Microfiltration of oil in water (O/W) emulsions: Effect of membrane microstructure and surface properties

Abstract

In this work, oil in water (O/W) emulsions prepared with a natural emulsifier and different oil phase concentrations were processed by using Anodisc, cellulose acetate (CA), polyester/nylon, silicon nitride microsieves and polycarbonate track etched (PCTE) membranes of different pore sizes (0.22–0.8μm). The effect of membrane characteristics on properties of the emulsions was assessed by droplet size distribution, ζ-potential and pH. Results suggest that membrane hydrophilicity is critical to avoid breaking during microfiltration of O/W emulsions. Partial or total retention of oil droplets from concentrated emulsions (10–30% oil) occurred with all 0.22μm membranes, except with the 0.26μm microsieves. PCTE membrane (uniform straight pores) performance was function of the d¯droplet/dpore ratio, i.e. (a) if d¯droplet/dpore<1, emulsions fully filtered, (b) if 1.0<d¯droplet/dpore≤1.5, partial breaking of larger droplets occurs and (c) if d¯droplet/dpore≥2, retention and probably coalescence of larger drops led to fouling and total pore blockage. Performance of CA membranes (interconnected pores) was rather related to the oil concentration and the number of droplets found in the emulsion. Breaking into the pores and coalescence onto the 0.22μm CA membrane surface started when processing a 5% oil emulsion with estimated concentration of ≥2.42×1012 oil droplets/mL.