Abstract
Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PW12O40]3− (PW12). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]3PW12 (BMIM as 1-butyl-3-methylimidazolium), [BPy]3PW12 (BPy as 1-butylpyridinium) and [HDPy]3PW12 (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF6 solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H2O2/S = 8) at 70 °C. However, their stability and activity showed some weakness in continuous reused oxidative desulfurization cycles. An improvement of stability in continuous reused cycles was reached by the immobilization of the Keggin polyanion in a strategic positively-charged functionalized-SBA-15 support. The PW12@TM–SBA-15 composite (TM is the trimethylammonium functional group) presented similar oxidative desulfurization efficiency to the homogeneous IL–PW12 compounds, having the advantage of a high recycling capability in continuous cycles, increasing its activity from the first to the consecutive cycles. Therefore, the oxidative desulfurization system catalyzed by the Keggin-type composite has high performance under sustainable operational conditions, avoids waste production during recycling and allows catalyst recovery.
Highlights
The traditional technology for fuel desulfurization, hydrodesulfurization (HDS), has been widely used in refineries as it is highly efficient in the removal of aliphatic sulfur compounds from feedstock [1].the process presents a high effective cost that is associated with the harsh experimental conditions that are necessary to achieve high efficiency [2]
Different catalysts were prepared based on the Keggin [PW12 O40 ]3− anion (PW12 ), namely, ionic liquid–PW12 (IL–PW12 ) hybrids and a composite material
The hybrids were prepared by replacing the protons in phosphotungstic acid by the cations of the ionic liquids, 1-butyl-3-methylimidazolium (BMIM), 1-butylpyridinium (BPy) and hexadecylpyridinium (HDPy)
Summary
The traditional technology for fuel desulfurization, hydrodesulfurization (HDS), has been widely used in refineries as it is highly efficient in the removal of aliphatic sulfur compounds from feedstock [1].the process presents a high effective cost that is associated with the harsh experimental conditions that are necessary to achieve high efficiency (high temperature and pressure and high consumption of high quality hydrogen) [2]. The traditional technology for fuel desulfurization, hydrodesulfurization (HDS), has been widely used in refineries as it is highly efficient in the removal of aliphatic sulfur compounds from feedstock [1]. Is one of the most advantageous technologies for producing ultra-clean fuels due to its ability to efficiently remove the aromatic sulfur compounds from fuel under mild operating conditions [3]. Over the last few years, numerous catalysts have been reported for ECODS application, such as mixed metal oxides [4,5], ionic liquids [6,7], metal–organic frameworks [8,9], titanium– zeolites [10,11,12], titanium-containing mesoporous silicas (SBA-15, MCM-41) [13,14] and polyoxometalates (POMs) [15,16].
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