An efficient oxidative desulfurization process using terbium-polyoxometalate@MIL-101(Cr)

Abstract

An efficient and recyclable oxidative desulfurization process (ODS) to remove the most refractory sulfur-compounds (dibenzothiophene, 1-benzothiophene and 4,6-dimethyldibenzothiophene) from fuel is reported. The ODS process was catalyzed by terbium-polyoxometalate [Tb(PW11O39)(2)](11-) (Tb(PW11)(2)) and its composite Tb(PW11)(2)@MIL-101. The tetrabutylammonium (TBA) salt of Tb(PW11)(2) was prepared and further incorporated in the porous metal-organic framework MIL-101(Cr). The TBA compound and its composite were characterized by various techniques (powder X-ray diffraction, FT-IR, FT-Raman, SEM and elemental analysis), and their electrochemical behavior was investigated, indicating that the structure of the polyoxometalate anion must be retained after immobilization. The studied ODS process was based on a biphasic system formed by a model oil with various refractor sulfur-compounds and an extracting solvent using H2O2 as the oxidant. Two main steps in the process were carefully investigated: the initial extraction and the oxidative catalytic stage. The optimization of the ODS process was performed by the analysis of the most suitable extracting solvent and also comparing the desulfurization performance of the homogeneous Tb(PW11)(2) and the heterogeneous Tb(PW11)(2)@MIL-101 catalysts. Acetonitrile was selected as the best solvent because it allowed the highest desulfurization rate, conciliating good initial extraction and high catalytic performance. The presence of the porous catalyst Tb(PW11)(2)@MIL-101 seemed not to influence the initial extraction step; however, with this porous hybrid catalyst were obtained higher desulfurization rates during the catalytic stage. Remarkably, using Tb(PW11)(2)@MIL-101 and the oil-acetonitrile system complete desulfurization of oil was achieved only after 5 h. The recyclability of the solid catalyst was investigated for three consecutive ODS cycles and its stability was confirmed by several techniques

Desulfurization of model diesel by extraction/oxidation using a zinc-substituted polyoxometalate as catalyst under homogeneous and heterogeneous (MIL-101(Cr) encapsulated) conditions

“…On the other hand, when PW 11 Zn@MIL-101 is used as catalyst in the oil/MeCN ODS system, total desulfurization only occurs after 6 h but in this system the catalyst seems to be more robust, suffering no leaching. Similar behaviour was observed previously by our group using other catalysts of the type POMs@MIL-101(Cr) in ODS [21,34,40]. Therefore, these results suggest that POMs@MIL-101(Cr) are efficient and robust heterogeneous catalysts for oxidative desulfurization of multicomponent oils containing various benzothiophene derivatives when MeCN is used as extraction solvent.…”

“…A few papers have been published on the immobilization of catalytically active POMs in MIL-101(Cr) (POMs@MIL-101) and the study of the resultant materials as heterogeneous catalysts in various oxidative reactions [21,38,40,42,43,[46][47][48][49]. Only recently have POMs@MIL-101 been identified as promising catalysts for ODS processes [21,34,40,46,49].…”

“…The stability of POMs combined with their structural flexibility to incorporate various elements in their framework make them attractive catalysts. To date, POMs have proved to be among the best catalysts for ODS processes [6][7][8][20][21][22][23][24][25][31][32][33][34][35]. One of the main characteristics that limits the use of POMs as catalysts is their generally good solubility, which complicates their recovery and reuse.…”

Deep extractive desulfurization of oil over 12-molibdophosphoric acid encapsulated in metal-organic frameworks

“…Therefore, solvents with higher polarity extracted the products effectively. Also, the affinity of the solvent with the catalyst is also a parameter that must be taken into account to optimize the ODS process [6]. The reason for this enhancement in ODS reaction rate with MeCN and especially EtOH may be that the formation of micro-droplets of the products was prevented and the reaction rate was improved due to removal of reaction products from the nonpolar phase [42].…”

“…Therefore, they can easily be removed by separation operations such as distillation, solvent extraction, adsorption, and decomposition [5]. The presence of an efficient catalyst in the oxidation step of the ODS procedure is crucial for the success of this process [6]. ODS in the presence of a solid catalyst and extraction solvent is defined in two consecutive steps [7]: oxidation to the corresponding sulfones, followed by removal of sulfur compounds by extraction from the treated fuel to the extractive solvent.…”