Extractive Desulfurization of Gas Oils: A Perspective Review for Use in Petroleum Refineries

Deep oxidative desulfurization of gas oil by iron(III)-substituted polyoxometalate immobilized on nickel(II) oxide, ((n-C4H9)4N)4H[PW11FeO39]@NiO, as an efficient nanocatalyst

Sulfur compounds are among the most unfavorable constituents of petroleum derivatives, so stringent regulations have been established to curb their atmospheric emissions. In this regard, a new nanocomposite ((n-C4H9)4N)4H[PW11FeO39]@NiO) was synthesized composed of quaternary ammonium bromide salt of ironIII-substituted Keggin-type polyoxometalate immobilized on nickel(II) oxide nanoceramics via sol-gel method. The assembled (n-C4H9)4N)4H[PW11FeO39]@NiO nanocomposite was identified by FT-IR, UV-Vis, XRD, SEM, EDX, and TGA-DTG methods. The characterization results exhibited that ((n-C4H9)4N)4H[PW11FeO39] dispersed uniformly over the surface of the NiO nanoceramics. The ((n-C4H9)4N)4H[PW11FeO39]@NiO nanocomposite was employed as a heterogeneous nanocatalyst in the extractive coupled oxidation desulfurization (ECOD) of real gas oil and dibenzothiophene (DBT) as a model compound. Under relatively moderate conditions, the catalytic performance of the ((n-C4H9)4N)4H[PW11FeO39]@NiO in the ECOD procedure was studied by incorporating acetic acid/hydrogen peroxide as an oxidant system at a volume ratio of 1:2. According to the ECOD results, the ((n-C4H9)4N)4H[PW11FeO39]@NiO demonstrated the effectiveness of up to 95% with 0.1 g at 60 °C under optimal operating conditions. Moreover, the ((n-C4H9)4N)4H[PW11FeO39]@NiO nanocatalyst could be separated and reused for five runs without a noticeable decrease in the ECOD process. This study provides a promising way to meet the target of ultra-low sulfur as an essential process in oil refineries.

A Short Review of Aerobic Oxidative Desulfurization of Liquid Fuels over Porous Materials

Oxidative desulfurization (ODS) has attracted much attention owing to the mild working conditions and effective removal of the aromatic sulfur-containing compounds which are difficult to desulfurize using the industrial hydrodesulfurization (HDS) technique. Molecular oxygen in ambient air have been recognized as an ideal oxidant in ODS due to its easy availability, non-toxicity and low cost in recent years. However, molecular oxygen activation under mild operating conditions is still a challenge. Porous materials and their composites have drawn increasing attention due to their advantages, such as high surface area and confined pore space, along with their stability. These merits contribute to the fast diffusion of oxygen molecules and the formation of more exposed active sites, which make them ideal catalysts for aerobic oxidation reactions. The confined space pore size offers a means of catalytic activity and durability improvement. This gives rise to copious attention toward the porous catalysts in AODS. In this review, the progress in the characteristics and AODS catalytic activities of porous catalysts is summarized. Then, emphasis on the molecular oxygen activation mechanism is traced. Finally, the breakthroughs and challenges of various categories of porous catalysts are concluded.

A current overview of the oxidative desulfurization of fuels utilizing heat and solar light: from materials design to catalysis for clean energy

The ceaseless increase of pollution cases due to the tremendous consumption of fossil fuels has steered the world towards an environmental crisis and necessitated urgency to curtail noxious sulfur oxide emissions. Since the world is moving toward green chemistry, a fuel desulfurization process driven by clean technology is of paramount significance in the field of environmental remediation. Among the novel desulfurization techniques, the oxidative desulfurization (ODS) process has been intensively studied and is highlighted as the rising star to effectuate sulfur-free fuels due to its mild reaction conditions and remarkable desulfurization performances in the past decade. This critical review emphasizes the latest advances in thermal catalytic ODS and photocatalytic ODS related to the design and synthesis routes of myriad materials. This encompasses the engineering of metal oxides, ionic liquids, deep eutectic solvents, polyoxometalates, metal-organic frameworks, metal-free materials and their hybrids in the customization of advantageous properties in terms of morphology, topography, composition and electronic states. The essential connection between catalyst characteristics and performances in ODS will be critically discussed along with corresponding reaction mechanisms to provide thorough insight for shaping future research directions. The impacts of oxidant type, solvent type, temperature and other pivotal factors on the effectiveness of ODS are outlined. Finally, a summary of confronted challenges and future outlooks in the journey to ODS application is presented.

Desulfurization through Photocatalytic Oxidation: A Critical Review

Fuel oil, the most important strategic resource, has been widely used in industrial applications. However, the sulfur-containing compounds in fuel oil also present humanity with huge environmental issues and health concerns due to the hazardous combustion waste. To address this problem, the low vulcanization of fuel production technology has been intensively explored. Compared with traditional hydrodesulfurization technology, the newly emerged photocatalytic desulfurization has the advantages of milder operating conditions, lower energy consumption, and higher efficiency, holding great prospect to achieve deep desulfurization. Though great efforts have been made, the desulfurization catalysts still suffer from inferior light absorption, fast recombination of photocarriers, and poor structure modification. This Review summarizes recent development of photocatalytic desulfurization, including the desulfurization principle, current desulfurization challenges, and corresponding solutions. Particularly, the roles of defect engineering, hybrid coupling, and structure modifications in the enhancement of photocatalytic performance are emphasized. In addition, the photocatalytic desulfurization mechanism is also introduced with the ^. OH and ^. O₂ ^- radicals as main active species. Finally, some perspectives on the photocatalytic desulfurization are provided, which can further optimize the desulfurization efficiency and guide future photocatalyst design.

Assessment of the Oxidative Desulfurization of Middle Distillate Surrogate Fuels with Spectroscopic Techniques

The oxidative desulfurization of five (5) model sulfur compounds and eleven (11) surrogate blends was investigated using the hydrogen peroxide (H₂O₂)-acetic acid (CH₃COOH) system. Consequently, extractive desulfurization was carried out using conventional solvents. The model sulfur compounds, as well as the solvent, are present in petroleum middle distillates. The selection of the compounds was made so that they represent various kinds of sulfur compounds. The goal of this study was the implementation of a simple and economical oxidative and extractive system for the desulfurization of surrogate mixtures with an intermediate sulfur concentration 1% w/w, at the mild temperature of 70°C, and without the use of supplementary and assisting methods such as heterogeneous catalysis or ultrasound irradiation. The sulfur content was estimated using X-ray fluorescence. The progress of the oxidation reaction was monitored using liquid FT-IR. The solid sediments of the oxidation procedure were identified with solid-state FT-IR and ¹H NMR spectroscopy.