Separation of gas-borne nanoparticles in bubble columns

The separation efficiency of bubble columns was studied for gas-borne nanoparticles with different properties ranging from sodium chloride (NaCl) spheres to carbon agglomerates. In addition, the influence of the concentration of a polymeric stabiliser (polyvinylpyrrolidone (PVP) K25) on the separation efficiency was investigated. For pure water, it was found that the experimentally determined separation efficiencies were well recovered by employing the Fuchs model based on the measured relative bubble rise velocities. In particular, it was shown that the particles exhibit a sticking probability of one at the gas–liquid interface. With increasing stabiliser concentration, the gas–liquid interfaces become increasingly rigid, finally leading to the complete cease of internal circulation inside the bubble. Then, the Fuchs approach is no longer valid and a model based on pure Brownian diffusion applies. This so called Friedlander model was capable of quantitatively predicting the separation efficiencies. Beside the larger bubbles, very small bubbles were formed when using PVP solutions. The extremely high separation efficiencies of these microbubbles may indicate a new way for high performance nanoparticle deposition in bubble columns.