Flow Characteristics and Mass-Transfer in Droplet Layer Formed in an Emulsion-Flow Column by Using Extraction of Iodine from Organic Phase

The novel extraction method called "emulsion-flow" is characterized by using a layer of accumulated droplets in the column to supply both phases in the form of droplets. To clarify the flow behavior of both phases in the layer, extraction of iodine from organic to aqueous phase was carried out to enhance visibility of organic phase with the help of iodine. In addition, the mass-transfer in the organic phase was examined by extracting iodine from organic phase to aqueous Na2S2O3 solution. The results indicated that two phases in the droplet layer were in the state of O/W/O emulsion where most of the water flows down in the form of film around the droplets. Also, progress of coalescence of organic-phase droplets during extraction of iodine from organic phase was observed. The height of droplet layer increased with the square of organic-phase flow velocity. The trend was the same as that observed for extraction of iodine from the aqueous phase. The mass-transfer capacity coefficient of the organic phase increased linearly with the organic-phase flow velocity, with a small dependence on the aqueous-phase flow velocity. The trend of the distribution of iodine concentration in the column was predicted by solving the convection-diffusion equation with an appropriate setting of the Peclet number.