Colloids and Surfaces A: Physicochemical and Engineering Aspects (473), S. 85-94 (link)
The surface activity of amphiphilic molecules such as proteins lead to an affine adsorption at gas–liquid interfaces. Using this physicochemical property for separation like in foam fractionation these amphiphilic molecules can be separated and/or concentrated via the adsorption on gas bubbles out of aqueous solutions. Hence, in foam fractionation the bubble size plays a fundamental role on the performance as it influences the foam structure and determines the available surface area for the adsorption of surface active molecules. Therefore, the bubble size constitutes a key parameter in foam fractionation and thus, needs to be characterized and investigated experimentally in more detail. In this study, a method for optically measuring the bubble size in a device for continuous foam fractionation is introduced which is based on the detection and subsequent analysis of spherical bubbles in digital images using an ideal circle for the template matching technique. With the help of the implemented bubble size measurement method a performance study for the model system β-casein was performed to point out the role of bubble size on the performance of a foam fractionation process in stripping mode. The crosslink between process parameters like the superficial feed and gas velocity with the bubble size and the separation efficiency is presented and discussed. For the first time, the validity to use a single mean bubble diameter for characterization of a whole foam bed in continuous foam fractionation operated in stripping mode was shown for two different gas spargers. It was shown that the foam fractionation performance is directly adjustable via bubble size by changing the ratio of superficial feed to gas velocity.