen pressure. This review focuses for the first time on the heavy fuels initially containing more than 0.5 wt.%S and upgraded by the ODS process. Different attractive approaches of the literature towards ODS are reported using homogeneous and heterogeneous catalysis. Recent developments in ODS assisted with ultrasound technology and the use of ionic liquid to enhance ODS efficiency will be fully detailed and discussed to better understand their viability when applied to high sulfur content, high viscosity, and high boiling point feeds.

Current knowledge and potential applications of cavitation technologies for the petroleum industry

Technologies based on cavitation, produced by either ultrasound or hydrodynamic means, are part of growing literature for individual refinery unit processes. In this review, we have explained the mechanism through which these cavitation technologies intensify individual unit processes such as enhanced oil recovery, demulsification of water in oil emulsions during desalting stage, crude oil viscosity reduction, oxidative desulphurisation/demetallization, and crude oil upgrading. Apart from these refinery processes, applications of this technology are also mentioned for other potential crude oil sources such as oil shale and oil sand extraction. The relative advantages and current situation of each application/process at commercial scale is explained.

One-pot synthesis of polyoxomolybdate anion intercalated layered double hydroxides and their application in ultra-deep desulfurization of fuels under mild conditions

1 mol sulfur-containing compounds can be directly oxidized by 2 mol oxidants into their corresponding sulfones.

Efficient and selective oxidation of sulfides in batch and continuous flow using styrene-based polymer immobilised ionic liquid phase supported peroxotungstates

Good conversion and high selectivity for sulfoxidation have been achieved under segmented and continuous flow using a polystyrene-based polymer immobilised ionic liquid phase (PIILP) peroxotungstate.

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.

Ultra-deep desulfurization via reactive adsorption on peroxophosphomolybdate/agarose hybrids

A catalyst system composed of peroxophosphomolybdates as catalytic center and agarose as matrix material had been designed. The [C16H33N(CH3)3]3[PO4{MoO(O2)2}4]/agarose (C16PMo(O2)2/agarose) hybrid was found to be active for oxidation desulfurization (ODS) of dibenzothiophene (DBT) or real fuel into corresponding sulfone by H2O2 as an oxidant, while the sulfur content could be reduced to 5ppm. The higher activity comes from its components including [PO4{MoO(O2)2}4] catalytic sites, the hydrophobic quaternary ammonium cation affinity to low polarity substrates, and agarose matrix affinity to H2O2 and sulfone. During the oxidative reaction, the mass transfer resistance between H2O2 and organic sulfurs could be decreased and the reaction rate could increase by the assistance of agarose and hydrophobic tails of [C16H33N(CH3)3]3[PO4{MoO(O2)2}4]. Meanwhile, the oxidative products could be adsorbed by agarose matrix to give clean fuel avoiding the post-treatment. In addition, the hybrid was easily regenerated to be reused.

A review of extractive desulfurization of fuel oils using ionic liquids

Extractive desulfurization of fuel oils using ionic liquids as extractive reagents.

Synthesis, characterization and application of 1-butyl-3 methylimidazolium chloride as green material for extractive desulfurization of liquid fuel

The possible application of imidazolium ionic liquids as energy-efficient green material for extractive deep desulfurization of liquid fuel has been investigated. 1-Butyl-3-methylimidazolium chloride [BMIM]Cl was synthesized by nucleophilic substitution reaction of n-methylimidazolium and 1-chlorobutane. Molecular structures of the ILs were confirmed by FTIR, ¹H-NMR, and ¹³C-NMR. The thermal properties, conductivity, solubility, water content and viscosity analysis of [BMIM]Cl were carried out. The effects of reaction time, reaction temperature, sulfur compounds, and recycling of IL without regeneration on dibenzothiophene removal of liquid fuel were presented. In the extractive desulfurization process, the removal of dibenzothiophene in n-dodecane using [BMIM]Cl was 81% with mass ratio of 1 : 1, in 30 min at 30°C under the mild reaction conditions. Also, desulfurization of real fuels with IL and multistage extraction were studied. The results of this work might offer significant insights in the perceptive use of imidazoled ILs as energy-efficient green material for extractive deep desulfurization of liquid fuels as it can be reused without regeneration with considerable extraction efficiency.

Deep extractive and oxidative desulfurization of dibenzothiophene with C5H9NO·SnCl2 coordinated ionic liquid

A new C5H9NO·SnCl2 coordinated ionic liquid (IL) was prepared by reacting N-methyl-pyrrolidone with anhydrous SnCl2. Desulfurization of dibenzothiophene (DBT) via extraction and oxidation with C5H9NO·SnCl2 IL as extractant, H2O2 and equal mol of CH3COOH as oxidants was investigated. The Nernst partition coefficients k(N) of C5H9NO·SnCl2 IL for the DBT in n-octane was above 5.0, showing its excellent extraction ability. During the oxidative desulfurization process, the optimal molar ratio of H2O2/DBT was six. Sulfur removal of DBT in n-octane was 94.8% in 30 min at 30 °C under the conditions of H2O2/DBT molar ratio of six and V (IL):V (oil)=1:3. Moreover, the sulfur removal increased with increasing temperature because of the high reaction rate constant, low viscosity, and high solubility of dibenzothiophene-sulfone in the IL. The kinetics of oxidative desulfurization of DBT was also investigated, and the apparent activation energy was found to be 32.5 kJ/mol. The IL could be recycled six times without a significant decrease in activity.