Extractive desulfurization of liquid fuel with FeCl₃-based deep eutectic solvents: Experimental design and optimization by central-composite design

The extractive desulfurization of simulated fuel containing dibenzothiophene (DBT) and thiophene as sulfur compounds and commercial diesel was carried out using FeCl₃-based deep eutectic solvent (DES). The study was conducted using the response surface method of experimental design technique, which aided in the modeling and optimization of the desulfurization process. High performance liquid chromatography (HPLC) was employed for the quantitative monitoring of the sulfur compounds in the fuel. The results showed that extraction efficiencies as high as 64% and 44% (for DBT and thiophene) could be achieved with the solvent in a single stage extraction, thus showing that the solvent has higher DBT removal than thiophene. Due to their observed extraction performances and zero solubility with the simulated fuel, the solvents were further used for the desulfurization of real commercial diesel and 32% total sulfur removal from the diesel was achieved. The work has not only shown that FeCl₃-based DESs can be used in desulfurization of liquid fuels but also proved their desulfurization ability in the presence of multiple component fuel particularly the real commercial diesel fuel whose sulfur content was eventually lowered to below the environmental sulfur regulation in Oman. Finally, it was shown that the DESs were effectively regenerated and reused five times without significant decrease in their sulfur removal ability from both simulated fuel and commercial diesel.