Continuous Membrane Emulsification with Pulsed (Oscillatory) Flow

Abstract

Tubular micron pore sized sieve type membranes with internal diameter of 14 mm and length of 60 mm containing uniform pores of diameter 10 and 20 µm were used to generate emulsions of sunflower oil dispersed in water and stabilised by Tween 20 using oscillatory flow of the continuous phase. Drop diameters between 30 and 300 µm could be produced, in a controllable way and with span values of down to 0.4. By using pulsed flow it was possible to provide dispersed phase concentrations of up to 45% v/v in a single pass over the membrane, i.e. without the need to recirculate the continuous phase through the membrane tube. It was possible to correlate the drop size produced with the shear conditions at the membrane surface using the wave shear stress equation. The oscillatory Reynolds number indicated flow varying from laminar to substantially turbulent, but the change in flow conditions did not show a notable influence on the drop diameters produced, over what is predicted by the varying wall shear stress applied to the wave equation. However, the 20 µm pore sized sieve type membrane appeared to allow the passage of the pressure pulse through the membrane pores, under certain operating conditions, which did lead to finer drop sizes produced than would be predicted. These through-membrane pulsations could be suppressed by changes in operating conditions: a higher dispersed phase injection rate or more viscous continuous phase, and they did not occur under similar operating conditions used with the 10 2 µm pore sized sieve type of membrane. Generating emulsions of this size using pulsed continuous phase flow provides opportunities for combining drop generation at high dispersed phase concentration, by membrane emulsification, with downstream processing such as reaction in plug flow reactors.

Microencapsulation of oil droplets using cold water fish gelatine/gum arabic complex coacervation by membrane emulsification

“…Therefore the continuous membrane emulsification with pulsed (oscillatory) flow (Holdich et al, 2013) was investigated.…”

“…In the case of continuous membrane emulsification with pulsed (oscillatory) flow if the occurrence of turbulence and bursts near the membrane surface can be neglected, then it may be possible to correlate droplet size with the shear stress at the membrane surface based on the wave equation for shear stress (Holdich et al, 2013):…”

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Formation of size-tuneable biodegradable polymeric nanoparticles by solvent displacement method using micro-engineered membranes fabricated by laser drilling and electroforming

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