Abstract
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.
Highlights
Problems of environmental pollution caused by exhaust emissions are receiving more and more attention worldwide with the development of society
Ionic liquids (ILs) hybrids are compared in Figure 1. [Bmim]3 PMo12 O40 shows the characteristic bands of the Keggin-type structure: P–O stretching mode at 1062 cm−1, Mo–Ot at 959 cm−1, Mo–Ob –Mo at 883 cm−1, and Mo–Oc –Mo at 798 cm−1, which are in agreement with those of [Bmim]3 PMo12 O40 reported in the literature [46]
Processes were performed in an immiscible liquid–liquid phase system formed by the model oil phase and the traditional an immiscible liquid–liquid phase system formed by thebymodel oil phase and theand traditional
Summary
Problems of environmental pollution caused by exhaust emissions are receiving more and more attention worldwide with the development of society. Some alternative or supplementary processes have been studied, such as extractive desulfurization (EDS) [7,8], biodesulfurization [9], oxidative desulfurization (ODS) [10,11,12,13,14], adsorptive desulfurization [15], ultrasound desulfurization [16], and others [17,18,19]. Our group reported catalytic oxidation desulfurization using cesium salts of the transition metal mono-substituted phosphomolybdates as heterogeneous catalysts, with H2 O2 as the oxidant and acetonitrile as the extractant. The results showed that the transition metal mono-substituted phosphomolybdates exhibited higher catalytic activity than their parent (Cs3 PMo12 O40 ), and Cs5 [PCo(H2 O)Mo11 O39 ] was found to be the best catalyst, with the removal of most DBT at optimal reaction conditions [45].
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