The ultrafiltration characteristics of surfactant (Triton X-100)-oil field brine with a cellulosic membrane were analyzed. Triton X-100 permeate concentration was found to be invariant with ultrafiltration time and remained below or close to the surfactant critical micelle concentration (cmc), suggesting a permeate free of micelles. With an increase of the surfactant feed concentration, the permeate surfactant composition also remained unchanged (~1.7 × 10-4M) at a surfactant feed concentration of 5 x cmc and 10 x cmc and was slightly above the cmc (2.4 × 10-4M) at a feed concentration 50 times the cmc. This indicates that micelles are completely rejected, which is desirable in micellar enhanced ultrafiltration (MEUF) applications. The removal of traces of petroleum oil from oil field brine by MEUF was examined. Excellent oil rejection (∼99.5%) were achieved in the seldom-explored surfactant concentration regime around the cmc. Unexpected oil rejection (99.6%) was observed at surfactant concentrations moderately below the cmc (0.7 × cmc). This was attributed to concentration polarization that results in a build-up of surfactant molecules at the solution-membrane interface where micelles are present. These high oil rejections were achieved with an extremely low surfactant feed concentration (∼0.34 mg/L), making the MEUF process economically and environmentally viable.
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