Production of O/W emulsions using SPG membranes, ceramic α-aluminium oxide membranes, microfluidizer and a silicon microchannel plate -: a comparative study

O/W emulsions consisting of rapeseed oil as the dispersed phase and 2 wt.% Tween 80 dissolved in dernineralized water as the continuous phase were prepared by using different emulsification methods, such as membrane emulsification (ME) with Shirasu porous glass (SPG) and alpha-aluminium oxide (alpha-Al2O3) membranes, microfluidization (MF) and microchannel (MC) emulsification. The influence of operating conditions and membrane structure on the emulsification process and the emulsion proper-ties was investigated and compared. Under the same conditions and for the same pore size, the SPG membrane enabled to obtain more uniform droplets (span = 0.26-0.45) than alpha-Al2O3 membrane. However, the span of the droplet size distribution of 0.51-0.59 for the ct-Al2O3 membrane at the wall shear stress of 8 Pa and the dispersed phase flux up to 91 m(-2) h(-1) was significantly smaller than that reported elsewhere for the same membrane type, which was due to careful membrane cleaning by ultrasonication. The calculated maximum proportion of active pores for unhindered droplet growth was higher for the alpha-Al2O3 than for SPG membrane, due to the smaller porosity and smaller mean droplet/pore size ratio for the alpha-Al2O3 membrane. At the same DeltaP(tm)/P-cap ratio, the actual proportion of active pores was also higher for this membrane, due to the smaller thickness of active layer. The microfluidization is a suitable method for producing O/W emulsions with a very small mean droplet sizes of 0.085-0.30 mum, that cannot be attained by membrane or microchannel emulsification. However, the span of the droplet size distribution was in the range between 0.91 and 2.7. (C) 2003 Elsevier B.V. All rights reserved.