Biodiesel, a sustainable oil, in high temperature stable microemulsions containing a room temperature ionic liquid as polar phase

Abstract

Biodiesel has gained more and more attention in recent years resulting from the fact that it is made of renewable resources. Parallel to its environmental compatibility, biodiesel also exhibits a high thermal stability. We demonstrate here that biodiesel can replace conventional oils as apolar phase in nonaqueous microemulsions containing the room temperature ionic liquid ethylammonium nitrate as polar phase. In addition to the phase diagram and the viscosity of the microemulsions, we study the thermal stability of these systems. Along an experimental path in the phase diagram, no phase change could be observed between 30 °C and 150 °C. Conductivity measurements confirm the high thermal stability of these systems. The microemulsion exhibits a percolative behavior between 30 °C and 150 °C. Small angle X-ray scattering spectra show a single broad scattering peak similar to aqueous microemulsions. The spectra could well be described by the Teubner–Strey model. Furthermore, the adaptability of different models ranging from bicontinuous structures to ionic liquid in oil spheres as well as disordered open connected cylinders has been checked. These high temperature stable, nonaqueous, free of crude oil based organic solvent microemulsions highlight an efficient way towards the formulation of environmentally compatible microemulsions and open a wide field of potential applications.