A fundamental study of the ultrafiltration of oil-water emulsions

Factors affecting both flux and rejection in the ultrafiltration of oil-water emulsions have been investigated. Droplet size distributions measured by laser-light scattering provided evidence of coalescence in the polarized layers which had a broader distribution and substantially larger mean drop size than the feed. The permeate had an even wider size range, including a few very large drops caused by coalescence within the membrane. However, oil rejections were high (> 99.9%) with less than 20 ppm oil in the permeate. Rejection of total organic carbon (TOC) was > 96%, equivalent to 1000 to 2000 ppm content. An increase in permeate TOC was observed resulting from release of surfactants and additives following droplet coalescence. Permeate flux generally followed gel-polarized, film model, behaviour. Reasonable agreement was obtained with flux predictions based on the smallest drop size in the gel layer. Membrane fouling was observed and most easily reversed when using cellulosic membranes.