Azimuthally oscillating membrane emulsification for controlled droplet production

A novel membrane emulsification system is reported consisting of a tubular metal membrane, periodically azimuthally (tangentially) oscillated with frequencies up to 50 Hz and 7 mm displacement in a gently cross flowing continuous phase. A CFD analysis showed consistent axial shear at the membrane surface, which became negligible at distances from the membrane surface greater than 0.5 mm. For comparison, CFD analysis of a fully rotating membrane emulsification system showed local vortices in the continuous phase leading to a variable shear along the axis of the membrane. Using an azimuthally oscillating membrane, oil-in-water emulsions were experimentally produced with a median diameter of 20-120 µm, and a coefficient of variation of droplet size of 8%. The drop size was correlated with shear stress at the membrane surface using a force balance. In a single pass of continuous phase it was possible to achieve high dispersed phase concentrations of 40% v/v.