A makeup remover-inspired chitosan-based emulsion for heavy oil removal in oily sludge treatment

Abstract

During oil production processes, oily sludges are inevitably produced and accumulating, which are extremely hazardous to our living environment. Due to their complex compositions mainly containing oil-contaminated solids and emulsified water and oil, it has been always a great challenge to treat oily sludges before solids can be properly disposed, and oil and water can be recycled. In this study, inspired by the makeup remover and for the first time, a chitosan-based emulsion was developed to treat oily sludges. The emulsion can efficiently remove the heavy oil from solids with removal efficiency of ∼94.7%–98.0% varying with solution pH, sludge to emulsion ratio, and settling time. It has been revealed that the oil liberates from solid surfaces resulted from the wettability alteration of the solid surface in emulsion solution due to the decrease in oil/water interfacial tension as well as oil layer softening by the solvent penetration. A rag layer formed after oil liberation due to the unresolved dispersed oil droplets carrying solid particles, which was further treated by the addition of ∼1.4–6.1 wt‰ of HCl to the mixture. With HCl addition, the dispersed oil drops were found to coalesce attributed the charge neutralization and interfacial property change of chitosan molecules at oil/water interfaces evident from the zeta potential measurement. Our work proposes an environmental-friendly approach to treat oily sludges, and provides valuable information on the oil removal mechanisms using emulsion solution shielding lights on the development of emulsion-based treating technology for both oily sludge and oil-contaminated solids treatment.