Green aerobic oxidative desulfurization of diesel by constructing an Fe-Anderson type polyoxometalate and benzene sulfonic acid-based deep eutectic solvent biomimetic cycle

Abstract

A unique redox-coupled biomimetic system was developed, in which Fe-Anderson type polyoxometalates (POMs) were employed as electron transfer mediators (ETMs) and benzenesulfonic acid (BSA)-based deep eutectic solvents (DESs) were used as electron-donors for aerobic oxidative desulfurization (AODS) of diesel fuel. Different compositions of DESs were used and the polyethylene glycol 2000 (PEG2000)/2.5BSA system showed the highest desulfurization activity, with the removal of dibenzothiophene (DBT) at 60 °C reaching 95% in 60 min. The excellent desulfurization activity of the system is due to the in situ formation of peroxysulfonate via a biomimetic process. By constructing a coupled redox system, Fe-Anderson type POMs as ETMs reduce the activation energy of oxygen-activated sulfonate. The physical characteristics of four different DESs were tested. The results show that the conductivity of DESs is correlated with the composition of BSA-based DESs. However, there is no similar trend in viscosity testing at the same temperature, and the maximum viscosity value is obtained for the PEG2000/2.5BSA system at 60 °C, which may be associated with the stronger hydrogen bonds. It is worth noting that the PEG2000/2.5BSA system also possesses the best desulfurization activity, which suggests that the activity of the desulfurization system is related to the strength of the hydrogen bond in DESs. Finally, the biomimetic desulfurization system exhibits excellent performance and good stability under mild reaction conditions (60 °C, atmospheric pressure, oxygen as the oxidant).