Competitive adsorption of surfactant–protein mixtures in a continuous stripping mode foam fractionation column

Abstract

In this paper a detailed experimental study on the application of continuous stripping mode foam fractionation to separate a model surfactant–protein mixture was performed with emphasis on the competitive adsorption behaviour and transport processes of surfactant–protein mixtures in the rising foam column. Bubble size measurements of the foamate showed that at steady state conditions the bubbles rising from the liquid pool were stabilised by BSA. However at the top of the column the recovery of Triton X−100 in the foamate (75–100%) was always greater than the recovery of BSA (13–76%) for all foam fractionation experiments. The enrichment of BSA remained at almost unity for experiments with high feed concentrations of both components and low air flow rates, and only increased when the recovery of Triton X−100 reached 100%. Thus it was concluded that Triton X–100 displaced the adsorbed BSA from the surface. The surface activity and diffusivity of the two components was determined from surface tension and nuclear magnetic resonance (NMR) measurements. These results illustrated that competitive adsorption behaviour was due to the greater maximum surface pressure (2.05 times) and diffusivity (19.6 times) of Triton X−100 than BSA. In addition to investigating the effect of foam fractionation process parameters on the separation of mixed systems, the results from the characterisation studies of surface adsorption and foam properties provided insight and deeper understanding of the competitive adsorption behaviour of surfactants and proteins in a foam fractionation process.