Studies on treatment of sodium dodecyl benzene sulfonate solution by high shear ultrafiltration system

The dynamic ultrafiltration of anionic surfactant solution, sodium dodecyl benzene sulfonate (SDBS), using a rotating disk system with hydrophilic polyethersulfone (PES) membranes (MWCO 10 kDa) was studied in this paper. The effects of mean transmembrane pressure (TMP) and disk rotating speed on the permeate flux and surfactant retention have been reported. When the rotating speed of the disk with vanes was above 1000 rpm, it was found that the permeate flux kept rising without reaching a plateau up to a TMP of 2100 kPa. The surfactant retention of the 10-kDa membranes was observed to be 81.5% for a micellar SDBS solution of 1 Critical Micelle Concentration (CMC) at the highest TMP of 2100 kPa and a rotating speed of 1000 rpm, and it reached 92.5% at a rotating speed of 2750 rpm. The dynamic filtration system was proved to be very efficient for decreasing concentration polarization, due to high shear rates on the membrane generated by disk rotation. Then, the influence of the feed concentration on the permeate flux and surfactant retention was investigated at different concentrations up to 5CMC. The unexpected result obtained was that the flux increased with increasing feed concentration, which could be explained by the reduction of concentration polarization by enhanced diffusion of surfactant micelles due to high shear rates. The adsorption of surfactant anions on the membrane surface probably increased the hydrophilicity of PES membrane.