Continuous and high flux demulsification of viscous water-in-oil emulsions by superhydrophobic/oleophobic sponges

Abstract

The separation of water-in-oil (W/O) emulsions is crucial for addressing resource shortages and environmental protection. Superoleophilic/superhydrophobic materials, owing to their selective wettability, can effectively separate W/O emulsions by low-viscosity oils. However, when dealing with viscous water-in-oil emulsions from oils with high viscosity, challenges such as severe oil adhesion and pore blockage significantly hinder separation performance. In this study, a superhydrophobic/oleophobic sponge was fabricated by introducing “ rod-dot ” Co₃O₄ nanoparticles onto the sponge’s inner surfaces, followed by fluorination modification. For emulsions prepared with low-viscosity oils (η_O < 1 mPa·s), the sponge achieved a separation efficiency of over 98 % with a permeation flux exceeding 10,000 L·m^–2·h^–1. Under an applied pressure of 5000 Pa, after continuously treating 400 mL of emulsion, the fluxes for water-in-vegetable oil emulsions (η_V = 59 mPa·s) and water-in-lubricating oil emulsions (η_L = 65 mPa·s) remained above 1207 L·m^–2·h^–1, with separation efficiencies of 99.49 % and 99.82 %, respectively. These results demonstrate the sponge’s high-efficiency and durable separation performance for water-in-oil emulsions by high-viscosity oils. The superior performance is attributed to the inherent oleophobicity of the material, which suppresses the formation of boundary layers and maintains unobstructed pore channels. This study offers a novel approach for the efficient and durable separation of viscous W/O emulsions, with significant potential in waste oil recovery and fuel purification.