Kinetic model for surfactant-induced pore wetting in membrane distillation

Appendix CMembrane pore wetting is a unique and important technical challenge for membrane distillation (MD). While the general principle of pore wetting is well known, the detailed mechanism of pore wetting induced by surfactants that can actively adsorb onto membrane pore surface has not been theoretically elucidated. In this study, we developed a theoretical model, based on surfactant transport in a partially wetted membrane pore under the pseudo-steady state assumption, to quantify the kinetics of pore wetting. The theoretical model predicts several key dependences of wetting kinetics on operating parameters and solution properties, which are highly consistent with results from MD experiments using feed solution containing sodium dodecyl sulfate. It was found that kinetics of pore wetting is strongly dependent on vapor flux, surfactant concentration, but relatively independent of the transmembrane hydraulic pressure. The critical surfactant concentration below which pore wetting does not occur was also predicted by the wetting model. Finally, the impact of surfactant species on wetting kinetics was also discussed.