Sustainable Utilization of Surfactant-Free Microemulsion Regulated by CO₂ for Treating Oily Wastes: A Interpretation of the Response Mechanism

Abstract

Surfactant-free microemulsions (SFMEs) have been explored extensively to avoid the residual surfactant problem caused by traditional surfactant microemulsions. Many researchers focused on the SFMEs with tertiary amine, which exhibited the typical CO 2 response behavior. In this study, the phase diagram of the SFMEs consisting of tripropylamine (TPA), ethanol, and water was readily prepared via the measurements of electrical conductivity. The CO 2 response behavior of SFME was confirmed by determination of conductivity and measurement of the average diameter of SFME, which was mainly dependent on the protonation of TPA induced by the additional CO 2 . The transition of protonated TPA to a more hydrophilic nature from lipophilicity to hydrophilicity should be responsible for the variation of SFME average diameter. In addition, the SFMEs exhibited remarkable solubilizing capacity of crude oil, and three types of SFMEs achieved more than 80% oil removal rate in the washing process of oil sands. It was noted that both oil-in-water and bicontinuous SFMEs could be circularly utilized at least three times with a relatively high oil removal rate (%). Our work provided the insight perspective on the mechanism of SFMEs with a CO 2 response behavior.

Fluorine-Functionalized Covalent Organic Framework Superhydrophobic Modified Melamine Sponge for Efficient oil–water Separation

“…Traditional treatment techniques of oily wastewater include oil in situ combustion, bioremediation, and dispersant treatment . In recent years, the utilization of microemulsion extraction technology, free from surfactants, as a means of oil removal has been viewed as a promising approach . However, many of these techniques have drawbacks, such as high cost, low absorption capacity, and limited reusability and also are a source for environmental secondary contamination.…”