Catalytic oxidative desulfurization of diesel fuel utilizing alumina supported cobalt manganese oxides

Abstract

The available technique of hydrodesulfurization (HDS) is no longer suitable in the purpose of achieving Euro-IV standard diesel due to high operational cost, low efficiency and operating at high temperature in the presence of hydrogen gas. In this study, the catalytic oxidative desulfurization was carried out in the presence of Co/Mn/Al2O3 catalyst and tert-butyl hydroperoxide (TBHP) as oxidant to achieve ultra low sulfur concentration in the model diesel fuel, Petronas commercial and crude diesel. The experimental variables involved were the effect of calcination temperatures of catalysts, dopant ratios, catalyst dopants, reaction times, reaction temperatures, extraction solvents, type of oxidants, reproducibility test and molar ratio of tert-butyl hydroperoxide/sulfur (TBHP/S) were studied to achieve optimum conditions for sulfur removal in the diesel fuel. From XRD analysis, the Co/Mn(10:90)/Al2O3 catalyst formed amorphous structure at 400°C while at 700°C and 900°C calcination temperature produced intermediate and highly crystalline structure, respectively. Further investigation by FESEM showed the particle size of as-synthesized Co/Mn (10:90)/Al2O3 catalyst reduced from the range of 70.3 - 90.2 nm to 50.6 - 52.6 nm after calcination at 400°C. For the EDX analysis, the chloride ions in as-synthesized Co/Mn (10:90)/Al2O3 catalyst reduced from 7.77% to 2.88% and 0.73% after calcination at 400°C and 900°C, respectively. Analysis using nitrogen adsorption showed that the surface area of Co/Mn (10:90)/Al2O3 as-synthesized catalyst was 103.8 m2g-1 which was lower than Co/Mn(10:90)/Al2O3 after calcination at 400°C which was 128.2 m2g-1. The optimum conditions for catalytic oxidative desulfurization of model diesel fuel was identified to perform at 60°C, with oxidant TBHP, molar ratio of TBHP/S = 3, in the presence of catalyst Co/Mn(10:90)/Al2O3 and using extraction solvent, dimethylformamide, where the sulfur contents was reduced from 600 ppm to 164 ppm. This optimum condition for oxidative desulfurization reaction was applied to the Petronas commercial diesel and Petronas crude diesel resulted in the reduction from 500 ppm to 127 ppm and 8269 ppm to 413 ppm of sulfur content respectively analyzed by Gas-Chromatography-Flame Photometric Detector.