Recent technological developments have established size-sieving mechanism as a promising method for emulsion separation. For effective application, this technique demands that the membrane pore be smaller or comparable to the emulsion droplet in order to deform the droplet and achieve demulsification. Such demands have led to the successful utilization of microfiltration and ultrafiltration membranes owing to their efficient size-sieving effect. The Hagen- Poiseuille equation describes the mechanism of membrane separation. More so, it also highlights some intrinsic shortcoming inherent to the size-sieving membranes. This problem becomes more pronounced when separating mixed surfactant-stabilized emulsions. Possible solution to this problem is to decrease the membrane thickness which in turn compromises on the mechanical strength of the membrane.
In addition, another challenge emerges during the simultaneous removal of the surfactant from the emulsion together with the separation of water from oil since the surfactant may still permeate the membrane pore to cause contamination of the filtrate. This problem has not been well addressed in existing literature.
Recently, Sichuan University scientists developed a new conceptual emulsion separation membrane by using multiple walled carbon nanotubes (MWCNTs) as heterogeneous competitive adsorption-type demulsifying sites, and a 3D hierarchically fibrous structured collagen fiber membrane (CFM) as a nonporous substrate with high flux and strong mechanical strength. They anticipated that their as-prepared separation membrane would be completely different from the conventional ultrathin microfiltration or ultrafiltration membrane. Their work is currently published in Journal of Material Chemistry A.
In brief, the research method employed entailed the application of CFM as a thick rather than an ultrathin substrate to ensure that the emulsion droplets had a long enough pathway to contact the dispersed MWCNTs. As a result of the competitive nature of the adsorption mechanism, the emulsion droplets were demulsified accordingly, and surfactant permeation though the separation membrane was completely suppressed. Moreover, the use of superhydrophobic CFM further allowed selective permeation of oil as the collected filtrate.
The authors observed that the simultaneous removal of surfactant and emulsified water from the oil was achieved using their rationally designed membrane. Additionally, they noted that their separation membrane was highly efficient for separating a variety of nano- and microemulsions stabilized by mixed nonionic surfactants, and the separation efficiency was proportional to the content of dispersed MWCNTs.
In summary, the study by Sichuan University scientists presented the successful development of a novel type of separation membrane by decorating MWCNTs into the 3D hierarchically fibrous structured CFM, followed by a polydimethylsiloxane coating. In general, it was seen that the use of the nonporous CFM ensured high separation flux, which simultaneously suppressed the fouling problems often suffered by ultrafiltration membranes. Altogether, the finding enlisted here might open up a new conceptual strategy for fabricating efficient, high-flux and mechanically robust emulsion separation membranes.
Xiaoxia Ye, Yaping Wang, Le Ke, Yiwen Cui, Wei Luo, Xiaoling Wang, Xin Huang, Bi Shi. Competitive adsorption for simultaneous removal of emulsified water and surfactants from mixed surfactant-stabilized emulsions with high flux. Journal of Material Chemistry A, 2018, volume 6, 14058.Go To Journal of Material Chemistry A