Phase-Field Modeling of Oil-Water Demulsification via a Porous Filter

Membrane demulsification, which utilizes two-dimensional (2D) porous membranes to coalesce oil droplets in oil-in-water emulsions, is a critical step in oil treatment before refining. However, membrane fouling and re-dispersion of coalesced droplets, caused by the confined pore size, pose significant challenges to its efficiency. In contrast, a three-dimensional (3D) gradient porous filter—with pores that widen from the feed side to the permeate side—offers a potential solution by reducing droplet re-dispersion and improving separation. To better understand oil-water demulsification in these filters, we developed a phase-field model to study the kinetics of oil-water separation and the stability of the emulsion under flow condition. The model accounts for interfacial tension, dynamic interactions between the emulsion and the porous structure, and flow dynamics. We explored the demulsification efficiency by analyzing the coupled effects of pore geometry, surface wettability, surfactant loading, and flow conditions, with special attention to selective surfactant adsorption driven by the oleophilic or hydrophilic nature of the porous structure. This study advances the fundamental understanding of the thermodynamic and kinetic behavior of multi-phase fluid systems in confined geometries, offering a promising pathway toward designing high-efficiency 3D gradient filters for demulsification in oil refinery applications.