Microbubbles enhance oil-in-water emulsion separation in fibrous coalescers

The principle of fibrous coalescers is to induce the coalescence and growth of small oil droplets in oil-in-water emulsions to achieve oil-water separation. However, they are poorly adaptable to emulsions containing high-viscosity oil. In this study, pressurized air is dissolved in the oil-in-water emulsion, microbubbles are released by reducing the pressure, and the emulsion is subsequently processed through a fibrous coalescer. Adding microbubbles altered the oil removal mechanism within the fibrous bed from oil droplet coalescence and growth to oil droplet-microbubble floc flotation, which significantly improved the emulsion separation efficiency of the fibrous bed, especially in complex emulsions containing surfactants and low salinity. Notably, the decrease in the interfacial energy of the oil droplet-microbubble floc caused oil droplets adhered to fibers to detach and renew quickly. Moreover, the curved interfacial tension increased oil droplet buoyancy and kinetic energy collectively drove the detachment of oil droplets from the fibrous bed. Effective, dynamic anti-fouling of the fibrous bed was able to maintain high throughput during long-term emulsion separation. This study provides a theoretical basis for the industrial application of fibrous coalescers for the treatment of oily wastewater produced during extraction high-viscosity crude oil.