Modeling surfactant removal in foam fractionation: I — Theoretical development

Abstract

Surfactant removal by foam fractionation was theoretically analyzed by treating surfactant mass transfer from a bulk solution onto a moving bubble as a convective diffusion process. A mathematical model expressing the removal rate as a function of pertinent parameters was developed. The parameters included superficial air velocity, bubble size, bubble rising velocity, surfactant diffusion coefficient, and concentration. The model indicated that surfactant removal can be described as a first-order process whose rate increases with the diffusion coefficient, the superficial air velocity and the surfactant concentration in the bulk solution, but decreases with bubble size and bubble rising velocity. Based on the assumption of a completely mixed reactor within a section of a foam fractionator, a simplified model for foam fractionation under batch operation conditions was also presented. This simplified model provides a theoretical basis according to which the diffusion coefficient of surfactants can be determined and the model itself can be verified with experimental data.