Nonfoaming adsorptive bubble separation processes

Two nonfoaming separations, bubble fractionation and solvent sublation, are reviewed. These unit operations are interfacial (gas bubble-liquid) separation techniques that have significant potential for the removal of several metal ions and hydrophobic organic compounds of environmental significance from aqueous solutions. Experimental and theoretical work on the two processes relating the effects of process variables are summarized. The underlying mechanisms of the two processes are identical although solvent sublation is found to have significant advantages over bubble fractionation, air stripping, and the related process of solvent extraction. Specifically, sublation can achieve a greater degree of removal than extraction, can remove both volatile and nonvolatile compounds, unlike air stripping, and has less sensitivity to axial dispersion than bubble fractionation. The potential use of these processes for large-scale separations is examined; the limitations and need for further work are clearly evident. Questions of scale-up, bubble generation, and reduction of axial dispersion all require further investigation.