Key factors in membrane emulsification

In contrast to widely used emulsification processes (high pressure homogenizers, rotor/stator, etc.), emulsions can be made with mineral membranes in relatively low and controlled shear conditions. In this system, the dispersed phase permeates through membrane pores into the continuous phase circulating in the retentate loop. Droplets detach from the membrane owing to the shearing of the continuous phase. This process produces only a little heating, energy consumption is low. This is interesting both from economic and technological points of view, because it may limit the denaturation of macromolecular emulsifiers. The influence of some factors (membranes, working conditions, emulsifiers) on the droplet size of oil-water emulsions was studied. The sizes depended mainly on the adsorption speed of emulsifiers: emulsions were much finer with emulsifiers adsorbing quickly at the interface, such as SDS (sodium dodecyl sulfate) than with emulsifiers lowering the interfacial tension more slowly, such as beta-casein or 11S soya globulin. The membrane pore size, the shear rate at the membrane surface and, to a lesser extent, the volume fraction of the oil phase (between 0 and 30%) had also a significant effect, unlike the oil flux. The emulsions were finer and more stable than those obtained in the same conditions with a rotor/stator system.