Technical Evaluation of Ionic Liquid-Extractive Processing of Ultra Low Sulfur Diesel Fuel

Recent trends in legislation across the world are aimed toward the reduction of the levels of sulfur in fuel oils to less than 10 ppm (ultra low sulfur diesel, ULSD) due to its toxic and environmental effects. Hydrodesulfurization (HDS) is the current method used for desulfurization and faces technical challenges, due to the extreme conditions and energy consumption necessary to reach low sulfur levels. Recently, ionic liquid (IL) technology has been proposed as a possible solution toward achieving ULSD. ILs represent a new class of "green" solvents that are gaining popularity due to their favorable properties and have recently been shown to be effective extractants for desulfurization on a laboratory scale. In this work, the feasibility of industrial scale IL-extractive processing of ULSD has been examined via the simulation and optimization of a conceptual process in ASPEN Plus. The widely used [C(n)mim] [NTF2] series of ionic liquids have been employed, due to their favorable properties and the availability of experimental data in literature. User-defined ionic liquid components have been created within ASPEN Plus, incorporating several thermodynamic and physical property parameters derived from literature, to allow the process to be simulated via the UNIFAC thermodynamic method. On the basis of the technical analysis, it is proposed that the most feasible process configuration consists of HDS as a preliminary treatment, followed by IL extraction as intermediate treatment to reduce the sulfur content to SO ppm, with adsorption as the final treatment to achieve ULSD levels.