Thesis
Modelling surface active species transport during a foam fractionation process with reflux
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2023
- Thesis identifier
- T16691
- Person Identifier (Local)
- 202067623
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Surface active species can be encountered in various process industries. This can then result in demand for their separation. Most of the conventional separation methods are limited when the separation of surfactant from a dilute solution is required. However, foam fractionation is an economical and environmentally friendly method that can overcome this limitation. In a fractionation column, bubbles rise, while surfactants adsorb on the surface of the bubbles. Thus, the foamate taken from the top of the column is richer in surfactant concentration than the initial feed. In the foam fractionation system with reflux, which is the subject of this study, a part of this rich foamate is returned to the column. Hence, reflux enriches the interstitial liquid in contact with bubbles. Consequently, the difference in surface concentration of the richer Plateau borders and the leaner adjacent foam films results in a flow of fluid from the Plateau border towards the centre of the film. This is due to the Marangoni stress which arises in turn due to the difference in surface tension in those regions. In addition, film drainage is the other significant mechanism that occurs, and is due to the much higher curvature of the Plateau borders compared to the neighbouring films. This difference can result in a pressure difference which causes a fluid flow from the films towards the Plateau borders. The interaction between the Marangoni flow and film drainage can result in the mass transport of surfactants on and within the foam films. The evolution of insoluble surfactants in this sort of system has previously been studied elsewhere [1]. However, recognition of the fact that surfactants are actually somewhat soluble in water motivated the present study. The novel contribution of this research is to study soluble surfactant transport on and within a foam film during a fractionation process with reflux. This can then lead to the ability of designing more efficient fractionation columns. The present study is thereby based on the work of Vitasari et al. [1], but with the difference that in the present study, surfactant solubility has also been included. To do this, surfactant transport processes are modelled. Nonetheless, to simplify the mathematical modelling used in the current study, we considered two specific limits. In the first, surfactants are considered to be highly diffusive, at least across the foam films. Hence, they are uniformly distributed across the films [2]. In the second limit however, surfactants are considered to have low diffusivities. Hence, they are only being transported via convection within the foam film, due primarily to flow associated with Marangoni induced stresses. In addition, we have employed a linear adsorption isotherm to relate surfactant surface and bulk concentrations, albeit with the option to vary that isotherm to capture, at least locally, the behaviour of a non-linear one. Note that each of the above mentioned limits (diffusion-dominated and convection-dominated) is relevant for surfactants with particular characteristics transported in a foam film with a specific geometry. Therefore, the real case is generally somewhere in between the two above mentioned limits. Despite this, these models and the limits we consider can still provide valuable information about surfactant transport which can eventually help with the design of a more efficient fractionation column. [See text for references]
- Advisor / supervisor
- Grassia, Paul
- Resource Type
- DOI
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PDF of thesis T16691 | 2023-09-19 | Public | Download |