Determination of the liquid pool surfactant and protein concentration for semi-batch foam fractionation columns

Abstract

Abstract - A model is derived for the change with time of the concentration of a surface-active component in the liquid pool of a semi-batch foam fractionation process. The transport of surface-active material to the gas-liquid interface was assumed to be limited by the mass transfer rates, and the concentration of the adsorbed material at the interface was assumed to be in equilibrium with the concentration of liquid adjacent to the bubble gas surface. This model was compared to experimental data obtained for semi-batch foam fractionation of aqueous solutions of bovine serum albumin and cetyltrimetylammonium bromide. Keywords : Foam fractionation; Proteins; Surfactant; Bubble column. INTRODUCTION Foam fractionation processes are based on the adsorption of a surface-active material at the gas-liquid interface originating in the introduction of a gas phase at the bottom of the liquid that contains the surfactant. The swarm of bubbles ascends in the liquid pool and produces a foam column on the top of the liquid. The foam that leaves the column, after transformed in liquid, will yield a solution with a higher surfactant concentration than the liquid pool due to the drainage of some of the liquid in the foam and the enrichment of solute at the gas-liquid interface. Since drainage is faster in a more unstable foam column, process efficiency increases with a decrease in surfactant concentration, provided that there is enough surfactant in the liquid to form foam. This factor enables use of the process to separate very dilute solutions of surface-active species where other processes are, in general, economically impractical (Brown et al., 1990). Proteins are surface-active materials that are found downstream of many processes in the dilute concentration regime therefore, foam fractionation techniques can be used either to recover the material or to reduce the amount of nitrogen in the wastewater before release. Some examples of this are the concentration of bovine serum albumin (Ahmad, 1975; Lalchev and Exerowa, 1981; Gehle and Schurgerl, 1984). For instance, lactoferrin is a protein found in human and bovine milk, tears, blood, and other secretory fluids that has been used to prevent infection with potential microbial pathogens by its ability to bind with iron