Study on the mechanism and recoverability of magnetically enhanced ionic liquid microemulsion for oily sludge treatment

Abstract

Magnetic ionic liquid (MIL) 1-hexadecyl-3-methylimidazolium tetrachloroferrate (III) ([C16mim]FeCl4) with high surface activity and magnetic responsiveness was synthesized and chosen as surfactant for the preparation of MIL-microemulsion, which could be applied to the effective treatment of oily sludge based on its large specific surface area and good solubilization. Under the optimal conditions of MIL concentration of 3.0 wt%, stirring time of 40 min, stirring speed of 500 r/min and temperature of 25 °C, the residual oil rate reached up to 1.36%. Scanning electron microscope (SEM) and fourier infrared spectrometer (FT-IR) measurement proved the successful removal of crude oil. The interaction between [C16mim]FeCl4 and each component in crude oil was explored by interfacial tension (IFT) and quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that MIL exhibited the lowest interfacial tension of 13.48 mN/m and the highest desorption rate of 28.18% with asphaltene. In addition, based on the magnetic responsiveness of MIL, the application of magnetic field made it possible for the recovery of MIL, which could be reused for the preparation of microemulsion. Even after 5 cycles, the residual oil content in the oily sludge remained below 1.92%. The controllable recovery and reuse of [C16mim]FeCl4 by external magnetic field expanded the application of MIL-microemulsion in the field of oily sludge treatment.