Predispersed solvent extraction of dilute products using colloidal gas aphrons and colloidal liquid aphrons: Aphron preparation, stability and size

Early work on colloidal gas aphrons (CGAs) and Colloidal liquid aphrons (CLAs) has shown that they have considerable potential in the field of predispersed solvent extraction (PDSE). While their area of application is potentially very broad, their most promising use is in downstream separation in biotechnology where products are very dilute and occur in complex mixtures. Since little work has been done in this area, this preliminary study examined the influence of a range or solvents, varying from non-polar to mildly polar, and a variety of ionic and non-ionic surfactants, on CLA size, stability and phase volume ratio (PVR, volume ratio of the dispersed oil phase to the continuous aqueous phase). In addition, the effect of surfactant type, stirring speed and time, on the formation of CGAs was also studied. The results show that CLAs can be formulated with quite polar solvents (e.g. pentanol), and their stability increases as the HLB (hydrophilic/lipophilic balance) number of the non-ionic surfactant increases. CLAs could be formulated with PVRs as high as 20 without coalescence, which is markedly higher than with microemulsions, and seems to indicate that the liquid aphrons are stabilised by more than a surfactant monolayer. Finally, it was found that CGAs could be formulated as a foam with a half-life of 6 min, and that they could be used to separate dispersed CLAs effectively from a bulk solution.