In this work, the extractive desulfurization of liquid fuel was investigated using a new polymeric DES based on the salt tetrabutyl ammonium bromide (TBAB). Two different light grades of Polyethylene glycol (PEG) were used as hydrogen bond donors. Central Composite Design (CCD) was employed to optimize the operating conditions. The solvents showed high sulfur removal efficiency of DBT and thiophene in simulated fuel. Using a solvent to fuel volume ratio of 1:1 (VDES/VFuel = 1:1), the extraction efficiency reached 82.40% and 62.16% in the first extraction stage at room temperature. Effect of solvent to volume ratio, time, temperature, initial concentration and speed of mixing on extraction efficiency were investigated. The results showed that increasing the speed of mixing has a great influence on the extraction efficiency. The deep desulfurization of the simulated fuel was also carried out in multiple extraction stages. Using a volumetric ratio of VDES/VFuel = 1:1, the DBT and thiophene extraction efficiencies were 100% and 95.15% respectively after three extraction stages. On the other hand, the volumetric ratio of VDES/VFuel = 3:1, achieved efficiencies of 100% and 97.79% after two extraction stages only. This is the minimum number of extraction cycles so far reported using quaternary ammonium based eutectic solvents. Moreover, the deep desulfurization of real diesel was achieved using six extraction stages. Finally, the used DES was successfully regenerated and reused five times without significant loss of solvent activity, which is of utmost necessity from an economical and practical point of view.
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