Foam fractionation is an economical and environmentally friendly separation method for surface active material using a rising column of foam. The system of foam fractionation column with reflux is selected since such a system can improve the enrichment of the product collected from the top of the column. Due to the reflux, it is assumed that there is more surface active material (surfactant and/or protein) in the Plateau border than that in the foam lamella, so that the Plateau border acts as a surfactant/protein reservoir. The aim of this thesis is to investigate the adsorption and transport of surface active material such as surfactant and/or protein onto the surface of a lamella in a foam fractionation column with reflux using mathematical simulation. There are two steps involved in adsorption of surface active material onto a bubble surface within foam, which are diffusion from the bulk solution into the subsurface, a layer next to the interface, followed by adsorption of that material from the subsurface onto the interface. The diffusion follows the Fick's second law, while the adsorption may follow the Henry, Langmuir or Frumkin isotherms, depending on the properties of the surface active material. The adsorption of mixed protein-surfactant follows the Frumkin isotherm. When there is a competition between protein and surfactant, the protein arrives onto the interface at a later time due to a slower diffusion rate and it displaces the surfactant molecules already on the surface since protein has a higher affinity for that surface than surfactant. The surfactant transport from a Plateau border onto a foam lamella is determined by the interaction of forces applied on the lamella surface, such as film drainage, due to the pressure gradient between the lamella and the Plateau border, the Marangoni effect, due to the gradient of surface tension, and surface viscosity, as a reaction to surface motion. In this thesis, there are two different models of film drainage. One approach uses assumption of a film with a mobile interface and the other model assumes a film with a rigid interface. In the absence of surface viscosity, the Marangoni effect dominates the film drainage resulting in accumulation of surfactant on the surface of the foam lamella in the case of a lamella with a rigid interface. In the case of a film with a mobile interface, the film drainage dominates the Marangoni effect and surfactant is washed away from the surface of the lamella. When the drainage is very fast, such as that which is achieved by a film with a mobile interface, the film could be predicted to attain the thickness of a common black film, well within the residence time in a foam fractionation column, at which point the film stops draining and surfactant starts to accumulate on the lamella surface. The desirable condition in operation of a foam fractionation column however is when the Marangoni effect dominates the film drainage and surfactant accumulates on the surface of a foam lamella such as the one achieved by a film with a rigid interface. In the presence of surface viscosity and the absence of film drainage, the surface viscous forces oppose the Marangoni effect and reduce the amount of surfactant transport onto the foam lamella. A larger surface viscosity results in less surfactant transport onto the foam lamella. In addition, the characteristic time scale required for surfactant transport is shorter with a shorter film length.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:626932 |
| Date | January 2014 |
| Creators | Vitasari, Denny |
| Contributors | Grassia, Paul; Martin, Peter |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/adsorption-and-transport-of-surfactantprotein-onto-a-foam-lamella-within-a-foam-fractionation-column-with-reflux(8258925c-455b-4df4-8aa7-d8cff0e3b4e0).html |
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