A combination desulfurization method for diesel fuel: Oxidation by ionic liquid with extraction by solvent

Ionic liquids (ILs) are intensively studied in the oxidative desulfurization of diesel fuel, where ILs act as both extractants and catalysts with adding another oxidant such as H2O2 solution. Some thiophenic sulfur compounds can be effectively removed from some model diesel fuels with this method, while it is hard to reduce the sulfur content to a desirable level like less than 10 ppm with this method when people investigated the real diesel fuels. In this work, we developed a new combination desulfurization method, first oxidative desulfurization by ILs as both extractants and catalysts with 30 w% H2O2 as oxidant, then followed by desulfurization by solvent extraction. Four ILs and ten solvents were investigated for real diesel fuels. The effects of different factors on desulfurization performance were systematically studied, e.g., ILs species, solvents species, temperature, time, IL/oil mass ratio, extractant/oil mass ratio, multiple desulfurization, regeneration of ILs and solvents. The results show such a combination method is effective to reduce the sulfur content in real diesel fuels to a desirable level, e.g., the sulfur content in FCC diesel fuel was reduced to 8.1 ppm from original 150 ppm after one step oxidation by [(CH2)4SO3HMIm][Tos] (ILs/oil mass ratio of 1/2; 3 h, 348.15 K, O/S molar ratio of 40/1) and two-step extraction by DMF (extractant/oil mass ratio 1/2, 30 min, 298.15 K). ILs and solvents can be regenerated and recycled with negligible activity loss.