چكيده به لاتين
The oxidative desulfurization (ODS) process is a promising complement process to the hydrodesulfurization (HDS) to remove refractory sulfur compounds of liquid fossil fuels such as benzothiophene (BT), dibenzothiophene (DBT) and their alkyl derivatives under mild operation conditions (low temperature and atmospheric pressure). Cerium oxide has shown unique structure and redox properties in the different catalytic reactions. In this study, the catalytic activity of nanostructured cerium-containing catalysts in the oxidative desulfurization was investigated using ceria-vanadia/γ-Al2O3 (CeO2 - VOx / γ-Al2O3) catalysts. The catalysts were labeled CV/x that x is weight percentage of Ce. The catalysts with metal loading of 13 wt% prepared by modified incipient wetness impregnation aided with ultrasonic waves to enhance catalyst performances. The oxidative desulfurization was conducted in a batch reactor with model fuel that consisted of 500 ppmw sulfur as dibenzothiophene in n-dodecane. Tert-butyl hydroperoxide (t-BuOOH) was used as oxidant and the molar ratio of oxidant to sulfur (O/S) was 5. The catalyst dosage was 0.03 g for 3 g model fuel that includes 500 ppmw Dibenzothiophene in n-dodecane, at 80 °C and 1 atmosphere. The effect of bimetallic catalysts, ultrasonic modification, reaction temperature, molar ratio O/S and Indole, Quinoline and Cyclohexene as nitrogen, olefin and aromatic compounds were investigated. The conversion of dibenzothiophene was determined with gas-chromatography equipped pulsed flame photometric detector (PFPD). The catalyst samples were characterized by X-Ray diffraction (XRD), N2 adsorption – desorption, fourier-transform infrared spectroscopy (FTIR), diffuse reflectance UV-vis spectrum (UV-Vis DRS), field emission scanning electron microscopy (FESEM), energy dispersive X-Ray (EDX) and Mapping. The best catalytic activity was observed for CV/7 sample with 7 wt% Ce and 6 wt% V on the support and achieved 90% DBT conversion after only 1 min of the reaction. However the DBT conversion for the catalyst prepared without ultrasonic modifications was 32% in 1 min. The catalyst activities were decreased in order of CV/7 > CV/5 > CV/10 > CV/11. The decrease of reaction temperature from 80 °C to 60 and 40 °C, reduced reaction rate constant from 1.956 mol. L-1. min-1 to 0.1116 and 0.0256 mol. L-1. min-1, respectively, so decreased desulfurization percentage from 98% to 10% and 5% in 2 min. The present nitrogen, olefin and aromatic compounds decreased the DBT oxidation to 82%, 78% and 32% for quinoline, indole, and cyclohexene.
