Retention of surfactants by organic solvent nanofiltration and influences on organic solvent flux

For the first time, the non-ionic surfactant Marlipal 24/70 was removed from 1-dodecene using organic solvent nanofiltration. Fluxes of up to 40 Lm−2 h−1 and retentions of more than 90% were achieved. The flux increase with increasing pressure was non-linear, whilst the retention increase appeared to be almost linear over the observed range. Both effects could be attributed to membrane swelling and compaction which influence the morphology of the membrane. Retention decreased with increasing temperature whilst the flux increased. It could be shown that the temperature influence on the pure solvent flux might be due to a decrease in solvent viscosity, additional to the increased membrane swelling at higher temperatures, which strongly influences the retention of surfactant solutions (retention is reduced). Higher surfactant concentrations led to lower fluxes but to substantially higher retentions due to a decreased membrane swelling degree, surfactant aggregation into micelles, or increased adsorption onto the membrane. The characteristic membrane behaviour seen in this study can be coherently explained but additional effects have been carefully considered. Additionally, the experimental data were compiled to allow, firstly, predictions of the number of batch filtration steps needed to achieve a certain surfactant concentration in the permeate and, secondly, the determination of the characteristic membrane performance.