Ultrafiltration of surfactant solutions

The ultrafiltration of colloid solutions containing hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and alkylpolyglucoside (APG) through hydrophilic membranes with a 10,000 mol wt cut-off from regenerated cellulose was studied. The effects of experimental conditions on the permeate flux and secondary resistance were determined. It was found that both CTAB and APG were convenient surfactants for ultrafiltration, as high permeability of their solutions was observed. The secondary resistance was always significantly lower than the resistance of the membrane. Additionally, electrolytes had a relatively weak negative effect upon ultrafiltration fluxes. SDS was the least convenient surfactant due to formation of a gel layer, susceptibility of its colloid solutions to electrolyte content, and a high secondary resistance. The concentration of the surfactant in the permeate could increase above critical micelle concentration, especially under conditions inducing high polarization. Migration of CTAB on the surface of pores seemed responsible for that transfer.