Extractive desulfurization of fuel oils using deep eutectic solvents – A comprehensive review

In the coming decades, the importance of delivering clean energy and related applications cannot be understated. The minimisation and elimination of toxic emissions have been shown to be of critical importance to the survival of our planet. Sulfur (S) compounds in fuel create toxic emissions which are a serious threat to the environment. Therefore, research on the desulfurization process to produce fuel with low S-content has intensified around the globe. The conventional hydrodesulfurization (HDS) technique is not widely adopted due to certain limitations such as higher cost, increased consumption of electricity, enhanced hydrogen creation and noble catalyst consumption. A promising alternative to HDS is the extractive desulfurization (EDS) process due to its mild operating conditions. Deep eutectic solvents (DESs) formed from a eutectic mixture of Lewis/Brønsted acids and bases have been prominent in research over the last few years. This review aims to discuss the advantages of EDS using DESs over other desulfurization techniques, together with a description of the diversified desulfurization factors such as the nature of DESs, DESs-fuel oil mass ratio, temperature, mutual solubility, time, initial S-contents, and multiple extraction and regeneration steps. The potential problems and flaws of EDS using DESs have been studied extensively. Owing to the promising advantageous physicochemical properties of DESs, this review recommends DESs as a preferable candidate over the many molecular organic solvents in the field of cleaner fuel oil production.