Effect of process parameters on oil-in-water emulsion droplet size and distribution in swirl flow membrane emulsification

Swirl flow membrane emulsification is a very high disperse phase flux method for high throughput production of emulsions. The extremely vigorous, turbulent flow eddies generated exert an extremely high radial drag force on the membrane wall, which prevents the transition of droplet formation from the dripping regime to the continuous outflow regime, at extremely high disperse flux emulsion production. In the presentstudy, the effects of surfactant, disperse phase flux, viscosity, and swirl flow velocity on the mean droplet diameter (D₅₀) and droplet size distribution coefficient (span) of an oil-in-water (O/W) emulsion are analyzed. The results indicated that highly monodispersed emulsions could be prepared at very high dispersed phase fluxes of 2.0 to 15.6 m³ m^-2 h^-1. The most monodispersed emulsions produced were of D₅₀ of 33.4μm and of span of 0.24, obtained at various process conditions. The emulsion D₅₀ and corresponding span decreased with swirl flow velocity until the critical velocity of 8.5 m/s, beyond which the D₅₀ decreased further while its corresponding span increased slightly. The increase of the dispersed phase viscosity resulted in anincrease of the emulsion D₅₀, while theincrease in viscosity ratio in respect to the continuous phase viscosity led to a decrease in D₅₀. The disperse flux had no significant effect on D₅₀ until the critical disperse flux of 11.7 m³ m^-2 h^-1, beyond which the inertial force became the dominant force of droplet formation and the D₅₀ increased drastically; although it could be counterbalanced at high surfactant concentration and at higher swirl flow velocities.