A mechanism for internal reflux in foam fractionation

Multiple equilibrium stages can be engendered in foam fractionation, a process used for the enrichment of streams of proteins, by returning some of the foamate stream to the top of the column as external reflux liquor. However, it was recognised, 40 years ago that reflux could be autogenously created through the coalescence of bubbles in fractionation columns. By invoking the hydrodynamic theory of rising foam, we suggest a mechanism for the creation of internal reflux in foam fractionation. This method can give internal reflux rate as a function of bubble size. However, since the bubble size profile in a rising foam cannot be estimated, we cannot yet estimate how internal reflux varies with position in the column.