Preparation and analysis of oil-in-water emulsions with a narrow droplet size distribution using Shirasu-porous-glass (SPG) membranes

Shirasu-porous-glass (SPG) membranes with a mean pore size from 0.4–6.6 µm were used to produce O/W emulsions consisting of vegetable (rape seed) oil as the dispersed phase and Span 80 dissolved in demineralized water as the continuous phase. The emulsion droplets with a mean droplet size 3.5 times larger than the mean pore size and the span of the droplet size distribution between 0.26 and 0.45 were produced using 2% emulsifier at a transmembrane pressure slightly exceeding the capillary pressure. Under these conditions the dispersed phase flux through the membrane was in the range of 0.7–7 l·m–2·h–1 and only about 2% of the pores were active. However, if the transmembrane pressure was considerably higher than the capillary pressure, the dispersed phase flux strongly increased and droplets with a broad droplet size distribution were produced. The hydraulic resistance of the SPG membrane was inversely proportional to the square of the mean pore size, which is in agreement with the HagenPoiseuille law. The membrane porosity is independent on the pore size and ranged from 53–60%.

The SPG membrane can be successfully used to produce O/W emulsions with a very narrow droplet size distribution, on the condition that the transmembrane pressure is not much higher than the capillary pressure. Under these conditions the mean droplet size is 3.5 times larger than the mean pore size and not significantly affected by the dispersed phase content up to 20 vol%. However, the transmembrane flux is very low, because at any moment only about 2% of the pores are active.