Superhydrophilic and mixed-charge sponge: Revealing the mechanism of three-dimensional demulsification materials for oil-in-water emulsions under charge effect

In petroleum industries, the problem of difficult oil-water separation requires an urgent solution, superhydrophilic charged three-dimensional materials was verified effect for separating oil-in-water (o/w) emulsions, however, the mechanism was unclear. A superhydrophilic sponge SPP with various negative charge amounts and A-SPP with mixed-charge were modified by impregnation. Under gravity-driven filtration, the demulsification effect of SPP and A-SPP on the oil content, zeta potential, and size distribution of emulsion and their mechanism was explored. SPP treated the cationic surfactant stabilized o/w emulsion by electrostatic attraction, the more charged, the better effect, its separation efficiency reached 99.5%, reducing the emulsion zeta potential from 79.18 mV to 23.28 mV, but the droplet size fluctuated sharply illustrated the unstable effect, the single-charge was affected by surfactants. A-SPP realized demulsification by synergize of mixed-charge, treating anionic/cationic surfactant stabilized o/w emulsions with separation efficiency exceeded 99.9%, zeta potential of filtrate below ±15.75 mV, droplet size increased from 500 nm to 10 μm. A-SPP could treat o/w emulsions with different components and concentrations, had cycle stability (99% after 15 times), and tolerated abrasion and brine. A-SPP resembled a filter, the demulsification process of emulsified oil droplets was surface interception - electrostatic demulsification - contact coalescence - skeleton adhesion, the electrostatic, hydrophobic, capillary effects were the main roles of materials. The superhydrophilic mixed-charge sponge can treat diverse emulsions with low energy consumption and high efficiency, revealing the mechanism of three-dimensional demulsification materials for o/w emulsions and creating potential for practical applications.