Processing effects during rotating membrane emulsification

In this study, a rotating membrane emulsification setup incorporating a 6.1 μm pore diameter SPG membrane was used to produce O/W emulsions of average droplet sizes between 23.4 and 216.6 μm. All emulsions consisted of 10 vol% of sunflower oil or silicone oil stabilised by 1 wt% Tween 20. The transmembrane pressure (0.1-1.8 bar), rotational speeds (100-2000 RPM) annular gap width (5-45 mm), dispersed and continuous phase viscosity were all investigated as to their effect on emulsion droplet size and dispersed phase flux. Modification of the dispersed phase flow properties alters the droplet size with four regions being suggested; a decrease in size (as droplet coalescence is minimised), a plateau (size-stable zone), a gradual increase in size (due to transfer of mass via droplet neck) and then a rapid increase (due to jetting). The importance of Taylor vortices development was seen with larger droplets formed in their absence; typically at low rotational speeds, narrow vessel diameters and more viscous continuous phases. It was concluded that the flow behaviour of each phase requires careful consideration to understand the likely formation mechanism(s) during operation. Across the pressure and viscosity ranges investigated, the dispersed phase flux ranged between 50 and 12,500 Lm−2 h−1 and pore activity was within the range of 0.5-2.7%.