Aerobic Oxidative Desulfurization by Supported Polyoxometalate Ionic Liquid Hybrid Materials via Facile Ball Milling

With the increasingly strict limitations on emission standards of vehicles, deep desulfurization in fuel is indispensable for social development worldwide. In this study, a series of hybrid materials based on SiO2-supported polyoxometalate ionic liquid were successfully prepared via a facile ball milling method and employed as catalysts in the aerobic oxidative desulfurization process. The composition and structure of prepared samples were studied by various techniques, including FT-IR, UV-vis DRS, wide-angle XRD, BET, XPS, and SEM images. The experimental results indicated that the synthesized polyoxometalate ionic liquids were successfully loaded on SiO2 with a highly uniform dispersion. The prepared catalyst (C16PMoV/10SiO2) exhibited good desulfurization activity on different sulfur compounds. Moreover, the oxidation product and active species in the ODS process were respectively investigated via GC-MS and ESR analysis, indicating that the catalyst can activate oxygen to superoxide radicals during the reaction to convert DBT to its corresponding sulfone in the fuel.

Trihexyl tetradecyl phosphonium bromide as an effective catalyst/extractant in ultrasound-assisted extractive/oxidative desulfurization

Phosphonium-based ionic liquid (PIL) has been used as a catalyst and extractant. Here, the PIL, trihexyl tetradecyl phosphonium bromide ([THTDP]Br) was utilized for the S-removal of model oil (MO) and acted as the reaction-induced self-separation catalyst. The influence of oxidant to sulfur molar ratio (n(O/S)), mass ratio of model oil to ionic liquid (m(MO/IL)), sonication time, and temperature was observed to investigate the optimal conditions for the ultrasound-assisted extractive/oxidative desulfurization (UEODS) catalyzed by [THTDP]Br. A kinetic study was performed, and the reaction rate constant and half-life were calculated as the oxidation reaction was following pseudo-first-order reaction kinetics. Moreover, the oxidation reactivity and selectivity of various sulfur substrates were in the following order: DBT > BT > TH > 3-MT. The DBT removal with various initial S-content was observed to be constant, which makes it feasible for practical application. The interaction energy between [THTDP]Br and S-compounds was examined using Density Functional Theory. The sulfur removal of base oil (BO) was also examined using various desulfurization systems at DBT optimized conditions. The highest desulfurization efficiency of BO was obtained during the UEODS process, which made it industrially feasible. [THTDP]Br was regenerated and recycled six times with a slight variation in efficiency.

Polyoxometalate Dicationic Ionic Liquids as Catalyst for Extractive Coupled Catalytic Oxidative Desulfurization

Wettability is an important factor affecting the performance of catalytic oxidative desulfurization. In order to develop an efficient catalyst for the extractive coupled catalytic oxidative desulfurization (ECODS) of fuel oil by H2O2 and acetonitrile, a novel family of imidazole-based polyoxometalate dicationic ionic liquids (POM-DILs) [Cn(MIM)2]PW12O40 (n = 2, 4, 6) was synthesized by modifying phosphotungstic acid (H3PW12O40) with double imidazole ionic liquid. These kinds of catalysts have good dispersity in oil phase and H2O2, which is conducive to the deep desulfurization of fuel oil. The catalytic performance of the catalysts was studied under different conditions by removing aromatic sulfur compound dibenzothiophene (DBT) from model oil. Results showed that [C2(MIM)2]PW12O40 had excellent desulfurization efficiency, and more than 98% of DBT was removed under optimum conditions. In addition, it also exhibited good recyclability, and activity with no significant decline after seven reaction cycles. Meanwhile, dibenzothiophene sulfone (DBTO2), the only oxidation product of DBT, was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS), and a possible mechanism of the ECODS process was proposed.

Synthesis of novel magnetic ionic liquids as high efficiency catalysts for extraction-catalytic oxidative desulfurization in fuel oil

Deep desulfurization of magnetic ionic liquids [C₄(mim)₂]Cl₂/2FeCl₃.

Construction of adsorptive nanorods from polyoxometalates and ionic liquid and their adsorption properties for silver ion from AMD

A new structure of hybrid nanorods adsorbent ([n-BBIM]9PW9O34) was synthesized by a simple molecular assembly of polyoxometalates with ionic liquids (ILs). The nanocomposite was characterized by Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), scanning electron microscope, energy dispersive X-ray and X-ray diffractometer. Adsorption of silver from acid mine drainage (AMD) was studied using batch experiments. The impact of several parameters, like ion concentration, pH, adsorbent dosage, and temperature was elucidated and optimization was carried out by single-factor experiment and response surface methodology. Analysis of variance of the quadratic model suggested that experimental data were excellently fitted to the quadratic model. Optimum conditions for removal of Ag(+) from AMD were determined to be an initial concentration 143 mg/L, adsorbent dosage 2.69 g/L, temperature 35 °C to achieve the maximum adsorption of Ag(+) 99.03%, which was very close to the predicted value (100%). The adsorption was confirmed as oxidation-reduction mechanism following a complexation process, and has been verified according to results from FT-IR and UV-vis spectra. The selective experiment suggested that the nanorods adsorbent could adsorb silver ions in AMD well. Based on the adsorption/desorption study result, the adsorbent can be efficiently recovered.

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.

Hybrid Organic-Inorganic Materials Based on Polyoxometalates and Ionic Liquids and Their Application in Catalysis

An overview of the recent advances in the field of polyoxometalate, ionic liquid hybrids, is proposed with a special attention paid to their application in catalysis, more precisely biphasic and heterogeneous catalysis. Both components of the hybrids are separately outlined pointing to their useful properties and potential for catalysis, followed by the description of the hybrids preparation and synergy between components in a large range of organic transformations. And finally a vision on the future developments is proposed.