Surfactant transport mechanisms during foam fractionation

DEMOSTHENES KIVOTIDES; PAUL GRASSIA; RUBEN ROSARIO; SEBASTIÁN UBAL

Dublin

Congreso; 11st European Conference on Foams, Emulsions and Applications (EUFOAM 2016); 2016

IOP Liquids and Complex Fluids Group - TCD Foams and Complex Systems Group

Foam fractionation is a process for partial separation of surface active compounds, surfactants, from a solution, using adsorption on bubble surfaces. Gas is injected into the solution creating bubbles that rise through a vertical column to form a foam, carrying the desired surfactant(s) out by overflow. It is possible to operate the process in various different ways including via reflux mode or stripping mode. Foam fractionation with reflux consists of returning some collapsed foam overflow to the top of the column to improve the enrichment of the overflow. Stripping mode meanwhile involves raising the feed inlet close to the overflow to remove as much surfactant as possible from solution. In both of these modes of operation comparatively surfactant-rich Plateau borders are brought into contact with comparatively surfactant-lean lamellae leading to mass transfer between the Plateau borders and lamellae. For insoluble surfactants the mass transfer is exclusively along the surface. For slightly soluble surfactant, some of the mass transfer occurs also in the bulk underneath the surface. In this latter case, a number of additional mechanisms for surfactant transport become relevant. To determine the overall amount of surfactant on and within the lamellae it is necessary to account for: mass transfer from the bulk Plateau border to the bulk lamella, driven by Marangoni flows; leakage of surfactant from the film surface to the film bulk; and liquid drainage from the film that carries surfactant from the bulk back to the Plateau border. This study will look at the interplay between all these mechanisms, identifying which particular mechanism(s) will dominate in various parameter regimes.